A superconducting quantum bit reader with josephson transmission line

Abstract

The application discloses a superconducting quantum bit reader with a Josephson transmission line, which reads out a superconducting quantum bit after receiving an excitation signal, reads out the superconducting quantum bit simply, and represents a reading result by using RSFQ, thereby well adapting to a trend of expansion of the number of superconducting quantum bits, that is, the superconducting quantum bit reader can adapt to the trend of expansion of the number of superconducting quantum bits when being used in combination with RSFQ digital circuits.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of quantum computing, and in particular to a superconducting quantum bit reader with a Josephson transmission line. BACKGROUND

[0002] Transmon is a superconducting quantum bit commonly used in the design of superconducting quantum processors, which is usually read out by a dispersive readout scheme. The dispersive readout scheme requires coupling the superconducting quantum bit and a resonator, and the frequency detuning of the two is much larger than the coupling strength. Since the change of the resonator scattering parameter depends on the state of the superconducting quantum bit, the superconducting quantum bit can be read out by measuring the change of the scattering parameter. At present, this method of measuring the superconducting quantum bit is realized by a room temperature measurement and control device equipped with microwave circuits and analog-to-digital converters. However, with the expansion of the number of superconducting quantum bits, it is difficult to continue using the method of measuring superconducting quantum bits by microwave circuits due to the difficulties of synchronous multi-device, reducing the power consumption of amplifiers, breaking through the interconnection bottleneck, and eliminating delay. At the same time, more and more readout lines will inevitably occupy a large amount of internal space and refrigeration capacity of the dilution refrigerator, thereby hindering the expansion of the number of superconducting quantum bits in the future. SUMMARY

[0003] The present application provides a superconducting quantum bit reader with a Josephson transmission line, which can read out superconducting quantum bits simply and well adapt to the trend of expansion of the number of superconducting quantum bits.

[0004] The present application provides a superconducting quantum bit reader with a Josephson transmission line, which can read out superconducting quantum bits simply and well adapt to the trend of expansion of the number of superconducting quantum bits.

[0005] One end of the resonator is provided with a first port and a second port as ports of the superconducting quantum bit reader, and the other end of the resonator is coupled with the inductor; the resonator is used to receive an excitation signal through the first port and form a capacitive coupling with a superconducting quantum bit to be read out through the second port, so as to realize the dispersive readout of the superconducting quantum bit;

[0006] The inductor is coupled with the resonator and is used to reflect the size of the oscillation current of the resonator when reading out the superconducting quantum bit;

[0007] The Josephson transmission line is connected in series with the inductor and is used to convert the current signal of the inductor into a readout result of a digital signal in the form of a fast single flux quantum (RSFQ) and output the readout result from the third port.

[0008] In an exemplary example, a capacitor is further included.

[0009] The capacitor is connected in series with the inductor and grounded, which is used to isolate the connection between the inductor and the ground plane and eliminate the DC signal of the inductor.

[0010] In an exemplary embodiment, the Josephson transmission line comprises one or more Josephson transmission line modules.

[0011] When the Josephson transmission line comprises two or more Josephson transmission line modules, each Josephson transmission line module is connected in series.

[0012] In an exemplary embodiment, the Josephson transmission line module comprises a current source, a first overdamped Josephson junction circuit module, a second overdamped Josephson junction circuit module, a first inductor, a second inductor, a third inductor, a fourth inductor and a fifth inductor.

[0013] The first inductor, the second inductor, the third inductor and the fourth inductor are connected in series.

[0014] One end of the first overdamped Josephson junction circuit module is connected to the connection point of the first inductor and the second inductor, and the other end of the first overdamped Josephson junction circuit module is grounded.

[0015] One end of the second overdamped Josephson junction circuit module is connected to the connection point of the third inductor and the fourth inductor, and the other end of the second overdamped Josephson junction circuit module is grounded.

[0016] One end of the fifth inductor is connected to the connection point of the second inductor and the third inductor, and the other end of the fifth inductor is connected to the current source, and the other end of the current source is grounded.

