Multi-pole multi-band isolator device

Abstract

The device comprises a filter circuit and a nonlinear mixing device. The filter circuit has a first port, a second port, a first band-pass filter, and a second band-pass filter. The nonlinear mixing device responds to a control signal by coupling the poles of the first band-pass filter to the respective poles of the second band-pass filter in order to cause non-reciprocal transmission of the signal from the first port to the second port.

Description

[Background technology]

[0001] This disclosure relates in general to quantum computing, and more particularly to microwave isolator devices and isolation technologies for use, for example, in superconducting quantum computing systems. Superconducting quantum computing systems are implemented using circuit quantum electrodynamics (QED) devices that utilize the quantum dynamics of electromagnetic fields in superconducting circuits, including superconducting qubits, to generate and process quantum information. Generally, a superconducting qubit is an electronic circuit that behaves as a quantum mechanical anharmonic (nonlinear) oscillator with quantized states when implemented using components such as superconducting tunnel junctions (e.g., Josephson junctions), inductors, and / or capacitors, and cooled to cryogenic temperatures.

[0002] The cryogenic hardware used to build quantum computers with superconducting qubits requires a variety of microwave components, including microwave couplers, filters, amplifiers, circulators, and isolators. Traditionally, these components were implemented via discrete components in the qubit control and readout signal paths. As the number of qubits implemented in a quantum processor increases to hundreds, thousands, or more, integrating these peripheral components in a way that reduces the overall system footprint, thermal load, and added noise has become a critical scaling challenge. Ferrite-based microwave isolators remain one of the largest physically large devices, persisting as discrete components. They are commonly used in qubit readout chains to protect qubits and resonators from broadband noise and unwanted signals emitted from downstream components such as amplifiers. The need to place numerous such ferrite-based microwave isolators in the mixing chamber of a dilution refrigerator results in a bulky structure, limiting system scaling and integration to accommodate increasing qubit numbers. [Overview of the project]

[0003] Exemplary embodiments of this disclosure include techniques for implementing isolated circuits that provide non-reciprocal transmission of signals in a signal path of a quantum computing system. For example, an exemplary embodiment has a device comprising a filter circuit and a nonlinear mixed device. The filter circuit comprises a first port, a second port, a first band-pass filter, and a second band-pass filter. The nonlinear mixed device responds to a control signal to couple the poles of the first band-pass filter to the respective poles of the second band-pass filter in order to cause non-reciprocal transmission of signals from the first port to the second port.

[0004] Advantageously, by using the device as a replacement for discrete ferrite-based isolator devices, non-reciprocal transmission of signals in the signal paths of quantum computing systems, such as qubit control and readout chains, can be enabled, thereby reducing the cost and footprint of implementing isolation in such control and readout chains. The device provides a non-magnetic solution for isolation, can be positioned relatively close to the quantum processor and / or integrated on an integrated circuit chip, while having a much smaller footprint compared to discrete ferrite-based isolation devices, and at the same time providing similar isolation and electrical properties to ferrite-based isolation devices.

[0005] In another exemplary embodiment, the system comprises a quantum processor having qubits, and a readout signal path configured to transmit signals read from one or more of the qubits of the quantum processor. The readout signal path includes an isolator circuit. The isolator circuit includes a first port, a second port, a first band-pass filter, and a second band-pass filter, and a nonlinear mixed device. The nonlinear mixed device responds to a control signal to couple the poles of the first band-pass filter to the respective poles of the second band-pass filter in order to cause non-reciprocal transmission of signals from the first port to the second port through the isolator circuit.

[0006] In another exemplary embodiment, as can be combined with the preceding paragraph, a first band-pass filter includes a first passband having a first center frequency, and a second band-pass filter includes a second passband having a second center frequency. The first and second passbands are non-overlapping passbands. The control signal applied to the nonlinear mixed device includes a radio frequency signal having a frequency that is a function of the difference between the first and second center frequencies.

[0007] Advantageously, an isolator circuit with a multi-bandpass filter structure allows the bandpass filters to be designed with separate, non-overlapping passbands, where the control signals can have frequencies outside the first and second passbands of the first and second multi-pole bandpass filters. Additionally, the relationship between the control signal frequencies and the first and center frequencies of the respective first and second passbands provides flexibility in the design of the isolator circuit. For example, given a desired center frequency and a desired control signal frequency for the first bandpass filter, the second bandpass filter can be designed to have the required center frequency based on the desired control signal frequency and the center frequency of the first bandpass filter.

[0008] Another exemplary embodiment comprises a device including an isolator circuit. The isolator circuit comprises a first port and a second port, a first multipole immittance inverting bandpass filter, a second multipole immittance inverting bandpass filter, a nonlinear mixer device, and a transmission line commonly connected to each of the nonlinear mixer devices. The nonlinear mixer device connects the poles of the first multipole immittance inverting bandpass filter to each of the poles of the second multipole immittance inverting bandpass filter. The transmission line is configured to apply a control signal to each of the nonlinear mixer devices at a predetermined frequency with different phase shifts to cause non-reciprocal transmission of a signal from the first port to the second port of the isolator circuit.

[0009] Advantageously, the transmission line can be designed to have an electrical / physical length (based on the frequency of the control signal) that gives a desired phase shift (phase difference) to the control signal applied to the nonlinear mixed devices at different points along the transmission line. This configuration allows for the use of a single common control signal line to drive all nonlinear mixed devices connected at different points along the transmission line, for example, extending through a cryostat to an isolated circuit and providing a single control signal (e.g., one or more radio frequency signals on the order of GHz). If the frequency of the control signal is on the order of GHz, the electrical length of the transmission line is small enough to be fabricated "on-chip" with the isolated circuit, reducing the control signal I / O overhead to the isolator circuit and other similar isolator circuits in the signal path of a given quantum processing system.

[0010] Another exemplary embodiment comprises a quantum processor having qubits, and a system having a readout signal path configured to transmit signals read from one or more of the qubits of the quantum processor. The readout signal path includes an isolator circuit. The isolator circuit comprises a first port and a second port, a first multipole immittance inverting bandpass filter, a second multipole immittance inverting bandpass filter, a nonlinear mixed device, and a transmission line commonly connected to each of the nonlinear mixed devices. The nonlinear mixed device connects the poles of the first multipole immittance inverting bandpass filter to each pole of the second multipole immittance inverting bandpass filter. The transmission line is configured to apply control signals to each of the nonlinear mixed devices at predetermined frequencies with different phase shifts to cause non-reciprocal transmission of signals from the first port to the second port of the isolator circuit.

[0011] Another embodiment includes a method that involves applying a control signal to a nonlinear mixed device configured to couple the poles of the first band-pass filter to the respective poles of the second band-pass filter in order to cause non-reciprocal transmission of a signal from a first port of the first band-pass filter to a second port of the first band-pass filter.

[0012] In another exemplary embodiment, as can be combined with the preceding paragraph, the nonlinear mixed device includes a DC superconducting quantum interference device.

[0013] In another exemplary embodiment, as can be combined with the preceding paragraph, the nonlinear mixed device includes Josephson parametric transducer devices, each Josephson parametric transducer device including a Josephson ring modulator configured to couple the poles of the first bandpass filter and the second bandpass filter, respectively.

[0014] Other embodiments will be described in the following detailed description of exemplary embodiments, which should be read in conjunction with the attached figures. [Brief explanation of the drawing]

[0015] [Figure 1] This is a high-level schematic diagram of a Josephson multipole multiband isolator circuit according to an exemplary embodiment of the present disclosure.

[0016] [Figure 2] This figure schematically illustrates a Josephson multipole multiband isolator circuit according to another exemplary embodiment of the present disclosure.

[0017] [Figure 3] This figure schematically illustrates a Josephson multipole multiband isolator circuit according to another exemplary embodiment of the present disclosure.

[0018] [Figure 4-1] Figures 4A and 4B schematically show the scattering parameters of a Josephson multipole multiband isolator circuit according to an exemplary embodiment of the present disclosure. [Figure 4-2] Figures 4C and 4D schematically show the scattering parameters of a Josephson multipole multiband isolator circuit according to an exemplary embodiment of the present disclosure.

[0019] [Figure 5] This figure schematically illustrates a Josephson multipole multiband isolator circuit according to another exemplary embodiment of the present disclosure.

[0020] [Figure 6] This figure schematically illustrates a superconducting Josephson parametric transducer that may be used to implement a three-wave mixing device of the Josephson multipole multiband isolator circuit shown in Figure 5, according to an exemplary embodiment of the present disclosure.

[0021] [Figure 7] This figure schematically illustrates a Josephson multipole multiband isolator circuit according to another exemplary embodiment of the present disclosure.

[0022] [Figure 8] This figure schematically illustrates a readout circuit for a quantum processing system, according to an exemplary embodiment of the present disclosure, in which a Josephson multipole multiband isolator circuit can be implemented in the qubit readout signal path to provide isolation.

[0023] [Figure 9] This figure schematically illustrates a quantum computing system according to an exemplary embodiment of the present disclosure.

[0024] [Figure 10] This figure schematically illustrates an exemplary structure of a computing environment for hosting a quantum computing platform and performing quantum information processing, according to exemplary embodiments of the present disclosure. [Modes for carrying out the invention]

[0025] Exemplary embodiments of the present disclosure are described in further detail here with respect to isolator circuits for use in quantum computing systems. In particular, exemplary embodiments of the present disclosure include Josephson multipole multiband isolator circuits that can be used to provide isolation between cryogenic components in a dilution refrigeration system. For example, the exemplary Josephson multipole multiband isolator circuits discussed herein may be implemented to provide isolation in the read signal chain between a quantum processor and a read circuit when reading the quantum state of a superconducting qubit of a quantum processor.

