CN114118429B - Quantum circuit and control method thereof, superconducting quantum chip and superconducting quantum computer - Google Patents
Quantum circuit and control method thereof, superconducting quantum chip and superconducting quantum computer Download PDFInfo
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Abstract
本公开提供了一种量子电路，涉及量子计算技术领域。具体实现方案为：量子数据比特；控制子电路；以及可调量子耦合器，可调量子耦合器设置为与量子数据比特和控制子电路耦合，使得在量子数据比特的有效操作时段，开启控制子电路与量子数据比特之间的耦合；在量子数据比特的无效操作时段，关闭控制子电路与量子数据比特之间的耦合。本公开还提供了一种控制方法、超导量子芯片以及超导量子计算机。
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
The embodiment of the disclosure relates to the technical field of quantum computing, in particular to a quantum circuit, a control method of the quantum circuit, a superconducting quantum chip and a superconducting quantum computer.
Background
The quantum computation has natural parallelism, so that the data processing speed is obviously improved. Superconducting quantum circuits are considered as an excellent way to realize quantum computation, and superconducting quantum chips have high requirements on the coherence time and relaxation time of quantum bits.
Disclosure of Invention
The present disclosure provides a quantum circuit, a control method of the quantum circuit, a superconducting quantum chip, and a superconducting quantum computer.
According to a first aspect there is provided a quantum circuit comprising a quantum data bit, a control sub-circuit, and an adjustable quantum coupler arranged to be coupled to the quantum data bit and the control sub-circuit such that coupling between the control sub-circuit and the quantum data bit is turned on during an active operation period of the quantum data bit, and coupling between the control sub-circuit and the quantum data bit is turned off during an inactive operation period of the quantum data bit.
According to a second aspect there is provided a control method applied to a quantum circuit provided by the present disclosure, the method comprising applying an on signal to the superconducting quantum interference device during an active operation period of the quantum data bit such that the adjustable quantum coupler operates at an on frequency, and applying an off signal to the superconducting quantum interference device during an inactive operation period of the quantum data bit such that the adjustable quantum coupler operates at an off frequency.
According to a third aspect, there is provided a superconducting quantum chip comprising the quantum circuit provided by the present disclosure.
According to a fourth aspect, there is provided a superconducting quantum computer comprising a superconducting quantum chip provided by the present disclosure.
It should be understood that the description in this section is not intended to identify key or critical features of the embodiments of the disclosure, nor is it intended to be used to limit the scope of the disclosure. Other features of the present disclosure will become apparent from the following specification.
Drawings
The drawings are for a better understanding of the present solution and are not to be construed as limiting the present disclosure. Wherein:
FIG. 1 is a block diagram of a quantum circuit according to one embodiment of the present disclosure;
fig. 2 is a circuit diagram of a quantum circuit according to one embodiment of the present disclosure;
fig. 3 is a circuit diagram of a quantum circuit according to another embodiment of the present disclosure;
FIG. 4 is a schematic diagram of a superconducting quantum interference device according to one embodiment of the present disclosure;
FIG. 5 is a schematic diagram of a quantum circuit according to one embodiment of the present disclosure;
FIG. 6 is a circuit diagram of a direct control circuit according to the present disclosure;
FIG. 7 is a flow chart of a control method according to one embodiment of the present disclosure;
FIG. 8 is a flow chart of a control method according to another embodiment of the present disclosure;
FIG. 9 is a block diagram of a quantum chip according to one embodiment of the present disclosure, and
Fig. 10 is a block diagram of a quantum computer according to another embodiment of the present disclosure.
Detailed Description
Exemplary embodiments of the present disclosure are described below in conjunction with the accompanying drawings, which include various details of the embodiments of the present disclosure to facilitate understanding, and should be considered as merely exemplary. Accordingly, one of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the present disclosure. Also, descriptions of well-known functions and constructions are omitted in the following description for clarity and conciseness.
The quantum circuit may include at least one quantum data bit coupled together in a particular manner. Microwave pulse signals can be applied to vector sub-data bits to realize single-bit quantum gates or two-bit quantum gates, thereby realizing complex logic operation.
