Quantum computation system and quantum device manufacturing method

Abstract

A quantum computation system (1) has a quantum device (21), and a control unit (10) that controls the quantum device. The quantum device has a first qubit (100), a second qubit (200), a magnetic flux qubit (300) for coupling that can couple with the first qubit and the second qubit, and a first magnetic flux application unit (340) that applies a magnetic flux to the magnetic flux qubit for coupling. The control unit causes the first magnetic flux application unit to apply a first magnetic flux, which is provided with a first time modulation, during a first period, and apply a second magnetic flux, which is provided with a second time modulation differing from the first time modulation, during a second time period differing from the first time period. This quantum computation system can be used, for example, in quantum computing.

Description

Quantum computing system and quantum device control method

[0001] The present disclosure relates to a quantum computing system and a method for controlling a quantum device.

[0002] Conventionally, quantum computing systems have been proposed that use flux qubits to couple two flux qubits.

[0003] International Publication No. 2008 / 029815 Special Publication No. 2019-508876 Special Publication No. 2022-525910

[0004] In conventional quantum computing systems, it is not possible to break the coupling between quantum bits, and there is a risk that unwanted couplings will cause interactions.

[0005] An object of the present disclosure is to provide a quantum computing system and a method for controlling a quantum device that can turn off the coupling between two quantum bits.

[0006] According to one aspect of the present disclosure, there is provided a quantum computing system comprising: a quantum device; and a control unit that controls the quantum device, wherein the quantum device comprises a first quantum bit, a second quantum bit, a coupling flux qubit that can be coupled to the first quantum bit and the second quantum bit; and a first magnetic flux application unit that applies magnetic flux to the coupling flux qubit, wherein the control unit causes the first magnetic flux application unit to apply a first magnetic flux having a first time modulation in a first period, and to apply a second magnetic flux having a second time modulation that is different from the first time modulation in a second period that is different from the first period.

[0007] According to the present disclosure, the coupling of two qubits can be turned off.

[0008] FIG. 1 is a block diagram showing a quantum computing system according to a first embodiment. FIG. 2 is a circuit diagram showing a quantum device according to the first embodiment. FIG. 3 is a timing chart showing the time change of the magnetic flux applied to the SQUID during a first period. FIG. 4 is a timing chart showing the time change of the magnetic flux applied to the SQUID during a second period. FIG. 5 is a diagram (part 1) showing the energy state of a flux qubit. FIG. 6 is a diagram (part 2) showing the energy state of a flux qubit. FIG. 7 is a diagram (part 1) showing the results of a first simulation. FIG. 8 is a diagram (part 2) showing the results of the first simulation. FIG. 9 is a timing chart (part 1) showing the time change of the magnetic flux applied to the SQUID during a second period in a second simulation. FIG. 10 is a timing chart (part 2) showing the time change of the magnetic flux applied to the SQUID during a second period in a second simulation. FIG. 11 is a timing chart (part 3) showing the time change of the magnetic flux applied to the SQUID during a second period in a second simulation. FIG. 12 is a timing chart (part 4) showing the time change of the magnetic flux applied to the SQUID during the second period in the second simulation. FIG. 13 is a diagram (part 1) showing the results of the second simulation. FIG. 14 is a diagram (part 2) showing the results of the second simulation. FIG. 15 is a diagram (part 1) showing the results of the third simulation. FIG. 16 is a diagram (part 2) showing the results of the third simulation. FIG. 17 is a block diagram showing a quantum computing system according to the second embodiment. FIG. 18 is a circuit diagram showing a quantum device according to the second embodiment. FIG. 19 is a timing chart showing the time change of the current generated by the current source and the magnetic flux applied to the SQUID during the first period. FIG. 20 is a timing chart showing the time change of the current generated by the current source and the magnetic flux applied to the SQUID during the second period. FIG. 21 is a diagram showing the relationship between the magnetic flux of a coupling flux qubit and the internal current of a coupled charge qubit. FIG. 22 is a plan view showing a first example of the configuration of a quantum device according to the second embodiment. FIG. 23 is a cross-sectional view showing a first example of the configuration of a quantum device according to the second embodiment.Fig. 24 is a cross-sectional view showing a portion of a quantum bit substrate in the second embodiment. Fig. 25 is a cross-sectional view showing a portion of another quantum bit substrate in the second embodiment. Fig. 26 is a plan view showing a second example of the configuration of a quantum device in the second embodiment. Fig. 27 is a cross-sectional view showing a second example of the configuration of a quantum device in the second embodiment. Fig. 28 is a plan view showing a third example of the configuration of a quantum device in the second embodiment.