[0017] In an exemplary embodiment, the first overdamped Josephson junction circuit module and the second overdamped Josephson junction circuit module are the same or different in structure.

[0018] In an exemplary embodiment, the first overdamped Josephson junction circuit module comprises a first intrinsic Josephson junction, a first resistor, a sixth inductor and a seventh inductor.

[0019] One end of the first intrinsic Josephson junction is connected to the connection point of the first inductor and the second inductor, and the other end of the first intrinsic Josephson junction is connected to the sixth inductor, and the other end of the sixth inductor is grounded.

[0020] One end of the first resistor is connected to the connection point of the first inductor and the second inductor, and the other end of the first resistor is connected to the seventh inductor, and the other end of the seventh inductor is grounded.

[0021] In an example, the second overdamped Josephson junction circuit module comprises: a second intrinsic Josephson junction, a second resistor, an eighth inductor and a ninth inductor.

[0022] One end of the second intrinsic Josephson junction is connected to the connection point of the third inductor and the fourth inductor, and the other end of the second intrinsic Josephson junction is connected to the eighth inductor, and the other end of the eighth inductor is grounded.

[0023] One end of the second resistor is connected to the connection point of the third inductor and the fourth inductor, and the other end of the second resistor is connected to the ninth inductor, and the other end of the ninth inductor is grounded.

[0024] In an example, the resonator is a quarter wavelength transmission line resonator.

[0025] In an example, the resonator is a coplanar waveguide transmission line, or a microstrip transmission line, or a stripline transmission line.

[0026] In an example, the Josephson transmission line is specifically used for:

[0027] When the resonator resonates at the frequency of the excitation signal input to the first port, the oscillation current induced by the inductor through coupling with the tenth inductor of the resonator causes the current of the first intrinsic Josephson junction in the Josephson transmission line to exceed the critical current thereof, and the Josephson transmission line outputs a plurality of RSFQ voltage pulses from the third port as a readout result, and the readout result is a state |1>.

[0028] When the resonator cannot resonate at the frequency of the excitation signal, the oscillation current induced by the inductor is not large enough to cause the current of the first intrinsic Josephson junction in the Josephson transmission line to exceed the critical current thereof, and the third port does not output RSFQ voltage pulses, and the readout result is a state |0>.

[0029] In an example, the superconducting quantum bit to be read out comprises a Transmon.

[0030] The superconducting quantum bit readout device with a Josephson transmission line provided by the embodiments of the present application reads out a superconducting quantum bit after receiving an excitation signal, simply and conveniently reads out the superconducting quantum bit, and expresses the readout result in RSFQ, which is well adapted to the trend of expansion of the number of superconducting quantum bits, that is, can adapt to the trend of expansion of the number of superconducting quantum bits when combined with RSFQ digital circuits.

[0031] Other features and advantages of the present application will be set forth in the description that follows, and in part will be apparent from the description, or can be learned by practice of the application. The purposes and other advantages of the present application will be realized and attained by the structure particularly pointed out in the description and claims hereof as well as the appended drawings. BRIEF DESCRIPTION OF DRAWINGS

[0032] The accompanying drawings are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and are used to explain the technical solutions of the application, and do not constitute a limitation on the technical solutions of the application.

[0033] Figure 1 A schematic structural diagram of a superconducting quantum bit reader with a Josephson transmission line in an embodiment of the present application;

[0034] Figure 2 A schematic structural diagram of an embodiment of a superconducting quantum bit reader with a Josephson transmission line in an embodiment of the present application. DETAILED DESCRIPTION

[0035] In order to make the purposes, technical solutions and advantages of the present application more clear, the embodiments of the present application will be described in detail below with reference to the drawings. It should be noted that, in the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other at will.

[0036] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the related drawings. The embodiments of the present application are shown in the drawings. However, the present application can be realized in many different forms, and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the description of the present application herein is only for the purpose of describing the specific embodiments of the present application, and is not intended to limit the present application.