[0026] Please understand that the various features shown in the attached drawings are schematic diagrams and not drawn to scale. Furthermore, the same or similar reference numerals are used throughout the drawings to indicate the same or similar features, elements, or structures, and therefore, detailed descriptions of the same or similar features, elements, or structures are not repeated in each of the drawings. In addition, the term “exemplary” as used herein means “serving as an example, illustration, or descriptive example.” Any embodiment or design described “exemplary” herein shall not be construed as preferable or advantageous to other embodiments or designs.

[0027] Furthermore, it should be understood that the expression “configured to be used with circuits, structures, elements, components, etc. to perform one or more functions or provide any functions” is intended to encompass the following embodiments, where circuits, structures, elements, components, etc. are implemented in hardware, software, and / or combinations thereof, and are implemented in hardware-inclusive implementations, the hardware may include quantum circuit elements (e.g., quantum processors, qubits, Josephson junction devices, Josephson parametric converters (JPCs), quantum limit amplifiers (QLAs), qubit coupler circuits, Josephson multipole multiband isolator circuits, etc.), discrete circuit elements (e.g., transistors, inverters, etc.), programmable elements (e.g., application-specific integrated circuit (ASIC) chips, field-programmable gate array (FPGA) chips, etc.), processing devices (e.g., central processing units (CPUs), graphics processing units (GPUs), etc.), one or more integrated circuits, and / or combinations thereof. Therefore, as an example only, when a circuit, structure, element, component, etc. is defined as being configured to provide a particular function, the intent is to cover, but is not limited to, embodiments comprising elements, processing devices, and / or integrated circuits that perform a particular function when the circuit, structure, element, component, etc. is in an operational state (e.g., connected in a system or otherwise deployed, powered on, receiving input, and / or producing output), and also cover embodiments when the circuit, structure, element, component, etc. is in a non-operational state (e.g., not connected, not located in a system, not powered on, not receiving input, and / or not producing output), or in a partially operational state.

[0028] Figure 1 is a high-level schematic diagram of a Josephson multipole multiband isolator circuit according to an exemplary embodiment of the present disclosure. In particular, Figure 1 schematically shows a Josephson multipole multiband isolator circuit 100 including a first multipole bandpass filter 110, a second multipole bandpass filter 120, and a plurality (n) nonlinear mixing devices 130-1, ..., 130-n (typically mixing device 130). The first multipole bandpass filter 110 has an admittance inverting multipole bandpass filter network including a first port (port 1), a second port (port 2), a plurality (m) admittance inverters 112-1, ..., 112-m (typically admittance inverter 112), and a plurality (n) shunt resonators 114-1, ..., 114-n (typically shunt resonator 114). The shunt resonators 114-1, ..., 114-n (for example, LC resonators) have respective resonant (angular) frequencies ω1, ..., ω n This consists of, where n is the number of "poles" of the first multi-pole bandpass filter 110. Each shunt resonator 114-1, ..., 114-n is placed between two admittance inverters 112, so that the number m of admittance inverters 112 is m = n + 1. The admittance inverters 112 essentially function as impedance matching circuits (for example, to match the impedance between adjacent shunt resonators 114, and to match the impedance between port 1 and port 2 and the shunt resonators 114 adjacent to the ports). The admittance inverters 112 can be implemented using capacitive π networks, inductive π networks, and / or quarter-wavelength transmission lines.

[0029] Similarly, the second multipole bandpass filter 120 includes an admittance inverting multipole bandpass filter network including a first termination T1 and a second termination T2 (e.g., 50-ohm terminations), a plurality (m) admittance inverters 122-1, ..., 122-m (generally admittance inverters 122), and a plurality (n) shunt resonators 124-1, ..., 124-n (generally shunt resonators 124). In an exemplary embodiment, the second multipole bandpass filter 120 includes ports to terminated ports 3 and 4. The shunt resonators 124-1, ..., 124-n (e.g., LC resonators) each have their respective resonant (angular) frequencies

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[0030] As schematically shown in Figure 1, the shunt resonators 114-1, ..., 114-n of the first multipole bandpass filter 110 are coupled to the shunt resonators 124-1, ..., 124-n of the second multipole bandpass filter 120, respectively. In particular, shunt resonators 114-1 and 124-1 are coupled via a mixing device 130-1, and shunt resonators 114-n and 124-n are coupled via a mixing device 130-n. Generally, the nonlinear mixing device 130 includes a superconducting nonlinear element (e.g., a Josephson junction) to enable, for example, a three-wave mixing function (parametric signal mixing). As will be described in more detail below, the nonlinear mixing device 130 can be implemented using a device with superconducting nonlinear inductance, such as a DC-superconducting quantum interference device (DC-SQUID) or a Josephson-parametric converter (JPC) with a Josephson-ring modulator.

[0031] The Josephson multipole multi-band isolator circuit 100 is configured to provide isolation (e.g., broadband non-reciprocal transmission) by designing the first and second multipole bandpass filters 110 and 120 to have different non-overlapping passbands. For example, the first multipole bandpass filter 110 has a first passband (e.g., B C shown as the signal passband) with a center (angular) frequency of ω Signal , and the second multipole bandpass filter 120 has a second passband (e.g., B C shown as the idler passband) with a center (angular) frequency of ω Idler '. In some embodiments, the hybrid devices 130-1,..., 130-n have the same frequency ω p but different phases and / or the same (e.g., nominally identical) or different amplitudes depending on the application for the radio frequency (RF) pump signals P1,..., P n respectively.

[0032] Specifically, the RF pump signals P1,..., P n driving each of the hybrid devices 130-1,..., 130-n have the same frequency ω C which is a function of the difference between the center frequencies ω C ' and ω p of the respective multipole bandpass filters. For example, in an exemplary embodiment, when ω C > ω C ', ω p = ω C ― ω C ', and when ω C < ω C ', ω p = ω C ' ― ω<​​​​​​​​​​​​The frequency and

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[0033] In the calculation, the nonlinear mixing device 130 enables non-reciprocal transmission of signals between port 1 and port 2, and the signal passband B Signal and idler passband B Idler It facilitates energy conversion (frequency conversion) between them. For example, the Josephson multipole multiband isolator circuit 100 has a second multipole bandpass filter 120 that passes through the idler passband B Idler It includes and the first multi-pole bandpass filter 110 has a signal passband B Signal It is assumed that it is configured to include the following: The nonlinear mixing device 130 transmits from port 1 to port 2 of the first multi-pole bandpass filter 110 (S 21 ) may be driven to enable unity power transmission, and at the same time, from port 2 to port 1 (S 12 This suppresses the transmission of power in the opposite direction. In this example, the ports of the second multi-pole bandpass filter 120 can be cold-terminated (e.g., 50Ω termination) as shown in Figure 1, or open-ended depending on the filter configuration.

[0034] More specifically, the same frequency ω p =|ω C ―ω C '| and when driven by an RF pump signal with an appropriate phase difference, forward (e.g., S 21 The energy that moves in the reverse direction (S) eventually returns to the carrier frequency, resulting in unity transmission, and simultaneously in the reverse direction (S 12 The energy that proceeds to the idler passband B Idler Mixing devices 130-1, ..., 130-n distribute the signal through the first and second multi-pole bandpass filters 110 and 120 so that it is terminated in a matched load, and the signal passband B Signal From idler passband B Idler up to and signal passband B Signal This facilitates the frequency conversion of the microwave signal returning to port 1. Essentially, as the microwave signal propagates between port 1 and port 2 through the filter stage, the phase difference is imposed on the signal that is converted back to its original frequency. If the converted signal is mixed with the unconverted signal, the converted and unconverted signals will have the same frequency but different phases, which suppresses unidirectional transmission through destructive interference (e.g., S 12 ), or in order to achieve unity transmission in other directions, they are coupled together in phase via constitutive interference (for example, S 21 It functions in such a way.

[0035] Note that the Josephson multipole multiband isolator circuit 100 can implement four-wave mixing. In this example, the frequency of the RF pump control signal is as follows:

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[0036] Furthermore, while the exemplary embodiment in Figure 1 (and other embodiments discussed herein) is described in the context of admittance-inverting multipole bandpass filters, a Josephson multipole multiband isolator circuit may be an impedance-inverting multipole bandpass filter implemented using an impedance inverter instead of an admittance inverter. In this regard, the exemplary Josephson multipole multiband isolator circuits discussed herein may be implemented using an immittance-inverting multipole bandpass filter, and the terms “immittance-inverting” or “immittance inverter” broadly refer to terms such as admittance-inverting, admittance inverter, impedance-inverting, or impedance inverter.

[0037] Figure 1 shows how, in order to cause non-reciprocal transmission of signals from the first port to the second port, the poles of the first bandpass filter (e.g., shunt resonator 114) are connected to each pole of the second bandpass filter (e.g., shunt resonator 124), with respect to each control signal (e.g., pump signals P1, ..., P n It should be understood that this shows an exemplary high-level structure of an isolator circuit having a filter circuit including a first port (e.g., port 1) responding to a second port (e.g., port 2), a first band-pass filter (e.g., first multipole band-pass filter 110), a second band-pass filter (e.g., second multipole band-pass filter 120), and a nonlinear mixing device (e.g., nonlinear mixing device 130). Various embodiments of the Josephson multipole multiband isolator circuit can be implemented based on the general isolator structure shown in Figure 1.

[0038] For example, Figure 2 schematically illustrates a Josephson multipole multiband isolator circuit according to another exemplary embodiment of the present disclosure. Generally, Figure 2 schematically illustrates a Josephson multipole multiband isolator circuit 200 based on the structure of Figure 1, where the mixed device 130 of Figure 1 is implemented using DC-SQUIDs. In particular, the Josephson multipole multiband isolator circuit 200 has a nonlinear mixed device 230 including a first multipole bandpass filter 210, a second multipole bandpass filter 220, and a first DC-SQUID 230-1 and a second DC-SQUID 230-2. Additionally, the Josephson multipole multiband isolator circuit 200 includes a nonlinear mixed device 230 having an RF signal generator circuit 240 including a first RF signal generator 240-1 and a second RF signal generator 240-2, and a coupling inductor L disposed adjacent to each of the first and second DC-SQUIDs 230-1 and 230-2. C1 and L C2 It has a circuit for driving it.