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description may be omitted.

[0010] First Embodiment First, the first embodiment will be described. The first embodiment relates to a quantum computing system. Fig. 1 is a block diagram showing a quantum computing system according to the first embodiment.

[0011] The quantum computing system 1 according to the first embodiment includes a control unit 10 and a quantum device 21. The control unit 10 controls the quantum device 21.

[0012] The control unit 10 is a computer and includes a bus 11, an input device 12, an output device 13, a storage device 14, a memory device 15, a processing unit 16, and an interface device 17. The input device 12, the output device 13, the storage device 14, the memory device 15, the processing unit 16, and the interface device 17 are connected to the bus 11. The input device 12, the output device 13, the storage device 14, the memory device 15, the processing unit 16, and the interface device 17 are connected to each other via the bus 11.

[0013] The input device 12 is a device for inputting various types of information and is realized by, for example, a keyboard, a pointing device, etc. The output device 13 is for outputting various types of information and is realized by, for example, a display, etc. The interface device 17 includes, for example, a LAN card, etc., and is used for connecting to a network.

[0014] A control program for controlling the quantum device 21 is stored in the storage device 14. The memory device 15 reads and stores the control program from the storage device 14 when the quantum computing system 1 is started. The computing device 16 then performs various processes, as will be described later, in accordance with the control program stored in the memory device 15.

[0015] 2 is a circuit diagram showing quantum device 21. Quantum device 21 has flux qubit 100, flux qubit 200, and coupling flux qubit 300. Coupling flux qubit 300 is capable of inductive coupling with flux qubits 100 and 200. While an example of inductive coupling between flux qubit 100 and flux qubit 200 is disclosed here, the coupling may also be capacitive coupling, or may include both inductive and capacitive coupling. Quantum device 21 further has flux application units 130, 140, 230, 240, 330, and 340.

[0016] Flux qubit 100 includes a main loop 110 and a superconducting quantum interference device (SQUID) 120. SQUID 120 includes a Josephson junction element 121, a Josephson junction element 122, an inductor 123, and an inductor 124 connected in a circular fashion in this order. Main loop 110 includes inductors 112 and 113 connected in series. The end of inductor 112 opposite to inductor 113 is connected between Josephson junction elements 121 and 122. The end of inductor 113 opposite to inductor 112 is connected between inductor 123 and inductor 124. For example, flux qubit 100 includes niobium as a superconducting material. Flux qubit 100 is an example of a first qubit and a first flux qubit.

[0017] Flux qubit 200 includes a main loop 210 and a SQUID 220. SQUID 220 includes a Josephson junction element 221, a Josephson junction element 222, an inductor 223, and an inductor 224, which are connected in a circular fashion and in series, in that order. Main loop 210 includes inductors 212 and 213 connected in series. The end of inductor 213 opposite to inductor 212 is connected between Josephson junction elements 221 and 222. The end of inductor 212 opposite to inductor 213 is connected between inductor 223 and inductor 224. For example, flux qubit 200 includes niobium as a superconducting material. Flux qubit 200 is an example of a second qubit and a second flux qubit.

[0018] The coupling flux qubit 300 has a main loop 310 and a SQUID 320. The SQUID 320 has a Josephson junction device 321, a Josephson junction device 322, an inductor 323, and an inductor 324 connected in a ring shape and in series in this order. The main loop 310 has inductors 311, 313, and 312 connected in series in this order. The end of the inductor 312 opposite to the inductor 313 is connected between the Josephson junction device 321 and the Josephson junction device 322. The end of the inductor 311 opposite to the inductor 313 is connected between the inductor 323 and the inductor 324. The inductor 311 and the inductor 112 are inductively coupled to each other, and the inductor 312 and the inductor 212 are inductively coupled to each other.