[0038] It can be understood that the terms "first", "second" used in the present application are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0039] It can be understood that the "connection" in the following embodiments should be understood as "electrical connection", "communication connection" and the like if the circuits, modules, units and the like connected with each other have the transmission of electrical signals or data.

[0040] As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. It will be further understood that the terms "comprises", "comprising", "includes" and / or "including", or "has" and / or "having", as used herein, specify the presence of stated features, integers, steps, operations, components, parts, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, components, parts, or combinations thereof.

[0041] Figure 1 A schematic diagram of a superconducting quantum bit reader with a Josephson transmission line in an embodiment of the present application is shown in FIG. 1. The superconducting quantum bit reader is a three-port device, which includes a resonator 10, an inductor 20, and a Josephson transmission line 40. The resonator 10 has a first port 50 and a second port 60 as ports of the superconducting quantum bit reader. The resonator 10 is configured to receive an excitation signal through the first port 50 and form a capacitive coupling with a superconducting quantum bit to be read out through the second port 60, so as to realize a dispersive readout of the superconducting quantum bit. The resonator 10 is coupled to the inductor 20. Figure 1

[0042] The resonator 10 has a first port 50 and a second port 60 as ports of the superconducting quantum bit reader. The resonator 10 is configured to receive an excitation signal through the first port 50 and form a capacitive coupling with a superconducting quantum bit to be read out through the second port 60, so as to realize a dispersive readout of the superconducting quantum bit. The resonator 10 is coupled to the inductor 20.

[0043] The inductor 20 is coupled to the resonator 10 and is configured to reflect a magnitude of an oscillation current of the resonator 10 when the superconducting quantum bit is read out.

[0044] The Josephson transmission line 40 is connected in series with the inductor 20 and is configured to convert a current signal of the inductor 20 into a readout result of a digital signal in a Rapid Single Flux Quantum (RSFQ) representation and output the readout result from a third port 70.

[0045] In an exemplary example, the superconducting quantum bit reader provided by the embodiment of the present application can further include a capacitor 30 connected in series with the inductor 20 and grounded, which is configured to isolate the inductor 20 from a ground plane and eliminate a direct current signal of the inductor 20.

[0046] In an exemplary example, the Josephson transmission line 40 includes at least one Josephson transmission line module 41. When the Josephson transmission line 40 includes a plurality of Josephson transmission line modules 41, the Josephson transmission line modules 41 are connected in series. In an embodiment, as shown in FIG. 2, the Josephson transmission line 40 includes two Josephson transmission line modules 41 connected in series. Figure 1 ​As shown, the Josephson transmission line 40 can include a first Josephson transmission line module 41, a second Josephson transmission line module 41, …, and an Nth Josephson transmission line module 41, and the first Josephson transmission line module 41, the second Josephson transmission line module 41, …, and the Nth Josephson transmission line module 41 are connected in series to constitute the Josephson transmission line 40.

[0047] The superconducting quantum bit reader with the Josephson transmission line provided in the embodiments of the present application reads out the superconducting quantum bit after receiving the excitation signal, simply reads out the superconducting quantum bit, and represents the read-out result by RSFQ, which well adapts to the trend of expansion of the number of superconducting quantum bits, that is, can adapt to the trend of expansion of the number of superconducting quantum bits when combined with the RSFQ digital circuit.

[0048] In an exemplary instance, as shown in Figure 2 One end of the Josephson transmission line 40 is connected with the inductor 20, and the other end of the Josephson transmission line 40 is the third port 70 of the superconducting quantum bit reader.