For quantum computation, the quantum data bits may be controlled, such as by setting control circuitry for the quantum data bits. The control circuitry also causes coupling of the qudata bits to the environment. Taking superconducting quantum data bits (Transmon) as an example, microwave control lines can be introduced to perform quantum logic gate control on the superconducting quantum data bits. The introduction of microwave control lines also results in coupling of the quantum data bits to the environment. Thus, the quantum data bits are inevitably affected by ambient noise, resulting in a reduction of their energy relaxation time (coherence time) and, ultimately, in computational fidelity.
Fig. 1 is a block diagram of a quantum circuit according to one embodiment of the present disclosure.
As shown in fig. 1, the quantum circuit 100 may include a quantum data bit 110, a control sub-circuit 120, and an adjustable quantum coupler 130.
Tunable quantum coupler 130 is configured to couple to quantum data bit 110 and control sub-circuit 120.
For example, tunable quantum coupler 130 is configured to couple with quantum data bit 110 and control sub-circuit 120 such that the coupling between control sub-circuit 120 and quantum data bit 110 is turned on during an active period of operation of quantum data bit 110.
For another example, tunable quantum coupler 130 is configured to couple with quantum data bit 110 and control sub-circuit 120 such that during periods of non-operation of quantum data bit 110, the coupling between control sub-circuit 120 and quantum data bit 110 is turned off.
For example, the effective operational period may be a period during which the quantum data bits 110 need to be manipulated. The quantum data bit 110 may be manipulated by applying control signals via the control sub-circuit 120.
For example, the period of invalid operation may be a period in which the quantum data bit 110 does not need to be manipulated.
In one example, the control subcircuit 120 includes a control line. For example, in the control sub-circuit 120, the environment introduced by the control line may be equivalent to a resistor R (hereinafter referred to as equivalent resistance). For example, the equivalent resistance is about 50 ohms for impedance matching. However, the equivalent resistance is a dissipative element such that superconducting qubit 110, when coupled to control sub-circuit 120, produces a fixed dissipation factor, resulting in energy dissipation of qubit 110 and, in turn, a reduction in energy relaxation time and coherence time of qubit 110. In one example, in large-scale quantum computing, the coherence time of the quantum data bits is unnecessarily reduced, resulting in an unnecessary reduction in quantum computing fidelity.
By way of an embodiment of the present disclosure, an adjustable quantum coupler 130 is inserted as a "switch" in the direct control circuit. When the switch is turned on, the control sub-circuit 120 can effectively control the quantum data bit 110, and when the switch is turned off, the coupling between the quantum data bit 110 and the control sub-circuit 120 is turned off, so that the energy dissipation of the quantum data bit is reduced, the coherence time of the quantum data bit is increased, and the fidelity of quantum computing is further improved.
The adjustable quantum coupler can be widely applied to the design and experiment of superconducting quantum chips. However, in the related art, an adjustable quantum coupler is disposed between the quantum data bits to control the coupling between the quantum data bits. The adjustable quantum coupling is inserted into the control sub-circuit, so that the basic structure of the existing quantum data bit is not required to be changed, and the scalability is extremely strong.
Some examples of quantum circuits of embodiments of the present disclosure will be described below with reference to fig. 2-5.
Fig. 2 is a circuit diagram of a quantum circuit according to one embodiment of the present disclosure.
As shown in fig. 2, quantum circuit 200 includes quantum data bits 210, control sub-circuit 220, and tunable quantum coupler 230. The above description of the quantum data bits 110, the control sub-circuit 120 and the tunable quantum coupler 130 applies equally to this embodiment.
For example, the quantum circuit 200 may further include a first capacitance C qc. A first end of the first capacitor C qc is connected to the quantum data bit 210 and a second end of the first capacitor C qc is connected to the tunable quantum coupler 230.
For example, the quantum circuit 200 may further include a second capacitance C cR. A first terminal of the second capacitor C cR is connected to the tunable quantum coupler 230 and a second terminal of the second capacitor C cR is connected to the control sub-circuit 220.
For example, tunable quantum coupler 230 may include a third capacitance C c. The first end of the third capacitor C c is connected to the second end of the first capacitor C qc and the first end of the second capacitor C cR.
