Quantum circuit and control method thereof, superconducting quantum chip and superconducting quantum computer

Abstract

The present disclosure provides a quantum circuit, which relates to the field of quantum computing technology. The specific implementation scheme is: quantum data bit; control subcircuit; and adjustable quantum coupler, the adjustable quantum coupler is configured to couple with the quantum data bit and the control subcircuit, so that during the effective operation period of the quantum data bit, the coupling between the control subcircuit and the quantum data bit is turned on; during the invalid operation period of the quantum data bit, the coupling between the control subcircuit and the quantum data bit is turned off. The present disclosure also provides a control method, a superconducting quantum chip, and a superconducting quantum computer.

Description

Technical Field

[0001] The embodiments of the present disclosure relate to the field of quantum computing technology, and in particular to a quantum circuit, a control method for the quantum circuit, a superconducting quantum chip, and a superconducting quantum computer. Background Art

[0002] Quantum computing has a natural parallelism, which significantly improves the data processing speed. Superconducting quantum circuits are considered to be an excellent way to achieve quantum computing. Superconducting quantum chips have high requirements for the coherence time and relaxation time of quantum bits. Summary of the invention

[0003] The present disclosure provides a quantum circuit, a control method of the quantum circuit, a superconducting quantum chip, and a superconducting quantum computer.

[0004] According to a first aspect, a quantum circuit is provided, comprising: a quantum data bit; a control subcircuit; and an adjustable quantum coupler, wherein the adjustable quantum coupler is configured to couple with the quantum data bit and the control subcircuit, so that during a valid operation period of the quantum data bit, the coupling between the control subcircuit and the quantum data bit is turned on; and during an invalid operation period of the quantum data bit, the coupling between the control subcircuit and the quantum data bit is turned off.

[0005] According to a second aspect, a control method is provided, which is applied to the quantum circuit provided by the present disclosure, and the method comprises: during an effective operation period of the above-mentioned quantum data bit, applying an on signal to the above-mentioned superconducting quantum interference device, so that the above-mentioned adjustable quantum coupler operates at an on frequency; and during an invalid operation period of the above-mentioned quantum data bit, applying an off signal to the above-mentioned superconducting quantum interference device, so that the above-mentioned adjustable quantum coupler operates at a off frequency.

[0006] According to a third aspect, a superconducting quantum chip is provided, comprising the quantum circuit provided by the present disclosure.

[0007] According to a fourth aspect, a superconducting quantum computer is provided, comprising the superconducting quantum chip provided by the present disclosure.

[0008] It should be understood that the content described in this section is not intended to identify the key or important features of the embodiments of the present disclosure, nor is it intended to limit the scope of the present disclosure. Other features of the present disclosure will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The accompanying drawings are used to better understand the present solution and do not constitute a limitation of the present disclosure.

[0010] Figure 1 is a block diagram of a quantum circuit according to one embodiment of the present disclosure;

[0011] Figure 2 is a circuit diagram of a quantum circuit according to an embodiment of the present disclosure;

[0012] Figure 3 is a circuit diagram of a quantum circuit according to another embodiment of the present disclosure;

[0013] Figure 4 is a schematic diagram of a superconducting quantum interference device according to an embodiment of the present disclosure;

[0014] Figure 5 is a schematic diagram of a quantum circuit according to an embodiment of the present disclosure;

[0015] Figure 6 is a circuit diagram of a direct control circuit according to the present disclosure;

[0016] Figure 7 is a flow chart of a control method according to an embodiment of the present disclosure;

[0017] Figure 8 is a flow chart of a control method according to another embodiment of the present disclosure;

[0018] Fig. 9 is a block diagram of a quantum chip according to one embodiment of the present disclosure; and

[0019] Fig.10 is a block diagram of a quantum computer according to another embodiment of the present disclosure. DETAILED DESCRIPTION

[0020] The following is a description of exemplary embodiments of the present disclosure in conjunction with the accompanying drawings, including various details of the embodiments of the present disclosure to facilitate understanding, which should be considered as merely exemplary. Therefore, it should be recognized by those of ordinary skill in the art that various changes and modifications may be made to the embodiments described herein without departing from the scope and spirit of the present disclosure. Similarly, for the sake of clarity and conciseness, descriptions of well-known functions and structures are omitted in the following description.

