Compact tileable cryogenic circulator

Abstract

An example stripline circulator can include one or more ground structures. The example circulator can include one or more dielectrics. The example circulator can include at least one center conductor. The example circulator can include a first port. The first port can include a female connector attached to the at least one center conductor. The example circulator can include a second port. The example circulator can include a third port. The example circulator can be characterized by non-reciprocal signal transmission behavior. The non-reciprocal signal transmission behavior can include, responsive to a first signal being provided as an input signal to the first port, the second port providing the first signal as an output signal. The non-reciprocal signal transmission behavior can include, responsive to a second signal being provided as the input signal to the second port, the third port providing the second signal as the output signal.

Description

COMPACT TILEABLE CRYOGENIC CIRCULATORPRIORITY CLAIM

[0001] The present application is based on and claims priority to United States Provisional Application Number 63 / 636,319 having a filing date of April 19, 2024 and United States Provisional Application Number 63 / 574,503 having a filing date of April 4, 2024. Application claims priority to and the benefit of each of such applications and incorporates all such applications herein by reference in their entirety.FIELD

[0002] The present disclosure relates generally to systems and methods for quantum computing.BACKGROUND

[0003] Quantum computing is a computing method that takes advantage of quantum effects, such as superposition of basis states and entanglement to perform certain computations more efficiently than a classical digital computer. In contrast to a digital computer, which stores and manipulates information in the form of bits, e.g., a “1” or “0,” quantum computing systems can manipulate information using quantum bits (“qubits”). A qubit can refer to a quantum device that enables the superposition of multiple states, e.g., data in both the “0” and “1” state, and / or to the superposition of data, itself, in the multiple states. In accordance with conventional terminology, the superposition of a “0” and “1” state in a quantum system may be represented, e.g., as a |0) + b | 1) The “0” and “1” states of a digital computer are analogous to the |0) and 11) basis states, respectively of a qubit.SUMMARY

[0004] Aspects and advantages of embodiments of the present disclosure will be set forth in part in the following description, or can be learned from the description, or can be learned through practice of the embodiments.

[0005] Example aspects of the present disclosure provide an example stripline circulator. The stripline circulator can include one or more ground structures. The stripline circulator can include one or more dielectrics. The stripline circulator can include at least one center conductor. The stripline circulator can include a first port comprising a female connector attached to the at least one center conductor. The stripline circulator can include a secondport. The stripline circulator can include a third port. The stripline circulator can be characterized by non-reciprocal signal transmission behavior. The non-reciprocal signal transmission behavior can comprise, responsive to a first signal being provided as an input signal to the first port, the second port providing the first signal as an output signal. The non- reciprocal signal transmission behavior can comprise, responsive to a second signal being provided as the input signal to the first port, the third port providing the second signal as the output signal.

[0006] Example aspects of the present disclosure provide an example quantum computing system. The quantum computing system can include a plurality of qubits. The quantum computing system can include a quantum logic circuit configured to perform one or more quantum operations on the plurality of qubits. The quantum computing system can include a multi-circulator assembly comprising at least a first stripline circulator and a second stripline circulator. The first stripline circulator can include one or more ground structures. The first stripline circulator can include one or more dielectrics. The first stripline circulator can include at least one center conductor. The first stripline circulator can include a first port comprising a female connector attached to the at least one center conductor. The first stripline circulator can include a second port. The first stripline circulator can include a third port. The first stripline circulator can be characterized by non-reciprocal signal transmission behavior. The non-reciprocal signal transmission behavior can comprise, responsive to a first signal being provided as an input signal to the first port, the second port provides the first signal as an output signal. The non-reciprocal signal transmission behavior can comprise, responsive to a second signal being provided as the input signal to the first port, the third port provides the second signal as the output signal. The second stripline circulator can include at least one center conductor electrically connected to the at least one center conductor of the first stripline circulator via the first port. The second stripline circulator can include at least one ground structure electrically connected with at least one ground structure of the one or more ground structures of the first stripline circulator.

[0007] Example aspects of the present disclosure provide an example method for assembling a quantum computing system. The method can include testing a respective isolation performance of each respective stripline circulator of a plurality of respective stripline circulators. Each respective stripline circulator can include one or more ground structures. Each respective stripline circulator can include one or more dielectrics. Each respective stripline circulator can include at least one center conductor. Each respective stripline circulator can include at least one port comprising at least one female connectorattached to the at least one center conductor. The at least one female connector can be flush with or recessed from an exterior surface of the one or more ground structures. The method can include selecting, based on the testing, at least one first stripline circulator and at least one second stripline circulator, wherein the isolation performance of the first stripline circulator is better than the isolation performance of the second stripline circulator. The method can include assembling a readout circuit comprising at least one first stage and at least one second stage, the first stage being sequentially before the second stage in a readout circuit. The first stage can include the first stripline circulator. The second stage can include the second stripline circulator.

[0008] These and other features, aspects, and advantages of various embodiments of the present disclosure will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate example embodiments of the present disclosure and, together with the description, explain the related principles.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Detailed discussion of embodiments directed to one of ordinary skill in the art is set forth in the specification, which refers to the appended figures, in which:

[0010] FIG. 1 depicts a simplified block diagram of a top-down view of an example assembly comprising two circulators according to aspects of the present disclosure;

[0011] FIG. 2A depicts a three-quarter profile view of an example ground plane component of an example stripline circulator according to aspects of the present disclosure;

[0012] FIG. 2B depicts a top-down view of an example ground plane component of an example stripline circulator according to aspects of the present disclosure;

[0013] FIG. 2C depicts a three-quarter profile view of an example ground plane component of an example stripline circulator according to aspects of the present disclosure;

[0014] FIG. 3 depicts a top-dow n view of portions of an example stripline circulator according to aspects of the present disclosure;

[0015] FIG. 4 depicts a top-down view of portions of an example stripline circulator according to aspects of the present disclosure;

[0016] FIG. 5 depicts a schematic diagram of an example isolation circuit according to aspects of the present disclosure;

[0017] FIG. 6 depicts a top-down view of portions of an example multi-circulator assembly according to aspects of the present disclosure;

[0018] FIG. 7 depicts a three-quarter profile view of portions of an example multicirculator assembly according to aspects of the present disclosure;

[0019] FIG. 8 depicts an example of a quantum computing system according to example aspects of the present disclosure;

[0020] FIG. 9 depicts a flow chart diagram of an example method for operating a quantum computing system according to example aspects of the present disclosure;

[0021] FIG. 10 depicts a flow chart diagram of an example method for assembling a quantum computing system according to example aspects of the present disclosure.DETAILED DESCRIPTION

[0022] Example embodiments according to some aspects of the present disclosure are directed to precision circulators for microwave signals and / or radio-frequency electromagnet (EM) signals. The precision circulators of the embodiments may be employed, for instance, in quantum computing systems. More specifically, the circulators may be employed to route and / or isolate microwave and / or radiofrequency (RF) signals generated in quantum computing systems (e.g.. qubit control and / or qubit readout signals). Precision circulators of the embodiments may be operable within a cryogenic system (e.g., a cryogenic system within a quantum computer) or within other microwave or RF systems that require circulators for signal routing or signal isolation. One general property of circulators of the embodiments includes non-reciprocal signal routing and signal isolation. Such non-reciprocal devices provide an asymmetry in the direction of flow' of an EM signal.

[0023] At least some of the embodiments are directed to stripline circulators. A stripline circulator can include, for example, a center conductor for transmitting an EM signal. The center conductor can include, for example, a central junction portion and three “arms.” In some instances, the central junction portion of a center conductor can be sandwiched between two ferrites. Each arm of the center conductor can be sandwiched, for example, betw een two dielectrics. The ferrites, dielectrics, and center conductor can in some instances be sandwiched between two ground structures.

[0024] At least some of the embodiments are directed to compact tileable circulators. For example, a plurality of circulators (e.g., interchangeable circulators having a similar or same geometry', components, etc.) can be configured to be modularly connected together to form a compact multi-circulator assembly. A compact multi-circulator assembly can include, for example, an assembly where a ground structure of a first circulator is in direct contact (e.g., physical contact, electrical contact, thermal contact, etc.) with a ground structure of asecond circulator of the multi-circulator assembly. For example, all or almost all of a second- circulator-facing exterior surface of a ground structure of the first circulator can be in direct contact with a ground structure of the second circulator.

[0025] To facilitate compact modular connection, in some embodiments, a circulator can include one or more ports (e.g., three ports) comprising a female connector attached (e.g., soldered, etc.) to an arm of the center conductor. In some instances, to facilitate contact between ground structures of a first circulator and second circulator, the female connector can be flush with or recessed from an exterior surface of the circulator. In some instances, a female connector of a first circulator can be connected to a female connector of a second circulator via a male connector (e.g., male pin) inserted into both female connectors. In this manner, for instance, a plurality of circulators can be interchangeable (e.g.. identical, almost identical, comprising interchangeable port configurations, etc.), with no requirement to distinguish between circulators or ports with male connectors vs. female connectors.

[0026] In some instances, a circulator can include an interface for attaching (e.g., bolting, screwing, clipping, fastening, etc.) the circulator to other circulators (e.g., circulators having a same or similar design). For example, in some instances, a ground structure can include one or more holes (e.g., threaded or unthreaded holes, etc.) for inserting a fastener (e.g., bolt, screw, etc.) to attach the ground structure to a ground structure of a neighboring circulator. In this manner, for instance, a circulator can be configured to be modularly attached to other circulators in a compact tileable multi-circulator assembly.

[0027] In some instances, a plurality of circulators can be modularly assembled into a multi-circulator assembly. In some instances, a multi-circulator assembly can be configured to provide isolation and / or amplification of an EM signal. For example, in some instances, one or more circulators of a multi-circulator assembly can be connected to a resistive terminator to provide isolation of the EM signal. In some instances, one or more circulators of the multi-circulator assembly can be connected to a short to provide amplification of the EM signal.

