Devices for the phase-sensitive microwave control of superconducting qubits
Patent Information
- Application Number
- PCT/US2026/021290
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-03-27
- Filing Date
- 2026-03-27
- Publication Date
- 2026-10-01
Smart Images
Figure US2026021290_01102026_PF_FP_ABST
Abstract
Description
[0001] DEVICES FOR THE PHASE- SENSITIVE MICROWAVE CONTROL OF SUPERCONDUCTING QUBITS
[0002] PRIORITY CLAIM
[0003] [1] This application claims priority to the U. S. Provisional Application No. 63 / 779,080 entitled DEVICES FOR THE PHASE-SENSITIVE MICROWAVE CONTROL OF SUPERCONDUCTING QUBITS, filed on March 27, 2025, the contents of which are herein incorporated in their entirety.
[0004] FIELD
[0005] [2] The present disclosure relates generally to quantum computing and information processing systems, and more particularly to devices for the phase-sensitive microwave control of superconducting qubits.
[0006] BACKGROUND
[0007] [3] Quantum computing is a computing method that takes advantage of quantum effects, such as superposition of basis states and entanglement to perform certain computations more efficiently than a classical digital computer. In contrast to a digital computer, which stores and manipulates information in the form of bits, e.g., a “1” or “0,” quantum computing systems can manipulate information using quantum bits (“qubits”). A qubit can refer to a quantum device that enables the superposition of multiple states, e.g., data in both the “0” and “1” state, and / or to the superposition of data, itself, in the multiple states. In accordance with conventional terminology, the superposition of a “0” and “1” state in a quantum system may be represented, e.g., as a |0) + b |1). The “0” and “1” states of a digital computer are analogous to the |0) and |1) basis states, respectively of a qubit.
[0008] SUMMARY
[0009] [4] Aspects and advantages of embodiments of the present disclosure will be set forth in part in the following description, or can be learned from the description, or can be learned through practice of the embodiments.
[0010] [5] In an aspect, examples of the present disclosure are directed to a method for controlling a qubit. The method includes, while driving a first mixer with a first localoscillator (LO) signal, providing a first baseband signal to the first mixer. Providing the first baseband signal to the first mixer generates a first output signal of the first mixer. Whiledriving a second mixer with a second LO signal that is shifted by a phase-shift that is relative to the first LO signal, a second baseband signal is provided to the second mixer. Providing the second baseband signal to the second mixer generates a second output signal of the second mixer. The first output signal and the second output signal are combined at a common load line. Combining the first output signal and the second output signal at the common load line generates a microwave signal with a controlled phase. The common load line is common to the first mixer and the second mixer. The microwave signal is provided to the qubit. Providing the microwave signal to the qubit controls one or more operations of the qubit.
[0011] [6] These and other features, aspects, and advantages of various embodiments of the present disclosure will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate example embodiments of the present disclosure and, together with the description, explain the related principles.
[0012] BRIEF DESCRIPTION OF THE DRAWINGS
[0013] [7] Detailed discussion of embodiments directed to one of ordinary skill in the art is set forth in the specification, which refers to the appended figures, in which:
[0014] [8] FIG. 1 depicts a controller system for a qubit, according to example embodiments of the present disclosure;
[0015] [9] FIG. 2 provides a circuit diagram for an adiabatic quantum flux parametron mixer, according to various embodiments;
[0016]
[0010] FIG. 3 illustrates a controller system 300, according to various embodiments;
[0017]
[0011] FIG. 4 A provides a circuit diagram for an adiabatic quantum flux parametron, according to various embodiments;
[0018]
[0012] FIG. 4B provides a plot of operational dynamics for an adiabatic quantum flux parametron, according to various embodiments;
[0019]
[0013] FIG. 5 depicts a flowchart of a method for controlling a qubit, according to various embodiments; and
[0020]
[0014] FIG. 6 provides a schematic representation of a quantum computing system, according to various embodiments.DETAILED DESCRIPTION
[0021]
[0015] Superconducting qubits operating at microwave frequencies may utilize phasesensitive microwave signals for control. This control may be achieved by mixing arbitrary-waveform-generator channels with a local oscillator signal. In some approaches, the mixing of these signals takes place at room temperature. The resulting microwave signal may then be routed to the quantum chip and filtered before reaching the qubits. Sending signals from room temperature down to the cold environment may not be a scalable solution.
[0022]
[0016] The embodiments provide solutions for implementing phase-sensitive microwave control directly inside the cold environment. Some embodiments generate precise control signals for superconducting qubits using highly energy-efficient components. By using two separate mixing devices (e.g., mixers) connected to the same load, some embodiments may achieve double-quadrature microwave control. The phase of a signal delivered to one of the devices may be shifted to allow for this phase-sensitive control. Because the current at the load may be proportional to the induced flux, the signals from both devices may be combined (e.g., mixed). This may generate an output microwave signal with a controlled phase and a controlled pulse-shape. Some embodiments may allow the control electronics to be placed (or located) within the cryogenic environment of the qubits, reducing the heat load and allowing a scaling of a quantum computing system (QCS).
[0023]
[0017] Some embodiments may utilize adiabatic quantum flux parametron (AQFP) devices (e.g., AQFP mixers) to mix (or combine) signals. Some embodiments may include two AQFP mixers coupled with a shared load (e.g., a common load line). A first AQFP mixer of the two AQFP mixers may be responsible for an in-phase quadrature. A second AQFP mixer of the two AQFP mixers is responsible for a quadrature phase. A first local-oscillator (LO) signal may be provided to the first AQFP mixer. Providing the first LO signal to the first AQFP mixer may drive the first AQFP mixer. A second LO signal, which may be phase-shifted by approximately ninety degrees relative to the first LO signal, may be provided to the second AQFP mixer. Providing the second LO signal to the second AQFP mixer may drive the second AQFP mixer. These two LO signals can originate from the same source or from independent phase-locked sources. That is, the two LO signals can be generated via a common local-oscillator or by separate local-oscillators. Furthermore, direct current (de) loops (e.g., dc-SQUID loops) within the mixers may be biased by an external current that alternates between two biasing conditions, such as
[0024]
[0025] ™ 0anj -- d>0This can createan absolute potential minimum at ~ An input current may also be applied to a loop within the mixer to break a degeneracy between two possible current states, which determines the sign of a circulating current.
[0026]
[0018] Some embodiments are directed to methods for controlling a qubit. One method includes, while driving a first mixer with a first local-oscillator (LO) signal, providing a first baseband signal to the first mixer. Providing the first baseband signal to the first mixer generates a first output signal of the first mixer. The method further includes, while driving a second mixer with a second LO signal that is shifted by a phase-shift that is relative to the first local-oscillator signal, providing a second baseband signal to the second mixer.
[0027] Providing the second baseband signal to the second mixer may generate a second output signal of the second mixer. The method also includes combining (or mixing) the first output signal and the second output signal at a common load line. Combining the first output signal and the second output signal at the common load line generates a microwave signal with a controlled phase (and a controlled shape). The common load line may be common to the first mixer and the second mixer. Additionally, the method includes providing the microwave signal to the qubit. Providing the microwave signal to the qubit may control one or more operations of the qubit.
[0028]
[0019] The embodiments provide technical effects and benefits for quantum computing systems. By utilizing highly efficient superconducting logic, the embodiments may reduce the heat load of co-located electronics. This reduction in energy dissipation may enable ultra-low-power cryogenic control of qubits. Furthermore, some embodiments enable universal control of superconducting qubits that operate at frequencies in the microwave range. Some embodiments are scalable for a superconducting quantum computer with current dilutionrefrigerator technology. Some embodiments may reduce fabrication and operating costs while supporting the expansion of quantum computing architectures.