[0021] A quantum circuit may include at least one quantum data bit coupled together in a specific manner. A microwave pulse signal may be applied to the quantum data bit to implement a single-bit quantum gate or a two-bit quantum gate, thereby implementing complex logic operations.

[0022] In order to perform quantum computing, quantum data bits can be controlled, such as by setting up control circuits for quantum data bits. The control circuit will also cause the coupling of quantum data bits with the environment. Taking superconducting quantum data bits (Transmon) as an example, microwave control lines can be introduced to manipulate quantum logic gates. The introduction of microwave control lines also leads to the coupling of quantum data bits with the environment. Therefore, quantum data bits will inevitably be affected by environmental noise, resulting in a decrease in their energy relaxation time (relaxation time) and coherence time, which ultimately leads to a decrease in computational fidelity.

[0023] Figure 1 is a block diagram of a quantum circuit according to one embodiment of the present disclosure.

[0024] like Figure 1 As shown, the quantum circuit 100 may include a quantum data bit 110 , a control subcircuit 120 , and an adjustable quantum coupler 130 .

[0025] The tunable quantum coupler 130 is configured to couple with the quantum data bit 110 and the control subcircuit 120 .

[0026] For example, the adjustable quantum coupler 130 is configured to be coupled to the quantum data bit 110 and the control subcircuit 120 , so that during an effective operation period of the quantum data bit 110 , the coupling between the control subcircuit 120 and the quantum data bit 110 is turned on.

[0027] For another example, the adjustable quantum coupler 130 is configured to couple with the quantum data bit 110 and the control subcircuit 120 , so that during an invalid operation period of the quantum data bit 110 , the coupling between the control subcircuit 120 and the quantum data bit 110 is turned off.

[0028] For example, the effective operation period may be a period during which the quantum data bit 110 needs to be manipulated. The quantum data bit 110 may be manipulated by applying a control signal via the control subcircuit 120.

[0029] For example, the invalid operation period may be a period during which the quantum data bit 110 does not need to be manipulated.

[0030] In one example, the control subcircuit 120 includes a control line. For example, in the control subcircuit 120, the environment introduced by the control line can be equivalent to a resistor R (hereinafter referred to as an equivalent resistor). For example, in order to match the impedance, the equivalent resistor is about 50 ohms. However, the equivalent resistor is a dissipative element, so that the superconducting quantum data bit 110 will produce a fixed dissipation coefficient after coupling with the control subcircuit 120, resulting in energy dissipation of the quantum data bit 110, which in turn leads to a decrease in the energy relaxation time and coherence time of the quantum data bit 110. In one example, in large-scale quantum computing, the unnecessary reduction of the coherence time of the quantum data bit will lead to an unnecessary reduction in the fidelity of quantum computing.

[0031] Through the disclosed embodiment, an adjustable quantum coupler 130 is inserted into the direct control circuit as a "switch". When the "switch" is turned on, the control subcircuit 120 can effectively control the quantum data bit 110; when the "switch" is turned off, the coupling between the quantum data bit 110 and the control subcircuit 120 is turned off, thereby reducing the energy dissipation of the quantum data bit, increasing the coherence time of the quantum data bit, and thus improving the fidelity of quantum computing.

[0032] Adjustable quantum couplers can be widely used in the design and experiment of superconducting quantum chips. However, in related technologies, adjustable quantum couplers are placed between quantum data bits to control the coupling between quantum data bits. Inserting adjustable quantum coupling into the control subcircuit does not require changing the basic structure of the existing quantum data bits, so it is highly scalable.

[0033] The following will refer to Figures 2 to 5 Some examples of quantum circuits according to the embodiments of the present disclosure are described below.