[0039] The first multipole bandpass filter 210 has an admittance inverting multipole bandpass filter network including a first port (port 1), a second port (port 2), a plurality of admittance inverters 212-1, 212-2, and 212-3 (generally, admittance inverters 212), and a plurality of shunt resonators 214-1 and 214-2 (generally, shunt resonators 214). The shunt resonators 214 have LC resonators, where shunt resonator 214-1 includes an inductor L1 and a capacitor C1, and shunt resonator 214-2 includes an inductor L2 and a capacitor C2. The admittance inverters 212 can be implemented using a capacitive π network, an inductive π network, and / or a quarter-wavelength transmission line.

[0040] The second multipole bandpass filter 220 has an admittance inverting multipole bandpass filter network including a third port (port 3), a fourth port (port 4), a plurality of admittance inverters 222-1, 222-2, and 222-3 (generally admittance inverter 222), and a plurality of shunt resonators 224-1 and 224-2 (generally shunt resonator 224). The shunt resonators 224 have LC resonators, where shunt resonator 224-1 includes an inductor L3 and a capacitor C3, and shunt resonator 224-2 includes an inductor L4 and a capacitor C4. The admittance inverters 222 can be implemented using a capacitive π network, an inductive π network, and / or a quarter-wavelength transmission line.

[0041] The first and second DC-SQUIDs 230-1 and 230-2 each include a first Josephson junction J1 and a second Josephson junction J2 connected in parallel so that an external magnetic flux φ, which can be threaded to perform parametric mixed operations as discussed herein, forms a superconducting loop (referred to as a SQUID loop) through it. Each DC-SQUID 230-1 and 230-2 has an effective critical current I CS A single Josephson junction having a magnetic flux Φ, and a Josephson energy E that can be adjusted by inductively coupling the magnetic flux Φ to the SQUID loop. JS It operates effectively as such. Josephson junctions J1 and J2 have nonlinear inductances, and their critical currents may be the same, similar, or different.

[0042] As schematically shown in Figure 2, the first DC-SQUID 230-1 is connected between the first node N1 and the ground node, and the second DC-SQUID 230-2 is connected between the second node N2 and the ground node. Additionally, the inductors L1 and L3 of the shunt resonators 214-1 and 224-1, respectively, have terminals that are commonly connected to the first node N1. Similarly, the inductors L2 and L4 of the shunt resonators 214-2 and 224-2, respectively, have terminals that are commonly connected to the second node N2. In this exemplary configuration, shunt resonator 214-1 has an LC resonator in which capacitor C1 is connected in parallel with the inductance formed by the series connection of inductor L1 and inductance of the first DC-SQUID 230-1, and shunt resonator 214-2 has an LC resonator in which capacitor C2 is connected in parallel with the inductance formed by the series connection of inductor L2 and inductance of the second DC-SQUID 230-2. Similarly, shunt resonator 224-1 has an LC resonator in which capacitor C3 is connected in parallel with the inductance formed by the series connection of inductor L3 and inductance of the first DC-SQUID 230-1, and shunt resonator 224-2 has an LC resonator in which capacitor C4 is connected in parallel with the inductance formed by the series connection of inductor L4 and inductance of the second DC-SQUID 230-2.

[0043] Figure 2 schematically shows exemplary two-pole embodiments of the first and second multipole bandpass filters 210 and 220, where the first and second DC-SQUIDs 230-1 and 230-2 facilitate the coupling of filter modes. The first and second DC-SQUIDs 230-1 and 230-2 are DC-biased in such a manner that each of the first and second multipole bandpass filters 210 and 220 has its own bandpass filter response with little or no crosstalk. On the other hand, when driven by an RF pump signal with a phase difference, the energy is in the signal passband B Signal From idler passband B Idler Converted to idler passband B Idler From signal passband BSignal It is returned to its original state. In this case, if the phase of the signals is shifted due to an effective phase difference, signals from one direction are constitutively coupled (in phase), and signals from the other direction cancel each other out (through destructive interference).

[0044] For example, as schematically shown in Figure 2, the first RF signal generator 240-1 has a coupling inductor L C1 The first DC-SQUID 230-1 is configured to generate a first pump signal P1 which is interconnected via the second DC-SQUID 230-1. Similarly, the second RF signal generator 240-2 is configured to generate a first pump signal P1 which is interconnected via the second interconnected inductor L C2 It is configured to generate a second pump signal P2 which is interconnected with the second DC-SQUID230-2 via the first and second DC-SQUID230-1 and 230-2. In some embodiments, the first and second RF pump signals P1 and P2 applied to the first and second DC-SQUID230-1 and 230-2 are configured to have the same pump frequency f p It has but includes an RF current signal with different phases and / or amplitudes. For example, as noted above, the pump frequency is f p =|f C -f C Selected as '|, where f C The signal passband B Signal This indicates the center frequency and f C ' is idler passband B Idler This indicates the center frequency.

[0045] Furthermore, in the exemplary two-pole embodiment shown in Figure 2, the first RF pump signal P1 applied to the first DC-SQUID230-1 has a phase θ, and simultaneously, the second RF pump signal P2 applied to the second DC-SQUID230-2 has a phase θ.

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[0046] The phase difference between pump signals P1 and P2 is

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[0047] Figure 3 schematically illustrates a Josephson multipole multiband isolator circuit according to another exemplary embodiment of the present disclosure. Generally, Figure 3 shows a Josephson multipole multiband isolator circuit 300 in which a first coupled inductor L C1 One end and a second connecting inductor L are connected to it. C2 A transmission line 310 having another end connected to the first and second DC-SQUID 230-1 and 230-2 (frequency f pA schematic Josephson multipole multiband isolator circuit 300 is similar in structure to the Josephson multipole multiband isolator circuit 200 in Figure 2, except that it includes a single RF signal generator 340 for generating an RF pump signal P (which has the following characteristics). In this configuration, the transmission line 310 has first and second linked inductors L C1 and L C2 This gives the desired phase difference of the RF pump signal P (frequency f p It has an electrical / physical length (based on), for example, L C1 Then the phase is θ, and L C2 So, phase

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[0048] Figures 4A, 4B, 4C, and 4D show simulations of scattering parameter waveforms for a Josephson multipole multiband isolator circuit according to exemplary embodiments of the present disclosure. More specifically, Figures 4A, 4B, 4C, and 4D show simulations of scattering parameter waveforms in exemplary calculation modes for a Josephson multipole multiband isolator circuit having an exemplary structure as illustrated in Figure 2. For illustrative purposes, as shown in Figure 4A, the first multipole bandpass filter 210 has a signal passband B from approximately 7.75 GHz to approximately 9.5 GHz. Signal The signal (S) band includes the signal passband B, and the second multi-pole bandpass filter 220 has a signal passband B SignalAn idle passband B from approximately 3.75 GHz to approximately 6.25 GHz that does not overlap Idler is assumed to include an idle (I) band having. The signal passband B Signal and the idle passband B Idler Note that the illustrated bandwidths are defined by the equal ripple points (and not the 3 dB points) of their respective filter passbands.

[0049] FIGS. 4A and 4B show the linear scattering characteristics of a Josephson multipole multiband isolator circuit 200 in which each of the first and second DC-SQUIDs 230-1 and 230-2 is flux biased by a DC magnetic flux bias Φ of approximately one-half of the magnetic flux quantum Φ0 DC where,

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[0050] FIG. 4A shows the simulation waveforms 400 of the scattering parameters S 11 , S 21 , , S 33 and S 43 with respect to the power in dB (y-axis) as a function of the frequency in GHz (x-axis). FIG. 4A shows that the power transmission from port 1 to port 2 (S 21 ) has low reflection loss at port 1 (S 11 ) and is close to unity in the signal passband B Signal [[ID=4x8]]In addition, FIG. 4A shows that the power transmission from port 3 to port 4 (S 43 ) has low reflection loss at port 3 (S<0U00094>Idle passband B having Idler shows being close to unity. The simulation waveforms in FIG. 4A show that appropriate DC biasing of the first and second DC-SQUIDs 230-1 and 230-2 results in the operation of two independent bandpass filters having different passbands, where the bandpass filters are well matched with an in-band rejection of 10-15 dB.

[0051] Next, FIG. 4B shows the simulation waveforms 410 of the scattering parameters S 31 , S 32 , S 41 and S 42 with respect to the power in dB (y-axis) as a function of the frequency in GHz (x-axis). In particular, the simulation waveform 411 in FIG. 4B represents both (i) power transmission from port 2 to port 3 (S 32 ), and (ii) power transmission from port 1 to port 4 (S 41 ). Additionally, the simulation waveform 412 represents both (i) power transmission from port 1 to port 3 (S 31 ), and (ii) power transmission from port 2 to port (S 42 ). The simulation waveforms 411 and 412 in FIG. 4B show that appropriate DC biasing of the first and second DC-SQUIDs 2,30-1 and 230-2 results in significantly reduced crosstalk (e.g., crosstalk suppression better than 20 dB) between the first and second multipole bandpass filters 210 and 220. FIG. 4B shows that appropriate DC biasing of the first and second DC-SQUIDs 230-1 and 230-2 results in good suppression of crosstalk between the first and second multipole bandpass filters 210 and 220.