[0028] In some instances, a circulator or multi-circulator assembly of the present disclosure can be a component of a quantum computing system comprising a plurality of qubits and a quantum logic circuit configured to perform one or more quantum operations on the qubits. The quantum computing system may include, for instance, a readout circuit having one or more tileable circulators. In some instances, example tileable circulators can provide improved calibration and assembly of a quantum computing system. For example, one or more electrical properties (e.g., signal isolation performance, impedance, etc.) of eachof a plurality of circulators can be tested. Testing can include, for example, separately testing each port of a plurality of individual circulators. Based on the testing, individual tileable circulators can be selected and / or calibrated for use in particular quantum computing components (e.g., components comprising multi-circulator assemblies, etc.). For example, circulators providing the best electrical performance can be selected for use in quantum computing components associated with more demanding specifications (e.g., first two stages of a readout circuit) and other circulators can be used in quantum computing components associated with less demanding requirements (e.g., final two stages of a readout circuit).

[0029] In addition to compactness and tileability , some example circulators of the present disclosure can have a variety of additional properties that may provide improved technical performance compared to some alternative circulators. In some implementations, one or both ground structures can include one or more cavities. In some implementations, a shape of the cavities can be similar to (e.g., same as) a combined shape of the dielectrics, ferrites, and center conductor. For example, in some implementations, a circulator can include two ferrites, each shaped as a round disk. In some implementations, a circulator can include six dielectrics, each shaped as a rectangular prism. In such instances, each ground structure can include a cavity comprising a central disk-shaped cavity and three rectangular- prism-shaped “arm” cavities. Other ferrite and dielectric shapes are possible. In some implementations, the dielectrics, ferrites, and center conductor can be inserted in the cavity along with a compliant layer of vacuum grease or other suitable lubricant, which can offer full contact to the entire surface areas of the dielectrics, ferrites, and center conductor for better thermalization in a cry ogenic environment (e.g., when one or more circulators are positioned within a cryogenic chamber).

[0030] In some implementations, each arm can be sandwiched between a first dielectric and a second dielectric, with a length of the first dielectric being different from a length of the second dielectric. In this manner, for instance, a portion of the center conductor can be exposed to enable soldering of a female connector to the center conductor. In some implementations, a width of the center conductor can be adjusted to compensate for a different dielectric constant in the exposed region.

[0031] In some implementations, a circulator can include a compliant conductive gasket between the two ground structures. In some instances, the conductive gasket can be impervious to light. In this manner, for instance, a light-tight environment can be provided, and a signal transmission environment (e.g.. quantum computing signal transmission environment) can be protected from, for example, millimeter-wave and infrared radiation.Additionally, in some implementations, a circulator can include a light-tight and thermally conductive exterior cover to cover some components of a circulator (e.g.. cavities of a ground structure, components inside the cavities such as bolts, etc.) that might otherwise be exposed to an exterior of the circulator. In some implementations, this exterior cover can form a portion of a ground structure (e.g., ground plane component, etc.) of the circulator.

[0032] In some implementations, a circulator can be tuned after assembly and installation (e.g.. after installation in a cryogenic quantum computing system). For example, in some instances, a circulator comprising a compliant gasket can be tuned by adjusting a contact pressure between the ground structures, thereby adjusting an impedance between the ground pieces. In some instances, a contact pressure of an installed circulator can be increased or decreased merely by tightening or loosening one or more exterior screws of the circulator.

[0033] In some implementations, components of the circulator can be removable or interchangeable. For example, in contrast to alternative circulators comprising a monolithic ferrite-dielectric assembly, example circulators according to example aspects of the present disclosure can comprise a plurality of (e.g., six) removable or interchangeable dielectrics; one or more (e.g., two) removable or interchangeable ferrites; and other removable or interchangeable components.

[0034] Example embodiments according to some aspects of the present disclosure can provide for a number of technical effects and benefits, such as improvements to computing technology (e g., quantum computing technology). In particular, example embodiments can provide improved quantum computing performance (e.g., improved isolation, reduced noise, etc.); improved tuning and assembly (e.g., reduced labor cost, improved tuning accuracy, etc.); and improved configurability (e.g., choice of circulators, ports, etc. in a multi-circulator assembly; choice of materials, shapes, etc. in a single circulator) compared to alternative circulators.

[0035] For example, in contrast to alternative multi-circulator assembly designs having a monolithic construction, example multi-circulator assemblies of the present disclosure can include a plurality of removable or interchangeable circulators. This removability and interchangeability can provide a variety of advantages. For example, modular multi-circulator assemblies can be more efficiently and thoroughly tested compared to monolithic assemblies, and systems (e.g., quantum computing systems) comprising modular circulators can be more efficiently and accurately calibrated compared to systems comprising monolithic multicirculator assemblies. For example, a monolithic multi-circulator assembly may not haveenough exterior ports to allow separate testing of every relevant component of a monolithic multi-circulator assembly. In contrast, a modular multi-circulator assembly of the present disclosure can be taken apart, and every port of every individual circulator can be separately tested. As another example, a monolithic multi-circulator assembly may be difficult to calibrate. For example, alternative calibration strategies based on relaxational tuning may be time-consuming, labor-intensive, and / or provide less precise calibration results compared to calibrating based on separate testing of every port of a plurality of modular circulators. Additionally, in contrast to monolithic multi-circulator assemblies, interchangeable circulators can be mixed and matched in multi-circulator assemblies, thereby allowing each circulator of a multi-circulator assembly to be separately selected based on one or more aspects of an operating environment (e.g., electrical properties of neighboring circulators, performance requirements associated with a particular quantum computing operation, etc.). For example, better-performing individual circulators (e.g., circulators having the best signal isolation properties, etc.) can be individually selected for a demanding component of a quantum circuit, which can provide better signal isolation than merely selecting the bestperforming multi-circulator monoliths. In this manner, signal isolation of a multi-circulator assembly in a sensitive quantum computing circuit can be improved.

[0036] Another example technical effect and benefit of aspects of the present disclosure can include improved thermalization compared to some alternative methods. For example, in contrast to alternative multi-circulator circuit designs where circulators may be connected via coaxial ports, example multi-circulator assemblies of the present disclosure can provide a large thermal contact surface between ground structures of neighboring circulators, thereby providing improved thermal performance of a cryogenic system (e.g., cryogenic quantum computing system) comprising two or more circulators. Similarly, example multi-circulator assemblies of the present disclosure can provide a large electrical contact surface between adjacent circulators, thereby providing better grounding compared to alternative implementations. Additionally, a large electrical contact surface can provide improved connection reliability by providing a more mechanically reliable connection between grounds. Additionally, example multi-circulator assemblies of the present disclosure can provide improved impedance matching compared to alternative implementations.

[0037] In some instances, example circulators according to aspects of the present disclosure can provide improved quantum computing performance and / or signal isolation compared to alternative circulators. For example, in some example experiments according to the present disclosure, circulators according to examples of the present disclosure provided a10 decibel (dB) increase in reverse isolation compared to alternative circulators. In some instances, example circulators according to aspects of the present disclosure can provide reduced thermal noise compared to alternative circulators by providing better thermalization of circulator components (e.g., dielectrics and ferrites). In some instances, example circulators according to aspects of the present disclosure can provide a light-tight (i.e., impervious to light) environment, which can reduce disruption (e g., to sensitive quantum computing devices made with Josephson junctions) from infrared or millimeter- wave radiation. In some instances, example circulators according to aspects of the present disclosure can have a reduced cavity volume, and can therefore be associated with increased cavity mode frequencies, compared to alternative circulators. For example, in some instances, a minimum box mode of example circulators can be greater than about 12 gigahertz (GHz), which can provide improved isolation in operating environments where a signal of interest is below about 12 GHz (e.g., about 4-8 GHz, etc.). In some instances, example circulators according to aspects of the present disclosure can provide reduced parasitic capacitances compared to alternative circulators, which may introduce parasitic capacitances at a tab for soldering an electrical contact to a center conductor. In some instances, example circulators can be associated with reduced scintillation compared to alternative stripline circulators. For example, mode rejection ferrites of some alternative stripline circulators can cause scintillation, whereas example circulators according to aspects of the present disclosure can in some instances be built without mode rejection ferrites.

[0038] In some instances, example circulators according to aspects of the present disclosure can provide improved tunability compared to alternative circulators. For example, tuning alternative circulators can in some instances require manual adjustment (e.g., using glue and tweezers) of internal components of the circulator, which can be highly labor- intensive and may not be feasible after a circulator is fully installed (e.g., in a cryogenic quantum computing system). In contrast, example circulators according to aspects of the present disclosure can be tuned merely by tightening or loosening an exterior actuator (e.g., screw, etc.) of the circulator, thereby enabling reduced-labor-cost in-situ tuning of a circulator. In some instances, in situ tuning of a circulator after assembly and installation can be associated with improved tuning accuracy compared to pre-assembly and pre-installation tuning of alternative circulators.

[0039] In some instances, example circulators according to aspects of the present disclosure can provide improved configurability compared to alternative circulators. For example, some embodiments can include interchangeable or removable individualcomponents (e.g., ferrites, dielectrics, conductive gaskets, etc ). This interchangeability can facilitate, for example, experimentation with different materials and combinations of materials (e.g., ferrite materials, dielectric materials); different component shapes; and other design choices. In this manner, for instance, example circulators according to aspects of the present disclosure can enable rapid experimentation with circulator configurations to determine an optimal configuration for a particular use case.

[0040] As used herein, the terms ‘‘about” or ‘‘approximately” in conjunction with a numerical value refer to within 10% of the stated amount.

[0041] With reference now to the Figures, example embodiments of the present disclosure will be discussed in further detail.

[0042] FIG. 1 is a simplified block diagram of a top-down view of an example assembly comprising two example circulators according to aspects of the present disclosure. Each circulator 102a-b can include one or more ground structures 104a-b and one or more center conductors 106a-b. Each circulator 102a-b can include a plurality of female connectors 108a- f attached to the center conductors 106a-b, which can act as ports of the circulators 102a-b. The circulators 102a-b can be electrically connected by a male pin 112 inserted into adjacent female connectors 108c, 108e of the two circulators 102a-b. In some instances, the female connectors 108a-f can be flush with or recessed from a surface of the ground structure 104a-f. In this manner, for instance, one or more exterior surfaces 114a of the ground structures 104a of a first circulator can be in physical contact with one or more exterior surfaces 114b of the ground structures 104b of a second circulator.