For example, tunable quantum coupler 230 may include a superconducting quantum interference device (Superconducting Quantum INTERFERENCE DEVICE, SQUID), such as superconducting quantum interference device J c in fig. 2. The superconducting quantum interference device J c may be connected in parallel with the third capacitor C c.
In one example, superconducting quantum interference device J c may include at least two josephson junctions in parallel.
For example, the capacitance value of the first capacitance C qc, the capacitance value of the second capacitance C cR, the capacitance value of the third capacitance C c, and the equivalent inductance value of the superconducting quantum interference device J c are set such that the coupling strength value between the quantum data bit 210 and the control sub-circuit 220 is equal to the coupling strength value when the quantum data bit 210 is directly connected to the control sub-circuit 220 during the active operation period of the quantum data bit 210.
Unlike the direct connection of the quantum data bits and the control sub-circuit, after insertion of the adjustable quantum coupler, an indirect coupling is formed between the quantum data bits and the control sub-circuit, which is adjusted by the adjustable quantum coupler. The coupling strength of this indirect coupling is lower than the coupling strength of the original direct coupling, which results in longer pulse control times being required to implement the same quantum logic gates, resulting in a reduced number of quantum logic gate manipulations that can be made within the quantum data bit coherence time. Therefore, it is necessary to ensure that the coupling strength of the indirect coupling when the coupling "switch" is turned on is close to the original coupling strength of the direct coupling after the tunable quantum coupler is added, so as to ensure that the time length of the pulse control of the quantum logic gate is basically unchanged. According to the embodiment of the disclosure, by setting the capacitance value of the first capacitor C qc, the capacitance value of the second capacitor C cR, the capacitance value of the third capacitor C c and the equivalent inductance value of the superconducting quantum interference device J c, it is ensured that the original direct coupling strength between the quantum data bit and the control sub-circuit is maintained after the adjustable quantum coupler is inserted, and the quantum data bit is controlled conveniently.
For example, the quantum data bit 210 may include a fourth capacitance C q. The first end of the fourth capacitor C q is connected to the first end of the first capacitor C qc. For another example, the qudata bits 210 may also include a josephson junction J q. The josephson junction J q may be connected in parallel with the fourth capacitance C q. In one example, the frequency of the quantum data bits 210 is not tunable.
Fig. 3 is a circuit diagram of a quantum circuit according to another embodiment of the present disclosure.
As shown in fig. 3, the quantum circuit 300 may include a quantum data bit 310, a control sub-circuit 320, and an adjustable quantum coupler 330. The above description of the quantum data bits 110, the control sub-circuit 120 and the tunable quantum coupler 130 applies equally to this embodiment.
As shown in fig. 3, the difference from quantum circuit 200 is that the frequency of the quantum data bits 310 of quantum circuit 300 is tunable. The difference from the quantum data bit 210 in fig. 2 is that the quantum data bit 310 comprises at least two josephson junctions in parallel. In one example, the quantum data bits 310 include two josephson junctions in parallel, josephson junction J' q and josephson junction j″ q, respectively. The josephson junctions J' q and j″ q are connected in parallel with a fourth capacitance C q, respectively.
By embodiments of the present disclosure, quantum circuit 300 may enable control of a coupled tunable quantum data bit. And the frequency of the quantum data bit is adjustable, so that the parameter of the adjustable quantum coupler can be selected more freely, and the physical realization in experiments is facilitated. In the invalid operation period of the quantum data bit, the adjustable quantum coupler closes the coupling between the control sub-circuit and the quantum data bit, so that the dissipation of the quantum data bit can be better shielded through the control sub-circuit, and the dissipation of the quantum data bit is lower.
Fig. 4 is a schematic diagram of a superconducting quantum interference device according to one embodiment of the present disclosure.
As shown in fig. 4, for example, tunable quantum coupler 230 of fig. 2 may include a superconducting quantum interference device as shown in fig. 4. The superconducting quantum interference device can be equivalently an adjustable nonlinear inductor.
The superconducting quantum interference device may include josephson junctions J c1 and josephson junctions J c2. Wherein the nonlinear current response I of each josephson junction can be calculated by the following formula:
i=i c sin (phi) (equation one)
Where phi is the magnetic flux through the Josephson junction and I c is the critical current. The corresponding josephson energy is E J. For example, as shown in fig. 3, the magnetic flux through josephson junction J c1 is Φ 1 and the magnetic flux through josephson junction J c2 is Φ 2.