[0019] The magnetic flux application unit 130 has inductors 131 and 132 and a pulse signal generator 133. The inductors 131 and 132 are connected in series to each other. The end of the inductor 132 opposite to the inductor 131 is grounded. The pulse signal generator 133 is connected between the end of the inductor 131 opposite to the inductor 132 and the ground. The inductors 131 and 123 are inductively coupled to each other. The inductors 132 and 124 are inductively coupled to each other. The magnetic flux application unit 130 is an example of a second magnetic flux application unit.

[0020] The magnetic flux application unit 230 has inductors 231 and 232 and a pulse signal generator 233. The inductors 231 and 232 are connected in series to each other. The end of the inductor 231 opposite to the inductor 232 is grounded. The pulse signal generator 233 is connected between the end of the inductor 232 opposite to the inductor 231 and the ground. The inductors 231 and 223 are inductively coupled to each other. The inductors 232 and 224 are inductively coupled to each other. The magnetic flux application unit 230 is an example of a third magnetic flux application unit.

[0021] The magnetic flux application unit 330 has inductors 331 and 332 and a pulse signal generator 333. The inductors 331 and 332 are connected in series to each other. The end of the inductor 332 opposite to the inductor 331 is grounded. The pulse signal generator 333 is connected between the end of the inductor 331 opposite to the inductor 332 and the ground. The inductors 331 and 323 are inductively coupled to each other. The inductors 332 and 324 are inductively coupled to each other. The magnetic flux application unit 330 is an example of a first magnetic flux application unit.

[0022] The magnetic flux application unit 140 has an inductor 141 and a DC power supply 142. The positive electrodes of the inductor 141 and the DC power supply 142 are connected to each other. The end of the inductor 141 opposite the DC power supply 142 is grounded. The negative electrode of the DC power supply 142 is grounded. The inductor 141 and the inductor 113 are inductively coupled to each other. The main loop 310 is an example of an annular wiring.

[0023] The magnetic flux application unit 240 has an inductor 241 and a DC power supply 242. The positive electrodes of the inductor 241 and the DC power supply 242 are connected to each other. The end of the inductor 241 opposite to the DC power supply 242 is grounded. The negative electrode of the DC power supply 242 is grounded. The inductor 241 and the inductor 213 are inductively coupled to each other.

[0024] The magnetic flux application unit 340 has an inductor 341 and a DC power supply 342. The positive electrodes of the inductor 341 and the DC power supply 342 are connected to each other. The end of the inductor 341 opposite to the DC power supply 342 is grounded. The negative electrode of the DC power supply 342 is grounded. The inductor 341 and the inductor 313 are inductively coupled to each other.

[0025] Controller 10 turns on the coupling between flux qubit 100 and flux qubit 200 during a first period, and turns off the coupling between flux qubit 100 and flux qubit 200 during a second period. Figure 3 is a timing chart showing the time variation of the magnetic flux applied to SQUIDs 120, 220, and 320 during a first period. Figure 4 is a timing chart showing the time variation of the magnetic flux applied to SQUIDs 120, 220, and 320 during a second period. Figures 5 and 6 are diagrams showing the energy states of the flux qubits. In Figures 3 and 4, Φ120 indicates the magnetic flux applied to SQUID 120, Φ220 indicates the magnetic flux applied to SQUID 220, and Φ320 indicates the magnetic flux applied to SQUID 320. Φ ０ is the magnetic flux quantum. The horizontal axis in Figures 5 and 6 represents the magnetic flux applied to the main loop.

[0026] 2, some inductors, such as inductors 123 and 124, are shown as separate inductors, but an inductor formed integrally with these may also be used. Furthermore, some DC power supplies, such as DC power supply 142, are merely examples of power supplies, and other forms of power supplies, such as arbitrary waveform sources, may also be used. Furthermore, the coupling between flux qubit 200 and coupling flux qubit 300 is indirect, and may be inductive, capacitive, or other types of coupling.