[0043] A circulator 102a-b can generally include any electrical component having three or more ports configured to provide non-reciprocal signal transmission behavior. Nonreciprocal signal transmission can include, for example, signal transmission that proceeds through the center conductor 106a, b in only one rotational direction (e.g., clockwise, counterclockwise), wherein a signal exits from an exit port that comes immediately after an entry port of the signal in the rotational direction. For example, non-reciprocal signal transmission can include, responsive to a first signal being provided as an input signal to the first port, the second port providing the first signal as an output signal. Non-reciprocal signal transmission can further include, for example, responsive to a second signal being provided as the input signal to the second port, the third port providing the second signal as the output signal. In some instances, non-reciprocal signal transmission can further include, responsive to a third signal being provided as the input signal to the third port, the first port providing the third signal as the output signal.

[0044] In some example embodiments, a circulator 102a-b can include a stripline circulator. A stripline circulator can include, for example, a center conductor 106a-b for transmitting an EM signal. The center conductor 106 can include, for example, a central junction portion and three ’‘arms.” In some instances, the central junction portion of a center conductor can be sandwiched between two ferrites. Each arm of the center conductor can be sandwiched, for example, between two dielectrics. The ferrites, dielectrics, and center conductor can in some instances be sandwiched between two ground structures 104. Additional details of some example stripline circulators are further provided below with respect to FIGS. 2-4.

[0045] Ground structures 104a-b can comprise, for example, any appropriate conductive material (e.g., metal material such as copper, etc.). Ground structures 104a-b can be configured to be connected to a ground to provide a ground plane for a stripline assembly. In some instances, an example circulator 102a-b can comprise two ground structures 104, which can be the same as or different from each other. In some instances, a ground structure 104 can be monolithic, or can comprise two or more ground structure components in electrical, physical, and / or thermal contact with each other. For example, a ground structure 104 can include a cover (e g., light-tight cover, conductive cover, etc.) covering one or more parts (e.g., cavities, etc.) of the ground structure 104. In some instances, an example shape of a ground structure 104a-b when viewed from the top down can be approximately rectangular (e.g.. approximately square, etc.). Other shapes are possible (e.g.. hexagonal, triangular, etc.). In some instances, a ground structure 104a-b can include one or more cavities in which one or more circulator components (e.g., center conductors 106, female connectors 108, dielectrics, ferrites, fasteners such as screws or bolts, etc.) can be inserted or contained. For example, in some embodiments, an example three-dimensional shape of a ground structure 104a-b can generally correspond to a rectangular prism with one or more cavities (e.g., recessions, grooves, trenches, pockets, notches, concavities, etc.). Other three-dimensional shapes are possible. Additional details of an example ground structure 104 are further provided below with respect to FIGS. 2A-C.

[0046] A center conductor 106 can include, for example, a conductor configured to transmit EM signals (e.g., RF signals, microwave signals, etc.) between ports 108 of the circulator. The center conductor 106 can comprise, for example, any appropriate conductive material (e.g., metal material such as copper, etc.). Additional example details of an example center conductor 106 according to aspects of the present disclosure are provided below with respect to FIG. 3.

[0047] A female connector 108 can include, for example, a conductive connector configured to receive a conductive male pin 112. The female connectors 108 can include, for example, any appropriate conductive material (e.g., metal material such as copper, etc.). In some instances, the female connectors 108 can be attached (e.g., soldered, etc.) to the center conductor 106. In some instances, female connectors 108 can be recessed from or flush with an exterior surface 114 of a circulator 102 to facilitate physical contact between the exterior surface 114 and an exterior surface 114 of another circulator 102. In contrast to some alternative ports or connectors (e.g., coaxial connectors, etc.), a female connector 108 can be a single-conductor connector, and a port comprising the female connector 108 can be a single-conductor port. For example, in contrast to a coaxial connector having two conductors (e.g., with one conductor connected to a ground structure 104 and one conductor connected to a center conductor 106, e.g. separated by a dielectric material), the female connector 108 can be a single-conductor connector electrically connected to the center conductor 106 and not electrically connected to the ground structure 104. For example, an electrical connection between adjacent ground structures 104a,b can be provided by a mechanism that does not involve the female connector 108 or a port comprising it, such as physical contact (e.g., direct physical contact, intermediated physical contact, etc.) between adjacent exterior surfaces 114.

[0048] A male pin 112 can include, for example, a conductive pin configured to be inserted into one or more female connectors 108c. e. In some instances, a male pin 112 can have a length that is less than twice an exterior length of a female connector 108. In some instances, a male pin 1 12 can have a length that is approximately equal to or slightly larger than twice an interior length of a female connector 108, such that an exterior surface of a first female connector 108c can be close (e g., within 0.2 inches, 0.1 inches, 1 mm, 0.5 mm, etc.) to an exterior surface of a second female connector 108e when the male pin 112 is inserted into both female connectors 108c, e. In some instances, a male pin 112 can have a length that is small enough to permit physical contact between exterior surfaces 114a, b when the male pin 112 is inserted into two female connectors 108c, e. For example, the male pin can have a length that is less than or equal to twice a distance from a point on an interior surface of a female connector 108c to a plane comprising an exterior surface 114a of a ground structure 104a. In contrast to some alternative connection mechanisms (e.g., flexible coaxial cables, etc.), a male pin 112 can be a single (e.g., monolithic) pin inserted into two female connectors 108. In some instances, a male pin 112 can be a rigid structure. In some instances, a male pin 112 can be a straight pin.

[0049] An exterior surface 114 or a ground structure 104 can include, for example, a surface of a ground structure 104 that faces toward an exterior of the circulator 102 (i.e., does not face toward a component of the circulator 102). In some instances, an exterior surface 114 can be a surface facing a single direction (e.g., a single face of a rectangular prism or similar structure, etc.). In some instances, each circulator 102 can be configured to provide physical contact, electrical contact, and / or thermal contact between exterior surfaces 114a,b when connected to a neighboring circulator 102 via female connectors 108c,e. Physical, electrical, and thermal contact can include, for example, direct physical contact, wherein the exterior surface 114a touches the exterior surface 114b. Physical, electrical, and thermal contact can also include, for example, intermediated contact, wherein contact may be intermediated by a small conductive (e.g.. electrically conductive, thermally conductive, etc.) component such as a foil gasket, cover, spacer, washer, or the like. In some instances, such an intermediating component can have a width that is small, such that a distance between exterior surfaces 114a, b is small (e.g., less than about 0.2 inches, 0.1 inches, 1 mm, 0.5mm, 0.2mm, 0.1 mm, etc.). In some instances, direct or intermediated contact can include contact with a substantial percentage (e.g.. greater than about 20 percent; 30 percent; 50 percent; 70 percent; 80 percent; 90 percent; etc.) of an exterior surface 114a and / or an exterior surface 114b. For example, in some instances, a larger contact surface can provide better thermalization in cryogenic quantum computing applications compared to a smaller contact surface.

[0050] FIGS. 2A, 2B, and 2C are illustrations, from different viewing angles, of an example ground structure 104 of an example stripline circulator. FIG. 2 A shows a three- quarter profile view of a first side of the example ground structure 104, while FIG. 2B shows a top-down view of the first side. FIG. 2C shows a three-quarter profile view of a second side of the example ground structure 104, wherein the second side can be opposite the first side. The ground structure 104 can comprise one or more stripline cavities 216 and one or more contact surfaces 220A-C. In some instances, a cavity7216 can comprise multiple cavitysections 218A-D configured to hold particular circulator components. In some instances, the ground structure 104 can include or not include one or more gasket cavities 222A-C. In some instances, the ground structure 104 can include one or more interfaces 236, 238 (e.g., fastener interfaces, etc.) for attaching the ground structure 104 to other ground structures 104 (e.g., using a fastener, etc.).

[0051] The ground structure 104 can comprise, for example, any appropriate conductive material (e.g., metal material such as copper, etc.). The ground structure 104 can beconfigured to be connected to a ground to provide a ground plane for a stripline assembly. In some instances, an example circulator can comprise two ground structures 104, which can be the same as or different from each other. The ground structure 104 can have a shape that is similar to (e.g., same as) or different from the shape depicted in FIGS. 2A and 2B. In some instances, a ground structure 104 can have a shape having three-way rotational symmetry (e.g., triangular, hexagonal, circular, etc.) when viewed from the top down (e.g., as depicted in FIG. 2B). In some example embodiments, FIGS. 2A or 2B can be approximately to scale, and a depicted width 224 at a widest point depicted in FIG. 2B can be in a range between about 1 and about 3 inches, such as between about 1.5 and about 2.5 inches; such as between about 1.75 inches and about 2.25 inches; such as about 2 inches. Other widths and shapes are possible.

[0052] The stripline cavity 216 can have a shape that is similar to (e.g., same as) or different from the shape depicted in FIGS. 2A and 2B. In some instances, the stripline cavity 216 can be characterized by a top-facing surface that is recessed from a topmost surface (e g., contact surfaces 220 A-C) of the ground structure 104. such as a cavity, recession, groove, trench, pocket, notch, concavity, etc. In some instances, the stripline cavity 216 can comprise a central junction cavity 218D, and three arm cavities 218A-C, which can have a shape that is similar to (e.g., same as) or different from the shape depicted in FIGS. 2A and 2B. In some instances, the central junction cavity 218D can have a shape that is approximately circular (e.g.. thin cylindrical disk, etc.) or not circular. In some instances, the central junction cavity 218D can have a shape having three-fold rotational symmetry when viewed from the top down as in FIG. 2B (e.g., triangular such as thin triangular prism; hexagonal; circular; etc.). In some instances, the arm cavities 218A-C can have a shape that is similar to (e.g., same as) or different from each other. In some instances, each arm cavity 218A-C can be shaped as a thin rectangular prism (e.g., three identical rectangular prisms, etc.). In some instances, the arm cavities 218A-C can be configured such that a stripline cavity 216 or ground component 102 has a shape having three-fold rotational symmetry' when view ed from a top-down view' (e.g., as depicted in FIG. 2B). In some instances, the cavities 216, 218A-D can have a shape configured to match a shape of one or more stnpline components described below with respect to FIGS. 3-4. For example, a stripline component and corresponding cavity can be configured so that the stripline component fits snugly into a corresponding cavity’ with little or no gap between the stripline component and one or more cavity' walls.