[0029]
[0020] FIG. 1 depicts a controller system 100 for a qubit 102, according to example embodiments of the present disclosure. The qubit 102 may be a superconducting transmon qubit or a resonator-based dual-rail qubit. Controller system 100 includes a first mixer 120 and a second mixer 140. Controller system 100 further includes a local oscillator (LO) 104. The LO 104 provides a first LO signal 106 to the first mixer 120 and a second LO signal 108 to the second mixer 140. The first LO signal 106 may have a first phase and the second LO signal 108 may have a second phase. The second phase of the second LO signal 108 may be shifted by a phase-shift that is relative to the first phase of the first LO signal 106. Although not shown in FIG. 1, in some embodiments, the first LO signal 106 may be generated via afirst LO (e.g., LO 104) and the second LO signal 108 may be generated via a second LO. In embodiments where separate LOs are employed to generate the first LO signal 106 and the second LO signal, the first LO may be a first phase-locked LO that generates the first LO signal 106. A second phase-locked LO generates the second LO signal 108. The second phase-locked LO may be separate and independent of the first phase-locked LO. The first LO signal 106 may correspond to an in-phase (I) quadrature. The second LO signal 108 may correspond to a quadrature (Q) phase.
[0030]
[0021] The first LO signal 106 may drive the first mixer 120 and the second LO signal 108 may drive the second mixer 140. While driving the first mixer 120 with the first LO signal 106, a first baseband signal 112 may be provided to the first mixer 120. Providing the first baseband signal 112 to the first mixer 120 may generate a first output signal 130 of the first mixer 120. While driving the second mixer 140 with the second LO signal 108, a second baseband signal 114 may be provided to the second mixer 140. Providing the second baseband signal 114 to the second mixer 140 may generate a second output signal 150 of the second mixer 140. As noted above, the second phase of the second LO signal 108 may be shifted by a phase-shift that is relative to the first phase of the first LO signal 106. The phase-shift of the second LO signal 108, relative to the first LO signal 106, may be approximately 90-degrees (e.g., «nl^-
[0022] The first output signal 130 and the second output signal 150 may be combined (or mixed) at a common load line 110. Combining the first output signal 130 and the second output signal 150 at the common load line 110 may generate a microwave signal 162 with a controlled phase. The common load line 110 may be common to the first mixer 120 and the second mixer 140. The microwave signal 162 may be provided to the qubit 102. Providing the microwave signal 162 to the qubit 102 may control one or more operations of the qubit 102.
[0031]
[0023] In various embodiments, the first mixer 120, the second mixer 140, and the qubit 102 may be located within a cryogenic chamber such that the microwave signal 162 is generated and provided to the qubit 102 at a cryogenic temperature. As shown in FIG. 1, in some embodiments, the controller system 100 may include a bandpass filter (BPF) 160. In these embodiments, prior to providing the microwave signal 162 to the qubit 102, the microwave signal 162 may be provided to BPF 160. Providing the microwave signal 162 to the BPF 160 may filter the microwave signal 162 such that, downstream of the BPF 160, themicrowave signal 162 may be a filtered microwave signal 164. In these embodiments, the filtered microwave signal 164 may then be provided to the qubit 102.
[0032]
[0024] In various embodiments, the first mixer 120 may be a first adiabatic quantum flux parametron (AQFP) mixer. The second mixer 140 may be a second AQFP mixer. The first mixer 120 may include a first pair of AQFPs 122. The second mixer 140 may include a second pair of AQFPs 142. A first AQFP 124 of the first pair of AQFPs 122 may include a first direct current (dc)-superconducting quantum interference device (SQUID) loop 132 and a first radiofrequency (rf)-SQUID loop 134. A second AQFP 126 of the first pair of AQFPs 122 may include a second dc-SQUID loop 136 and a second rf-SQUID loop 138. A third AQFP 144 of the second pair of AQFPs 142 may include a third dc-SQUID loop 152 and a third rf-SQUID loop 154. A fourth AQFP 146 of the second pair of AQFPs 142 may include a fourth dc-SQUID loop 156 and a fourth rf-SQUID loop 158.
[0033]
[0025] As noted above, various embodiments include a controller system (e.g., controller system 100). The controller system may be enabled to implement a method for controlling a qubit (e.g., qubit 102). The controller system may be a subsystem of a quantum computing system (QCS). As discussed in conjunction with at least FIG. 1, a controller system (or a QCS) may include a first mixer (e.g., first mixer 120), a second mixer (e.g., second mixer 140), and a qubit. The first mixer may be an adiabatic quantum flux parametron (AQFP) and the second mixer may be a second AQFP mixer.
[0034]
[0026] FIG. 2 provides a circuit diagram for an adiabatic quantum flux parametron mixer 200, according to various embodiments. The adiabatic quantum flux parametron (AQFP) mixer 200 may be similar to the first mixer 120 and / or the second mixer 140 of FIG. 1. One or more copies of AQFP mixer 200 may be employed in the controller system 100 of FIG. 1.
[0035]
[0027] Similar to the first mixer 120 and the second mixer 140, AQFP mixer 200 includes a pair of AQFP circuits (e.g., AQFPs) that includes a first AQFP (e.g., labeled as AQFP A) and a second AQFP (labeled as AQFP B). For instance, AQFP A may be similar to the first AQFP 124 and / or the third AQFP 144 of FIG. 1.? XQFP B may be similar to the second AQFP 126 and / or the fourth AQFP 146 of FIG. 1. As such, AQFP A (e.g., the first AQFP) may include a first dc-SQUID loop and a first rf-SQUID loop. Similarly, AQFP B (e.g., the second AQFP) may include a second dc-SQUID loop and a second rf-SQUID loop. The first AQFP may include a first resistor configured to shunt the first dc-SQUID loop. Likewise, the second AQFP may include a second resistor configured to shunt the second dc-SQUID loop. Shunting the first dc-SQUID loop may reduce current oscillations during adiabatic switching.
[0028] In the orientation of FIG. 2, the two AQFPs may be stacked vertically. These AQFP circuits (AQFP A and AQFP B) may interface with various input lines on the left, which carry both the digital control signals and the excitation signals. The right side of AQFP mixer 200 includes a shared load line that inductively couples to the outputs of both AQFPs. This load line connects to ground through a resistor
[0036]
[0037] at the bottom and leads into a bandpass filter, labeled BPF, at the top before providing a microwave output
[0038]
[0039]
[0029] A local-oscillator (LO) signal may drive the AQFP mixer 200. The AQFP mixer 200 may utilize a nonlinearity of the AQFP A and AQFP B to mix two distinct signals.
[0040] Microwave excitation currents h and baseband excitation currents ^ are supplied to both AQFP A and AQFP B. These excitation currents may be calibrated so that each delivers a flux bias of approximately ^4 / 2 t0their respective dc-SQUID loops included in the respective AQFP. The nonlinear mixing of these signals may yield a combined LO signal and baseband current.
[0041]
[0030] The overall output delivered to the common load line is then modulated by the digital logical inputs n and
[0042]
[0043] When the input n is approximately equal to the negative of 4 the output fluxes (e.g.,
[0044]
[0045] and &) from AQFP A and AQFP B (respectively) may at least approximately cancel each other out, resulting in no combined signal reaching the bandpass filter (BPF). Conversely, when
[0046]
[0047] approximately equals -4'^, the output fluxes may constructively add together, producing an active output signal that combines the microwave and baseband currents. In practical operation,
[0048]
[0049] may be held constant, allowing the input signal 4n to act as a digital switch that turns the shaped microwave signal on and off at the input of the bandpass filter. Furthermore, a target pulse shape of the resulting microwave output may be achieved by shaping the baseband excitation current 4d.