[0049] In an exemplary instance, Figure 2 In the Josephson transmission line 40, only one Josephson transmission line module 41 is taken as an example, as shown in Figure 2 The Josephson transmission line module 41 can include a current source 407, two overdamped Josephson junction circuit modules, as shown in Figure 2 a first overdamped Josephson junction circuit module 401 and a second overdamped Josephson junction circuit module 402 in the Josephson transmission line 40, and five inductors: a first inductor 403, a second inductor 404, a third inductor 405, a fourth inductor 406, and a fifth inductor 408. The first inductor 403, the second inductor 404, the third inductor 405, and the fourth inductor 406 are connected in series, one end of the first overdamped Josephson junction circuit module 401 is connected with the connection point of the first inductor 403 and the second inductor 404, the other end of the first overdamped Josephson junction circuit module 401 is grounded, one end of the second overdamped Josephson junction circuit module 402 is connected with the connection point of the third inductor 405 and the fourth inductor 406, and the other end of the second overdamped Josephson junction circuit module 402 is grounded. The fifth inductor 408 is connected with the current source 407, one end of the fifth inductor 408 is connected with the connection point of the second inductor 404 and the third inductor 405, the other end of the fifth inductor 408 is connected with the current source 407, and the other end of the current source 407 is grounded.

[0050] In one embodiment, the first overdamped Josephson junction circuit module 401 includes: a first intrinsic Josephson junction 4011, a first resistor 4012, a sixth inductor 4013, and a seventh inductor 4014. One end of the first intrinsic Josephson junction 4011 is connected to the connection point of the first inductor 403 and the second inductor 404, and the other end of the first intrinsic Josephson junction 4011 is connected to the sixth inductor 4013. The other end of the sixth inductor 4013 is grounded. In other words, the first intrinsic Josephson junction 4011 and the sixth inductor 4013 are connected in series to form a first branch circuit. One end of the first resistor 4012 is connected to the connection point of the first inductor 403 and the second inductor 404, and the other end of the first resistor 4012 is connected to the seventh inductor 4014. The other end of the seventh inductor 4014 is grounded. In other words, the first resistor 4012 and the seventh inductor 4014 are connected in series to form a second branch circuit.

[0051] The circuit structure of the second overdamped Josephson junction circuit module 402 may be the same as or different from that of the first overdamped Josephson junction circuit module 401. In one embodiment, the second overdamped Josephson junction circuit module 402 includes: a second intrinsic Josephson junction 4021, a second resistor 4022, an eighth inductor 4023, and a ninth inductor 4024. One end of the second intrinsic Josephson junction 4021 is connected to the connection point of the third inductor 405 and the fourth inductor 406, and the other end of the second intrinsic Josephson junction 4021... One end of the second resistor 4021 is connected to the eighth inductor 4023, and the other end of the eighth inductor 4023 is grounded. In other words, the second intrinsic Josephson junction 4021 and the eighth inductor 4023 are connected in series to form the first branch circuit. One end of the second resistor 4022 is connected to the connection point of the third inductor 405 and the fourth inductor 406, and the other end of the second resistor 4022 is connected to the ninth inductor 4024. The other end of the ninth inductor 4024 is grounded. In other words, the second resistor 4022 and the ninth inductor 4024 are connected in series to form the second branch circuit.

[0052] In one exemplary instance, such as Figure 2 As shown, resonator 10 can be a quarter-wavelength transmission line resonator, which can be, but is not limited to, transmission lines of types such as coplanar waveguides, microstrip lines, and striplines. Figure 2 As shown, in this embodiment, one end of the resonator 10 is grounded, and the other end receives the excitation signal from the first port 50. Simultaneously, it forms a capacitive coupling with the superconducting quantum bit 80 to be read out through the second port 60, thereby achieving dispersive readout of the superconducting quantum bit 80. In one embodiment, the resonator 10 includes two parts; the first part of the resonator 10... Figure 2 In the illustrated embodiment, transmission line 101 is used, such as... Figure 2As shown, the first end of the transmission line 101 is connected to the first port 50 and the second port 60, and the second end of the transmission line 101 is connected to one end of the second part of the resonator 10; the second part of the resonator 10 includes a first capacitor 102 and a tenth inductor 103 in parallel, one end of the first capacitor 102 and the tenth inductor 103 is grounded, and the other end is connected to the second end of the transmission line 101, and the resonator 10 is coupled to the inductor 20 through the tenth inductor 103.