[0034] Figure 2 is a circuit diagram of a quantum circuit according to an embodiment of the present disclosure.

[0035] like Figure 2 As shown, quantum circuit 200 includes quantum data bit 210, control subcircuit 220 and adjustable quantum coupler 230. The above description about quantum data bit 110, control subcircuit 120 and adjustable quantum coupler 130 is also applicable to this embodiment.

[0036] For example, the quantum circuit 200 may further include a first capacitor C qc The first capacitor C qc The first end of the first capacitor C is connected to the quantum data bit 210. qc The second end of is connected to the adjustable quantum coupler 230.

[0037] For example, the quantum circuit 200 may further include a second capacitor C cRThe second capacitor C cR The first end of the capacitor C is connected to the adjustable quantum coupler 230, and the second capacitor C cR The second end of is connected to the control sub-circuit 220.

[0038] For example, the tunable quantum coupler 230 may include a third capacitor C c The third capacitor C c The first end of the first capacitor C qc The second terminal and the second capacitor C cR connected to the first end of .

[0039] For example, the tunable quantum coupler 230 may include a superconducting quantum interference device (SQUID), such as Figure 2 Superconducting quantum interference device in J c . Superconducting quantum interference device J c The third capacitor C c in parallel.

[0040] In one example, a superconducting quantum interference device J c It may include at least two Josephson junctions connected in parallel.

[0041] For example, the first capacitor C qc The capacitance value of the second capacitor C cR The capacitance value of the third capacitor C c Capacitance value and superconducting quantum interference device J c The equivalent inductance value of is set to: make the coupling strength value between the quantum data bit 210 and the control subcircuit 220 equal to the coupling strength value when the quantum data bit 210 and the control subcircuit 220 are directly connected during the effective operation period of the quantum data bit 210.

[0042] Unlike the direct connection between the quantum data bit and the control subcircuit, after inserting the adjustable quantum coupler, an indirect coupling is formed between the quantum data bit and the control subcircuit, which is adjusted by the adjustable quantum coupler. The coupling strength of this indirect coupling will be lower than the coupling strength of the original direct coupling, which results in a longer pulse control time to achieve the same quantum logic gate, reducing the number of quantum logic gate operations that can be performed within the coherence time of the quantum data bit. Therefore, it is necessary to ensure that after adding the adjustable quantum coupler, the coupling strength of the indirect coupling when the coupling "switch" is turned on is close to the coupling strength of the original direct coupling, so as to ensure that the time length of the quantum logic gate pulse control remains basically unchanged. According to the embodiment of the present disclosure, by setting the first capacitor C qc The capacitance value of the second capacitor C cR The capacitance value of the third capacitor C cCapacitance and superconducting quantum interference device J c The equivalent inductance value can ensure that the original direct coupling strength between the quantum data bit and the control subcircuit is maintained after the adjustable quantum coupler is inserted, which facilitates the control of the quantum data bit.

[0043] For example, the quantum data bit 210 may include a fourth capacitor C q The fourth capacitor C q The first end of the first capacitor C qc For another example, the quantum data bit 210 may also include a Josephson junction J q . Josephson knot q Can be connected with the fourth capacitor C q In one example, the frequency of the quantum data bit 210 is not adjustable.

[0044] Figure 3 is a circuit diagram of a quantum circuit according to another embodiment of the present disclosure.

[0045] like Figure 3 As shown, the quantum circuit 300 may include a quantum data bit 310, a control subcircuit 320, and an adjustable quantum coupler 330. The above description of the quantum data bit 110, the control subcircuit 120, and the adjustable quantum coupler 130 is also applicable to this embodiment.

[0046] like Figure 3 As shown, the difference from quantum circuit 200 is that the frequency of quantum data bit 310 of quantum circuit 300 is adjustable. Figure 2 The difference between the quantum data bit 210 in FIG. 3 is that the quantum data bit 310 includes at least two Josephson junctions connected in parallel. In one example, the quantum data bit 310 includes two Josephson junctions connected in parallel, namely, Josephson junctions J′ and J′. q and Josephson q . Josephson junction J′ q and Josephson q and the fourth capacitor C q in parallel.