[0027] As shown in FIG. 3, in the first period, under the control of the control unit 10, all of the magnetic fluxes Φ120, Φ220, and Φ320 are 0 (Wb) until time t12, and Φ ０ From time t13, it rises to Φ ０The increase in magnetic flux Φ 320 does not have to be linear with respect to time. Note that the energy potential of coupling flux qubit 300 can be expressed as Φ = 0 (Wb) and Φ = Φ ０ Therefore, the magnetic flux Φ320 is set to Φ ０ Alternatively, the voltage may be maintained at 0 (Wb), decreased to 0 (Wb) between time t12 and time t13, and controlled to 0 (Wb) from time t13 onwards.

[0028] As shown in FIG. 4, in the second period, under the control of the control unit 10, both the magnetic fluxes Φ120 and Φ220 are 0 (Wb) until time t22, and Φ220 are 0 (Wb) from time t22 to time t23. ０ From time t23, it rises to Φ ０ On the other hand, under the control of the control unit 10, the magnetic flux Φ320 is 0 (Wb) until time t21, which is before time t22, and is 0.5Φ from time t21 to time t22. ０ and from time t22 it rises to 0.5Φ ０ Note that the magnetic flux Φ320 is set to 0.5Φ before time t22. ０ It may be controlled so that

[0029] In any of the flux qubits, flux qubit 100, flux qubit 200, and coupling flux qubit 300, the applied magnetic flux is Φ ０ 6, there are two base states. In addition, in all of the flux qubits, flux qubit 100, flux qubit 200, and coupling flux qubit 300, when the applied magnetic flux is 0.5Φ ０As a result, there is one ground state, as shown in Figure 5. Here, as shown in Figure 5, when there is one ground state of energy, the energy value of the ground state is low. On the other hand, as shown in Figure 6, when there are two ground states of energy, the energy value of the ground state is higher than that of the state in Figure 5. When coupling flux qubit 300 is in the state shown in Figure 5 during the period between times t22 and t23, if there is a difference in energy potential between flux qubit 100 and flux qubit 200, quantum tunneling between flux qubit 100 and flux qubit 200 becomes less likely to occur. This makes it easier to control the coupling between flux qubit 100 and flux qubit 200 to be off.

[0030] Therefore, in the first period, the magnetic fluxes Φ120, Φ220, and Φ320 are simultaneously 0.5Φ ０ The magnetic flux Φ120, Φ220 and Φ320 are 0.5Φ ０ When Φ120, Φ220, and Φ320 are in a superposition state, flux qubit 100 and flux qubit 200 are in a superposition state. ０ , flux qubits 100 and 200 enter a classical state and the solution converges. Therefore, in the first period, the coupling between flux qubit 100 and flux qubit 200 is in the on state.

[0031] On the other hand, in the second period, the magnetic fluxes Φ120 and Φ220 are 0.5Φ ０ Before this, the magnetic flux Φ320 becomes 0.5Φ ０ There is no period during which flux qubit 100 and flux qubit 200 are in a superposition state. Therefore, during the second period, the coupling between flux qubit 100 and flux qubit 200 is in an off state.

[0032] (First Simulation) Next, a first simulation of the first embodiment conducted by the present inventors will be described. In the first simulation, flux qubit 100 was placed in a state in which it was likely to assume the "1" state by controlling flux application unit 140, and two types of bias were applied to flux qubit 200 by controlling flux application unit 240. One bias was set so that flux qubit 200 had a 50% probability of assuming the "1" state, and the other bias was set so that flux qubit 200 was likely to assume the "0" state. Control was then performed during the first and second periods described above. For reference, magnetic fluxes Φ120 and Φ220 were changed in the same manner as in the first period, assuming that coupling flux qubit 300 was not present.