[0050]
[0031] AQFP mixer 200 may rely on various elements and signals that work in concert to produce the final modulated output (e.g., the microwave output). AQFP A and AQFP B may be two superconducting logic elements that perform the nonlinear signal mixing. The signals
[0051]
[0052] hn and ’’ may represent the digital logical inputs that control whether the mixer is in an active or inactive state. The signal llo may denote a high-frequency microwave, or LO, excitation current. In contrast, 4d may be a lower-frequency baseband excitation current whose custom shape (e.g., achieved via pulse shaping) dictates the envelope of the final output (e.g., the microwave output). The intermediate signals 4t.<ia and outb may represent the output currents generated by AQFP A and AQFP B, which subsequently may produce the corresponding output fluxes
[0053]
[0054] and. The load line may be a central inductive transmissionpathway where these two localized fluxes are physically combined. The resistor may be a source resistor connected to the load line, providing a termination to ground. The BPF may be a bandpass filter responsible for isolating the desired frequency range of the combined signal before it is outputted by the AQFP mixer 200. tu may represent a shaped (and filtered) microwave output voltage (e.g., a microwave signal) that is delivered to a target device for phase-sensitive control.
[0055]
[0032] FIG. 3 illustrates a controller system 300, according to various embodiments. The controller system 300 may be similar to controller system 100 of FIG. 1. The controller system 300 may be a double-quadrature microwave control device. The controller system 300 may include a combination of two copies of the AQFP mixer 200 of FIG. 2 (e.g,, first AQFP mixer 320 and second AQFP mixer 340, each of which may be similar to AQFP mixer 200 of FIG. 2. That is, the controller system 300 includes two distinct and separate AQFP mixers that are coupled together to a single, shared load. In controller system 300, the first mixer 320 may provide a similar functionality to first mixer 120 in controller system 100 of FIG. 1. Likewise, in controller system 300, the second mixer 340 may provide a similar functionality to second mixer 140 in controller system 100. As shown in FIG. 3, the first mixer 320 may be responsible for I-quadrature driving and the second mixer 340 may be responsible for Q-quadrature driving. These two sections feed their outputs into a central load line that connects to a bandpass filter (BPF), which yields the final microwave output signal.
[0056]
[0033] An operation of controller system 300 includes employing the first AQFP mixer 320 and the second AQFP mixer 340 (e.g., two separate single-quadrature mixers) to implement phase-sensitive, double-quadrature microwave control. This may be enabled by adjusting the r r+90
[0057] LO signals (e.g., *LO andiLO ), which drive the first AQFP mixer 320 and the second AQFP mixer 340, respectively, so that the phase of the current provided to the second AQFP mixer 340 is shifted by ninety degrees relative to the LO signal that is driving the first AQFP mixer 320. These offset LO signals can originate from a common LO or from two independent, phase-locked oscillators. The baseband excitation currents (e.g., hb and &) for the first AQFP mixer 320 and the second?\QFP mixer 340, respectively, operate independently, meaning the pulse shape for the in-phase and quadrature components may be controlled without needing to be related to one another. Because the current at the common load line may be linearly proportional to the induced flux, the signals from the I-quadrature and Q- quadrature constructively sum together at the input of the bandpass filter, generating a combined output microwave signal with a controlled phase and pulse shape.
[0034] The controller system 300 may include elements and signals that facilitate this mixing process. More specifically, the first AQFP mixer 320 (e.g., the I-quadrature mixer) includes a first pair of AQFP mixers. The first pair of AQFP mixers includes a first AQFP mixer (e.g., AQFP A) and a second AQFP mixer (e g., AQFP B). The second AQFP mixer 340 (e.g., the Q-quadrature mixer) includes a second pair of AQFP mixers. The second pair of AQFP mixers includes a third AQFP mixer (e.g,, AQFP C) and a fourth AQFP mixer (e.g,, AQFP D). The digital inputs, identified as An, n, and Au-, may be used to switch the shaped microwave signal on and off at the input of the filter. The local -oscillator signals are denoted S j-i-90
[0058] as for the first AQFP mixer 320 and for the second AQFP mixer 340, highlighting the ninety-degree phase shift that may enable double-quadrature operation. Baseband excitation currents, designated u) and Ab, may be utilized to independently dictate the target pulse shapes for their respective quadratures. These inputs induce (or generate) output fluxes, labeled ^
[0059]
[0060] L,, ^b, ^c, and $<1, which flow into the central load line. These signals are combined and pass through the bandpass filter, labeled BPF, to emerge as the shaped
[0061]
[0062] microwave output.
[0063]
[0035] The controller system 300 may be enabled to implement a method for controlling a qubit. The qubit is not shown in FIG. 3. However, the qubit may be similar to qubit 102 of controller system 100 of FIG. 1. Accordingly, the qubit may be downstream of the BPF. In some embodiments, the BPF may not be included in controller system 300, and thus be coupled directly to the common load line. In some embodiments, while driving the first AQFP mixer 320 with a first local-oscillator (LO) signal (e.g.,.o), a first baseband signal (e.g., h ) may be provided to the first AQFP mixer 320. Providing the first baseband signal to the first AQFP mixer 320 may generate a first output signal (e.g., a combination of the currents generated via the output fluxes
[0064]
[0065] and ^&) of the first AQFP mixer 320. While driving the second AQFP mixer 340 with a second LO (e.g.,1LO ) signal that is shifted by a phase-shift that is relative to the first LO signal, a second baseband signal (A?;) to the second AQFP mixer 340. Providing the second baseband signal to the second AQFP mixer 340 may generate a second output signal (e.g., a combination of the currents generated via the output fluxes and d) of the second AQFP mixer 340. The first output signal and the second output signal may be combined at the common load line. Combining the first output signal and the second output signal at the common load line may generate a microwave signal (e.g..with a controlled phase. The common load line is common to the first AQFP mixer 320 and the second AQFP mixer 340.
[0066]
[0036] FIG. 4A provides a circuit diagram for an AQFP 400, according to various embodiments. FIG. 4B provides a plot 420 of operational dynamics for an adiabatic quantum flux parametron, according to various embodiments. Plot 420 is a plot of a normalized potential of the AQFP 400, as a function of the phase of the AQFP 400.
[0067]
[0037] As shown in the circuit diagram, AQFP 400 includes a rf-SQUID loop 402 and a dc-SQUID loop 404. The rf-SQUID loop 402 may be a loop formed by an inductively shunted Josephson junction. When employed in an AQFP mixer (e.g., any of AQFP A, AQFP B. AQFP C, or AQFP D in controller system 300 of FIG. 3) the single Josephson junction may be replaced by a complete dc-SQUID loop (e.g., dc-SQUID loop 404). This architectural substitution includes a secondary inner loop (e.g., dc-SQUID loop 404) that is threaded by a magnetic flux designated as
[0068]
[0069] . On the left side of the circuit diagram, an excitation current labeled i clock. may be inductively coupled to the dc-SQUID loop 404. The outer rf-SQUID loop 402 may include a node representing the superconducting phase denoted as
[0070]
[0071] and the rf-SQUID loop 402 may be threaded by a flux labeledrf. On the right side of the schematic, this rf-SQUID loop 402 may be inductively coupled to two distinct transmission lines, one carrying an input current designated as n and another carrying an output current designated as ut.