[0047] Through the disclosed embodiment, the quantum circuit 300 can realize the control of quantum data bits with adjustable coupling. Moreover, since the frequency of the quantum data bit is adjustable, the selection of the adjustable quantum coupler parameters can be more free, which is more conducive to the physical realization in the experiment. During the invalid operation period of the quantum data bit, the adjustable quantum coupler turns off the coupling between the control subcircuit and the quantum data bit, which can better shield the dissipation of the quantum data bit through the control subcircuit, so that the dissipation of the quantum data bit is lower.

[0048] Figure 4 is a schematic diagram of a superconducting quantum interference device according to an embodiment of the present disclosure.

[0049] like Figure 4 As shown, for example Figure 2 The adjustable quantum coupler 230 may include Figure 4 The superconducting quantum interference device shown. The superconducting quantum interference device can be equivalent to an adjustable nonlinear inductor.

[0050] Superconducting quantum interference devices can include Josephson junctions. c1 Josephson c2 Among them, the nonlinear current response I of each Josephson junction can be calculated by the following formula:

[0051] I=I c *sin(φ) (Formula 1)

[0052] Where φ is the magnetic flux through the Josephson junction, I c is the critical current. The corresponding Josephson energy is E J For example, Figure 3 As shown, through the Josephson junction J c1 The magnetic flux is φ1, passing through the Josephson junction J c2 The magnetic flux is φ2.

[0053] According to the requirements of superconducting magnetic flux quantization, for a loop formed by two Josephson junctions, the sum of all magnetic fluxes passing through the loop must be an integer multiple of the superconductor unit magnetic flux Φ0. Therefore, the flux through the Josephson junction J can be determined by the following formula c1 The magnetic flux φ1 passes through the Josephson junction J c2 The magnetic flux φ2 and the external magnetic flux Φ ext The relationship between:

[0054]

[0055] According to Formula 1 and Formula 2, the overall current I′ passing through the superconducting quantum interference device can be obtained by the following formula:

[0056]

[0057] Next, the equivalent Josephson energy E′ of the superconducting quantum interference device can be calculated by the following formula J (Φ ext )

[0058]

[0059] Therefore, the external magnetic flux Φ extTo adjust the equivalent Josephson energy of the superconducting quantum interference device, and then adjust the frequency of the superconducting quantum interference device. Furthermore, by adjusting the frequency of the superconducting quantum interference device in the adjustable quantum coupler, the adjustable quantum coupler can become a "switch" that controls the coupling between the quantum data bit and the control sub-circuit.

[0060] Figure 5 is a schematic diagram of a quantum circuit according to an embodiment of the present disclosure.

[0061] like Figure 5 As shown, for example Figure 2 The quantum circuit 200 can be similar to a nonlinear Josephson junction as a linear inductor. Therefore, the quantum circuit can only contain linear resistance, inductance and capacitance. Further, the quantum circuit 200 can be similarly simplified as a combination of a series of RLC linear resonators. For example, a quantum data bit can be equivalent to an RLC linear resonator including a resistor R1, an inductor L1 and a capacitor C1, and an adjustable quantum coupler can be equivalent to an RLC linear resonator including a resistor R2, an inductor L2 and a capacitor C2.

[0062] against Figure 5 The combination of two RLC linear resonators in the quantized Hamiltonian is:

[0063]

[0064] where ω m is the resonant frequency of each RLC linear resonator. For the resonator corresponding to the quantum data bit, its conductance Y is determined by its equivalent resistance R1, inductance L1 and capacitance C1:

[0065]

[0066] r1 is the resistance value of the resistor R1, l1 is the inductance value of the inductor L1, and c1 is the capacitance value of the capacitor C1.