[0033] In the first simulation, the number of trials was 1000. The results of the first simulation are shown in Figures 7 and 8. Figure 7 shows the results when the probability of flux qubit 200 being in the "1" state was set to 50%, and Figure 8 shows the results when flux qubit 200 was set to be more likely to be in the "0" state. In Figures 7 and 8, "11" indicates that both flux qubit 100 and flux qubit 200 are in the "1" state, and "10" indicates that flux qubit 100 is in the "1" state and flux qubit 200 is in the "0" state.

[0034] 7, even when the probability of flux qubit 200 being in the "1" state was set to 50%, the control in the first period resulted in a high probability of flux qubit 200 being in the "1" state. Furthermore, the control in the second period produced results similar to those obtained when coupling flux qubit 300 was not operated.

[0035] 8, even when flux qubit 200 is made to be more likely to be in the "0" state, when control is performed during the first period, flux qubit 200 also has a high probability of being in the "1" state. Furthermore, when control is performed during the second period, the same results as when coupling flux qubit 300 is not operated are obtained.

[0036] From the above, it can be said that in the first period, the coupling between flux qubit 100 and flux qubit 200 is in an ON state, and in the second period, the coupling between flux qubit 100 and flux qubit 200 is in an OFF state.

[0037] (Second Simulation) Next, a second simulation of the first embodiment conducted by the present inventors will be described. In the second simulation, various control operations were performed during the second period. Similar to the first simulation, in the second simulation, flux qubit 100 was placed in a state in which it was likely to assume the "1" state by controlling flux application unit 140, and two types of bias were applied to flux qubit 200 by controlling flux application unit 240. With one bias, the probability of flux qubit 200 being in the "1" state was 50%, and with the other bias, the probability of flux qubit 200 being in the "0" state was 70%. FIGS. 9 to 12 are timing charts showing the time variation of the magnetic flux applied to SQUIDs 120, 220, and 320 during the second period in the second simulation. In the control patterns shown in FIGS. 9 to 12, the time variation of the magnetic flux applied to SQUIDs 120 and 220 is the same as control pattern C shown in FIG. 4.

[0038] In the control pattern A shown in FIG. 9, the magnetic flux Φ320 is always set to 0 (Wb).

[0039] In the control pattern B shown in FIG. 10, the magnetic flux Φ320 is set to 0 (Wb) until time t22, and set to 0.5Φ from time t22 to time t23. ０ and from time t23, the ０ It was decided.

[0040] In the control pattern C shown in FIG. 4, the magnetic flux Φ320 is set to 0 (Wb) until time t21, and set to 0.5Φ from time t21 to time t22. ０ and from time t22, the ０ It was decided.

[0041] In the control pattern D shown in FIG. 11, the magnetic flux Φ320 is set to Φ ０ Then, from time t22 to time t23, it is 0.5Φ ０From time t23, the ０ It was decided.

[0042] In the control pattern E shown in FIG. 12, the magnetic flux Φ320 is set to Φ ０ Then, from time t22 to time t23, the voltage is decreased to 0 (Wb), and from time t23 onwards the voltage is kept at 0 (Wb).

[0043] In the second simulation, the number of trials was set to 1000. The results of the second simulation are shown in Figures 13 and 14. Figure 13 shows the results when the probability of flux qubit 200 being in the "1" state was set to 50%, and Figure 14 shows the results when the probability of flux qubit 200 being in the "0" state was set to 70%. In Figures 13 and 14, "11" indicates that both flux qubit 100 and flux qubit 200 are in the "1" state, and "10" indicates that flux qubit 100 is in the "1" state and flux qubit 200 is in the "0" state.

[0044] 13 and 14 , control patterns B and C produced results similar to those obtained when coupling flux qubit 300 was not present and magnetic fluxes Φ120 and Φ220 were varied in the same manner as in the first period. In particular, control pattern C produced results similar to those obtained when coupling flux qubit 300 was not present. Control patterns B and C, in which the magnetic flux is biased so that the energy potential of coupling flux qubit 300 has a single ground state as shown in FIG. 5 , are more resistant to sudden external magnetic flux changes and more stable than control pattern A, in which the magnetic flux is not biased. Furthermore, in control patterns B and C, the quantum tunneling effect is reduced during the period between times t22 and t23 due to the difference in energy potential between flux qubit 100 and flux qubit 200 and coupling flux qubit 300. Therefore, control patterns B and C make it easier to control the coupling between flux qubit 100 and flux qubit 200 to be turned off than control pattern A.