[0052] Next, FIGS. 4C and 4D show the scattering characteristics of the Josephson multipole multi-band isolator circuit 200 with (as described above) the DC magnetic flux bias Φ DCIn addition to applying a magnetic flux bias to the first and second DC-SQUID230-1 and 230-2 respectively, an RF magnetic flux bias Φ is applied to the first and second DC-SQUID230-1 and 230-2 respectively via RF pump signals P1 and P2, which have the same frequency but different phases. RF The diagram shows the state with the parameter applied. For example, in an exemplary embodiment, the RF pump signals P1 and P2 applied to the first and second DC-SQUID230-1 and 230-2 respectively have a frequency of 4 GHz and a phase difference of approximately 90°. Figure 4C shows the scattering parameter S 21 and S 12 Figure 4D shows the simulation waveform 420 in terms of power in dB (y axis) as a function of frequency in GHz (x axis), and the scattering parameter S 11 and S 22 This figure shows the simulated waveform 430 in terms of power in dB (y axis) as a function of frequency in GHz (x axis).

[0053] In particular, Figure 4C shows the power transmission from port 1 to port 2 (S) when the appropriate RF pump signal is applied to the first and second DC-SQUID230-1 and 230-2. 21 ) is nearly unity over a predetermined bandwidth (indicated as BW) of approximately 600 MHz, which includes a signal frequency range of approximately 6.9 GHz to approximately 7.5 GHz, while the power transmission from port 2 to port 1 within the predetermined BW (S 12 ) indicates, for example, that it is highly suppressed by -40dB or more. Furthermore, Figure 4D shows the reflection coefficient S at each port, port 1 and port 2. 11 and S 22 The overlapping waveforms are shown, S 11 and S 22 The noise level is less than -15 dB within a given bandwidth BW. In this regard, Figure 4C shows that the Josephson multipole multiband isolator circuit 200 can provide unity transmission in one direction (e.g., from port 1 to port 2) while providing high isolation <-40 dB in the opposite direction (e.g., from port 2 to port 1). Additionally, Figure 4D shows S 11 and S 22The matching indicates that the Josephson multipole multiband isolator circuit is well matched across the bandwidth. The passband of the unmodulated signal filter B is shown in Figure 4A. Signal Note that the range (e.g., 7.75–9.5 GHz) is shown to be different from the separation bandwidth BW shown in Figures 4C and 4D. This is because the passband of the modulated signal filter is slightly reduced in frequency due to the modulation.

[0054] It should be noted that exemplary Josephson multipole multiband isolator circuits, such as the one discussed herein (e.g., Josephson multipole multiband isolator circuit 200, Figure 2), offer various advantages. For example, when properly configured and with optimized bandwidth and directivity, exemplary Josephson multipole multiband isolator circuits can easily replace conventional commercially available ferrite-based isolators, thereby reducing cost and footprint in both the control and readout chains of quantum computing systems. In fact, the exemplary Josephson multipole multiband isolator circuits disclosed herein provide a non-magnetic solution for isolation, can be deployed relatively close to and / or integrated with quantum processors. Indeed, exemplary Josephson multipole multiband isolator circuits can be easily fabricated on integrated circuit chips and have a smaller footprint and weight compared to discrete passive microwave isolation components. Again, the electrical properties of the Josephson multipole multiband isolator circuits are similar to those of passive ferrite-based isolators.

[0055] Additionally, exemplary Josephson multipole multiband isolator circuits discussed herein, which implement at least two multipole bandpass filters, offer several advantages over Josephson isolator circuits that can be implemented using a single multipole bandpass filter. In fact, a Josephson isolator circuit can be constructed using a single bandpass filter circuit with two or more poles implemented by shunt LC resonators with nonlinear inductance provided by DC-SQUIDs, the DC-SQUIDs can be driven by RF pump signals of different phases to enable three-wave mixing. By varying the phase of the pump to each DC-SQUID at each LC pole of the single bandpass filter, microwave energy applied to the input port can be modulated from the signal band and returned to the signal band, resulting in near-unity transmission, while energy applied to the output port is three-wave mixed and reflected out of the filter's band, resulting in asymmetric transmission. However, by adding a second bandpass filter with an unattenuated passband, exemplary Josephson multipole multiband isolator circuits disclosed herein offer several advantages over Josephson isolator circuits implemented using a single bandpass filter.

[0056] For example, compared to a Josephson isolator circuit with a single-bandpass filter, an exemplary Josephson multipole multiband isolator circuit with a multi-bandpass filter structure exhibits lower insertion loss and greater directivity. This is due to the fact that in a single-bandpass filter structure, the required energy is reflected outside the filter, resulting in a greater insertion loss. By adding a second filter, such energy can be preferentially mixed into the bandwidth of the second linked filter, preventing the energy from being reflected. Additionally, a Josephson multipole multiband isolator circuit with a multi-bandpass filter exhibits greater isolation due to the fact that more signal remains in the three-wave mixed filter. For example, as shown in Figure 4C, when an RF pump signal is applied to DC-SQUIDS, isolation of more than -40dB (e.g., S) is achieved in a 600MHz frequency band. 12 ) is achieved, and near-unity transmission (for example, S) is achieved within the same bandwidth. 21 Furthermore, if the admittance inverters in Figures 2 and 3 are implemented using capacitors (as opposed to, for example, a 50-ohm transmission line), simulations show that isolation within the bandwidth (e.g., S) is achieved. 12 It has been shown that -60dB can be achieved, which is at least three times the isolation that can be achieved with a single-junction magnetic ferrite isolator. On the other hand, a Josephson isolator circuit with a single-bandpass filter structure has an insertion loss of approximately 3-4dB (e.g., S 21 This allows for the achievement of high insulation, and the bandwidth required to achieve high insulation is much smaller.

[0057] Furthermore, compared to a Josephson isolator circuit with a single multipole passband filter including a mixed device, the Josephson multipole multiband isolator circuit structure allows each bandpass filter to be designed with fewer poles, thereby resulting in a smaller overall footprint for each Josephson multipole multiband isolator circuit within the cryostat and fewer RF pump I / O lines. For example, a Josephson multipole multiband isolator circuit with a 2-pole multibandpass filter may achieve better performance when compared to a Josephson isolator circuit with a single bandpass filter having, for example, three or more shunt LC poles. In addition to achieving greater directivity, exemplary Josephson multipole multiband isolator circuits with a multibandpass filter structure offer design flexibility with respect to pump frequency and RF pump signal amplitude.

[0058] In particular, a Josephson multipole multiband isolator circuit with a multibandpass filter structure allows for the design of a bandpass filter with separate, non-overlapping passbands, and the RF pump signal can have a pump frequency that is a function of the center frequencies of the separate, non-overlapping passbands, while the pump frequency lies outside the passband. For example, as described above, the RF pump frequency is f p =|f C -f C '| may be selected as, where f C The signal passband B Signal This indicates the center frequency and f C ' is idler passband B Idler This indicates the center frequency. A given Josephson multipole multiband isolator circuit has an RF pump frequency of 2 GHz and a signal passband B Signal Regarding the center frequency f of 8GHz C When constructed and operated using this method, the idler bandpass filter has a center frequency of 6 GHz or 10 GHz f as desired. CIt can be constructed as follows. Thus, an idler passband filter can be configured to allow the signal to be converted at any appropriate and desired RF pump frequency. In contrast, with a Josephson isolator circuit having a single bandpass filter including a mixing device, the flexibility of the RF pump frequency is limited because the idler frequency must be within the signal passband of the bandpass filter. This limits the available RF pump tones because the idler frequency must be able to pass through the passband of the bandpass filter. Advantageously, adding an idler bandpass filter provides more headroom in the available RF pump frequencies for the reasons mentioned above.

[0059] Figure 5 schematically illustrates a Josephson multipole multiband isolator circuit according to another exemplary embodiment of the present disclosure. More specifically, Figure 5 schematically illustrates a differential Josephson multipole multiband isolator circuit 500 comprising first and second immittance-inverting multipole bandpass filter networks 510 and 520 constructed using linked transmission lines 512 and 522, respectively, as immittance inverters, and a nonlinear mixing device 530 implemented using Josephson parametric transducers 530-1, 530-2, and 530-3. The Josephson parametric transducers 530-1, 530-2, and 530-3 implement the LC resonators of the first and second immittance-inverting multipole bandpass filter networks 510 and 520 and perform the mixing function as discussed herein.

[0060] Figure 5 shows (signal passband B Signal The first immittance inverting bandpass filter network 510 has a three-pole structure and (idler passband B IdlerA schematic diagram shows the three-pole structure of the second immittance inverting multipole bandpass filter network 520, which has the filter poles provided by three Josephson parametric transducers 530-1, 530-2, and 530-3. The coupling transmission line 512 includes coupling transmission lines 512-1, 512-2, 512-3, and 512-4 configured as immittance inverters for the first immittance inverting bandpass filter network 510, and the coupling transmission line 522 includes coupling transmission lines 522-1, 522-2, 522-3, and 522-4 configured as immittance inverters for the second immittance inverting multipole bandpass filter network 520. The coupling transmission lines 512-1, 512-2, 512-3, and 512-4 are defined by their even and odd modes. Similarly, the linked transmission lines 522-1, 522-2, 522-3, and 522-4 are defined by their even and odd modes.

[0061] Each of the Josephson parametric converters 530-1, 530-2, and 530-3 includes a first differential port (indicated as port a), a second differential port (indicated as port b), and a pump port (indicated as port P). In the exemplary embodiment shown in Figure 5, the first immittance inverting bandpass filter network 510 has a signal passband B Signal The second immittance inverting multipole bandpass filter network 520 includes and has idler passband B Idler It is assumed that this includes. Furthermore, as schematically shown in Figure 5, the differential ports (port a) of Josephson parametric converters 530-1, 530-2, and 530-3 are connected to the coupling transmission line 512, and the differential ports (port b) of Josephson parametric converters 530-1, 530-2, and 530-3 are connected to the coupling transmission line 522.