[0053] The contact surfaces 220 A-C can have a shape that is similar to (e.g., same as) or different from the shape depicted in FIGS. 2 A and 2B. In some instances, the contact surfaces220A-C can include a topmost surface of the ground structure 104, or any top-facing surface of the ground structure 104 that is not part of one or more cavities (e.g., stripline cavity’ 216; gasket cavity 222A-C; etc.). The contact surfaces 220A-C can have a shape that is similar to (e.g., same as) or different from each other. For example, in some instances, the ground structure 104 and stripline cavity 216 can have three-fold rotational symmetry’, wherein the contact surfaces 220A-C can have a shape that is similar to (e.g., same as) each other. In some instances, the ground structure 104 and stripline cavity 216 can have reflective symmetry, wherein contact surfaces 220 A-B and stripline cavities 218A, 218C on either side of an axis of reflection can have a shape that is similar to (e.g., same as) each other, and a third contact surface 220C or stripline cavity' 218B can have a different (e.g., similar but slightly different, etc.) shape. In some instances, the stripline cavities 216A-C can have similar (e.g., same) widths; be equally spaced in terms of angular spacing (e.g., angular spacing of 120 degrees or 2n / 3 radians between each pair of stripline cavities 216A-C, etc.); and can each extend to an edge of the ground structure 104.

[0054] In some instances, the ground structure 104 can include or not include one or more gasket cavities 222A-C. A gasket cavity 222 A-C can have a shape that is similar to (e.g., same as) or different from the shape depicted in FIGS. 2A and 2B. In some instances, a gasket cavity’ 222A-C can have a shape that is similar to one or more gasket components to be inserted into the gasket cavity 222A-C. In some instances, one or more compliant conductive gaskets can be inserted into gasket cavities 222A-C of a first ground structure 104. Additional circulator components can be inserted into a first and second ground structure 104 (e.g., as further described below with respect to FIGS. 2-3). The second ground structure 104 can be placed on top of the first ground structure 104, such that the compliant conductive gaskets enter the gasket cavities 222A-C of the second ground structure 104. In some instances, a compliant conductive gasket can include a wire (e.g., indium wire, etc.). In some instances, the compliant conductive gasket can comprise a material that is impervious to light (e.g., copper, indium, etc.), including millimeter- wave and infrared radiation. In some instances, a ground structure 104 can lack any gasket cavities 222A-C. In some instances, one or more compliant gaskets can be placed on top of one or more contact surfaces 220A-C. In some instances, a compliant gasket can comprise a textured foil (e g., light-tight metal foil, etc.). For example, in some instances, a metal foil (e.g., copper foil) can be pressed into sandpaper to imprint a texture of the sandpaper onto the foil before installing the foil in a stripline circulator.

[0055] In some instances, a fully assembled circulator comprising two ground structures 104 with a compliant conductive gasket between them can be tuned by adjusting a contact pressure between the ground structures 104. For example, a contact pressure between the ground structures 104 can be adjusted to tune an impedance between the ground pieces. In some instances, a circulator can be configured to enable increasing or decreasing a contact pressure of an assembled or installed circulator merely by adjusting one or more exterior actuators (e.g.. screws, bolts, nuts, knobs, clamps, clips, etc.) of the circulator. Adjusting an exterior actuator can include, for example, tightening or loosening one or more exterior screws of the circulator to increase or decrease a contact pressure between the ground pieces. An exterior actuator can include, for example, a screw, bolt, knob, clamp, clip, vice, or other device for increasing or decreasing a contact pressure between the ground pieces. In some instances, fine-grained tuning can be achieved by tightening an exterior side actuator (e.g., screw) that is orthogonal to an exterior tuning actuator (e.g., screw) for tuning an impedance, such that an amount of force required to loosen or tighten the exterior tuning actuator is increased. When such a side actuator is tightened, for instance, application of a given amount of force can cause a smaller adjustment to a contact pressure between two ground structures 104 (e g., due to increased friction associated with the tightened side actuator), thereby providing finer-grained tuning control. In some instances, a foil gasket can provide finer- grained tuning control compared to a wire gasket, while a wire gasket can in some instances provide for easier assembly compared to a foil gasket.

[0056] The interfaces 238 can be, for example, interfaces for attaching a ground structure 104 to a second ground structure 104 of a same circulator 102. Additional details of an example interface 238 are further described below with respect to FIG. 2C.

[0057] FIG. 2C is a three-quarter profile view of a second side of an example ground structure 104. In some instances, the ground structure 104 can include one or more first interfaces 236a-b for modularly connecting a ground structure 104a of a first circulator 102a to a ground structure 104b of a second circulator 102b. In some instances, the ground structure 104 can include one or more second interfaces 238 for connecting a first ground structure 104 of a circulator 102a to a second ground structure 104 of the same circulator 102a. In some instances, the ground structure can include a cover indentation 240 configured to hold a cover component (e.g., conductive cover, light-tight cover, etc.) of the ground structure 104.

[0058] The first interfaces 236a-b can include, for example, any interfaces for attaching a first ground structure 104a to a second ground structure 104b (e.g., via one or morefasteners, etc.). In some instances, the first interfaces 236a-b can include a fastener interface (e.g., holes for inserting one or more fasteners, other interfaces for applying one or more fasteners, etc.). The first interfaces 236a can be configured to interface with any appropriate fastener, such as a bolt, nut, screw, clip, clamp, quick-connect fastener, threaded fastener, pin, clasp, latch, snap, etc. For example, in some instances, the first interfaces 236a-b can include threaded or unthreaded holes for inserting fasteners, including threaded fasteners such as bolts or screws. For example, as depicted, first interfaces 236a can in some instances include threaded holes, and first interfaces 236b can include unthreaded holes.

[0059] Similarly, second interfaces 238 can include, for example, any interfaces for attaching a first ground structure 104 to a second ground structure 104 (e g., via one or more fasteners, etc.). In some instances, the second interfaces 238 can include a fastener interface (e.g., holes for inserting one or more fasteners, other interfaces for applying one or more fasteners, etc.). The second interfaces 238 can be configured to interface with any appropriate fastener, such as a bolt, screw, clip, clamp, quick-connect fastener, threaded fastener, pin, clasp, latch, snap, etc. For example, in some instances, the second interfaces 238 can include threaded or unthreaded holes for inserting fasteners, including threaded fasteners such as bolts or screws.

[0060] A cover indentation 240 can be a shallow cavity7(e.g., recession, notch, concavity, etc.) for holding a cover component (e.g., thermally conductive cover, electrically conductive cover, light-tight cover, etc.) of the ground structure 104. A cover component can include, for example, a thin metal component (e.g., approximately the same width as the cover indentation 240, etc.) configured to fit into two cover indentations 240 of two attached ground structures 104 of a single circulator 102. For example, the cover component can include a first face having a shape that is similar to (e.g., same as) a shape of a cover indentation 240 of a first ground structure 104; a second face having a shape that is similar to (e.g., same as) a shape of a cover indentation 240 of a second ground structure 104; and a third face connecting the first and second faces. Other configurations are possible.

[0061] FIG. 3 is a top-doyvn view of part of an example stripline circulator, including a plurality of example stripline components inserted into a stripline cavity 216 of the example ground structure 104 of FIG. 2B. A plurality of dielectrics 326A-C can be inserted into a plurality of cavity arms 218A-C. A ferrite 328 can be inserted into a central junction cavity 218D. A center conductor 330 can be placed on top of the dielectrics 326A-C and ferrite 328.

[0062] In some instances, the dielectrics 326A-C can have a shape that is similar to (e.g., same as) a shape of the arm cavities 218A-C. In some instances, the dielectrics 326A-C canhave a shape that is similar to (e.g., same as) each other. In some instances, the dielectrics 326A-C can be flush with or recessed from an exterior surface 114 of the ground structure 104. The dielectrics can comprise any appropriate dielectric (e.g., insulating, nonconductive, etc.) material, such as ceramic, silicon carbide, silicon, alumina, sapphire, germanium, magnesium titanate - calcium titanate blends, rogers 4350, macor, etc. In some instances, a dielectric 326A-C can include an injectable fluid or semisolid dielectric, such as a mixture of dielectric powder (e.g., silicon carbide powder, etc.) with a fluid or semisolid medium (e.g., vacuum grease, non-scintillating monomer chain such as paraffin wax, etc.). In some instances, a dielectric material can be a single-element or single-molecule dielectric material (e.g., pure silicon with no additives, etc.). For example, a single-element dielectric material can in some instances provide improved manufacturing consistency (e.g., more consistent dielectric constant, etc.) compared to alternative materials, thereby providing more precise and consistent fine-tuning of aspects (e.g., geometry' of various components, material of various components, etc.) of some example circulators. In some instances, a dielectric 326A- C can include a cavity in which the center conductor 330 can be inserted (e.g., a cavity having a shape that is approximately the same as an arm of the center conductor 330. etc.). Although FIG. 3 depicts a small gap between the dielectrics 326A-C and the side walls of the arm cavities 218A-C, this depiction is not necessarily to scale. For example, in some instances, the dielectrics 326A-C can have a shape that is very similar to a shape of the arm cavities 218A-C. such that any gap between the dielectrics 326A-C and the side walls of the arm cavities 218A-C can be smaller than depicted (e.g., less than 100 micrometers, 50 micrometers, 20 micrometers, 10 micrometers, etc.). In some instances, a gap may be larger than depicted without going outside the scope of the present disclosure. In some instances, the dielectrics 326A-C can be coated in a fluid or semisolid material such as vacuum grease (e.g., Apiezon N vacuum grease, etc.) to further provide surface contact between the dielectrics 326A-C and arm cavities 218A-C throughout a surface area of the dielectrics 326A-C. In this manner, for instance, thermalization of the dielectrics 326A-C can be facilitated or improved. Additionally, providing full surface contact can in some instances prevent unwanted changes in capacitance.