[0045] (Third Simulation) Next, a third simulation of the first embodiment conducted by the inventors will be described. In the third simulation, bias current I240 flowing through magnetic flux application unit 240 was changed, and the results were compared between control patterns A and C and a case in which coupling flux qubit 300 was not present. The third simulation was performed 1000 times. The results of the third simulation are shown in FIGS. 15 and 16. The vertical axis of FIG. 15 represents the probability that flux qubit 100 and flux qubit 200 will both be in the "11" state, in which case they are both in the "1" state. The vertical axis of FIG. 16 represents the probability that flux qubit 100 will be in the "1" state and flux qubit 200 will be in the "10" state, in which case they are both in the "0" state.

[0046] As shown in FIGS. 15 and 16, control pattern C produced results closer to those obtained when coupling flux qubit 300 was not present than control pattern A.

[0047] From the results of the above simulations, control pattern C is particularly preferable. Considering the change in the energy potential of flux qubit 100 and flux qubit 200, when fluxes Φ120 and Φ220 are 0.3Φ ０ Before the magnetic flux Φ320 becomes 0.4Φ ０ ~0.6Φ ０ It is preferable that the following is true.

[0048] The change in magnetic flux may be performed over a period of time ranging from 0.1 ns to 100 ms, or may be performed over a period of time ranging from 1 μs to 1 ms, for example.

[0049] Second Embodiment Next, a second embodiment will be described. The second embodiment relates to a quantum processing system. Fig. 17 is a block diagram showing a quantum processing system according to the second embodiment.

[0050] The quantum computing system 2 according to the second embodiment includes a control unit 10 and a quantum device 21. The control unit 10 controls the quantum device 21. The configuration of the control unit 10 is the same as that of the first embodiment, except for the contents of the control program.

[0051] 18 is a circuit diagram showing quantum device 22. Quantum device 22 has charge qubit 400, charge qubit 500, and coupling flux qubit 300. Coupling flux qubit 300 is capable of inductive coupling with charge qubits 400 and 500. Quantum device 22 also has charge supplies 430 and 530. The configuration of coupling flux qubit 300 is similar to that of the first embodiment.

[0052] The charge qubit 400 is, for example, a Transmon qubit, and includes a Josephson junction device 401 and a capacitor 402 connected in a ring. The charge qubit 400 further includes an inductor 403 electrically connected in parallel to the Josephson junction device 401 and the capacitor 402. The inductor 403 and the inductor 311 are inductively coupled to each other. One end of the Josephson junction device 401, the capacitor 402, and the inductor 403 are grounded. For example, the charge qubit 400 includes titanium nitride as a superconducting material. The charge qubit 400 is an example of a first qubit and a first charge qubit. Note that it is not necessary to ground one end of the Josephson junction device 401, the capacitor 402, and the inductor 403, and even if they are grounded, they may be connected to a ground plane via a capacitance.

[0053] A charge supply unit 430 is connected to the other ends of the Josephson junction device 401, the capacitor 402, and the inductor 403. The charge supply unit 430 has a current source 431 and a capacitor 432. The capacitor 432 is connected between one end of the current source 431 and the Josephson junction device 401, the capacitor 402, and the inductor 403. The other end of the current source 431 is grounded.

[0054] The charge qubit 500 is, for example, a transmon qubit, and includes a Josephson junction device 501 and a capacitor 502 connected in a ring. The charge qubit 500 further includes an inductor 503 electrically connected in parallel to the Josephson junction device 501 and the capacitor 502. The inductor 503 and the inductor 502 are inductively coupled to each other. One ends of the Josephson junction device 501, the capacitor 502, and the inductor 503 are grounded. For example, the charge qubit 500 includes titanium nitride as a superconducting material. The charge qubit 500 is an example of a second qubit and a second charge qubit.