[0072]
[0038] The plot 420 of FIG. 4B shows the normalized potential of the circuit on the y-axis against the adiabatic quantum flux parametron phase,
[0073]
[0074] on the x-axis, with the phase ranging from -10 to 10. The plot 420 features two distinct curves representing different biasing conditions for the dc-SQUID loop 404, while the flux bias of the outer rf-SQUID loop 402 is held constant at
[0075]
[0076] The go hcurveillustrates the AQFP’s 400 potential when the dc-SQUID loop 404 bias dc is approximately 0, revealing a single absolute potential minimum centered around at “ fl The dashed curve depicts the AQFP's 400 potential when the dc-SQUID loop 404 bias ®dc is elevated to
[0077]
[0078] which may transform the energy landscape into a double-well shape containing at least two separate minima. The arrow labeled "adiabatic switching" originates from the single minimum of the blue curve at 0 “ 0 and arches toward the rightmost minimum of the dashed double-well curve to represent the AQFP's 400 state transition.
[0079]
[0039] The operation of AQFP 400 may be based on alternating the bias of dc-SQUID loop 404 between 0 and
[0080]
[0081] using the external excitation current. When the bias dc isapproximately 0, the Josephson and inductive potentials of the circuit may constructively add together to form a single absolute minimum at a phase of C' ”
[0082]
[0083] which ensures that no (or very little) current flows through the outer rf-SQUID loop 402. As the excitation current adiabatically increases the bias to ^o, the Josephson potential may abruptly change sign. This sign change may counteract the inductive potential, thereby causing the original single well to evolve seamlessly into a double-well potential. This resulting double-well configuration establishes two metastable current states that are symmetric with respect to ~ I) which ultimately function as the logical "0" and "1" states of the device.
[0084]
[0040] The signal ^dock may serve as the excitation current that biases the dc-SQUID loop 404, directly driving the adiabatic evolution of the potential from a single well to a double well. The signal,-,. may act as a small input current that applies a flux bias
[0085]
[0086] to the rf-SQUID loop 402. This specific input current may break the degeneracy of the newly formed double-well potential by energetically favoring one of the two metastable states.
[0087] Consequently,
[0088]
[0089] may be responsible for determining the sign of the circulating current within the loop and, by extension, the sign of the output current
[0090]
[0091] that is delivered to an inductively coupled load. The variable ^dc may represent the magnetic flux threading the inner dc-SQUID loop 404, and its value may control the formation of the double-well potential. The variable
[0092]
[0093] may represent the flux threading the outer rf-SQUID loop 402, which is set to a fixed non-zero value by the input current to successfully select the final logical state during the switching process. The variable C may represent the superconducting phase of the circuit, functioning as the independent variable that defines the AQFP’s 400 potential energy landscape.
[0094]
[0041] FIG. 5 depicts a flowchart of a method 500 for controlling a qubit, according to various embodiments. Method 500 begins at block 502, where a first mixer is driven with a first local-oscillator (LO) signal. At block 504, a second mixer is driven with a second LO signal. The second LO signal is shifted by a phase-shift that is relative to the first LO signal. At block 506, and while driving the first mixer with the first LO signal, a first baseband signal is provided to the first mixer. Providing the first baseband signal to the first mixer may generate a first output signal of the first mixer. At block 508, and while driving the second mixer with the second LO signal, a second baseband signal is provided to the second mixer. Providing the second baseband signal to the second mixer generates a second output signal of the second mixer. At block 510, the first output signal and the second output signal are combined at a common load line. Combining the first output signal and the second outputsignal at the common load line generates a microwave signal with a controlled phase. The common load line is common to the first mixer and the second mixer. At block 512, the microwave signal is provided to a bandpass filter (BPF). Providing the microwave signal to the BPF transforms (or filters) the microwave signal into a filtered microwave signal. At block 514, the filtered microwave signal is provided to the qubit. Providing the filtered microwave signal to the qubit controls one or more operations of the qubit.
[0095]
[0042] In various embodiments, the first mixer is a first adiabatic quantum flux parametron (AQFP) mixer, and the second mixer is a second AQFP mixer.
[0096]
[0043] In at least one embodiment, the first AQFP mixer includes a first pair of AQFPs and the second AQFP mixer includes a second pair of AQFPs.
[0097]
[0044] In some embodiments, the method further comprises applying a first digital input and a first fixed input to the first pair of AQFPs. Applying the first digital input and the first fixed input to the first pair of AQFPs controls the first output signal of the first AQFP mixer.
[0098]
[0045] In various embodiments, a first AQFP of the first pair of AQFPs includes a first dc-SQUID loop and a first rf-SQUID loop, and a second AQFP of the first pair of AQFPs includes a second dc-SQUID loop and a second rf-SQUID loop. Furthermore, a third AQFP of the second pair of AQFPs includes a third dc-SQUID loop and a third rf-SQUID loop, and a fourth AQFP of the second pair of AQFPs includes a fourth dc-SQUID loop and a fourth rf-SQUID loop.
[0099]
[0046] In at least one embodiment, method 500 further includes flux-biasing the first dc-SQUID loop of the first AQFP with a first excitation current that alternates between a first biasing condition of zero flux and a second biasing condition of one superconducting quantum of flux. Method 500 may further include flux-biasing the second dc-SQUID loop of the second AQFP with a second excitation current that alternates between the first biasing condition and the second biasing condition. Method 500 may also include flux-biasing the third dc-SQUID loop of the third AQFP with a third excitation current that alternates between the first biasing condition and the second biasing condition. Additionally, the method comprises flux-biasing the fourth dc-SQUID loop of the fourth AQFP with a fourth excitation current that alternates between the first biasing condition and the second biasing condition.
[0100]
[0047] In some embodiments, the first excitation current drives a first transition of the first AQFP, adiabatically, from a no-output state to a logical circulating-current state. The second excitation current drives a second transition of the second AQFP, adiabatically, from the nooutput state to the logical circulating-current state. The third excitation current drives a third transition of the third AQFP, adiabatically, from the no-output state to the logical circulating-current state. The fourth excitation current drives a fourth transition of the fourth AQFP, adiabatically, from the no-output state to the logical circulating-current state.
[0101]
[0048] In various embodiments, providing the first baseband signal to the first mixer includes pulse-shaping the first baseband signal based on a target pulse shape such that a shape of the microwave signal is in accordance with the target pulse shape at the common load line.
[0102]
[0049] In at least one embodiment, a single LO generates each of the first LO signal and the second LO signal.
[0103]
[0050] In some embodiments, a first phase-locked LO generates the first LO signal, and a second phase-locked LO generates the second LO signal. The second phase-locked LO is separate and independent of the first phase-locked LO.
[0104]
[0051] In various embodiments, the phase-shift is a 90-degree phase-shift.
[0105]
[0052] In at least one embodiment, the method further comprises combining the first LO signal with a low-frequency oscillatory baseband current. Combining the first LO signal with the low-frequency oscillatory baseband current shifts a microwave frequency of the microwave signal relative to a local frequency of the first LO signal.
[0106]
[0053] In some embodiments, the qubit is a transmon qubit or a resonator-based dual-rail qubit.
[0107]
[0054] In various embodiments, prior to providing the microwave signal to the qubit, the method comprises providing the microwave signal to a bandpass filter (BPF). Providing the microwave signal to the BPF filters the microwave signal such that, downstream of the BPF, the microwave signal is a filtered microwave signal. The method further comprises providing the filtered microwave signal to the qubit.
[0108]
[0055] In at least one embodiment, the first mixer, the second mixer, and the qubit are located within a cryogenic chamber such that the microwave signal is generated and provided to the qubit at a cryogenic temperature.