[0067] In the resonant mode, the RLC linear resonator is open. At this time, the energy is stored in the RLC linear resonator and oscillates back and forth in the RLC linear resonator. In the resonant mode, the conductance of the RLC linear resonator is 0, that is:

[0068] Y(ω+iκ / 2)=0 (Formula 7) According to Formula 5 to Formula 7, the frequency ω and dissipation rate κ of the quantum data bit can be determined:

[0069]

[0070] κ=1 / r1c1 (Formula 9)

[0071] Figure 6 It is a circuit diagram of a direct control circuit.

[0072] like Figure 6 As shown, the direct control circuit 600 includes a quantum data bit 610 and a control subcircuit 620. The above description about the quantum data bit 110 and the control subcircuit 120 is also applicable to this embodiment.

[0073] For example, the direct control circuit 600 may further include a direct coupling capacitor C qR . Direct coupling capacitor C qR The first end of is connected to the quantum data bit 610, directly coupling the capacitor C qR The second end of is connected to the control sub-circuit 620.

[0074] For example, the quantum data bit 610 may include a fourth capacitor C q The fourth capacitor C q The first end of the direct coupling capacitor C qR For another example, the quantum data bit 610 may also include a Josephson junction J q . Josephson knot q Can be connected with the fourth capacitor C q In one example, the frequency of quantum data bit 610 is not tunable.

[0075] In some embodiments, for example, Figure 2 The quantum circuit 200 shown and for example Figure 3 The quantum circuit 300 shown is subjected to numerical simulation.

[0076] For example, as a comparison, Figure 6 The direct control circuit 600 is shown as Example 1 of the direct control circuit.

[0077] In this embodiment, for the direct control circuit 600, the direct coupling capacitor C qR The capacitance value is 0.5fF, so that the frequency ω1 of the quantum data bit is 5.93GHz.

[0078] In Example 2 of the quantum circuit 200 according to an embodiment of the present disclosure, the first capacitor C qc1 The capacitance value of the second capacitor C is 0.5fF. cR1 The capacitance value of is 100fF, and the frequency ω2 of the quantum data bit after coupling with the adjustable quantum coupler is 5.93GHz. In Example 2, since the first capacitor C qc1 The capacitance value of the second capacitor C is 0.5fF. cR1The capacitance value is 100fF, and when the magnetic flux applied to the quantum data bit is the same or similar to that in Example 1, the frequency ω2 of the quantum data bit can be maintained at 5.93GHz, which is the same as the frequency ω1 of the quantum data bit in Example 1. Compared with Example 1, the dissipation rate is significantly reduced.

[0079] In Example 3 of the quantum circuit 300 according to an embodiment of the present disclosure, unlike Example 2, the frequency of the quantum data bit 310 is adjustable. qcl The capacitance value of the second capacitor C is 9.8fF. cR2 The capacitance value is 0.5fF. In this case, when the magnetic flux applied to the quantum data bit is the same or similar to that in Example 1, the frequency ω3 of the quantum data bit cannot be maintained at 5.93GHz. Therefore, the frequency ω3 of the quantum data bit in Example 3 can be adjusted so that the frequency ω3 remains the same as the frequency ω1, and at the same time, the second capacitor C cR2 The capacitance value of is 0.5fF. Due to the small capacitance value, the dissipation rate is further significantly reduced compared with Example 2.

[0080] The numerical simulation results are shown in Table 1:

[0081] Table 1

[0082]

[0083] In some embodiments, for example, Figure 2 The quantum circuit 200 shown and for example Figure 3 The quantum circuit 300 shown was numerically simulated.

[0084] For example, as a comparison, Figure 6 The direct control circuit 600 is shown as Example 4 of the direct control circuit.

[0085] In this embodiment, the difference from the embodiment corresponding to Table 1 is that, for the direct control circuit 600, the direct coupling capacitor C qR2 The capacity is 0.4fF and the frequency ω4 of the quantum data bit is 5.58GHz.

[0086] In Example 5 of the quantum circuit 200 according to an embodiment of the present disclosure, the first capacitor C qc3 The capacitance value of the second capacitor C is 0.4fF. cR3 The capacitance value is 100fF. In this case, when the magnetic flux applied to the quantum data bit is the same or similar to that in Example 4, the frequency ω5 of the quantum data bit can be maintained at 5.58GHz, which is the same as the frequency ω4 of the quantum data bit in Example 4. Compared with Example 4, the dissipation rate is significantly reduced.