[0055] A charge supply unit 530 is connected to the other ends of the Josephson junction device 501, the capacitor 502, and the inductor 503. The charge supply unit 530 has a current source 531 and a capacitor 532. The capacitor 532 is connected between one end of the current source 531 and the Josephson junction device 501, the capacitor 502, and the inductor 503. The other end of the current source 531 is grounded.

[0056] Control unit 10 turns on the coupling between charge quantum bit 400 and charge quantum bit 500 during a first period, and turns off the coupling between charge quantum bit 400 and charge quantum bit 500 during a second period. Fig. 19 is a timing chart showing the time changes of the current generated by current source 431, the current generated by current source 531, and the magnetic flux applied to SQUID 320 during a first period. Fig. 20 is a timing chart showing the time changes of the current generated by current source 431, the current generated by current source 531, and the magnetic flux applied to SQUID 320 during a second period. In Figs. 19 and 20, I431 indicates the current generated by current source 431, I531 indicates the current generated by current source 531, and Φ320 indicates the magnetic flux applied to SQUID 320.

[0057] A case where the coupling between charge qubit 400 and charge qubit 500 is turned on and gate operation is performed on charge qubit 400 will be described with reference to FIG. 19 . In this example, the period from time t31 to time t32 corresponds to the first period. As shown in FIG. 19 , in the first period, under the control of control unit 10, current source 431 generates a current for gate operation so as to include the period from time t31 to time t32. While current source 431 is generating a current, gate operation of charge qubit 400 is performed. Under the control of control unit 10, magnetic flux Φ320 is 0.5Φ from time t30 to time t31. ０ The current generated by current source 531 is always 0 (A). Next, for the period between time t31 and time t32, magnetic flux Φ320 is set to 0 (Wb). During this period, the coupling between charge quantum bit 400 and charge quantum bit 500 is in the ON state. After that, from time t32 onwards, magnetic flux Φ320 is again set to 0.5Φ ０ After time t32, the magnetic flux Φ320 is set to 0.5Φ ０ However, it is also possible to maintain the magnetic flux Φ320 at 0 (Wb) after time t32. Note that the energy potential of the coupling flux qubit 300 can be varied between when Φ=0 (Wb) and when Φ=Φ ０ Since the cases are equivalent, during the period between time t31 and time t32, the magnetic flux Φ320 is set to Φ=Φ ０ It may also be possible to use the following.

[0058] Next, a case where the coupling between charge qubit 400 and charge qubit 500 is turned off and gate operation is performed on charge qubit 400 will be described with reference to FIG. 20 . In this example, the period from time t31 to time t32 corresponds to the second period. As shown in FIG. 20 , under the control of control unit 10, current source 431 generates a current for gate operation so as to include the period from time t31 to time t32. While current source 431 is generating a current, gate operation of charge qubit 400 is performed. Under the control of control unit 10, magnetic flux Φ320 is set to 0.5Φ during the period from time t31 to time t32 (second period). ０ The current generated by the current source 531 is always 0 (A). In FIG. 20, the magnetic flux Φ320 is set to 0.5Φ during the period from time t30 to time t31 and during the period after time t32.０ This shows an example of controlling the

[0059] As described above, in coupling flux qubit 300, when the applied magnetic flux is 0 (Wb) or Φ ０ As a result, as shown in FIG. 6, there are two ground states, and the applied magnetic flux is 0.5Φ ０ 5, there is one base state. Here, when the magnetic flux applied to coupling flux qubit 300 is set to 0 (Wb) or Φ ０ By setting the magnetic flux to 0.5Φ, the coupling can be controlled to the ON state. ０ This will explain why the coupling can be controlled to the OFF state.

[0060] 21 is a diagram showing the relationship between the magnetic flux of coupling flux qubit 300 and the internal current of coupled charge qubit 400. Fig. 21 shows the results of a simulation performed with the resonant frequency of charge qubit 400 and charge qubit 500 set to 8.1 GHz. An excitation signal of 8.1 GHz was applied to charge qubit 500 from current source 531, which serves as a signal source, and the internal state of charge qubit 400 was calculated and the internal current Ip was observed. In this case, the intensity of the signal applied to coupling flux qubit 300 (the output signal of pulse signal generator 333) was modulated.