[0109]
[0056] In some embodiments, the method further comprises pulse-shaping the first baseband signal to adjust the controlled phase and a pulse-shape of the microwave signal. The method includes pulse-shaping the second baseband signal to adjust the controlled phase and the pulse-shape of the microwave signal. Pulse-shaping the second baseband signal is performed independently of pulse-shaping the first baseband signal, and pulse-shaping the first baseband signal is performed independently of pulse-shaping the second baseband signal.
[0110]
[0057] In various embodiments, the first LO signal corresponds to an in-phase (I) quadrature and the second LO signal corresponds to a quadrature (Q) phase.
[0058] In at least one embodiment, the first mixer includes a first rf-SQUID loop. The method further comprises applying a first input current to the first rf-SQUID loop, wherein applying the first input current to the first rf-SQUID loop breaks a degeneracy between two possible current states. The method also includes determining, based on breaking the degeneracy between the two possible current states, a sign of a circulating current representing a logical state.
[0111]
[0059] In some embodiments, the first mixer further includes a first resistor that is configured to shunt the first dc-SQUID loop. Shunting the first dc-SQUID loop reduces current oscillations during adiabatic switching.
[0112]
[0060] FIG. 6 depicts an example quantum computing system 600. The system 600 is an example of a system of one or more classical computers and / or quantum computing devices in one or more locations, in which the systems, components, and techniques described below can be implemented. Those of ordinary skill in the art, using the disclosures provided herein, will understand that other quantum computing devices or systems can be used without deviating from the scope of the present disclosure.
[0113]
[0061] The system 600 includes quantum hardware 602 in data communication with one or more classical processors 604. The classical processors 604 can be configured to execute computer-readable instructions stored in one or more memory devices to perform operations, such as any of the operations described herein. The quantum hardware 602 includes components for performing quantum computation. For example, the quantum hardware 602 includes a quantum system 610, control device(s) 612, and readout device(s) 614 (e.g., readout resonator(s)). The quantum system 610 can include one or more multi-level quantum subsystems, such as a register of qubits (e.g., qubits 620). In some implementations, the multi-level quantum subsystems can include superconducting qubits, such as flux qubits, charge qubits, transmon qubits, gmon qubits, spin-based qubits, and the like. In some implementations, the superconducting qubits may be located in a cryostat to cool the qubits to superconducting temperatures (e.g., less than about 3 Kelvin). However, aspects of the present disclosure are not limited to superconducting qubits. In some examples, any suitable qubit structure may be used without deviating from the scope of the present disclosure, such as photonic qubits, trapped ion qubits, spin qubits, neutral atom qubits, quantum dot qubits, molecular qubits, or other qubits.
[0114]
[0062] The type of multi-level quantum subsystems that the system 600 utilizes may vary. For example, in some cases the system may include one or more readout device(s) 614 coupled (e.g., electromagnetically coupled) to one or more qubits, e.g., transmon, flux, gmon,xmon, or other qubits. In other cases, ion traps, photonic devices or superconducting cavities (e.g., with which states may be prepared without employing qubits) may be used. Further examples of realizations of multi-level quantum subsystems include fluxmon qubits, silicon quantum dot, or phosphorus impurity qubits.
[0115]
[0063] Quantum-circuits may be constructed and applied to the register of qubits included in the quantum system 610 via multiple control lines that are coupled to one or more control devices 612. Example control devices 612 that operate on the register of qubits can be used to implement quantum gates or quantum-circuits having a plurality of quantum gates, e.g., Pauli gates, Hadamard gates, controlled-NOT (CNOT) gates, controlled-phase gates, T gates, multi-qubit quantum gates, coupler quantum gates, etc. The one or more control devices 612 may be configured to operate on the quantum system 610 through one or more respective control parameters (e.g., one or more physical control parameters). For example, in some implementations, the multi-level quantum subsystems may be superconducting qubits and the control devices 612 may be configured to provide control pulses to control lines to generate magnetic fields to control the qubits. For example, in some implementations the multi-level quantum subsystems may be neutral atom qubits and the control devices 612 may be configured to provide control pulses to control lines to generate magnetic fields to control the qubits.
[0116]
[0064] The quantum hardware 602 may further include readout devices 614 (e.g., readout resonators). Measurement results 608 obtained via readout devices 614 may be provided to the classical processors 604 for processing and analyzing. In some implementations, the quantum hardware 602 may include a quantum-circuit and the control device(s) 612 and readout devices(s) 614 may implement one or more quantum logic gates that operate on the quantum system 610 through physical control parameters (e.g., microwave pulses) that are sent through wires included in the quantum hardware 602. The readout device(s) 614 may be configured to perform quantum measurements on the quantum system 610 and send measurement results 608 to the classical processors 604.
[0117]
[0065] In addition, the quantum hardware 602 may be configured to receive data specifying physical control qubit parameter values 606 from the classical processors 604. The quantum hardware 602 may use the received physical control qubit parameter values 606 to update the action of the control device(s) 612 and readout devices(s) 614 on the quantum system 610. For example, the quantum hardware 602 may receive data specifying new values representing voltage strengths of one or more digital to analog converters (DACs) included in the control devices 612 and may update the action of the DACs on the quantum system 610 accordingly.The classical processors 604 may be configured to initialize the quantum system 610 in an initial quantum state, e.g., by sending data to the quantum hardware 602 specifying an initial set of parameters 606.
[0118]
[0066] In some implementations, the readout device(s) 614 can take advantage of a difference in the impedance for the |0) and 11) states of an element of the quantum system, such as a qubit, to measure the state of the element (e.g., the qubit). For example, the resonance frequency of a readout resonator can take on different values when a qubit is in the state |0) or the state 11), due to the nonlinearity of the qubit. Therefore, a microwave pulse reflected from the readout device 614 carries an amplitude and phase shift that depend on the qubit state. In some implementations, a Purcell filter can be used in conjunction with the readout device(s) 614 to impede microwave propagation at the qubit frequency.
[0119]
[0067] In some embodiments, the quantum system 610 can include a plurality of qubits 620 arranged, for instance, in a two-dimensional grid 622. For clarity, the two-dimensional grid 622 depicted in FIG. 6 includes 4x4 qubits; however, in some implementations the system 610 may include a smaller or a larger number of qubits. In some embodiments, the multiple qubits 620 can interact with each other through multiple qubit couplers, e.g., qubit coupler 624. The qubit couplers can define nearest neighbor interactions between the multiple qubits 620. In some implementations, the strengths of the multiple qubit couplers are tunable parameters. In some cases, the multiple qubit couplers included in the quantum computing system 600 may be couplers with a fixed coupling strength.
[0120]
[0068] In some implementations, the multiple qubits 620 may include data qubits, such as qubit 626 and measurement qubits, such as qubit 628. A data qubit is a qubit that participates in a computation being performed by the system 600. A measurement qubit is a qubit that may be used to determine an outcome of a computation performed by the data qubit. That is, during a computation an unknown state of the data qubit is transferred to the measurement qubit using a suitable physical operation and measured via a suitable measurement operation performed on the measurement qubit.
[0121]
[0069] In some implementations, each qubit in the multiple qubits 620 can be operated using respective operating frequencies, such as an idling frequency and / or an interaction frequency and / or readout frequency and / or reset frequency. The operating frequencies can vary from qubit to qubit. For instance, each qubit may idle at a different operating frequency. The operating frequencies for the qubits 620 can be chosen before a computation is performed. In some examples, operating on the frequencies for the qubits 620 may be adjusted using ACStark shift according to examples of the present disclosure before a quantum computation, quantum gate, and / or a quantum algorithm is performed.