[0062] In particular, differential port a of Josephson parametric converter 530-1 is connected to the positive and negative input / output nodes between connected transmission lines 512-1 and 512-2, and differential port b of Josephson parametric converter 530-1 is connected to the positive and negative input / output nodes between connected transmission lines 522-1 and 522-2. Furthermore, differential port a of Josephson parametric converter 530-2 is connected to the positive and negative input / output nodes between connected transmission lines 512-2 and 512-3, and differential port b of Josephson parametric converter 530-2 is connected to the positive and negative input / output nodes between connected transmission lines 522-2 and 522-3. The differential port a of Josephson parametric converter 530-3 is connected to the positive and negative input / output nodes between linked transmission lines 512-3 and 512-4, and the differential port b of Josephson parametric converter 530-3 is connected to the positive and negative input / output nodes between linked transmission lines 522-3 and 522-4. This configuration allows the positive transmission line in the signal (S) band to be connected to the negative transmission line in the idler (I) band, and vice versa, via Josephson parametric converters 530-1, 530-2, and 530-3.

[0063] As further shown in Figure 5, Josephson parametric transducers 530-1, 530-2, and 530-3 have the same frequency f p It has different phases θ,

number

number

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[0064] The exemplary configuration shown in Figure 5 includes a differential filter structure for implementing the first and second immittance-inverting multipole bandpass filter networks 510 and 520 by constructing different portions of a coupling transmission line to connect to nonlinear filter poles (e.g., LC resonators) provided by the Josephson parametric converters 530-1, 530-2, and 530-3. It should be understood that the Josephson parametric converters 530-1, 530-2, and 530-3 can be implemented using any suitable structure that is sufficient to provide filter poles (e.g., LC poles) for the first and second immittance-inverting multipole bandpass filter networks 510 and 520 and to implement the mixed functions as discussed herein to achieve non-reciprocal transmission and isolation.

[0065] For example, Figure 6 schematically shows a Josephson parametric converter 600 that may be used to implement the differential Josephson multipole multiband isolator circuit of Figure 5 according to an exemplary embodiment of the present disclosure. The Josephson parametric converter 600 has three ports, indicated as port a, port b and port P, a Josephson ring modulator (JRM) 610, and a capacitor C a , C b , C c and C p , and inductor L P1 and L P2The JRM610 is a nonlinear element configured to perform three-wave mixing of microwave signals at the quantum limit. The JRM610 includes four outer Josephson junctions 611, 612, 613, 614 and four inner Josephson junctions 615, 616, 617, 618 configured to form an outer loop with nodes N11, N12, N13, N14.

[0066] The Josephson parametric transducer 600 has three eigenmodes: two differential resonant modes and one common mode. The two differential resonant modes include a signal (S) resonant mode (or mode a) and one idler (I) resonant mode (or mode b). For example, in the exemplary embodiment shown in Figure 6, in a non-degenerate embodiment, the Josephson parametric transducer 600 has different frequencies, for example, a first frequency f associated with the signal (S) mode. a and the second frequency f associated with the idler (I) mode. b It supports two differential resonant modes with a capacitor C. Generally, a The JRM610 is configured to provide a resonant mode (signal mode) and to implement the shunt LC poles of a first immittance inverting bandpass filter, such as the first immittance inverting bandpass filter network 510 in Figure 5, and capacitor C b The JRM610 provides a resonant mode b (idler mode) and is configured to implement a shunt LC pole for a second immittance inverting bandpass filter, such as the second immittance inverting multipole bandpass filter network 520 in Figure 5. In this exemplary configuration, the Josephson parametric transducer 600 provides two LC resonators (poles), one LC resonator for the signal (S) bandpass filter and another LC resonator for the idler (I) bandpass filter, which are coupled together via the JRM610, as in the embodiments shown in Figures 2 and 3, where, for example, the two LC resonators are coupled together via a DC-SQUID.

[0067] frequency f pAn RF pump signal is applied to port P, causing common-mode excitation of JRM610, resulting in a three-wave mixing of signals at ports a, b, and P. JRM610 is configured to perform non-degenerate mixing in the microwave region without loss and can achieve quantum-limit noise performance as a mixer. Differential port P is coupled to nodes N11 and N14 of the Josephson parametric converter 600 to enable common-mode excitation of JRM610, as will be understood by those skilled in the art. A DC flux viar is applied through JRM610 and the RF pump signal is applied to port P to bias and excite JRM610 to perform the mixing function discussed herein. It should be understood that the Josephson parametric converter 600 is merely an exemplary embodiment and that Josephson multipole multiband isolator circuits, such as the one shown in Figure 6, can be constructed using other suitable Josephson parametric converter circuit structures. Additionally, the Josephson parametric converter 600 shown in Figure 6 can be used in a differential bandpass filter structure as shown in Figure 5, but it can also be used in a single-ended filter structure, in which the input ports, port a and port b, are each connected to a 180-degree hybrid coupler, and one of the input terminals has a cold termination.

[0068] Figure 7 schematically illustrates a Josephson multipole multiband isolator circuit according to another exemplary embodiment of the present disclosure. More specifically, Figure 7 schematically illustrates a cascaded Josephson multipole multiband isolator circuit 700 formed by cascading a plurality of individual Josephson multipole multiband isolator circuit blocks. Figure 7 shows an exemplary embodiment of the cascaded Josephson multipole multiband isolator circuit 700 having three individual Josephson multipole multiband isolator stages 700-1, 700-2, and 700-3 in succession, connected between a first port (port 1) and a second port (port 2). The Josephson multipole multiband isolator stage 700-1 has a first immittance inverting bandpass filter including three shunt resonators 714-1, a second immittance inverting bandpass filter including three shunt resonators 724-1, and three mixing devices MD that link the respective filter modes. The Josephson multipole multiband isolator stage 700-2 has a first immittance inverted bandpass filter including three shunt resonators 714-2, a second immittance inverted bandpass filter including three shunt resonators 724-2, and three mixing devices MD that link the respective filter modes. The Josephson multipole multiband isolator stage 700-3 has a first immittance inverted bandpass filter including three shunt resonators 714-3, a second immittance inverted bandpass filter including three shunt resonators 724-3, and three mixing devices MD that link the respective filter modes.

[0069] In the exemplary embodiment shown in Figure 7, assume that the first immittance inverting bandpass filter is configured as a signal (S) bandpass filter, and the second immittance inverting bandpass filter is configured as an idler (I) bandpass filter. In this configuration, all input / output ports of the second immittance inverting bandpass filter are terminated with 50 ohm termination, while the input / output ports of the first immittance inverting bandpass filter are connected as schematically shown in Figure 7 to provide a single input port (port 1) and a single output port (port 2). Each of the Josephson multipole multiband isolator stages 700-1, 700-2, and 700-3 can be implemented using any embodiment of the exemplary Josephson multipole multiband isolator circuit, for example, as shown in Figures 2, 3, 5, and 6. The cascaded Josephson multipole multiband isolator circuit structure provides overall isolation (e.g., S 12 ) increases. For example, if each Josephson multipole multiband isolator stage 700-1, 700-2, and 700-3 provides 20 dB or more of isolation, the entire cascaded Josephson multipole multiband isolator circuit 700 may provide 60 dB or more of isolation.

[0070] Figure 8 schematically illustrates a readout circuit for a quantum processing system that, according to exemplary embodiments of the present disclosure, may implement a Josephson multipole multiband isolator circuit in a qubit readout signal path for providing isolation. More specifically, Figure 8 schematically illustrates a qubit readout control circuit 800 for a quantum computing system configured to read out the quantum state of at least one superconducting qubit 802. The qubit readout control circuit 800 is configured to generate an RF readout control signal (RF_RO) for reading out the state of the superconducting qubit 802, using a distributed readout scheme that enables quantum non-catastrophic measurements of the state of the superconducting qubit 802 in order to hold the state of the superconducting qubit 802. In exemplary embodiments, the qubit readout control circuit 800 receives and processes the readout control signal from a control process.

[0071] The qubit readout control circuit 800 has a readout signal chain including a waveform generator 810 (or pulse envelope generator), a digital-to-analog (DAC) circuit 811, a low-pass filter circuit 812, a first I / O mixer 813 (up-converter mixer), a local oscillator (LO) signal generator 814, a directional coupler 815, a readout resonator 816, and a Josephson multipole multiband isolator circuit 820, a quantum limit amplifier 821, a filter 822, a second I / Q mixer 823, and an analog-to-digital converter (ADC) circuit 824 that outputs a digital readout signal to a hardware or software-based discriminator to determine the readout state of the superconducting qubit 802.

[0072] The waveform generator 810 is configured to generate digital I and Q signals having a predetermined type of pulse envelope (e.g., a Gaussian square pulse envelope) for reading out qubit states in response to a readout control signal. The DAC circuit 811 is configured to convert the digital I and Q pulses into analog I and Q control pulses that are filtered by the low-pass filter circuit 812. The filtered analog I and Q control pulses are applied to the I / O mixer 813 along with the LO signal (LO_RO) generated by the signal generator 814 to generate an RF readout control pulse RF_RO. In particular, the I / O mixer 813 is configured to mix the analog I and Q control pulses with a predetermined LO frequency (e.g., 7 GHz) LO_Q signal to perform I / O modulation and upconversion and / or downconversion using known techniques (e.g., single sideband modulation) to generate the RF readout control pulse RF_RO.

[0073] An RF readout control signal RF_RO is applied to the input port of a directional coupler 815 and subsequently coupled to a readout resonator 816. The readout resonator 816 is capacitively coupled to a superconducting qubit 802, thereby providing a qubit / resonator system. In some embodiments, the readout resonator 816 has, for example, a half-wavelength coplanar waveguide resonator with a resonant frequency identical or similar to the center frequency of the RF readout control signal RF_RO. The resonant frequency of the readout resonator 816 is detuned from the transition frequency of the superconducting qubit 802. In the dispersion region of the qubit-resonator coupling, the RF readout control signal RF_RO (having the required frequency tone, pulse envelope shape, and pulse duration) interacts with a given qubit / resonator system in such a way that it results in the generation of a readout signal RO reflected from the readout resonator 816, the readout signal RO containing information dependent on the qubit state (e.g., phase and / or amplitude). In other words, the distributed readout process yields an RF readout signal RO with a state-dependent phase response, which is analyzed to identify the quantum state of the superconducting qubit 802.