[0087] In Example 6 of the quantum circuit 300 according to an embodiment of the present disclosure, unlike Example 5, the frequency of the quantum data bit 310 is adjustable. qc4 The capacitance value of the second capacitor C is 6.8fF. cR4 The capacitance value of is 0.4fF. In this case, the frequency ω6 of the quantum data bit cannot be maintained at 5.58GHz. Therefore, the frequency ω6 of the quantum data bit in Example 3 can be adjusted so that the frequency ω6 remains the same as the frequency ω4, and at the same time, the second capacitor C cR4 The capacitance value of is 0.4fF. Due to the small capacitance value, the dissipation rate is further significantly reduced compared with Example 5.

[0088] The numerical simulation results are shown in Table 2:

[0089] Table 2

[0090]

[0091] It should be noted that, as shown in Table 1 and Table 2, during the invalid operation period, compared with the quantum circuit 200 or the quantum circuit 300, the dissipation rate κ of the quantum data bit in the direct control circuit 600 is maintained at a higher level.

[0092] It should be noted that, in the direct control circuit 600 , the dissipation rate κ of the quantum data bit is always maintained at a high level (regardless of the effective operation period or the invalid operation period).

[0093] It should be noted that, in quantum circuit 200 or quantum circuit 300, after adding the adjustable quantum coupler, the coupling between the control subcircuit and the quantum data bit is turned on during the effective operation period to keep the coupling strength between the two the same or similar to the coupling strength of the direct control circuit 600. Moreover, during the effective operation period, the dissipation rate of the quantum data bit in quantum circuit 200 or quantum circuit 300 is similar to the dissipation rate of the quantum data bit in the direct control circuit 600.

[0094] It will be appreciated by those skilled in the art that quantum circuits (also referred to as quantum computing circuits) may include circuits for performing quantum processing operations. That is, quantum circuits are configured to utilize quantum mechanical phenomena, such as superposition and entanglement, to perform operations on data in a non-deterministic manner. Certain quantum circuit elements (such as quantum data bits) may be configured to simultaneously represent and manipulate information in multiple states. Examples of superconducting quantum circuit elements include circuit elements such as quantum LC oscillators, quantum bits (e.g., flux qubits, phase qubits, or charge qubits), and superconducting quantum interference devices SQUIDs (e.g., RF-SQUIDs or DC-SQUIDs), etc.

[0095] The following will refer to Figures 7 and 8 Some examples of the control method of the quantum circuit according to the embodiment of the present disclosure are described below.

[0096] Figure 7 is a flow chart of a control method according to an embodiment of the present disclosure.

[0097] like Figure 7 As shown, the method 700 can be applied to the quantum circuit described above. Detailed description will be given below with reference to operations S710 to S720.

[0098] In operation S710, during an effective operation period of a quantum data bit, a turn-on signal is applied to a superconducting quantum interference device so that the tunable quantum coupler operates at a turn-on frequency.

[0099] For example, an external magnetic flux signal may be applied as a turn-on signal.

[0100] For example, applying a turn-on signal to the superconducting quantum interference device causes the tunable quantum coupler to operate at a turn-on frequency to turn on the coupling between the control subcircuit and the quantum data bit.

[0101] In one example, when quantum logic gate control is required, an effective operation period can be entered, and an external magnetic flux signal can be applied to adjust the frequency of the adjustable quantum coupler to the turn-on frequency, thereby turning on the coupling between the control subcircuit and the quantum data bit, at which time the quantum data bit can be controlled.

[0102] In operation S720, during an ineffective operation period of the quantum data bit, a shutdown signal is applied to the superconducting quantum interference device so that the adjustable quantum coupler operates at a shutdown frequency.

[0103] For example, the external magnetic flux may no longer be applied to apply the shutdown signal.