According to the superconducting flux quantization requirement, for a loop formed by two josephson junctions, the sum of all the fluxes passing through the loop must be an integer multiple of the superconductor unit flux Φ 0. Thus, the relationship between the magnetic flux Φ 1 through the josephson junction J c1, the magnetic flux Φ 2 through the josephson junction J c2, and the applied magnetic flux Φ ext can be determined by the following equation:
according to formulas one and two, the overall current I' through the superconducting quantum interference device can be obtained by the following formulas:
next, the equivalent Josephson capability E' J(Φext of the superconducting quantum interference device can be calculated by the following formula
Therefore, the equivalent Josephson energy of the superconducting quantum interference device can be adjusted by adjusting the externally-applied magnetic flux phi ext, so that the frequency of the superconducting quantum interference device can be adjusted. Furthermore, the frequency of the superconducting quantum interference device in the adjustable quantum coupler can be adjusted, so that the adjustable quantum coupler becomes a switch for controlling the coupling between the quantum data bit and the control sub-line.
Fig. 5 is a schematic diagram of a quantum circuit according to one embodiment of the present disclosure.
As shown in fig. 5, for example, for the quantum circuit 200 of fig. 2, the nonlinear josephson junction can be approximately equivalent to a linear inductance. Thus, the quantum circuit may contain only linear resistances, inductances and capacitances. Further, the quantum circuit 200 may be approximated as a combination of a series of RLC linear resonators. For example, the quantum data bit may be equivalently an RLC linear resonator comprising resistor R 1, inductor L 1, and capacitor C 1, and the tunable quantum coupler may be equivalently an RLC linear resonator comprising resistor R 2, inductor L 2, and capacitor C 2.
For the combination of two RLC linear resonators in fig. 5, the quantized hamiltonian form is:
Where ω m is the resonant frequency each RLC linear resonator has. For the harmonic oscillator corresponding to the quantum data bit, the conductance Y is determined by the equivalent resistance R 1, inductance L 1 and capacitance C 1:
R 1 is the resistance value of the resistor R 1, L 1 is the inductance value of the inductor L 1, and C 1 is the capacitance value of the capacitor C 1.
In the resonant mode, the RLC linear resonator is open. At this time, 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, i.e.:
Y (ω+iκ/2) =0 (equation seven)
According to formulas five to seven, the frequency ω of the quantum data bits and the dissipation ratio κ can be determined:
kappa=1/r 1c1 (formula nine)
Fig. 6 is a circuit diagram of a direct control circuit.
As shown in fig. 6, the direct control circuit 600 includes a quantum data bit 610 and a control sub-circuit 620. The above description of the quantum data bits 110 and the control sub-circuit 120 applies equally to this embodiment.
For example, the direct control circuit 600 may also include a direct coupling capacitance C qR. A first end of the direct coupling capacitor C qR is connected to the quantum data bit 610 and a second end of the direct coupling capacitor C qR is connected to the control sub-circuit 620.
For example, the quantum data bit 610 may include a fourth capacitance C q. The first terminal of the fourth capacitor C q is connected to the first terminal of the direct-coupling capacitor C qR. For another example, the qudata bit 610 may also include a josephson junction J q. The josephson junction J q may be connected in parallel with the fourth capacitance C q. In one example, the frequency of the quantum data bits 610 is not tunable.
In some embodiments, a numerical simulation is performed on a quantum circuit 200, such as shown in fig. 2, and a quantum circuit 300, such as shown in fig. 3, respectively.
For example, as a comparison, the direct control circuit 600 shown in fig. 6 is taken as example 1 of the direct control circuit.
In the present embodiment, for the direct control circuit 600, the capacitance value of the direct coupling capacitor C qR is 0.5fF, so that the frequency ω 1 of the quantum data bit is 5.93GHz.