[0074] The readout signal RO returned from the readout resonator 816 is input to the directional coupler 815 and then coupled into a readout signal chain, where the readout signal RO flows through the Josephson multipole multiband isolator circuit 820, is amplified by the quantum limit amplifier 821, and then transmitted along a signal chain including a filter 822 and other possible Josephson multipole multiband isolator circuits and applied to the input of the second I / Q mixer 823. The Josephson multipole multiband isolator circuit 820 can be implemented using any of the exemplary microwave isolator circuits discussed here (e.g., Figures 1, 2, 3, 5, 6, or 7). As schematically shown in Figure 8, the Josephson multipole multiband isolator circuit 820 is configured to receive multiple RF pump control signals P1, ..., P as described above. nThe Josephson multipole multiband isolator circuit 820 is used to shield the superconducting qubit 802 from excessive signal reflections and amplification of quantum noise from downstream components in the readout signal path. The Josephson multipole multiband isolator circuit 820 is configured to ensure that all (or nearly all) of the power of the readout signal RO is transmitted to, for example, the quantum limit amplifier 821, while absorbing and isolating any power returning from, for example, the quantum limit amplifier 821 to prevent perturbation of the state of the superconducting qubit 802 and other superconducting qubits in the quantum processor.

[0075] The second I / Q mixer 823 mixes the RF readout signal RO with the LO_RO signal and performs a down-conversion operation that down-converts the RF readout signal RO into analog I and Q signals. The analog I and Q signals are input to the ADC circuit 824 and sampled by the ADC circuit 824 to generate the respective digital I and Q signals, which represent the amplitude and phase of the readout signal RO. The discriminator analyzes the digital I and Q signals to identify the measured quantum state of the superconducting qubit 802 based on the amplitude and phase components of the readout signal RO.

[0076] Figure 8 should be understood as an exemplary, non-limiting embodiment illustrating a high-level schematic diagram of the readout control circuit. The qubit readout control circuit 800 and the readout signal chain can be implemented using other components and configurations. For example, in a quantum computing system for reading the quantum states of superconducting qubits in a relatively large superconducting quantum computer, the readout chain can be scaled up using a frequency multiplexing readout system (implementing frequency domain multiplexing). In a frequency multiplexing readout system, multiple readout resonators (with different resonant frequencies) are coupled to separate qubits and commonly coupled to a communication bus. The communication bus is configured to allow the transmission of multiple readout signals having readout frequencies that match the resonant frequencies of the readout resonators, and as a result, the quantum states of multiple qubits can be read simultaneously using one input line and one output line.

[0077] Figure 9 schematically shows a quantum computing system 900 including a quantum computing platform 910, a control system 920, and a quantum processor 930. In some embodiments, the quantum computing platform 910 implements a software platform configured to program a quantum computer to execute quantum computing algorithms 912, which are implemented using quantum circuits that define computation routing consisting of coherent quantum operations on quantum data such as qubits. Additionally, in some embodiments, the control system 920 includes a multi-channel arbitrary waveform generator 922 and a qubit readout control system 924. The quantum processor 930 has one or more solid-state quantum chips, including, for example, a superconducting qubit array 932, a microwave isolator circuit 934, and a network 936 of qubit drive lines, coupler flux bias control lines, qubit state readout lines, isolator control lines, and other circuit QED components that may be required for a given application or quantum system configuration. The microwave isolator circuit 934 may have a Josephson multipole multiband isolator circuit implemented using any of the exemplary embodiments discussed herein (for example, Figures 1, 2, 3, 5, 6, or 7).

[0078] In some embodiments, the control system 920 and the quantum processor 930 are housed within a dilution refrigeration system 940 capable of generating cryogenic temperatures sufficient to operate the components of the control system 920 for quantum computing applications. For example, the quantum processor 930 may need to be cooled to near absolute zero, e.g., 10–15 millikelvin (mK), to allow the superconducting qubits to exhibit quantum behavior. In some embodiments, the dilution refrigeration system 940 includes a multi-stage dilution refrigerator, which can maintain the components of the control system 920 at different cryogenic temperatures as needed. For example, the quantum processor 930 may need to be cooled to, for example, 10–15 mK, but the circuit components of the control system 920 can operate at cryogenic temperatures higher than 10–15 mK (e.g., cryogenic temperatures in the range of 3K–4K), depending on the configuration of the quantum computing system. In some embodiments, all or part of the components of the control system 920 are housed in a room temperature environment.

[0079] In some embodiments, the superconducting qubit array 932 includes a quantum system of superconducting qubits, superconducting qubit couplers, and other components commonly used to support quantum processing using the qubits. The number of superconducting qubits in the superconducting qubit array 932 can be on the order of tens, hundreds, thousands, or more. Networks 936, including qubit drive lines, coupler flux bias control lines, and qubit state readout lines, are configured to apply microwave control signals to the superconducting qubits and coupler circuits in the superconducting qubit array 932 to perform various types of gate operations, such as single gate operations, entanglement gate operations, and error correction operations, and to read out the quantum states of the superconducting qubits. For example, microwave control pulses are applied to the qubit drive lines of each superconducting qubit to change the quantum state of the superconducting qubit during the execution of a quantum information processing algorithm (e.g., changing the quantum state of a given qubit between the ground state and excited state, or changing it to a superposition state).

[0080] Furthermore, as described above, the state readout line has a readout resonator coupled to each superconducting qubit. The state of a given superconducting qubit can be determined by microwave transmission or reflection measurement using the readout port of the readout resonator. The state of the superconducting qubit is read out after the quantum algorithm has been executed. In some embodiments, as described above, a distributed readout operation is performed in which a change in the resonant frequency of a given readout resonator coupled to a given superconducting qubit is used to read out the state of the given superconducting qubit (e.g., ground state or excited state).

[0081] Network 936, including qubit drive lines, coupler flux bias control lines, qubit state readout lines, and microwave isolator control lines, is connected to the control system 920 via appropriate hardware input / output (I / O) interfaces, connecting I / O signals between the control system 920 and the quantum processor 930. For example, the hardware I / O interface may have various types of hardware and components, such as RF cables, wiring, RF elements, optical fibers, heat exchangers, filters, amplifiers, and isolators.

[0082] In some embodiments, a multi-channel arbitrary waveform generator (AWG) 922 and other suitable microwave pulse signal generators are configured to generate qubit drive lines and microwave control pulses applied to coupler drive lines to control the operation of superconducting qubits and associated qubit coupler circuits when performing various gate operations to execute a given particular quantum information processing algorithm. In some embodiments, the multi-channel AWG 922 includes multiple AWG channels that control each superconducting qubit in the superconducting qubit array 932 of the quantum processor 930. In some embodiments, each AWG channel includes a baseband signal generator, a digital-to-analog converter (DAC) stage, a filter stage, a modulation stage, an impedance matching network, and a phase-locked loop system that generate local oscillator (LO) signals (e.g., quadrature LO signals LO_I and LO_Q) for each modulation stage of each AWG channel.

[0083] In some embodiments, the multi-channel AWG922 includes an orthogonal AWG system configured to process orthogonal signals, the orthogonal signals including an in-phase (I) signal component and an orthogonal-phase (Q) signal component. In each AWG channel, a baseband signal generator is configured to receive baseband data as input (e.g., from a quantum computing platform) and generate digital orthogonal signals I and Q representing the input baseband data. In this process, the baseband data input to the baseband signal generator of a given AWG channel is separated into two orthogonal digital components, including an in-phase (I) baseband component and an orthogonal-phase (Q) baseband component. The baseband signal generator of a given AWG channel generates the digital orthogonal baseband IQ signals necessary to generate an analog waveform (e.g., a sinusoidal voltage waveform) having a target center frequency, which is configured to operate or control a given qubit coupled to the output of the given AWG channel.

[0084] The DAC stage of a given AWG channel is configured to convert a digital baseband signal (e.g., a digital IQ signal output from a baseband signal generator) into an analog baseband signal having a baseband frequency (e.g., analog baseband signals I(t) and Q(t)). The filter stage of a given AWG channel is configured to filter the IQ analog signal component output from the DAC stage, thereby generating a filtered analog IQ signal. The modulation stage of a given AWG channel is configured to perform analog IQ signal modulation (e.g., single-sideband (SSB) modulation) by mixing the filtered analog signals I(t) and Q(t) output from the filter stage with quadrature LO signals (e.g., a common-mode LO signal (LO_I) and a quadrature-phase LO signal (LO_Q)), thereby generating and outputting an analog RF signal (e.g., a single-sideband modulated RF output signal).

[0085] In some embodiments, the qubit readout control system 924 comprises a microwave pulse signal generator configured to apply a microwave tone to a predetermined readout resonator line of a given superconducting qubit in order to perform a readout operation to read out the state of a given superconducting qubit, and a circuit configured to process the readout signal generated by the readout resonator line in order to determine the state of a given superconducting qubit using techniques known to those skilled in the art. In some embodiments, the qubit readout control system 924 is implemented based on the readout circuit of Figure 8.

[0086] The quantum computing platform 910 includes a software and hardware platform including various software layers configured to perform various functions, including, but not limited to, generating and implementing various quantum applications using an appropriate quantum programming language, configuring and implementing various quantum gate operations, compiling quantum programs into quantum assembly language, implementing and utilizing an appropriate quantum instruction set structure (ISA), and performing calibration operations to calibrate quantum circuit elements and gate operations. In addition, the quantum computing platform 910 includes hardware structures such as a processor and memory, and is configured to control the execution of quantum applications, and through an interface with a control system 920, (i) generates digital control signals that are converted into analog microwave control signals by the control system 920 to control the operation of the quantum processor 930 when executing a given quantum application, and (ii) acquires and processes digital signals received from the control system 920 that represent the processing results generated by the quantum processor 930 when executing various gate operations of a given quantum application.