[0053] As Figure 2 shown in the embodiment, the superconducting quantum bit 80 to be read out is a transmon, and forms a mutual capacitance 90 with the second port 60 of the superconducting quantum bit reader.

[0054] In an exemplary example, as Figure 2 shown, one end of the inductor 20 is connected to one end of the Josephson transmission line 40, the other end of the inductor 20 is connected to one end of the capacitor 30, and the other end of the capacitor 30 is grounded. In an embodiment, the inductor 20 forms mutual inductance by coupling with the inductor 103 in the resonator 10, which is used to reflect the oscillation current of the resonator 10 when reading out the quantum bit. The capacitor 30 is used to isolate the connection between the inductor 20 and the ground plane, and to eliminate the direct current signal of the inductor 20.

[0055] In Figure 2In an embodiment, when the resonator 10 can resonate at the frequency of the excitation signal input to the first port 40, the oscillating current induced by the inductor 20 coupling with the inductor 103 of the resonator 10 makes the current of the first intrinsic Josephson junction 4011 in the Josephson transmission line 40 exceed its critical current, eventually leading to the Josephson transmission line 40 outputting several RSFQ voltage pulses from the third port 70. These RSFQ voltage pulses can be directly input to the RSFQ superconducting digital circuit and stored in the RSFQ superconducting digital circuit as the readout result. At this time, the readout result of the superconducting quantum bit 80 is the state |1>, recorded as "1". When the resonator 10 cannot resonate at the original excitation signal frequency due to the a.c. Stark effect, the oscillating current induced by the inductor 20 is not large enough to make the current of the first intrinsic Josephson junction 4011 exceed its critical current, so the Josephson transmission line 40 (the third port 70) will not output RSFQ voltage pulses. At this time, the readout result of the superconducting quantum bit 80 is the state |0>, recorded as "0". According to the embodiment, it can be seen that the superconducting quantum bit readout device provided in the embodiment can distinguish whether the readout result of the superconducting quantum bit 80 is the state |0> or the state |1>. The a.c. Stark effect is a phenomenon of atomic energy level shift caused by the interaction between alternating current field and atomic electric dipole moment, which was first discovered experimentally by Cohen-Tannoudji in the 1960s.

[0056] In an exemplary embodiment, the RSFQ superconducting digital circuit has the advantages of high speed, low power consumption, compatibility with traditional integrated circuit processes, etc., and can be integrated in the same processor as the superconducting quantum bit (such as the superconducting quantum bit 80 in the processor 1000). Figure 2 In an exemplary embodiment, the RSFQ superconducting digital circuit has the advantages of high speed, low power consumption, compatibility with traditional integrated circuit processes, etc., and can be integrated in the same processor as the superconducting quantum bit (such as the superconducting quantum bit 80 in the processor 1000).

[0057] Although the embodiments disclosed in the present application are as described above, the content described is only the embodiments adopted for the purpose of facilitating the understanding of the present application, and is not intended to limit the present application. Any person skilled in the art of the present application can make any modification and change in the form and details without departing from the spirit and scope of the present application disclosed, but the patent protection scope of the present application shall be subject to the scope defined in the appended claims.

Claims

1. A superconducting quantum bit readout with a Josephson transmission line, comprising: Resonators, inductors, Josephson transmission lines; One end of the resonator is provided with a first port and a second port, which serve as ports for the superconducting quantum bit readout, and the other end of the resonator is coupled to the inductor. The resonator is used to receive an excitation signal through the first port and to form a capacitive coupling with the superconducting quantum bit to be read out through the second port, so as to realize the dispersion readout of the superconducting quantum bit; The inductor is coupled to the resonator and is used to reflect the magnitude of the oscillation current of the resonator when it reads out the superconducting quantum bit; The Josephson transmission line, connected in series with the inductor, is used to convert the current signal of the inductor into a digital signal represented by a fast single flux quantum (RSFQ) and output the readout result from the third port.