[0122]
[0070] FIG. 6 depicts one example quantum computing system that can be used to implement the methods and operations according to example aspects of the present disclosure. Other quantum computing systems can be used without deviating from the scope of the present disclosure.
[0123]
[0071] In various implementations, the example system 600 can be implemented as a client device, a server device, or both. The example system 600 can be implemented as part of a distributed computing system. The example system 600 can be implemented along with other example systems, which may be the same or different. The example system 600 can be implemented in a server farm or other facility that operates multiple computing systems to provide computational services to or on behalf of a plurality of client systems.
[0124] Advantageously, techniques according to example aspects of the present disclosure can provide for improved calibration and maintenance of computing facilities, increasing service uptime, decreasing failure rates, etc.
[0125]
[0072] In various embodiments, system 600 may be a quantum computing system (QCS). The QCS comprises a first mixer, a second mixer, a qubit, one or more processing units, and one or more memory devices. The one or more memory devices store computer-readable instructions that when executed by the one or more processing units cause the one or more processing units to perform specific operations. The operations comprise, while driving a first mixer with a first local-oscillator (LO) signal, providing a first baseband signal to the first mixer, wherein providing the first baseband signal to the first mixer generates a first output signal of the first mixer. The operations further comprise, while driving a second mixer with a second LO signal that is shifted by a phase-shift that is relative to the first LO signal, providing a second baseband signal to the second mixer, wherein providing the second baseband signal to the second mixer generates a second output signal of the second mixer. The operations include combining the first output signal and the second output signal at a common load line, wherein combining the first output signal and the second output signal at the common load line generates a microwave signal with a controlled phase and the common load line is common to the first mixer and the second mixer. The operations also comprise providing the microwave signal to the qubit.Additional Embodiments
[0126]
[0073] In some embodiments, a controller system is provided for operating a quantum computing system (QCS) that includes a set of qubits. The controller system comprises a first load line. A first mixer device is coupled to the first load line. The first mixer device is configured to receive a first input signal and a first local-oscillator (LO) signal. The first mixer device mixes the first input signal and the first LO signal to provide a first output signal to the first load line. A second mixer device is coupled to the first load line. The second mixer device is configured to receive a second input signal and a second LO signal that has a first phase-shift with respect to the first LO signal. The second mixer device mixes the second input signal and the second LO signal to provide a second output signal to the first load line.
[0127]
[0074] In various embodiments, the controller system is configured to combine the first output signal and the second output signal on the first load line to generate a combined output signal.
[0128]
[0075] In at least one embodiment, the combined output signal is a phase-sensitive microwave signal.
[0129]
[0076] In some embodiments, the first load line is configured to provide the combined output signal to a filter.
[0130]
[0077] In various embodiments, the filter is a bandpass filter (BPF).
[0131]
[0078] In at least one embodiment, the filter outputs a control signal.
[0132]
[0079] In some embodiments, the control signal is a phase-sensitive microwave signal.
[0133]
[0080] In various embodiments, an operation of a first qubit of the set of qubits is controlled by the control signal.
[0134]
[0081] In at least one embodiment, each qubit of the set of qubits is a superconducting qubit such that the set of qubits is a set of superconducting qubits.
[0135]
[0082] In some embodiments, each qubit of the set of superconducting qubits is a transmon qubit such that the set of superconducting qubits is a set of transmon qubits.
[0136]
[0083] In various embodiments, each qubit of the set of superconducting qubits is a dual-rail qubit such that the set of superconducting qubits is a set of dual-rail qubits.
[0137]
[0084] In at least one embodiment, each qubit of the set of superconducting qubits is a fluxonium qubit such that the set of superconducting qubits is a set of fluxonium qubits.
[0138]
[0085] In some embodiments, the first phase-shift is a 90-degree phase-shift.
[0139]
[0086] In various embodiments, the controller system is a double-quadrature microwave control device.
[0087] In at least one embodiment, the first output signal provides an in-phase signal to drive a first qubit of the set of qubits.
[0140]
[0088] In some embodiments, the second output signal provides a quadrature signal to drive the first qubit of the set of qubits.
[0141]
[0089] In various embodiments, a combination of the in-phase signal and the quadrature signal provide a phase-sensitive microwave signal to drive the first qubit.
[0142]
[0090] In at least one embodiment, the first mixer device is a first adiabatic quantum flux parametron (AQFP) mixer device. The second mixer device is a second AQFP mixer device.
[0143]
[0091] In some embodiments, the first AQFP mixer device comprises a first AQFP and a second AQFP. The second AQFP mixer device comprises a third AQFP and a fourth AQFP.
[0144]
[0092] In various embodiments, the second AQFP mixer device provides out-of-phase (Q) quadrature. The first AQFP device provides in-phase (I) quadrature.
[0145]
[0093] Implementations of the digital and / or quantum subject matter described in this specification can be implemented as one or more digital and / or quantum computer programs (e.g., one or more modules of digital and / or quantum computer program instructions encoded on a tangible non-transitory storage medium for execution by, or to control the operation of, data processing apparatus). The digital and / or quantum computer storage medium can be a machine-readable storage device, a machine-readable storage substrate, a random or serial access memory device, one or more qubits / qubit structures, or a combination of one or more of them. Alternatively or in addition, the program instructions can be encoded on an artificially-generated propagated signal that is capable of encoding digital and / or quantum information (e.g., a machine-generated electrical, optical, or electromagnetic signal) that is generated to encode digital and / or quantum information for transmission to suitable receiver apparatus for execution by a data processing apparatus.
[0146]
[0094] The terms quantum information and quantum data refer to information or data that is carried by, held, or stored in quantum systems, where the smallest non-trivial system is a qubit (i.e., a system that defines the unit of quantum information). It is understood that the term “qubit” encompasses at least some quantum systems that may be suitably approximated as a two-level system in the corresponding context. Such quantum systems may include multi-level systems, e.g., with two or more levels. By way of example, such systems can include atoms, electrons, photons, ions or superconducting qubits. In many implementations the computational basis states are identified with the ground and first excited states; however, it is understood that other setups where the computational states are identified with higher level excited states (e.g., qubits) are possible.
[0095] The term “data processing apparatus” refers to digital and / or quantum data processing hardware and encompasses at least some kinds of apparatus, devices, and machines for processing digital and / or quantum data, including by way of example a programmable digital processor, a programmable quantum processor, a digital computer, a quantum computer, or multiple digital and quantum processors or computers, and combinations thereof. The apparatus can also be, or further include, special purpose logic circuitry, e.g., an FPGA (field programmable gate array), or an ASIC (application-specific integrated circuit), or a quantum simulator, i.e., a quantum data processing apparatus that is designed to simulate or produce information about a specific quantum system. In particular, a quantum simulator is a special purpose quantum computer that does not have the capability to perform universal quantum computation. The apparatus can optionally include, in addition to hardware, code that creates an execution environment for digital and / or quantum computer programs, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them.
[0147]
[0096] A digital or classical computer program, which may also be referred to or described as a program, software, a software application, a module, a software module, a script, or code, can be written in any form of programming language, including compiled or interpreted languages, or declarative or procedural languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a digital computing environment. A quantum computer program, which may also be referred to or described as a program, software, a software application, a module, a software module, a script, or code, can be written in any form of programming language, including compiled or interpreted languages, or declarative or procedural languages, and translated into a suitable quantum programming language, or can be written in a quantum programming language, e.g., QCL, Quipper, Cirq, etc.