[0063] In some instances, the ferrite 328 can have a shape that is similar to (e.g., same as) a shape of the central junction cavity' 218D. A ferrite 328 can comprise any appropriate ferrite material (e.g., yttrium iron garnet with aluminum dopants, etc.). A ferrite 328 can include, for example, a ceramic material comprising iron and one or more other metallic elements. A ferrite 328 can comprise, for example, a ferrimagnetic or ferromagnetic material.Although FIG. 3 depicts a small gap between the ferrite 328 and the side walls of the central junction cavity 218D, this depiction is not necessarily to scale. For example, in some instances, the ferrite 328 can have a shape that is very similar to a shape of the central junction cavity 218D, such that any gap between the ferrite 328 and the side walls of the central junction cavity 218D can be smaller than depicted (e.g., less than 100 micrometers, 50 micrometers. 20 micrometers, 10 micrometers, etc.). In some instances, a gap may be larger than depicted without going outside the scope of the present disclosure. In some instances, the ferrite 328 can be coated in a fluid or semisolid material such as vacuum grease (e.g., Apiezon N vacuum grease, etc.) to further provide surface contact between the ferrite 328 and central junction cavity 218D throughout a surface area of the ferrite 328.

[0064] In some instances, a thickness measured from top to bottom (wherein FIG. 2B is a top-down view) of the ferrite 328 can be approximately equal to a thickness measured from top to bottom of one or more (e.g., all) dielectrics 326A-C. In some instances, a thickness of the dielectrics 326A-C can be, for example, approximately 0.05 inches. Thicker and thinner dielectrics 326A-C are possible. In some instances, a reduced dielectric 326A-C thickness can reduce a cavity size associated with a stripline circulator, advantageously increasing a minimum cavity mode frequency, such that unwanted noise at frequencies below the increased minimum cavity mode frequency can be eliminated or reduced. However, in some instances, a thinner (e.g.. approximately 0.025-inch. etc.) ferrite 328 can be more susceptible to error compared to a thicker ferrite 328. Thus, an optimal thickness of the ferrite 328 and dielectrics 326A-C can in some instances be dependent on one or more aspects (e.g., intended operating frequency, etc.) of a particular use case.

[0065] The center conductor 330 can comprise, for example, any appropriate conductive material (e.g., metal material such as copper, etc.). In some instances, the center conductor can have an approximately flat shape, wherein a height of the center conductor 330 in a top- to-bottom direction (wherein FIG. 2 is a top-down view) can be small (e.g., 1 millimeter, 0.5 millimeter, 2 millimeter, etc.). In some instances, a height of the center conductor 330 can be approximately constant throughout the center conductor 330. In some instances, the center conductor can comprise a central junction portion configured to be placed on top of a ferrite 328 and one or more (e.g., three) arm portions configured to be placed on top of one or more dielectrics 326A-C. In some instances, the center conductor 330 can have a shape that is similar to (e.g.. same as) or different from the shape depicted in FIG. 3. For example, in some instances, each arm portion can have a non-constant width 332 (e.g., as measured in a direction orthogonal to height and orthogonal to an axis extending through the arm from acenter of the center conductor 330). In some instances, an arm portion can have a width that becomes narrower in stages, before becoming wider at an end portion. In some instances, a width of an arm portion can be configured to compensate for differing dielectric constants in an environment of the center conductor 330 (e.g., dielectrics 326A-C, other circulator components, vacuum, etc.). For example, an end portion of each arm can in some instances be exposed (e.g., not fully sandwiched between dielectrics, as further depicted in FIG. 4) to facilitate soldering of an electrical contact (e.g.. female connector 108, etc.) to each arm of the center conductor 330. In such instances, a width of the arm portion can be configured to compensate for differing dielectric constants of the environments surrounding the exposed end portion and unexposed portions of the arm. In some instances, a center conductor 330 (including, e.g., a central junction portion) can have a shape having three-fold rotational symmetry. In some instances, a depiction in FIG. 3 of a shape of the center conductor can be approximately to scale. Other shapes are possible.

[0066] FIG. 4 is a top-down view of part of an example stripline circulator, including a plurality of example stripline components placed on top of the example components depicted in FIG. 3. A lurality of dielectrics 426A-C can be placed on top of a center conductor 330 (e.g., directly above dielectrics 326A-C, etc.). A ferrite 428 can be placed on top of a center conductor 330 (e.g., directly above ferrite 328, etc.). In some instances, an example circulator can comprise the components depicted in FIG. 4, along with a second ground structure 104 on top of the components depicted in FIG. 4.

[0067] In some instances, dielectrics 426A-C can be, comprise, be similar to (e.g., same as), or otherwise share one or more (e.g., almost all) properties with the dielectrics 326 A-C. In some instances, each dielectric 426 A-C can have a length 432 that is different from a corresponding length of a dielectric 326A-C. In this manner, for instance, a portion of the center conductor 330 can be exposed to enable attaching or connecting (e.g., soldering, etc.) the center conductor 330 to another conductive component (e.g., female connector 108, etc.). In some instances, dielectrics 426A-C can be otherwise identical to dielectrics 326A-C (e.g., in every respect other than length, etc.).

[0068] In some instances, ferrite 428 can be, comprise, be similar to (e.g.. same as), or otherwise share one or more (e.g., all) properties with the ferrite 328.

[0069] In some instances, a ferrite 428 and dielectrics 426A-C can be inserted into a stripline cavity 216 of a second ground structure 104. In some instances, the insertion can be done in a manner similar to (e.g., same as) a manner described with respect to FIG. 3 forinserting ferrite 328 and dielectrics 326A-C into a first ground structure 104 (e.g., using vacuum grease, etc.).

[0070] FIG. 5 depicts a schematic view of an example isolator circuit 502, in which a stripline circulator can be used to provide non-reciprocal signal transmission and reverse isolation (e.g., isolation from any noise traveling in a direction opposite an intended signal transmission). The isolator circuit can comprise a stripline circulator having a first port 508a, a second port 508b, and a third port 508c, along with a resistive terminator 550. In some instances, a quantum computing system can include one or more isolator circuits 502 to provide reverse isolation to protect one or more quantum computing components (e.g., qubits, Josephson junctions, etc.) from various kinds of noise.

[0071] The first port 508a, second port 508b. and third port 508c can be, for example, respective ports (e.g., connectors, terminals, etc.) connected to or comprising respective arms of a center conductor 330 of a stripline circulator. In some instances, a ferrite 328 of the stripline circulator can be magnetized (e.g., according to existing methods) to provide a static magnetic bias field. In some instances, a magnetic bias field can cause non-reciprocal signal transmission behavior in the stripline circulator. For example, in some instances, a microwave or RF signal entering the first port 508a can exit the second port 508b; a microwave or RF signal entering the second port 508b can exit the third port 508c; and a microwave or RF signal entering the third port 508c can exit the first port 508a. In this manner, for instance, a stripline circulator can transmit a signal from the first port 508a to the second port 508b, without transmitting a reverse signal from the second port 508b to the first port 508a. Although FIGS. 1-5 depict circulators having three ports (and three center conductor 330 arms, etc.), other numbers of ports (e.g., four, etc.) are possible without going outside the scope of the present disclosure.

[0072] The resistive terminator 550 can comprise, for example, a resistor component (e.g., standard or existing resistor component) connected to a ground. In combination with the non-reciprocal signal transmission described above, the resistive terminator can further provide reverse isolation for the first port 508a, such that the first port 508a does not receive unwanted transmissions (e.g., noise) associated with the second port 508b or third port 508c.

[0073] In some instances, an isolator circuit 502 can comprise a plurality (e.g., three, etc.) of stripline circulators connected in series. For example, a first port 508a of a second stripline circulator can be connected to a second port 508b of a first stripline circulator, such that a signal that enters the first port 508a of the first stripline circulator can exit the second port 508b of the second stripline circulator, while the first port 508a of the first striplinecirculator can be isolated from reverse signal transmission (e.g., noise). In some instances, each third port 508c of the plurality of stripline circulators can be connected to a resistive terminator 550 (e.g., 50 ohm terminator, etc.). In some instances, an isolator circuit 502 can comprise one or more additional circuits or components (e.g., integrated parametric amplifier, integrated band-pass filter such as combline band-pass filter, etc.). In some instances, a quantum computing system can include one or more isolator circuits 502 to provide reverse isolation for one or more quantum computing components (e.g., qubits, etc.). For example, in some instances, a quantum computing system can include an isolator circuit 502 between a qubit (e.g., connected to a first port 508a) and a readout component or measurement component (e.g., readout resonator connected to a second port 508b, etc.) to provide reverse isolation for the qubit.

[0074] FIG. 6 depicts a top-down view of portions of an example multi-circulator assembly according to example aspects of the present disclosure. The multi-circulator assembly can include, for example, a plurality (e.g., two, three, four, etc.) of circulators 102a- d connected via a plurality of female connectors 108 and male pins 112 (not visible) inserted into the female connectors 108. The multi-circulator assembly can include an entry port 642 through which a signal of interest (e g., quantum computing signal) can enter, and an exit port 644 through which the signal can exit. The multi-circulator assembly can also include subsidiary ports 646 for connecting other circuit components, such as resistive terminators 550, shorts configured to cause amplified reflection of a signal of interest, or other circuit components of interest.

[0075] An entry' port 642 can include, for example, any port through which a signal of interest (e.g., RF signal, microwave signal, quantum computing signal, etc.) can enter the multi-circulator assembly. In some instances, an entry port 642 can include a coaxial connector (e.g., subminiature connector such as subminiature push-on or subminiature version A, etc.). In some instances, an entry port 642 can be connected to a female connector 108 via a male pin (e.g., male pin 112, coaxial connector comprising a male pin, etc.). In some instances, an entry port 642 can be connected directly to a center conductor 106 (e.g., via soldering, etc.) without the need for a female connector 108. In some instances, an entry port 642 (e.g., coaxial port) can include a first component electrically connected to a center conductor 106 (e.g., via a female connector 108) and a second component electrically connected to a ground structure 104 of the circulator 102a.

[0076] An exit port 644 can include, for example, any port through which a signal of interest (e.g., RF signal, microwave signal, quantum computing signal, etc.) can exit themulti-circulator assembly. In some instances, an exit port 644 can include a coaxial connector (e.g., subminiature connector such as subminiature push-on or subminiature version A, etc.). In some instances, an exit port 644 can be connected to a female connector 108 via a male pin (e.g., male pin 112, coaxial connector comprising a male pin, etc.). In some instances, an exit port 644 can be connected directly to a center conductor 106 (e.g., via soldering, etc.) without the need for a female connector 108. In some instances, an exit port 644 (e.g., coaxial port) can include a first component electrically connected to a center conductor 106 (e.g., via a female connector 108) and a second component electrically connected to a ground structure 104 of the circulator 102a.