2. The superconducting quantum bit readout according to claim 1, wherein, Also includes: Capacitor; The capacitor is connected in series with the inductor and then grounded to isolate the inductor from the ground plane and eliminate the DC signal of the inductor.

3. The superconducting quantum bit readout according to claim 1 or 2, wherein, The Josephson transmission line includes one or more Josephson transmission line modules; When the Josephson transmission line includes two or more Josephson transmission line modules, the Josephson transmission line modules are connected in series.

4. The superconducting quantum bit readout according to claim 3, wherein, The Josephson transmission line module includes: a current source, a first overdamped Josephson junction circuit module, a second overdamped Josephson junction circuit module, a first inductor, a second inductor, a third inductor, a fourth inductor, and a fifth inductor. The first inductor, the second inductor, the third inductor, and the fourth inductor are connected in series. One end of the first overdamped Josephson junction circuit module is connected to the connection point of the first inductor and the second inductor, and the other end of the first overdamped Josephson junction circuit module is grounded. One end of the second overdamped Josephson junction circuit module is connected to the connection point of the third inductor and the fourth inductor, and the other end of the second overdamped Josephson junction circuit module is grounded. One end of the fifth inductor is connected to the connection point of the second inductor and the third inductor, and the other end of the fifth inductor is connected to the current source, the other end of the current source being grounded.

5. The superconducting quantum bit readout according to claim 4, wherein, The first overdamped Josephson junction circuit module may have the same or different structure as the second overdamped Josephson junction circuit module.

6. The superconducting quantum bit readout according to claim 4, wherein, The first overdamped Josephson junction circuit module includes: a first intrinsic Josephson junction, a first resistor, a sixth inductor, and a seventh inductor; One end of the first intrinsic Josephson junction is connected to the connection point of the first inductor and the second inductor, and the other end of the first intrinsic Josephson junction is connected to the sixth inductor, and the other end of the sixth inductor is grounded. One end of the first resistor is connected to the connection point of the first inductor and the second inductor, and the other end of the first resistor is connected to the seventh inductor, and the other end of the seventh inductor is grounded.

7. The superconducting quantum bit readout according to claim 4, wherein, The second overdamped Josephson junction circuit module includes: a second intrinsic Josephson junction, a second resistor, an eighth inductor, and a ninth inductor; One end of the second intrinsic Josephson junction is connected to the connection point of the third inductor and the fourth inductor, and the other end of the second intrinsic Josephson junction is connected to the eighth inductor, and the other end of the eighth inductor is grounded. One end of the second resistor is connected to the connection point of the third inductor and the fourth inductor, and the other end of the second resistor is connected to the ninth inductor, the other end of the ninth inductor being grounded.

8. The superconducting quantum bit readout according to claim 1, wherein, The resonator is a quarter-wavelength transmission line resonator.

9. The superconducting quantum bit readout according to claim 8, wherein, The resonator is a transmission line of a coplanar waveguide, a transmission line of a microstrip line, or a transmission line of a stripline.

10. The superconducting quantum bit readout according to claim 6, wherein, The Josephson transmission line is specifically used for: When the resonator resonates at the frequency of the excitation signal input to the first port, the oscillating current induced by the inductor through coupling with the tenth inductor of the resonator causes the current in the first intrinsic Josephson junction in the Josephson transmission line to exceed its critical current. The Josephson transmission line outputs several RSFQ voltage pulses from the third port as a readout result, which is the state. ; When the resonator fails to resonate at the excitation signal frequency, the oscillating current induced by the inductor is insufficient to cause the current in the first intrinsic Josephson junction in the Josephson transmission line to exceed its critical current. Consequently, the third port does not output an RSFQ voltage pulse, and the readout result is a status. .

11. The superconducting quantum bit readout according to claim 1 or 10, wherein, The superconducting qubits to be read out include the transport qubit Transmon.

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