In example 2 of the quantum circuit 200, for example, according to an embodiment of the present disclosure, the capacitance value of the first capacitance C qc1 is 0.5fF, the capacitance value of the second capacitance C cR1 is 100fF, and the frequency ω 2 of the quantum data bit after coupling with the tunable quantum coupler is 5.93GHz. In example 2, since the capacitance value of the first capacitor C qc1 is 0.5fF and the capacitance value of the second capacitor C cR1 is 100fF, in the case where the magnetic flux applied to the quantum data bit is the same as or similar to example 1, the frequency ω 2 of the quantum data bit can be kept to be 5.93GHz, which is the same as the frequency ω 1 of the quantum data bit in example 1. The dissipation ratio is significantly reduced compared to example 1.
In example 3, for example, quantum circuit 300 according to an embodiment of the present disclosure, unlike example 2, the frequency of quantum data bits 310 is tunable. The capacitance value of the first capacitor C qcl is 9.8fF, and the capacitance value of the second capacitor C cR2 is 0.5fF. In this case, in the case where the magnetic flux applied to the quantum data bit is the same as or similar to example 1, the frequency ω 3 of the quantum data bit cannot be kept at 5.93GHz. Thus, the frequency ω 3 of the quantum data bits in example 3 can be adjusted so that the frequency ω 3 remains the same as the frequency ω 1, while the capacitance value of the second capacitance C cR2 is 0.5fF, since this capacitance value is smaller, the dissipation ratio is further significantly reduced compared to example 2.
The numerical simulation results are shown in table 1:
TABLE 1
In some embodiments, a numerical simulation is performed on a quantum circuit 200, such as shown in fig. 2, and a quantum circuit 300, such as shown in fig. 3, respectively.
For example, as a comparison, the direct control circuit 600 shown in fig. 6 is taken as example 4 of the direct control circuit.
In the present embodiment, the difference from the embodiment corresponding to table 1 is that the capacity of the direct coupling capacitance C qR2 is 0.4fF and the frequency ω 4 of the quantum data bit is 5.58GHz for the direct control circuit 600.
In example 5 of the quantum circuit 200 according to an embodiment of the present disclosure, for example, the capacitance value of the first capacitance C qc3 is 0.4fF, and the capacitance value of the second capacitance C cR3 is 100fF. In this case, in the case where the magnetic flux applied to the quantum data bit is the same as or similar to example 4, the frequency ω 5 of the quantum data bit may be kept to be 5.58GHz, which is the same as the frequency ω 4 of the quantum data bit in example 4. The dissipation ratio is significantly reduced compared to example 4.
In example 6, for example, quantum circuit 300 according to an embodiment of the present disclosure, unlike example 5, the frequency of quantum data bits 310 is tunable. The first capacitor C qc4 has a capacitance of 6.8fF and the second capacitor C cR4 has a capacitance of 0.4fF. In this case, the frequency ω 6 of the quantum data bit cannot be kept at 5.58GHz. Thus, the frequency ω 6 of the quantum data bits in example 3 can be adjusted so that the frequency ω 6 remains the same as the frequency ω 4, while the capacitance value of the second capacitance C cR4 is 0.4fF, since this capacitance value is smaller, the dissipation ratio is further significantly reduced compared to example 5.
The numerical simulation results are shown in table 2:
TABLE 2
It should be noted that, as shown in tables 1 and 2, the dissipation rate κ of the quantum data bits in the direct control circuit 600 is maintained at a higher level than that of the quantum circuit 200 or the quantum circuit 300 during the inactive operation period.
It should be noted that, in the direct control circuit 600, the dissipation ratio κ of the quantum data bit is always maintained at a higher level (whether in the active operation period or the inactive operation period).
It should be noted that, in the quantum circuit 200 or the quantum circuit 300, after the tunable quantum coupler is added, the coupling between the control sub-circuit and the quantum data bit is turned on for an effective operation period, so as to keep the coupling strength between the two equal to or similar to the coupling strength of the direct control circuit 600. Also, during the active operation period, the dissipation ratio of the quantum data bits in quantum circuit 200 or quantum circuit 300 is similar to the dissipation ratio of the quantum data bits in direct control circuit 600.
Those skilled in the art will appreciate that a quantum circuit (also referred to as a quantum computing circuit) may include circuitry for performing quantum processing operations. That is, quantum circuits are configured to perform operations on data in a non-deterministic manner using quantum mechanical phenomena, such as superposition and entanglement. Some quantum circuit elements, such as quantum data bits, may be configured to represent and operate on information for multiple states simultaneously. 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), among others.