[0077] A subsidiary port 646 can include, for example, any port, connector, circuit or other assembly through which a signal (e.g.. RF signal, micro wave signal, signal of interest, unwanted signal such as noise or reverse transmission, etc.) may pass. For example, a subsidiary port 646 can include a connector (e.g., coaxial connector, etc.) to which other circuit components (e.g., resistive terminators 550, shorts, amplifiers, etc.) may be attached, or the subsidiary port may include other circuit components (e.g.. resistive terminators 550, shorts, amplifiers, etc.), which may be directly connected to a center conductor (e.g.. via a male pin and female connector 108, by soldering, etc.) without the need for an exterior connector (e.g., coaxial connector, etc.) protruding from an exterior surface 114 of the ground structure 104.

[0078] In an example configuration, four subsidiary ports 646 of a multi-circulator assembly can comprise or be connected to three resistive terminators 550 as described with respect to FIG. 5 and one subsidiary port 646 configured to amplify a signal of interest. For example, circulators 102a, c, and d can be configured as described with respect to FIG. 5, wherein a signal of interest is routed clockwise from a left-facing first port 508a to a rightfacing second port 508b, while a subsidiary port 646 can be a third port 508c connected to a resistive terminator 550. In some instances, circulator 102b can be configured to transmit a signal of interest in a counterclockwise direction, from a from a left-facing first port 108a to a subsidiary port 646 acting as a second port 108b. In some instances, a subsidiary port 646 of the circulator 102b can be configured to amplify’ (e.g., parametrically amplify, etc.) the signal of interest. For example, the subsidiary port 646 of the circulator 102b can be connected to one or more circuit components (e.g., a short) for providing amplification. For example, the subsidiary port 646 of the circulator 102b can be connected to a short, causing the signal of interest to be reflected back to the transmission path with a gain. In this manner, for instance, a signal of interest that is amplified at the second port 108b can be provided as output by thethird port 108c of the circulator 102b. Other multi-circulator configurations are possible (e.g., all circulators 102a-d connected to resistive terminators 550, etc.).

[0079] As depicted, FIG. 6 shows some components (e.g., dielectrics 426, ferrites 428, etc.) that can be interior components of some example circulators 102 or multi-circulator assemblies. Thus, some example multi-circulator assemblies can include additional components (e.g., additional ground structures 104 placed on top of the depicted components, etc.) that may enclose or otherwise cover all or part of some components depicted in FIG. 6.

[0080] FIG. 7 depicts a three-quarter profile view of portions of an example multicirculator assembly. The assembly can include a plurality of circulators 102a-d, with each circulator comprising a first ground structure 104a-d, a second ground structure 104e-h, and a plurality of interior components between the first and second ground structures 104 (e.g., located in stripline cavities 216 of the ground structures 104). The interior components can include, for example, a center conductor 106a and female connector 108a. The female connector 108a can be, for example, approximately flush with or slightly recessed from an exterior surface 114 of each ground structure. For example, as depicted, the center conductor 106a protrudes slightly past an end of one or more dielectrics 326, 426; the female connector 108a protrudes slightly past an end of the center conductor 106a; and the female connector 108a is approximately flush with the exterior surface 114. Other configurations are possible. The interior components can further include, for example, one or more components depicted in FIGS. 3 and 4.

[0081] For each circulator 102, the first ground structure 104a-d can be attached to the second ground structure 104e-f via a second interface 238 for attaching two ground structures of a single connector. For example, a fastener (e.g., bolt, screw, etc.) can be inserted into one or more holes of one or more second interfaces 238 of the first and second ground structures 104. In some instances, a fastener can be, comprise, or be comprised by an actuator (e.g., bolt, screw, etc.). In some instances, one or more actuators associated with one or more second interfaces 238 can be used to adjust a contact pressure between a first ground structure (e.g., 104a) and second ground structure (e.g., 104e) of a single circulator 102a (e.g.. to adjust an impedance, etc.). Similarly, a first circulator 102a can be connected to a second circulator 102b via one or more first interfaces 236a,b. For example, a fastener (e.g., bolt, screw, etc.) can be inserted into one or more holes of one or more first interfaces 236a, b of the adjacent pairs of ground structures 104 (e.g., 104a and 104b; 104e and 104f; etc.). In some instances, one or more fasteners (e.g., actuators) associated with one or more first interfaces 236a,b can be used to adjust a contact pressure between a first circulator 102a andsecond circulator 102b (e.g., according to methods described above with respect to adjusting a contact pressure between first and second ground structures 104 of a single circulator 102). A second circulator 102b can be connected to a third circulator 102c, and the third circulator 102c can be connected to a fourth circulator 102d in a similar (e.g., same) manner as the first circulator 102a is connected to the second circulator 102b. Additionally, one or more ports 642, 644. 646 (not depicted in FIG. 6B) can be attached to the circulators 102 (e.g., via interfaces 236a-b, etc.), and one or more cover components (not depicted) can be placed in a cover indentation 240 of each circulator 102.

[0082] FIG. 8 depicts an example quantum computing system 800. The example system 800 is an example of a system on one or more classical computers or quantum computing devices in one or more locations, in which the systems, components, and techniques described below can be implemented. Those of ordinary skill in the art, using the disclosures provided herein, will understand that other quantum computing structures or systems can be used without deviating from the scope of the present disclosure.

[0083] The system 800 includes quantum hardware 802 in data communication with one or more classical processors 804. The quantum hardware 802 includes components for performing quantum computation. For example, the quantum hardware 802 includes a quantum system 810, control device(s) 812, and readout device(s) 814 (e.g., readout resonator(s)). The quantum system 810 can include one or more multi-level quantum subsystems, such as a register of qubits. In some implementations, the multi-level quantum subsystems can include superconducting qubits, such as flux qubits, charge qubits, transmon qubits, gmon qubits, etc.

[0084] The type of multi-level quantum subsystems that the system 800 utilizes may vary. For example, in some cases it may be convenient to include one or more readout device(s) 814 attached to one or more superconducting qubits, e.g., transmon, flux, gmon, xmon, or other qubits. In other cases, ion traps, photonic devices or superconducting cavities (e.g., with which states may be prepared without requiring qubits) may be used. Further examples of realizations of multi-level quantum subsystems include fluxmon qubits, silicon quantum dots or phosphorus impurity qubits.

[0085] Quantum circuits may be constructed and applied to the register of qubits included in the quantum system 810 via multiple control lines that are coupled to one or more control devices 812. Example control devices 812 that operate on the register of qubits can be used to implement quantum gates or quantum circuits having a plurality of quantum gates, e.g., Pauli gates, Hadamard gates, controlled-NOT (CNOT) gates, controlled-phase gates, Tgates, multi-qubit quantum gates, coupler quantum gates, etc. The one or more control devices 812 may be configured to operate on the quantum system 810 through one or more respective control parameters (e.g., one or more physical control parameters). For example, in some implementations, the multi-level quantum subsystems may be superconducting qubits and the control devices 812 may be configured to provide control pulses to control lines to generate magnetic fields to adjust the frequency of the qubits.

[0086] The quantum hardware 802 may further include readout devices 814 (e.g.. readout resonators). Measurement results 808 obtained via measurement devices may be provided to the classical processors 804 for processing and analyzing. In some implementations, the quantum hardware 802 may include a quantum circuit and the control device(s) 812 and readout devices(s) 814 may implement one or more quantum logic gates that operate on the quantum system 802 through physical control parameters (e.g., microwave pulses) that are sent through wires included in the quantum hardware 802. Further examples of control devices include arbitrary' waveform generators, wherein a DAC (digital to analog converter) creates the signal.

[0087] The readout device(s) 814 may be configured to perform quantum measurements on the quantum system 810 and send measurement results 808 to the classical processors 804. In addition, the quantum hardware 802 may be configured to receive data specifying physical control qubit parameter values 806 from the classical processors 804. The quantum hardware 802 may use the received physical control qubit parameter values 806 to update the action of the control device(s) 812 and readout devices(s) 814 on the quantum system 810. For example, the quantum hardware 802 may receive data specifying new values representing voltage strengths of one or more DACs included in the control devices 812 and may update the action of the DACs on the quantum system 810 accordingly. The classical processors 804 may be configured to initialize the quantum system 810 in an initial quantum state, e.g., by sending data to the quantum hardware 802 specifying an initial set of parameters 806.

[0088] The readout device(s) 814 can take advantage of a difference in the impedance for the 10 > and 11) states of an element of the quantum system, such as a qubit, to measure the state of the element (e.g., the qubit). For example, the resonance frequency of a readout resonator can take on different values when a qubit is in the state |0) or the state 11), due to the nonlinearify of the qubit. Therefore, a microw ave pulse reflected from the readout device 814 carries an amplitude and phase shift that depend on the qubit state. In some implementations, a Purcell filter can be used in conjunction with the readout device(s) 814 to impede microwave propagation at the qubit frequency.

[0089] In some implementations, the quantum system 810 can include a plurality of qubits 820 arranged, for instance, in a two-dimensional grid 822. For clarity, the two- dimensional grid 822 depicted in FIG. 1 includes 16 qubits arranged in a square formation, however in some implementations the system 810 may include a smaller or a larger number of qubits. In some embodiments, the multiple qubits 820 can interact with each other through multiple qubit couplers, e.g.. qubit coupler 824. The qubit couplers can define nearest neighbor interactions between the multiple qubits 820. In some implementations, the strengths of the multiple qubit couplers are tunable parameters. In some cases, the multiple qubit couplers included in the quantum computing system 800 may be couplers with a fixed coupling strength. In some implementations, the multiple qubits 820 may include data qubits, such as qubit 826 and measurement qubits, such as qubit 828. A data qubit is a qubit that participates in a computation being performed by the system 800. A measurement qubit is a qubit that may be used to determine an outcome of a computation performed by the data qubit. That is, during a computation an unknow n state of the data qubit is transferred to the measurement qubit using a suitable physical operation and measured via a suitable measurement operation performed on the measurement qubit.