[0087] In some exemplary embodiments, the quantum computing platform 910 of the quantum computing system 900 may be implemented using any suitable computing system structure (for example, as shown in Figure 10) configured to implement quantum computing operations in a corresponding way by executing computer-readable program instructions embodied on a computer program product including a computer-readable storage medium (or medium) having such computer-readable program instructions on it, for causing a processor to perform a control method as discussed herein.

[0088] Various aspects of this disclosure are described by explanatory text, flowcharts, block diagrams of computer systems, and / or block diagrams of machine logic included in embodiments of computer program products (CPPs). With respect to any flowchart, depending on the technology involved, operations may be performed in a different order than those shown in a given flowchart. For example, also depending on the technology involved, two operations shown in consecutive blocks of a flowchart may be performed in reverse order, as a single integrated stage, simultaneously, or with at least partial time overlap.

[0089] Computer program product embodiment ("CPP embodiment" or "CPP") is a term used in this disclosure to describe any set of one or more storage media ("mediums") that collectively comprise a set of one or more storage devices that collectively contain machine-readable code corresponding to instructions and / or data for performing computer operations specified in a given CPP claim. A "storage device" is any tangible device capable of holding and storing instructions for use by a computer processor. Computer-readable storage media may be, but are not limited to, electronic storage media, magnetic storage media, optical storage media, electromagnetic storage media, semiconductor storage media, mechanical storage media, or any preferred combination thereof. Some known types of storage devices, including these media, include diskettes, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), compact disk read-only memory (CD-ROM), digital versatile disks (DVDs), memory sticks, floppy disks, mechanically encoded devices (e.g., punch cards or pits / lands formed on the main surface of a disk), or any suitable combination of those described above. Computer-readable storage media, as used in this disclosure, shall not be construed as storage in the form of transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides, optical pulses passing through optical fiber cables, electrical signals communicated through wires, and / or other transmission media. As will be understood by those skilled in the art, data is moved at several intermittent points in the normal operation of a storage device, such as during access, defragmentation, or garbage collection; however, data is not transient while it is stored, so the foregoing does not make a storage device transient.

[0090] The computing environment 1000 in Figure 10 includes an example of an environment for executing at least a portion of computer code (block 1026) involved in the execution of a quantum computing algorithm (e.g., quantum computing algorithm 912, Figure 9). In addition to block 1026, the computing environment 1000 includes, for example, a computer 1001, a wide area network (WAN) 1002, an end-user device (EUD) 1003, a remote server 1004, a public cloud 1005, and a private cloud 1006. In this embodiment, the computer 1001 has a processor set 1010 (including processing circuits 1020 and a cache 1021), a communication fabric 1011, volatile memory 1012, persistent storage 1013 (including an operating system 1022 and blocks 1026 as identified above), a peripheral device set 1014 (including a user interface (UI), a device set 1023, storage 1024, and an Internet of Things (IoT) sensor set 1025), and a network module 1015. The remote server 1004 includes the remote database 1030. The public cloud 1005 includes the gateway 1040, the cloud orchestration module 1041, the host physical machine set 1042, the virtual machine set 1043, and the container set 1044.

[0091] Computer 1001 may take the form of a desktop computer, laptop computer, tablet computer, smartphone, smartwatch, or other wearable computer, mainframe computer, quantum computer, or any other form of computer or mobile device, currently known or to be developed in the future, that can run programs, access networks, or query databases such as remote database 1030. As is well understood in the field of computer technology, and depending on the technology, the execution of a computer implementation method may be distributed among multiple computers and / or multiple locations. On the other hand, in this description of the computing environment 1000, in order to make the explanation as concise as possible, the detailed discussion will focus on a single computer, specifically computer 1001. Computer 1001 may be located in the cloud, although it is not shown in the cloud in Figure 10. On the other hand, computer 1001 is not required to be located in the cloud, except to any extent that can be definitively shown.

[0092] The processor set 1010 includes one or more computer processors of any type currently known or to be developed in the future. The processing circuitry 1020 may be distributed across multiple packages, for example, multiple interconnected integrated circuit chips. The processing circuitry 1020 may implement multiple processor threads and / or multiple processor cores. The cache 1021 is memory located within the processor chip package and is typically used for data or code that should be available for high-speed access by threads or cores running on the processor set 1010. The cache memory is typically organized into multiple levels depending on its relative proximity to the processing circuitry. Alternatively, some or all of the cache for the processor set may be located "off-chip". In some computing environments, the processor set 1010 may operate using qubits and be designed to perform quantum computing.

[0093] Computer-readable program instructions typically cause the processor set 1010 of computer 1001 to execute a series of operational steps, thereby loading them onto computer 1001 to implement a computer implementation method, and thereby the instructions thus executed instantiate the methods specified in the flowcharts and / or descriptions of the computer implementation methods contained herein (collectively referred to as the "Methods of the Invention"). These computer-readable program instructions are stored in various types of computer-readable storage media, such as the cache 1021 and other storage media discussed below. The program instructions and associated data are accessed by the processor set 1010 to control and direct the execution of the Methods of the Invention. In computing environment 1000, at least some of the instructions for executing the Methods of the Invention may be stored in block 1026 in persistent storage 1013.

[0094] The communication fabric 1011 is a signal conduction path that enables various components of the computer 1001 to communicate with one another. Typically, this fabric is made up of switches and conduction paths, such as buses, bridges, physical input / output ports, and similar components. Other types of signal communication paths, such as optical fiber communication paths and / or wireless communication paths, may be used.

[0095] Volatile memory 1012 is any type of volatile memory currently known or to be developed in the future. Examples include dynamic random-access memory (RAM) or static RAM. Volatile memory is typically characterized by random access, but this is not mandatory unless explicitly stated. In computer 1001, volatile memory 1012 is located in a single package and resides inside computer 1001, but alternatively or additionally, volatile memory may be distributed across multiple packages and / or located externally to computer 1001.

[0096] The persistent storage 1013 is any form of non-volatile storage for a computer that is currently known or may be developed in the future. The non-volatility of this storage means that the stored data is maintained regardless of whether power is supplied to the computer 1001 and / or directly to the persistent storage 1013. The persistent storage 1013 may be read-only memory (ROM), but typically at least a portion of the persistent storage allows for writing, deleting, and rewriting of data. Some well-known forms of persistent storage include magnetic disks and solid-state storage devices. The operating system 1022 may take several forms, such as various known proprietary operating systems or open-source portable operating system interface type operating systems that utilize a kernel. The code contained in block 1026 typically includes at least some computer code involved in performing the method of the present invention.

[0097] The peripheral device set 1014 includes a set of peripheral devices for the computer 1001. Data communication connections between the computer 1001's peripheral devices and other components may be implemented in various ways, such as Bluetooth® connections, near-field communication (NFC) connections, connections formed by cables (such as Universal Serial Bus (USB) type cables), insert-type connections (e.g., Secure Digital (SD) cards), connections formed through local area communication networks, and even connections formed through wide area networks such as the Internet. In various embodiments, the UI device set 1023 may include components such as a display screen, speaker, microphone, wearable devices (such as goggles and smartwatches), keyboard, mouse, printer, touchpad, game controller, and haptic devices. Storage 1024 is external storage such as an external hard drive, or insertable storage such as an SD card. Storage 1024 may be persistent and / or volatile. In some embodiments, storage 1024 may take the form of a quantum computing memory device for storing data in the form of qubits. In embodiments where computer 1001 requires a large amount of storage (for example, when computer 1001 locally stores and manages a large database), this storage may be provided by peripheral storage devices designed to store very large amounts of data, such as a storage area network (SAN) shared by multiple geographically distributed computers. The IoT sensor set 1025 consists of sensors that can be used in Internet of Things applications. For example, one sensor may be a thermometer and another may be a motion detector.

[0098] The network module 1015 is a collection of computer software, hardware, and firmware that enables computer 1001 to communicate with other computers via the WAN 1002. The network module 1015 may include hardware such as a modem or Wi-Fi signal transceiver, software for packetizing and / or depacketizing data for communication network transmission, and / or web browser software for transmitting data over the internet. In some embodiments, the network control and network forwarding functions of the network module 1015 are performed on the same physical hardware device. In other embodiments (e.g., embodiments utilizing Software-Defined Networking (SDN)), the control and forwarding functions of the network module 1015 are performed on physically separate devices, such that the control function manages several different network hardware devices. Computer-readable program instructions for performing the methods of the present invention can typically be downloaded from an external computer or external storage device to computer 1001 via a network adapter card or network interface included in the network module 1015.

[0099] WAN1002 is any wide area network (e.g., the Internet) that can communicate computer data over non-local distances using any currently known or future-developed technology for communicating computer data. In some embodiments, the WAN may be replaced and / or supplemented by a local area network (LAN), such as a Wi-Fi network, designed to communicate data between devices located in a local area. The WAN and / or LAN typically include computer hardware such as copper transmission cables, optical transmission fibers, wireless transmissions, routers, firewalls, switches, gateway computers, and edge servers.

[0100] An end-user device (EUD) 1003 is any computer system used and controlled by an end-user (e.g., a customer of the company operating computer 1001) and can take any of the forms discussed above in relation to computer 1001. EUD 1003 typically receives useful and valuable data from the operation of computer 1001. For example, in a hypothetical case where computer 1001 is designed to provide recommendations to an end-user, these recommendations would typically be transmitted from computer 1001's network module 1015 to EUD 1003 via WAN 1002. Thus, EUD 1003 can display or otherwise present recommendations to the end-user. In some embodiments, EUD 1003 may be a client device such as a thin client, heavy client, mainframe computer, or desktop computer.