[0104] For example, a shutdown signal is applied to the superconducting quantum interference device so that the tunable quantum coupler operates at a shutdown frequency to shut down the coupling between the control subcircuit and the quantum data bit.

[0105] In one example, when quantum logic gate control is not needed, an invalid operation period can be entered, and an external magnetic flux signal can be applied to adjust the frequency of the adjustable quantum coupler to the closing frequency, thereby turning off the coupling between the control subcircuit and the quantum data bit. At this time, the quantum data bit can be uncontrolled.

[0106] It should be noted that the frequency of the quantum data bit in method 700 may be adjustable or non-adjustable. For example, the quantum data bit in method 700 may be, for example Figure 2The quantum data bit 210 in the method 700 may also be, for example, Figure 3 Quantum data bit 310 in.

[0107] Through the embodiments of the present disclosure, during the invalid operation period, the indirect coupling between the quantum data bit and the control subcircuit is turned off, thereby greatly reducing the dissipation rate of the quantum data bit, thereby improving the coherence time of the quantum data bit.

[0108] Figure 8 is a flowchart of a control method according to another embodiment of the present disclosure.

[0109] like Figure 8 As shown, the method 800 can be applied to, for example, Figure 3 The quantum circuit shown will be described in detail below with reference to operations S810 to S830.

[0110] In operation S810, during the effective operation period of the quantum data bit, an opening signal is applied to the superconducting quantum interference device so that the adjustable quantum coupler operates at the opening frequency.

[0111] In operation S820, during an ineffective operation period of the quantum data bit, a shutdown signal is applied to the superconducting quantum interference device so that the adjustable quantum coupler operates at a shutdown frequency.

[0112] Those skilled in the art may understand that operation S810 and operation S820 in method 800 are the same as or similar to operation S710 and operation S720 in method 700, and are not described in detail herein.

[0113] In operation S830, the intensity of the magnetic flux signal applied to the quantum data bit is adjusted so that the operating frequency of the quantum data bit is within a predetermined range.

[0114] For example, Figure 3 The quantum data bit 310 shown is an example, and the frequency of the quantum data bit 310 is adjustable. During the effective operation period, the intensity of the magnetic flux signal applied to the quantum data bit 310 is adjusted so that the operating frequency of the quantum data bit 310 is within a predetermined range, thereby making the indirect coupling intensity between the quantum data bit 310 and the control subcircuit 320 close to the direct coupling intensity, so as to control the quantum data bit 310.

[0115] Through the embodiments of the present disclosure, a conventional capacitor can be selected as the first capacitor or the second capacitor, which expands the application scenarios of the quantum circuit provided by the present disclosure.

[0116] In some embodiments, the embodiments of the present disclosure can significantly improve the coherence time of quantum data bits in superconducting quantum chips. The coherence of quantum data bits is crucial to ensure the fidelity of quantum computing results. Figure 6 In the embodiment shown in FIG. 1 , in the invalid operation period, the coupling between the quantum data bit and the control subcircuit will bring unnecessary dissipation, which aggravates the decoherence of the quantum data bit. The present invention inserts an adjustable quantum coupler in a superconducting quantum circuit, and uses the adjustable chain coupler as a coupling "switch" between the quantum data bit and the control subcircuit, thereby realizing quantum control of the quantum data bit with adjustable coupling. In the effective operation period, the above coupling "switch" is turned on, so that the quantum data bit is easy to manipulate. In the invalid operation period, the above coupling "switch" is turned off, so that the dissipation of the quantum data bit is significantly reduced, thereby increasing the coherence time of the quantum data bit.

[0117] Fig. 9 is a block diagram of a quantum chip according to an embodiment of the present disclosure.

[0118] like Fig. 9 As shown, the quantum chip 900 may include a quantum circuit 910 .

[0119] For example, quantum circuit 910 can be used with e.g. Figure 1 , Figure 2 or Figure 3 The quantum circuits in any embodiment are the same or similar, and will not be described in detail in this disclosure.