[0090] In some implementations, each qubit in the multiple qubits 820 can be operated using respective operating frequencies, such as an idling frequency and / or an interaction frequency and / or readout frequency and / or reset frequency. The operating frequencies can vary from qubit to qubit. For instance, each qubit may idle at a different operating frequency. The operating frequencies for the qubits 820 can be chosen before a computation is performed by the calibration system. Some operating frequencies are better than other operating frequencies. One metric for assessing how- good a particular operating frequency is for a particular qubit is energy relaxation time (Tl) for the qubit at the frequency. Lower energy relaxation times can lead to larger quantum computational errors.

[0091] In various implementations, the example system 800 can be implemented as a client device, a server device, or both. The example system 800 can be implemented as part of a distributed computing system. The example system 800 can be implemented along with other example systems, which may be the same or different. The example system 800 can be implemented in a server farm or other facility that operates multiple computing systems to provide computational services to or on behalf of a plurality of client systems. Advantageously, techniques according to example aspects of the present disclosure can provide for improved calibration and maintenance of computing facilities, increasing service uptime, decreasing failure rates, etc.Example Methods

[0092] FIG. 9 depicts an example method 900 for performing a quantum computation using a quantum circuit according to example aspects of the present disclosure. Although FIG. 9 depicts steps performed in a particular order for purposes of illustration and discussion, the methods of the present disclosure are not limited to the particularly illustrated order or arrangement. The various steps of the method 900 can be omitted, rearranged, combined, and / or adapted in various ways without deviating from the scope of the present disclosure. The method 900 can be implemented by any suitable computing system, such as a quantum computing system including quantum hardware in communication with one or more quantum control devices, such as quantum computing system 800 of FIG. 8.

[0093] At 902, example method 900 can include obtaining data indicative of a quantum circuit. Obtaining data can include, for example, receiving data from a computing device (e.g. user device, server device); receiving data from a user (e.g. via input / output device); reading data from one or more non-transitory computer-readable media; generating data (e.g. using an algorithm); etc. Data indicative of a quantum circuit can include, for example, a circuit design, circuit diagram, one or more unitary matrices, software code (e.g. quantum software code in a quantum computing language), etc.

[0094] At 904, example method 900 can include preparing one or more qubits in a known quantum state. Preparing one or more qubits in a known quantum state can include, for example, preparing one or more qubits in a known basis state (e.g. by manipulating a plurality of qubits such that qubits characterized by a particular basis state, e.g. 10) or 11), can be separated from qubits not characterized by that basis state (e.g. physically separated, separately identified, etc ). Preparing one or more qubits in a known quantum state can include, for example, using a control device 812 to perform quantum gating to generate a known multi-qubit basis state. Preparing one or more qubits can include using a control device 812 in a manner described with respect to FIG. 8.

[0095] At 906, example method 900 can include applying one or more quantum gates to one or more qubits to execute a quantum algorithm. For example, in some instances control devices 812 can be used to implement quantum gates or quantum circuits having a plurality of quantum gates, e.g., Pauli gates, Hadamard gates, controlled-NOT (CNOT) gates, controlled-phase gates, T gates, multi-qubit quantum gates, coupler quantum gates, etc., in a manner described with respect to FIG. 8

[0096] At 908, example method 900 can include measuring, using a readout apparatus, a state of at least one of the one or more qubits. The readout apparatus can be, for example, areadout device 814, and method 900 at 908 can in some instances be performed in a manner described with respect to FIG. 8.

[0097] Figure 10 depicts a flowchart diagram of an example method for assembling a quantum computing system according to example embodiments of the present disclosure. Although Figure 10 depicts steps performed in a particular order for purposes of illustration and discussion, the methods of the present disclosure are not limited to the particularly illustrated order or arrangement. The various steps of example method 1000 can be omitted, rearranged, combined, and / or adapted in various ways without deviating from the scope of the present disclosure.

[0098] At 1002. example method 1000 can include testing a respective isolation performance (e.g., a measure of reverse isolation in decibels, etc.) of each respective stripline circulator of a plurality of respective stripline circulators. In some instances, a stripline circulator can be, comprise, or be comprised by a circulator 102. In some instances, testing an isolation performance can include testing a plurality of isolation performances (e.g., isolation of signal entering a first port and exiting a second port; isolation of signal entering the second port and exiting a third port; isolation of signal entering a third port and exiting the first port; etc.) for each circulator. In some instances, additional testing can be performed to determine additional electrical properties (e.g., impedance, etc.) associated with one or more ports; one or more other circulator components (e.g.. ground structures 104, center conductors 330, etc.) or combinations of components; or one or more respective circulators as a whole.

[0099] At 1004, example method 1000 can include selecting, based on the testing, at least one first stripline circulator and at least one second stripline circulator, wherein the isolation performance of the first stripline circulator is better than the isolation performance of the second stripline circulator. In some instances, selecting the first and second circulators can include sorting a plurality of respective circulators or respective ports based on a plurality of respective isolation performances of the circulators, and selecting the highest-performing circulator as the first circulator. In some instances, selecting the first and second circulators can include, for example, obtaining (e.g., determining, defining, receiving, retrieving, etc.) an isolation performance threshold (e.g., in decibels); selecting, responsive to determining that the first circulator exceeds the isolation performance threshold, the first circulator; and selecting, responsive to determining that the second circulator does not exceed the isolation performance threshold, the second circulator.

[0100] In some instances, additional circulators can be selected in a similar (e.g., same) manner. For example, a third stripline circulator can have a better isolation performance thanthe second stripline circulator, and can be selected for use in a circuit (e.g., multi-circulator assembly) in which the first stripline circulator is used.

[0101] In some instances, individual ports can be selected, based on the testing, for use in particular circuits or for use in combination with other ports. For example, in some instances, a first port associated with a first respective stripline circulator can be matched to a fourth port associated with a third stripline circulator based on one or more tested electrical properties (e.g., impedance, etc.). For example, in some instances, a fourth port can be selected based on the one or more tested electrical properties. In some instances, at least one electrical property (e.g., impedance) of the first port or fourth port can be adjusted based on the testing (e.g., to improve an impedance match between the first port and fourth port. etc.).

[0102] At 1006. example method 1000 can include assembling a readout circuit comprising at least one first stage and at least one second stage, the first stage being sequentially before the second stage in a readout circuit, wherein the first stage comprises the first stripline circulator, and the second stage comprises the second stripline circulator. In some instances, additional or alternative circuits can be assembled. For example, the first stripline circulator can be selected for and included in any circuit (e.g.. quantum computing circuit, etc.) having demanding performance requirements (e g., requiring strong reverse isolation, etc.) and the second selected stripline circulator can be selected for and included in any circuit (e.g., quantum computing circuit, etc.) having less demanding performance requirements. As another example, the first stripline circulator can be selected for and included in any first circuit (e.g., quantum computing circuit, etc.) wherein a reduction in reverse isolation performance (e.g., in decibels) of the first circuit has a greater impact on a fidelity of a qubit, quantum gate, or quantum algorithm compared to a same-magnitude (e.g., in decibels) reduction in reverse isolation performance of a second circuit comprising the second stripline circulator. In some instances, a first stage or second stage can be, comprise, or be comprised by a multi-circulator assembly, such as an example multi-circulator assembly described with respect to FIGS. 6-7.Additional Disclosure

[0103] Implementations of the digital, classical, and / or quantum subject matter and the digital functional operations and quantum operations described in this specification can be implemented in digital electronic circuitry, suitable quantum circuitry' or, more generally, quantum computational systems, in tangibly-implemented digital and / or quantum computer software or firmware, in digital and / or quantum computer hardware, including the structuresdisclosed in this specification and their structural equivalents, or in combinations of one or more of them. The term "‘quantum computing systems" may include, but is not limited to, quantum computers / computing systems, quantum information processing systems, quantum cryptography systems, or quantum simulators.

[0104] Implementations of the digital and / or quantum subject matter described in this specification can be implemented as one or more digital and / or quantum computer programs (e.g.. one or more modules of digital and / or quantum computer program instructions encoded on a tangible non-transitory storage medium for execution by, or to control the operation of, data processing apparatus). The digital and / or quantum computer storage medium can be a machine-readable storage device, a machine-readable storage substrate, a random or serial access memory device, one or more qubits / qubit structures, or a combination of one or more of them. Alternatively or in addition, the program instructions can be encoded on an artificially -generated propagated signal that is capable of encoding digital and / or quantum information (e.g., a machine-generated electrical, optical, or electromagnetic signal) that is generated to encode digital and / or quantum information for transmission to suitable receiver apparatus for execution by a data processing apparatus.

[0105] The terms quantum information and quantum data refer to information or data that is carried by, held, or stored in quantum systems, where the smallest non-trivial system is a qubit (i.e., a system that defines the unit of quantum information). It is understood that the term “qubit” encompasses all quantum systems that may be suitably approximated as a two- level system in the corresponding context. Such quantum systems may include multi-level systems, e.g., with two or more levels. By way of example, such systems can include atoms, electrons, photons, ions or superconducting qubits. In many implementations the computational basis states are identified with the ground and first excited states, however it is understood that other setups where the computational states are identified with higher level excited states (e.g., qubits) are possible.

[0106] The term “data processing apparatus” refers to digital and / or quantum data processing hardware and encompasses all kinds of apparatus, devices, and machines for processing digital and / or quantum data, including by way of example a programmable digital processor, a programmable quantum processor, a digital computer, a quantum computer, or multiple digital and quantum processors or computers, and combinations thereof. The apparatus can also be, or further include, special purpose logic circuitry, e.g., an FPGA (field programmable gate array), or an ASIC (application-specific integrated circuit), or a quantum simulator, i.e., a quantum data processing apparatus that is designed to simulate or produceinformation about a specific quantum system. In particular, a quantum simulator is a special purpose quantum computer that does not have the capability to perform universal quantum computation. The apparatus can optionally include, in addition to hardware, code that creates an execution environment for digital and / or quantum computer programs, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them.

[0107] A digital or classical computer program, which may also be referred to or described as a program, software, a software application, a module, a software module, a script, or code, can be written in any form of programming language, including compiled or interpreted languages, or declarative or procedural languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a digital computing environment. A quantum computer program, which may also be referred to or described as a program, software, a software application, a module, a software module, a script, or code, can be written in any form of programming language, including compiled or interpreted languages, or declarative or procedural languages, and translated into a suitable quantum programming language, or can be written in a quantum programming language, e g., QCL, Quipper, Cirq, etc..