[0148]
[0097] A digital and / or quantum computer program may, but need not, correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data, e.g., one or more scripts stored in a markup language document, in a single file dedicated to the program in question, or in multiple coordinated files, e.g., files that store one or more modules, sub-programs, or portions of code. A digital and / or quantum computer program can be deployed to be executed on one digital or one quantum computer or on multiple digital and / or quantum computers that are located at one site or distributed across multiple sites and interconnected by a digital and / or quantum data communication network. A quantum data communication network is understood to be a network that may transmit quantum data usingquantum systems, e.g., qubits. Generally, a digital data communication network does not transmit quantum data; however, a quantum data communication network may transmit both quantum data and digital data.
[0149]
[0098] The processes and logic flows described in this specification can be performed by one or more programmable digital and / or quantum computers, operating with one or more digital and / or quantum processors, as appropriate, executing one or more digital and / or quantum computer programs to perform functions by operating on input digital and quantum data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA or an ASIC, or a quantum simulator, or by a combination of special purpose logic circuitry or quantum simulators and one or more programmed digital and / or quantum computers.
[0150]
[0099] For a system of one or more digital and / or quantum computers or processors to be “configured to” or “operable to” perform particular operations or actions means that the system has installed on it software, firmware, hardware, or a combination of them that in operation cause the system to perform the operations or actions. For one or more digital and / or quantum computer programs to be configured to perform particular operations or actions means that the one or more programs include instructions that, when executed by digital and / or quantum data processing apparatus, cause the apparatus to perform the operations or actions. A quantum computer may receive instructions from a digital computer that, when executed by the quantum computing apparatus, cause the apparatus to perform the operations or actions.
[0151]
[0100] Digital and / or quantum computers suitable for the execution of a digital and / or quantum computer program can be based on general or special purpose digital and / or quantum microprocessors or both, or any other kind of central digital and / or quantum processing unit. Generally, a central digital and / or quantum processing unit will receive instructions and digital and / or quantum data from a read-only memory, or a random access memory, or quantum systems suitable for transmitting quantum data, e.g., photons, or combinations thereof.
[0152]
[0101] Some example elements of a digital and / or quantum computer are a central processing unit for performing or executing instructions and one or more memory devices for storing instructions and digital and / or quantum data. The central processing unit and the memory can be supplemented by, or incorporated in, special purpose logic circuitry or quantum simulators. Generally, a digital and / or quantum computer will also include, or be operatively coupled to receive digital and / or quantum data from or transfer digital and / or quantum datato, or both, one or more mass storage devices for storing digital and / or quantum data, e.g., magnetic, magneto-optical disks, or optical disks, or quantum systems suitable for storing quantum information. However, a digital and / or quantum computer need not have such devices.
[0153]
[0102] Digital and / or quantum computer-readable media suitable for storing digital and / or quantum computer program instructions and digital and / or quantum data include at least some forms of non-volatile digital and / or quantum memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magnetooptical disks; and CD-ROM and DVD-ROM disks; and quantum systems, e.g., trapped atoms or electrons. It is understood that quantum memories are devices that can store quantum data for a long time with high fidelity and efficiency, e.g., light-matter interfaces where light is used for transmission and matter for storing and preserving the quantum features of quantum data such as superposition or quantum coherence.
[0154]
[0103] Control of the various systems described in this specification, or portions of them, can be implemented in a digital and / or quantum computer program product that includes instructions that are stored on one or more tangible, non-transitory machine-readable storage media, and that are executable on one or more digital and / or quantum processing devices. The systems described in this specification, or portions of them, can each be implemented as an apparatus, method, or electronic system that may include one or more digital and / or quantum processing devices and memory to store executable instructions to perform the operations described in this specification.
[0155]
[0104] While this specification contains many specific implementation details, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features that may be specific to particular implementations. Certain features that are described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable sub combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.
[0156]
[0105] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood that such operations may be performed in the particular order shown or in sequential order, or that at least some of the illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system modules and components in the implementations described above should not be understood as such separation in at least some implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.
[0157]
[0106] Particular implementations of the subject matter have been described. Other implementations are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results. As one example, the processes depicted in the accompanying figures may not employ the particular order shown, or sequential order, to achieve desirable results. In some cases, multitasking and parallel processing may be advantageous.
[0158]
[0107] Aspects of the disclosure have been described in terms of illustrative implementations thereof. Numerous other implementations, modifications, or variations within the scope and spirit of the appended claims can occur to persons of ordinary skill in the art from a review of this disclosure. Any and at least some features in the following claims can be combined or rearranged in any way possible. Accordingly, the scope of the present disclosure is by way of example rather than by way of limitation, and the subject disclosure does not preclude inclusion of such modifications, variations or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art. Moreover, terms are described herein using lists of example elements joined by conjunctions such as “and,” “or,” “but,” etc. It should be understood that such conjunctions are provided for explanatory purposes. Lists joined by a particular conjunction such as “or,” for example, can refer to “at least one of’ or “any combination of’ example elements listed therein, with “or” being understood as “and / or” unless otherwise indicated. Also, terms such as “based on” should be understood as “based at least in part on.”
[0159]
[0108] Those of ordinary skill in the art, using the disclosures provided herein, will understand that the elements of any of the claims, operations, or processes discussed herein can be adapted, rearranged, expanded, omitted, combined, or modified in various ways without deviating from the scope of the present disclosure. Some of the claims are described with a letter reference to a claim element for exemplary illustrated purposes and is not meantto be limiting. The letter references do not imply a particular order of operations. For instance, letter identifiers such as (a), (b), (c),..., (i), (ii), (iii),.. etc. can be used to illustrate operations. Such identifiers are provided for the ease of the reader and do not denote a particular order of steps or operations. An operation illustrated by a list identifier of (a), (i), etc. can be performed before, after, or in parallel with another operation illustrated by a list identifier of (b), (ii), etc.
Claims
WHAT IS CLAIMED IS:
1. A method for controlling a qubit, the method comprising:while driving a first mixer with a first local-oscillator (LO) signal, providing a first baseband signal to the first mixer, wherein providing the first baseband signal to the first mixer generates a first output signal of the first mixer;while driving a second mixer with a second LO signal that is shifted by a phase-shift that is relative to the first LO signal, providing a second baseband signal to the second mixer, wherein providing the second baseband signal to the second mixer generates a second output signal of the second mixer;combining the first output signal and the second output signal at a common load line, wherein combining the first output signal and the second output signal at the common load line generates a microwave signal with a controlled phase and the common load line is common to the first mixer and the second mixer; andproviding the microwave signal to the qubit, wherein providing the microwave signal to the qubit controls one or more operations of the qubit.
2. The method of claim 1, wherein the first mixer is a first adiabatic quantum flux parametron (AQFP) mixer and the second mixer is a second AQFP mixer.
3. The method of claim 2, wherein the first AQFP mixer includes a first pair of AQFPs and the second AQFP mixer includes a second pair of AQFPs.
4. The method of claim 3, further comprising:applying a first digital input and a first fixed input to the first pair of AQFPs, wherein applying the first digital input and the first fixed input to the first pair of AQFPs controls the first output signal of the first AQFP mixer.
5. The method of claim 3 or 4, wherein a first AQFP of the first pair of AQFPs includes a first dc-SQUID loop and a first rf-SQUID loop, a second AQFP of the first pair of AQFPs includes a second dc-SQUID loop and a second rf-SQUID loop, and wherein a third AQFP of the second pair of AQFPs includes a third dc-SQUID loop and a third rf-SQUID loop, a fourth AQFP of the second pair of AQFPs includes a fourth dc-SQUID loop and a fourth rf-SQUID loop.