Some examples of the control method of the quantum circuit of the embodiment of the present disclosure will be described below with reference to fig. 7 to 8.
Fig. 7 is a flowchart of a control method according to one embodiment of the present disclosure.
As shown in fig. 7, the method 700 may be applied to the quantum circuits described above. The detailed description will be made with reference to operations S710 to S720.
In operation S710, an on signal is applied to the superconducting quantum interference device during an active operation period of the quantum data bit such that the tunable quantum coupler operates at an on frequency.
For example, an applied magnetic flux signal may be applied as the on signal.
For example, an on signal is applied to the superconducting quantum interference device such that the tunable quantum coupler operates at an on frequency to turn on the coupling between the control sub-circuit and the quantum data bits.
In one example, when quantum logic gate control is desired, an active period of operation may be entered by applying an applied magnetic flux signal to adjust the frequency of the tunable quantum coupler to an on frequency, thereby turning on the coupling between the control subcircuit and the quantum data bit, at which time the quantum data bit may be controlled.
In operation S720, a turn-off signal is applied to the superconducting quantum interference device during an inactive period of the quantum data bit such that the tunable quantum coupler operates at a turn-off frequency.
For example, the applied magnetic flux may no longer be applied to apply the off signal.
For example, a turn-off signal is applied to the superconducting quantum interference device such that the tunable quantum coupler operates at a turn-off frequency to turn off the coupling between the control sub-circuit and the quantum data bits.
In one example, when quantum logic gate control is not required, an inactive period of operation may be entered by applying an applied magnetic flux signal to adjust the frequency of the tunable quantum coupler to a turn-off frequency, thereby turning off the coupling between the control subcircuit and the quantum data bits, at which time the quantum data bits may not be controlled.
It should be noted that the frequency of the quantum data bits in the method 700 may or may not be adjustable. For example, the quantum data bits in method 700 may be, for example, quantum data bits 210 in fig. 2. As another example, the quantum data bits in method 700 may also be, for example, quantum data bits 310 in fig. 3.
Through the embodiment of the disclosure, in the invalid operation period, indirect coupling between the quantum data bit and the control sub-circuit is closed, so that the dissipation rate of the quantum data bit can be greatly reduced, and the coherence time of the quantum data bit is improved.
Fig. 8 is a flowchart of a control method according to another embodiment of the present disclosure.
As shown in fig. 8, the method 800 may be applied to a quantum circuit such as that shown in fig. 3, and will be described in detail with reference to operations S810 to S830.
In operation S810, an on signal is applied to the superconducting quantum interference device during an active operation period of the quantum data bit such that the tunable quantum coupler operates at an on frequency.
In operation S820, a turn-off signal is applied to the superconducting quantum interference device during an inactive period of the quantum data bit such that the tunable quantum coupler operates at a turn-off frequency.
Those skilled in the art will appreciate that operations S810 and S820 in method 800 are the same as or similar to operations S710 and S720 in method 700, and the disclosure is not repeated here.
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.
For example, taking the quantum data bit 310 shown in fig. 3 as an example, the frequency of the quantum data bit 310 is tunable. During the active operation period, the intensity of the magnetic flux signal applied to the quantum data bit 310 is adjusted such that the operating frequency of the quantum data bit 310 is within a predetermined range, thereby making the indirect coupling strength between the quantum data bit 310 and the control sub-circuit 320 approach the direct coupling strength in order to control the quantum data bit 310.
Through the embodiment of the disclosure, the conventional capacitor can be selected as the first capacitor or the second capacitor, so that the application scene of the quantum circuit provided by the disclosure is expanded.
In some embodiments, embodiments of the present disclosure may significantly improve the coherence time of the quantum data bits in a superconducting quantum chip. The coherence of the quantum data bits is critical to ensure the fidelity of the quantum computation results. In a direct control circuit (as shown in fig. 6), the coupling between the quantum data bits and the control sub-circuit during periods of non-operation can cause unnecessary dissipation, exacerbating decoherence of the quantum data bits. The present disclosure implements coupled tunable quantum control of a quantum data bit by inserting a tunable quantum coupler into a superconducting quantum circuit and using the tunable chain coupler as a coupling "switch" between the quantum data bit and a control sub-circuit. During the active operation period, the coupling "switch" is turned on, so that the quantum data bit is easy to handle. During periods of non-operation, the above-described coupling "switch" is turned off, such that dissipation of the quantum data bits is significantly reduced, thereby increasing the coherence time of the quantum data bits.