[0108] A digital and / or quantum computer program may, but need not, correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data, e.g., one or more scripts stored in a markup language document, in a single file dedicated to the program in question, or in multiple coordinated files, e.g., files that store one or more modules, sub-programs, or portions of code. A digital and / or quantum computer program can be deployed to be executed on one digital or one quantum computer or on multiple digital and / or quantum computers that are located at one site or distributed across multiple sites and interconnected by a digital and / or quantum data communication network. A quantum data communication network is understood to be a network that may transmit quantum data using quantum systems, e.g. qubits. Generally, a digital data communication network cannot transmit quantum data, however a quantum data communication network may transmit both quantum data and digital data.

[0109] The processes and logic flows described in this specification can be performed by one or more programmable digital and / or quantum computers, operating with one or more digital and / or quantum processors, as appropriate, executing one or more digital and / or quantum computer programs to perform functions by operating on input digital and quantum data and generating output. The processes and logic flows can also be performed by, andapparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA or an ASIC, or a quantum simulator, or by a combination of special purpose logic circuitry or quantum simulators and one or more programmed digital and / or quantum computers.

[0110] For a system of one or more digital and / or quantum computers or processors to be “configured to” or “operable to” perform particular operations or actions means that the system has installed on it software, firmware, hardware, or a combination of them that in operation cause the system to perform the operations or actions. For one or more digital and / or quantum computer programs to be configured to perform particular operations or actions means that the one or more programs include instructions that, when executed by digital and / or quantum data processing apparatus, cause the apparatus to perform the operations or actions. A quantum computer may receive instructions from a digital computer that, when executed by the quantum computing apparatus, cause the apparatus to perform the operations or actions.

[0111] Digital and / or quantum computers suitable for the execution of a digital and / or quantum computer program can be based on general or special purpose digital and / or quantum microprocessors or both, or any other kind of central digital and / or quantum processing unit. Generally, a central digital and / or quantum processing unit will receive instructions and digital and / or quantum data from a read-only memory, or a random access memory, or quantum systems suitable for transmitting quantum data, e.g. photons, or combinations thereof.

[0112] Some example elements of a digital and / or quantum computer are a central processing unit for performing or executing instructions and one or more memory devices for storing instructions and digital and / or quantum data. The central processing unit and the memory can be supplemented by, or incorporated in, special purpose logic circuitry or quantum simulators. Generally, a digital and / or quantum computer will also include, or be operatively coupled to receive digital and / or quantum data from or transfer digital and / or quantum data to, or both, one or more mass storage devices for storing digital and / or quantum data, e.g., magnetic, magneto-optical disks, or optical disks, or quantum systems suitable for storing quantum information. However, a digital and / or quantum computer need not have such devices.

[0113] Digital and / or quantum computer-readable media suitable for storing digital and / or quantum computer program instructions and digital and / or quantum data include all forms of non-volatile digital and / or quantum memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flashmemory' devices; magnetic disks, e.g., internal hard disks or removable disks; magnetooptical disks; and CD-ROM and DVD-ROM disks; and quantum systems, e.g.. trapped atoms or electrons. It is understood that quantum memories are devices that can store quantum data for a long time with high fidelity' and efficiency, e.g., light-matter interfaces where light is used for transmission and matter for storing and preserving the quantum features of quantum data such as superposition or quantum coherence.

[0114] Control of the various systems described in this specification, or portions of them, can be implemented in a digital and / or quantum computer program product that includes instructions that are stored on one or more tangible, non-transitory machine-readable storage media, and that are executable on one or more digital and / or quantum processing devices. The systems described in this specification, or portions of them, can each be implemented as an apparatus, method, or electronic system that may include one or more digital and / or quantum processing devices and memory to store executable instructions to perform the operations described in this specification.

[0115] While this specification contains many specific implementation details, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features that may be specific to particular implementations. Certain features that are described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable sub combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

[0116] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system modules and components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

[0117] Particular implementations of the subj ect matter have been described. Other implementations are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In some cases, multitasking and parallel processing may be advantageous.

[0118] Aspects of the disclosure have been described in terms of illustrative implementations thereof. Numerous other implementations, modifications, or variations within the scope and spirit of the appended claims can occur to persons of ordinary' skill in the art from a review of this disclosure. Any and all features in the following claims can be combined or rearranged in any way possible. Accordingly, the scope of the present disclosure is by way of example rather than by way of limitation, and the subject disclosure does not preclude inclusion of such modifications, variations or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art. Moreover, terms are described herein using lists of example elements joined by conjunctions such as "and." “or,” “but,” etc. It should be understood that such conjunctions are provided for explanatory purposes only. Lists joined by a particular conjunction such as “or,” for example, can refer to “at least one of’ or “any combination of’ example elements listed therein, with “or” being understood as “and / or” unless otherwise indicated. Also, terms such as “based on” should be understood as “based at least in part on.”

[0119] Those of ordinary skill in the art, using the disclosures provided herein, will understand that the elements of any of the claims, operations, or processes discussed herein can be adapted, rearranged, expanded, omitted, combined, or modified in various w ays without deviating from the scope of the present disclosure. Some of the claims are described w ith a letter reference to a claim element for exemplary illustrated purposes and is not meant to be limiting. The letter references do not imply a particular order of operations. For instance, letter identifiers such as (a), (b), (c),..., (i), (ii), (iii),... , etc. can be used to illustrate operations. Such identifiers are provided for the ease of the reader and do not denote a particular order of steps or operations. An operation illustrated by a list identifier of (a), (i), etc. can be performed before, after, or in parallel with another operation illustrated by a list identifier of (b), (ii), etc.

Claims

WHAT IS CLAIMED IS:

1. A stripline circulator comprising: one or more ground structures; one or more dielectrics; at least one center conductor; a first port comprising a female connector attached to the at least one center conductor; a second port; and a third port; wherein the stripline circulator is characterized by non-reciprocal signal transmission behavior comprising: responsive to a first signal being provided as an input signal to the first port, the second port provides the first signal as an output signal; and responsive to a second signal being provided as the input signal to the second port, the third port provides the second signal as the output signal.

2. The stripline circulator of claim 1, wherein the female connector is electrically connected to the at least one center conductor and is not electrically connected to the one or more ground structures.

3. The stripline circulator of claim 1, wherein the female connector is a single-conductor connector.

4. The stripline circulator of claim 1, wherein the female connector is flush with or recessed from at least one exterior surface of the one or more ground structures.

5. The stripline circulator of claim 1, further comprising an interface for attaching, using a fastener, at least one ground structure of the one or more ground structures to a ground structure of a second stripline circulator.

6. A quantum computing system, comprising: a plurality of qubits;a quantum logic circuit configured to perform one or more quantum operations on the plurality of qubits; and a readout circuit comprising a multi-circulator assembly, the multi-circulator assembly comprising at least a first stripline circulator and a second stripline circulator; wherein the first stripline circulator comprises: one or more ground structures; one or more dielectrics; at least one center conductor; a first port; a second port; and a third port; wherein the second stripline circulator comprises at least one center conductor electrically connected to the at least one center conductor of the first stripline circulator via the first port; and the second stripline circulator comprises at least one ground structure electrically connected with at least one ground structure of the one or more ground structures of the first stripline circulator.

7. The quantum computing system of claim 6, wherein the at least one ground structure of the second stripline circulator is in physical contact with the at least one ground structure of the first stripline circulator.

8. The quantum computing system of claim 6, wherein the at least one ground structure of the one or more ground structures of the first stripline circulator is attached to the at least one ground structure of the second stripline circulator using a fastener.

9. The quantum computing system of claim 6, wherein the first port comprises a first female connector attached to the at least one center conductor.

10. The quantum computing system of claim 9, wherein the second stripline circulator comprises a fourth port comprising a second female connector attached to a center conductor of the second stripline circulator, and further comprising: a male connector inserted into the first female connector and second female connector.

11. The quantum computing system of claim 9, wherein the first port is flush with or recessed from an exterior surface of the one or more ground structures.

12. The quantum computing system of claim 6, wherein the first stripline circulator is characterized by non-reciprocal signal transmission behavior comprising: responsive to a first signal being provided as an input signal to the first port, the second port provides the first signal as an output signal; and responsive to a second signal being provided as the input signal to the second port, the third port provides the second signal as the output signal.

13. The quantum computing system of claim 6, further comprising a resistive terminator connected to the second port.

14. The quantum computing system of claim 6, further comprising a cry ogenic chamber, wherein the plurality of qubits, the quantum logic circuit, and the multi-circulator assembly- are positioned within the cryogenic chamber.

15. The quantum computing system of claim 14, wherein the at least one ground structure of the one or more ground structures of the first stripline circulator is in thermal contact with a ground structure of the second stripline circulator.

16. A method for assembling a quantum computing system, comprising: providing a plurality of respective stripline circulators, wherein each respective stripline circulator comprises: one or more ground structures; one or more dielectrics; at least one center conductor; and at least one port comprising a female connector attached to the at least one center conductor, wherein the female connector is flush with or recessed from an exterior surface of the one or more ground structures; and assembling a readout circuit comprising at least one first stage and at least one second stage, the first stage being sequentially before the second stage in the readout circuit;wherein the first stage comprises a first stripline circulator of the plurality of respective stripline circulators, and the second stage comprises a second stripline circulator of the plurality of stripline circulators.

17. The method of claim 16, wherein the first stage comprises a multi-circulator assembly comprising the first stripline circulator and a third stripline circulator of the plurality of respective stripline circulators.

18. The method of claim 17, further comprising selecting, based at least in part on an isolation performance of the first stripline circulator, the first stripline circulator for inclusion in the at least one first stage, wherein: an isolation performance of the first stripline circulator is better than an isolation performance of the second stripline circulator; and an isolation performance of the third stripline circulator is better than the isolation performance of the second stripline circulator.

19. The method of claim 17, wherein the multi-circulator assembly comprises a male connector inserted into the female connector of the first stripline circulator and the female connector of the third stripline circulator.

20. The method of claim 17, wherein at least one exterior surface of the one or more ground structures of the first stripline circulator is in physical contact with at least one exterior surface of the one or more ground structures of the third stripline circulator.

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