6. The method of claim 5, further comprising:flux-biasing the first dc-SQUID loop of the first AQFP with a first excitation current that alternates between a first biasing condition of zero flux and a second biasing condition of one superconducting quantum of flux;flux -biasing the second dc-SQUID loop of the second AQFP with a second excitation current that alternates between the first biasing condition and the second biasing condition;flux -biasing the third dc-SQUID loop of the third AQFP with a third excitation current that alternates between the first biasing condition and the second biasing condition; andflux -biasing the fourth dc-SQUID loop of the fourth AQFP with a fourth excitation current that alternates between the first biasing condition and the second biasing condition.
7. The method of claim 6, wherein:the first excitation current drives a first transition of the first AQFP, adiabatically, from a no-output state to a logical circulating-current state;the second excitation current drives a second transition of the second AQFP, adiabatically, from the no-output state to the logical circulating-current state;the third excitation current drives a third transition of the third AQFP, adiabatically, from the no-output state to the logical circulating-current state; andthe fourth excitation current drives a fourth transition of the fourth AQFP, adiabatically, from the no-output state to the logical circulating-current state.
8. The method of any of claims 1-7, wherein providing the first baseband signal to the first mixer includes:pulse-shaping the first baseband signal based on a target pulse shape such that a shape of the microwave signal is in accordance with the target pulse shape at the common load line.
9. The method of any of claims 1-8, wherein a single LO generates each of the first LO signal and the second LO signal.
10. The method of any of claims 1-9, wherein a first phase-locked LO generates the first LO signal, a second phase-locked LO generates the second LO signal, and the second phase-locked LO is separate and independent of the first phase-locked LO.
11. The method of claim 1, wherein the phase-shift is a 90-degree phase-shift.
12. The method of any of claims 1-11, further comprising:combining the first LO signal with a low-frequency oscillatory baseband current, wherein combining the first LO signal with the low-frequency oscillatory baseband current shifts a microwave frequency of the microwave signal relative to a local frequency of the first LO signal.
13. The method of any of claims 1-12, wherein the qubit is a transmon qubit or a resonator-based dual-rail qubit.
14. The method of any of claims 1-13, further comprising:prior to providing the microwave signal to the qubit, providing the microwave signal to a bandpass filter (BPF), wherein providing the microwave signal to the BPF filters the microwave signal such that, downstream of the BPF, the microwave signal is a filtered microwave signal; andproviding the filtered microwave signal to the qubit.
15. The method of any of claims 1-14, wherein the first mixer, the second mixer, and the qubit are located within a cryogenic chamber such that the microwave signal is generated and provided to the qubit at a cryogenic temperature.
16. The method of any of claims 1-15, further comprising:pulse-shaping the first baseband signal to adjust the controlled phase and a pulseshape of the microwave signal;pulse-shaping the second baseband signal to adjust the controlled phase and the pulse-shape of the microwave signal, wherein pulse-shaping the second baseband signal is performed independently of pulse-shaping the first baseband signal and pulse-shaping the first baseband signal is performed independently of pulse-shaping the second baseband signal.
17. The method of any of claims 1-16, wherein the first LO signal corresponds to an in-phase (I) quadrature and the second LO signal corresponds to a quadrature (Q) phase.
18. The method of any of claims 1-17, wherein the first mixer includes a first rf-SQUID loop and the method further comprises:applying a first input current to the first rf-SQUID loop, wherein applying the first input current to the first rf-SQUID loop breaks a degeneracy between two possible current states; anddetermining, based on breaking the degeneracy between the two possible current states, a sign of a circulating current representing a logical state.
19. The method of claim 18, wherein the first mixer further includes a first resistor that is configured to shunt a first dc-SQUID loop, and wherein shunting the first dc-SQUID loop reduces current oscillations during adiabatic switching.
20. A quantum computing system comprising:a first mixer;a second mixer;a qubit;one or more processing units;one or more memory devices, the one or more memory devices storing computer-readable instructions that when executed by the one or more processing units cause the one or more processing units to perform operations comprising:while driving a first mixer with a first local-oscillator (LO) signal, providing a first baseband signal to the first mixer, wherein providing the first baseband signal to the first mixer generates a first output signal of the first mixer;while driving a second mixer with a second LO signal that is shifted by a phase-shift that is relative to the first LO signal, providing a second baseband signal to the second mixer, wherein providing the second baseband signal to the second mixer generates a second output signal of the second mixer; combining the first output signal and the second output signal at a common load line, wherein combining the first output signal and the secondoutput signal at the common load line generates a microwave signal with a controlled phase and the common load line is common to the first mixer and the second mixer; andproviding the microwave signal to the qubit.
21. A controller system for operating a quantum computing system (QCS) that includes a set of qubits, the controller system comprising:a first load line;a first mixer device coupled to the first load line, wherein the first mixer device is configured to receive a first input signal and a first local-oscillator (LO) signal, and wherein the first mixer device mixes the first input signal and the first LO signal to provide a first output signal to the first load line; anda second mixer device coupled to the first load line, wherein the second mixer device is configured to receive a second input signal and a second LO signal that has a first phaseshift with respect to the first LO signal, and wherein the second mixer device mixes the second input signal and the second LO signal to provide a second output signal to the first load line.
22. The controller system of claim 21, wherein the controller system is configured to combine the first output signal and the second output signal on the first load line to generate a combined output signal.
23. The controller system of claim 22, wherein the combined output signal is a phase-sensitive microwave signal.
24. The controller system of any of claims 22-23, wherein the first load line is configured to provide the combined output signal to a filter.
25. The controller system of claim 24, wherein the filter is a bandpass filter (BPF).
26. The controller system of any of claims 24-25, wherein the filter outputs a control signal.
27. The controller system of claim 26, wherein the control signal is a phasesensitive microwave signal.
28. The controller system of any of claims 26-27, wherein an operation of a first qubit of the set of qubits is controlled by the control signal.
29. The controller system of any of claims 21-28, wherein each qubit of the set of qubits is a superconducting qubit such that the set of qubits is a set of superconducting qubits.
30. The controller system of claim 29, wherein each qubit of the set of superconducting qubits is a transmon qubit such that the set of superconducting qubits is a set of transmon qubits.
31. The controller system of any of claims 29-30, wherein each qubit of the set of superconducting qubits is a dual-rail qubit such that the set of superconducting qubits is a set of dual-rail qubits.
32. The controller system of any of claims 29-31, wherein each qubit of the set of superconducting qubits is a fluxonium qubit such that the set of superconducting qubits is a set of fluxonium qubits.
33. The controller system of any of claims 21-32, wherein the first phase-shift is a 90-degree phase-shift.
34. The controller system of any of claims 21-33, wherein the controller system is a double-quadrature microwave control device.
35. The controller system of claim 34, wherein the first output signal provides an in-phase signal to drive a first qubit of the set of qubits.
36. The controller system of claim 35, wherein the second output signal provides a quadrature signal to drive the first qubit of the set of qubits.
37. The controller system of claim 36, wherein a combination of the in-phase signal and the quadrature signal provides a phase-sensitive microwave signal to drive the first qubit.
38. The controller system of any of claims 21-37, wherein the first mixer device is a first adiabatic quantum flux parametron (AQFP) mixer device and the second mixer device is a second AQFP mixer device.
39. The controller system of claim 38, wherein the first AQFP mixer device comprises a first AQFP and a second AQFP, and wherein the second AQFP mixer device comprises a third AQFP and a fourth AQFP.
40. The controller system of any of claims 38-39, wherein the second AQFP mixer device provides out-of-phase (Q) quadrature and the first AQFP mixer device provides in-phase (I) quadrature.