[0101] The remote server 1004 is any computer system that provides at least some data and / or functions to computer 1001. The remote server 1004 may be controlled and used by the same entity that operates computer 1001. The remote server 1004 represents a machine that collects and stores useful and beneficial data for use by other computers, such as computer 1001. For example, in a hypothetical case where computer 1001 is designed and programmed to provide recommendations based on historical data, this historical data may be provided to computer 1001 from the remote database 1030 of the remote server 1004.

[0102] Public Cloud 1005 is any computer system available for use by multiple entities, providing on-demand availability of computer system resources and / or other computing capabilities, particularly data storage (cloud storage) and computing power, without direct active management by the user. Cloud computing typically leverages resource sharing to achieve coherence and economies of scale. Direct and active management of the computing resources of Public Cloud 1005 is performed by the computer hardware and / or software of the Cloud Orchestration Module 1041. The computing resources provided by Public Cloud 1005 are typically implemented by virtual computing environments running on various computers that make up the host physical machine set 1042, which is a universe of physical computers located within and / or available to Public Cloud 1005. The virtual computing environment (VCE) typically takes the form of virtual machines from the virtual machine set 1043 and / or containers from the container set 1044. These VCEs can be stored as images and transferred either as images or after VCE instantiation, among and between hosts on various physical machines. The cloud orchestration module 1041 manages the transfer and storage of images, deploys new VCE instantiations, and manages the active instantiation of VCE deployments. The gateway 1040 is a collection of computer software, hardware, and firmware that enables the public cloud 1005 to communicate over the WAN 1002.

[0103] Here, some further explanation of virtualized computing environments (VCEs) is provided. A VCE can be stored as an "image." A new active instance of a VCE can be instantiated from an image. Two well-known types of VCEs are virtual machines and containers. A container is a VCE that uses operating system-level virtualization. This refers to an operating system feature where the kernel allows for the existence of multiple isolated user-space instances called containers. These isolated user-space instances typically behave like actual computers in terms of the programs running within them. Computer programs running on a normal operating system can utilize all of that computer's resources, including connected devices, files and folders, network shares, CPU power, and quantifiable hardware capabilities. However, programs running inside a container can only use the contents of the container and the devices allocated to the container; this feature is known as containerization.

[0104] Private Cloud 1006 is similar to Public Cloud 1005, except that its computing resources are available only for use by a single enterprise. While Private Cloud 1006 is shown as being in communication with WAN 1002, in other embodiments, the private cloud may be completely isolated from the internet and accessible only via a local / private network. A hybrid cloud is a combination of multiple clouds of different types (e.g., private, community, or public cloud types), often implemented by different vendors. Each of the multiple clouds remains a separate discrete entity, but the larger hybrid cloud structure is coupled by standardized or proprietary technologies that enable orchestration, management, and / or data / application portability between the multiple configured clouds. In this embodiment, both Public Cloud 1005 and Private Cloud 1006 are part of a larger hybrid cloud.

[0105] While the descriptions of various embodiments of this disclosure have been presented for illustrative purposes, they are not intended to be exhaustive or to limit oneself to the embodiments disclosed. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the embodiments described. The terminology used herein has been selected to best describe the principles of the embodiments, their practical applications, or the technical improvements to the art found in the market, or to enable other persons skilled in the art to understand the embodiments disclosed herein.

Claims

1. A filter circuit having a first port, a second port, a first band-pass filter, and a second band-pass filter; and A nonlinear mixing device that responds to a control signal to couple the poles of the first bandpass filter to the respective poles of the second bandpass filter in order to cause non-reciprocal transmission of a signal from the first port to the second port. A device equipped with the following features.

2. The device according to claim 1, wherein the first band-pass filter and the second band-pass filter each have an immittance inverting band-pass filter.

3. The nonlinear mixing device is driven by respective control signals having the same frequency and different phases, according to claim 1.

4. The device according to claim 3, wherein each of the aforementioned control signals includes similar or different amplitudes.

5. The first bandpass filter has a first passband with a first center frequency; The second band-pass filter has a second passband with a second center frequency; The first passband and the second passband are non-overlapping passbands; and The control signal is applied to the nonlinear mixing device and includes a radio frequency signal having a frequency that is a function of the difference between the first center frequency and the second center frequency. The device according to claim 1.

6. The nonlinear mixing device is the device according to claim 1, wherein the nonlinear mixing device has a DC superconducting quantum interference device.

7. The device according to claim 1, wherein the nonlinear mixing device has a Josephson parametric converter device, each Josephson parametric converter device includes a Josephson ring modulator configured to couple the poles of the first bandpass filter and the second bandpass filter, respectively.

8. The first bandpass filter has a first terminal connected to the first port and a second terminal connected to the second port; The second bandpass filter has a terminated first terminal and a terminated second terminal. The device according to claim 1.

9. A quantum processor with qubits; A readout signal path configured to transmit signals read from one or more of the qubits of the quantum processor, the readout signal path is A filter circuit including a first port, a second port, a first band-pass filter, and a second band-pass filter; and A nonlinear mixing device that responds to a control signal to couple the poles of the first band-pass filter to the respective poles of the second band-pass filter in order to cause non-reciprocal transmission of a signal from the first port to the second port via an isolator circuit. Having an isolator circuit including, A system equipped with these features.

10. The system according to claim 9, wherein the first band-pass filter and the second band-pass filter of the isolator circuit each include an immittance inverting band-pass filter.

11. The system according to claim 9, wherein the nonlinear mixing device of the isolator circuit is driven by respective control signals having the same frequency and different phases.

12. The system according to claim 11, wherein each of the aforementioned control signals has a similar or different amplitude.

13. The first bandpass filter has a first passband with a first center frequency; The second band-pass filter has a second passband with a second center frequency; The first passband and the second passband are non-overlapping passbands; and The control signal is applied to the nonlinear mixing device and includes a radio frequency signal having a frequency that is a function of the difference between the first center frequency and the second center frequency. The system according to claim 9.

14. The system according to claim 9, wherein the nonlinear mixing device has a DC superconducting quantum interference device.

15. The system according to claim 9, wherein the nonlinear mixing device includes a Josephson parametric converter device, each Josephson parametric converter device including a Josephson ring modulator configured to couple the poles of the first bandpass filter and the second bandpass filter, respectively.

16. The first bandpass filter has a first terminal connected to the first port and a second terminal connected to the second port; The second bandpass filter has a terminated first terminal and a terminated second terminal. The system according to claim 9.

17. A device comprising an isolator circuit, wherein the isolator circuit is The first port and the second port; First multipolar immittance inverting bandpass filter; Second multipolar immittance inverting bandpass filter; A nonlinear mixing device that connects the poles of the first multi-pole immittance inversion band-pass filter to the respective poles of the second multi-pole immittance inversion band-pass filter; and A transmission line is connected in common to each of the nonlinear mixing devices and configured to apply a control signal to each of the nonlinear mixing devices at a predetermined frequency having different phase shifts, in order to cause non-reciprocal transmission of a signal from the first port to the second port of the isolator circuit. A device having

18. The first multi-pole immittance inverting bandpass filter has a first passband with a first center frequency; The second multi-pole immittance inverting bandpass filter has a second passband with a second center frequency; The first passband and the second passband are non-overlapping passbands; and The predetermined frequency of the control signal is a function of the difference between the first center frequency and the second center frequency. The device according to claim 17.

19. A quantum processor having qubits; and A readout signal path configured to transmit signals read from one or more of the qubits of the quantum processor, the readout signal path is configured to transmit signals read from one or more of the qubits of the quantum processor, The first port and the second port; First multipolar immittance inverting bandpass filter; Second multipolar immittance inverted bandpass filter A nonlinear mixing device that connects the poles of the first multi-pole immittance inversion band-pass filter to the respective poles of the second multi-pole immittance inversion band-pass filter; and A transmission line is connected in common to each of the nonlinear mixing devices and configured to apply a control signal to each of the nonlinear mixing devices at a predetermined frequency having different phase shifts, in order to cause non-reciprocal transmission of a signal from the first port to the second port of the isolator circuit. Having an isolator circuit including, A system equipped with these features.

20. The first multi-pole immittance inverting bandpass filter has a first passband with a first center frequency; The second multi-pole immittance inverting bandpass filter has a second passband with a second center frequency; The first passband and the second passband are non-overlapping passbands; and The predetermined frequency of the control signal is a function of the difference between the first center frequency and the second center frequency. The system according to claim 19.

21. The system according to claim 19, further comprising a signal generator configured to generate the aforementioned control signal, wherein the control signal comprises a radio frequency current signal and a control line connected to the transmission line and configured to transmit the control signal from the signal generator to the transmission line.

22. A method comprising the step of applying a control signal to a nonlinear mixed device configured to couple the poles of the first band-pass filter to the respective poles of the second band-pass filter in order to cause non-reciprocal transmission of a signal from a first port of the first band-pass filter to a second port of the first band-pass filter.

23. The first bandpass filter has a first passband with a first center frequency; The second band-pass filter has a second passband with a second center frequency; The first passband and the second passband are non-overlapping passbands; and The step of applying a control signal to the nonlinear mixing device includes a step of driving the nonlinear mixing device, which includes control signals having predetermined frequencies and different phases, wherein the predetermined frequency of each of the control signals is a function of the difference between the first center frequency and the second center frequency. The method according to claim 22.

24. The method according to claim 22, wherein the nonlinear mixing device has a DC superconducting quantum interference device.

25. The method according to claim 22, wherein the nonlinear mixing device includes Josephson parametric converter devices, each Josephson parametric converter device includes a Josephson ring modulator configured to couple the poles of the first bandpass filter and the second bandpass filter, respectively.

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