[0120] Fig.10 is a block diagram of a quantum computer according to one embodiment of the present disclosure.

[0121] like Fig.10 As shown, the quantum computer 1000 may include a quantum chip 1010 .

[0122] For example, quantum chip 1010 can be used with Fig. 9 The quantum chip 900 shown is the same or similar and will not be described in detail in this disclosure.

[0123] In some embodiments, during the operation of a quantum computer using superconducting quantum circuits and / or superconducting classical circuits (such as the quantum circuits described herein), superconducting circuit elements are cooled in a cryostat to a temperature that allows superconducting materials to exhibit superconducting properties. Superconductor (alternatively, superconducting) materials can be understood as materials that exhibit superconducting properties at or below the superconducting critical temperature. Examples of superconducting materials include aluminum (superconducting critical temperature of 1.2 Kelvin) and niobium (superconducting critical temperature of 9.3 Kelvin). Therefore, superconducting structures (such as superconducting traces and superconducting ground planes) are formed of materials that exhibit superconducting properties at or below the superconducting critical temperature.

[0124] In some embodiments, control signals for quantum circuit elements (e.g., quantum data bits and couplers between quantum data bits) may be provided using classical circuit elements electrically and / or electromagnetically coupled to the quantum circuit elements. The control signals may be provided in digital and / or analog form.

[0125] Similarly, although the operations are described in a specific order in the drawings, this should not be understood as requiring the operations to be performed in the order shown. It should be understood that the various forms of the processes shown above can be used to reorder, add or delete steps. For example, the steps described in this disclosure can be performed in parallel, sequentially or in a different order, as long as the desired results of the technical solutions disclosed in this disclosure can be achieved, and this document is not limited here.

[0126] The above specific implementations do not constitute a limitation on the protection scope of the present disclosure. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. A quantum circuit, comprising: quantum data bits; control sub-circuit; as well as an adjustable quantum coupler, the adjustable quantum coupler being configured to couple with the quantum data bit and the control subcircuit so that the coupling between the control subcircuit and the quantum data bit is turned on during an effective operation period of the quantum data bit; During an invalid operation period of the quantum data bit, turning off the coupling between the control subcircuit and the quantum data bit; A first capacitor, wherein a first end of the first capacitor is connected to the quantum data bit, and a second end of the first capacitor is connected to the adjustable quantum coupler; as well as A second capacitor, wherein a first end of the second capacitor is connected to the adjustable quantum coupler, and a second end of the second capacitor is connected to the control subcircuit; Wherein, the adjustable quantum coupler comprises: a third capacitor, a first end of the third capacitor being connected to the second end of the first capacitor and the first end of the second capacitor; and A superconducting quantum interference device, wherein the superconducting quantum interference device is connected in parallel with the third capacitor; Among them, the capacitance value of the first capacitor, the capacitance value of the second capacitor, the capacitance value of the third capacitor and the equivalent inductance value of the superconducting quantum interference device are set so that during the effective operation period of the quantum data bit, the coupling strength value between the quantum data bit and the control subcircuit is maintained at the coupling strength value when the quantum data bit is directly connected to the control subcircuit.

2. The circuit according to claim 1, wherein The superconducting quantum interference device includes at least two Josephson junctions connected in parallel.

3. A control method, applied to the quantum circuit according to any one of claims 1 to 2, the method comprising: During an effective operation period of the quantum data bit, applying an on signal to the superconducting quantum interference device so that the adjustable quantum coupler operates at an on frequency; as well as During an inactive operation period of the quantum data bit, a shutdown signal is applied to the superconducting quantum interference device, so that the adjustable quantum coupler operates at a shutdown frequency.

4. The method according to claim 3, further comprising: The intensity of the magnetic flux signal applied to the quantum data bit is adjusted so that the operating frequency of the quantum data bit is within a predetermined range.

5. A superconducting quantum chip, comprising the quantum circuit according to any one of claims 1 to 2.

6. A superconducting quantum computer, comprising the superconducting quantum chip according to claim 5.

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