Fig. 9 is a block diagram of a quantum chip according to one embodiment of the present disclosure.
As shown in fig. 9, the quantum chip 900 may include a quantum circuit 910.
For example, the quantum circuit 910 may be the same as or similar to the quantum circuit in any of the embodiments of, for example, fig. 1, 2, or3, and is not described in detail herein.
Fig. 10 is a block diagram of a quantum computer according to one embodiment of the present disclosure.
As shown in fig. 10, the quantum computer 1000 may include a quantum chip 1010.
For example, quantum chip 1010 may be the same as or similar to quantum chip 900 shown in, for example, fig. 9, and this disclosure is not repeated here.
In some embodiments, during operation of a quantum computer using superconducting quantum circuits and/or superconducting classical circuits (such as the quantum circuits described herein), the superconducting circuit elements are cooled in a cryostat (Cryostat) to a temperature that allows the superconductor material to exhibit superconducting properties. A superconductor (alternatively, superconducting) material is understood to be a material that exhibits superconducting properties at or below the critical temperature of superconductivity. Examples of the superconducting material include aluminum (superconducting critical temperature of 1.2 kelvin) and niobium (superconducting critical temperature of 9.3 kelvin). Thus, the superconducting structure (such as the superconducting trace and the superconducting ground plane) is formed of a material exhibiting superconducting properties at or below the superconducting critical temperature.
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.
Similarly, although operations are depicted in the drawings in a particular order, this should not be understood as requiring that the various forms of flow shown above be used, reordered, added, or deleted steps. For example, the steps recited in the present disclosure may be performed in parallel, sequentially, or in a different order, provided that the desired results of the disclosed aspects are achieved, and are not limited herein.
The above detailed description should not be taken as limiting the scope of the present disclosure. It will be apparent to those skilled in the art that various modifications, combinations, sub-combinations and alternatives are possible, depending on design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present disclosure are intended to be included within the scope of the present disclosure.
Claims (6)
1. A quantum circuit, comprising:
A quantum data bit;
Control sub-circuit, and
An adjustable quantum coupler configured to couple with the quantum data bit and the control sub-circuit such that coupling between the control sub-circuit and the quantum data bit is turned on during an active operation period of the quantum data bit;
A first capacitor having a first end connected to the quantum data bit and a second end connected to the tunable quantum coupler, and
The first end of the second capacitor is connected with the adjustable quantum coupler, and the second end of the second capacitor is connected with the control sub-circuit;
wherein the tunable quantum coupler comprises:
A third capacitor having a first end connected to the second end of the first capacitor and the first end of the second capacitor, and
The superconducting quantum interference device is connected with the third capacitor in parallel;
Wherein the capacitance value of the first capacitance, the capacitance value of the second capacitance, the capacitance value of the third capacitance, and the equivalent inductance value of the superconducting quantum interference device are set such that the coupling strength value between the quantum data bit and the control sub-circuit is maintained as the coupling strength value when the quantum data bit is directly connected to the control sub-circuit during the effective operation period of the quantum data bit.
2. The circuit of claim 1, wherein the superconducting quantum interference device comprises at least two josephson junctions in parallel.
3. A control method applied to the quantum circuit of any one of claims 1 to 2, the method comprising:
applying an on signal to the superconducting quantum interference device during an active operation period of the quantum data bit such that the tunable quantum coupler operates at an on frequency, and
During periods of inactive operation of the quantum data bit, a turn-off signal is applied to the superconducting quantum interference device such that the tunable quantum coupler operates at a turn-off frequency.
4. A method according to claim 3, further comprising:
The intensity of the magnetic flux signal applied to the quantum data bits is adjusted so that the operating frequency of the quantum data bits is within a predetermined range.
5. A superconducting quantum chip comprising the quantum circuit of any one of claims 1 to 2.
6. A superconducting quantum computer comprising the superconducting quantum chip of claim 5.
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