[0061] 21 shows a normalized value of the internal current Ip according to the signal strength (magnetic flux applied by the pulse signal generator 333) with the internal current Ip when the signal magnitude is 0 as a reference. When the magnetic flux is set to 0 (Wb), the coupling between the charge quantum bit 400 and the charge quantum bit 500 is in the on state, while the magnetic flux is set to 0.5Φ ０ It can be seen that the coupling is in the OFF state when

[0062] Simulations have confirmed that when Xmon is used instead of charge qubit 400 and charge qubit 500, the same tendency as in FIG. 21 is observed, although the resonant frequencies are different.

[0063] Xmon is a flux qubit made of a single layer of wiring, and contains, for example, niobium, titanium nitride, or niobium nitride as a superconducting material. The coupling between coupling flux qubit 300 and charge qubits 400 and 500 may be capacitive.

[0064] (First Example of the Configuration of the Quantum Device 22) Next, a first example of the configuration of the quantum device 22 will be described. Fig. 22 is a plan view showing the first example of the configuration of the quantum device 22. Fig. 23 is a cross-sectional view showing the first example of the configuration of the quantum device 22. Fig. 23 corresponds to a cross-sectional view taken along line XXIII-XXIII in Fig. 22 .

[0065] 22 and 23 , quantum device 22A of the first example has quantum bit substrate 30 and quantum bit substrate 40. Quantum bit substrate 30 and quantum bit substrate 40 are joined to each other via bumps 25. For example, quantum bit substrate 30 is flip-chip bonded to quantum bit substrate 40. For example, bumps 25 are connected to a ground layer provided on quantum bit substrate 30 and a ground layer provided on quantum bit substrate 40.

[0066] Quantum bit substrate 30 includes coupling flux qubit 300, magnetic flux application unit 330, and magnetic flux application unit 340. Quantum bit substrate 30 has quantum bit region 31 in which coupling flux qubit 300 is arranged.

[0067] Although not shown in FIG. 23 , the quantum bit substrate 40 may have wiring or electrodes connected to the flux qubits 100 and 200. The quantum bits are not limited to flux qubits, and other quantum bits may be used. The quantum bit substrate 40 may also have a resonator for observing the quantum bit state and electrodes for manipulating the quantum bit state. Furthermore, a path for introducing a signal for manipulating the quantum bit state may be formed from the edge of the quantum bit substrate 40 by wire bonding, or a through-hole may be provided in the quantum bit substrate 40 so that the signal can be supplied from the back surface of the quantum bit substrate 40. The quantum bit substrate 30 may have a path for supplying a signal on the edge or back surface of the quantum bit substrate 30. Alternatively, the signal may be connected to a pattern provided on the quantum bit substrate 40 via a bump, and supplied from the back surface via the edge or through-hole of the quantum bit substrate 40.

[0068] 24 is a cross-sectional view showing a portion of the quantum bit substrate 30. The quantum bit substrate 30 includes, for example, a substrate 80, wiring layers 81, 82, 83, and 84, insulating layers 85, 86, and 87, and a Josephson junction element 88. The wiring layer 81 is provided on the substrate 80, and the Josephson junction element 88 is provided on the wiring layer 81. The insulating layer 85 is provided on the substrate 80 so as to cover the Josephson junction element 88 and the wiring layer 81. The wiring layer 82 is provided on the insulating layer 85 so as to contact the Josephson junction element 88 through an opening formed in the insulating layer 85. The insulating layer 86 is provided on the insulating layer 85 so as to cover the wiring layer 82. The wiring layer 83 is provided on the insulating layer 86. The insulating layer 87 is provided on the insulating layer 86 so as to cover the wiring layer 83. The wiring layer 84 is provided on the insulating layer 87 so as to contact the wiring layer 83 through an opening formed in the insulating layer 87. The material of the wiring layers 81, 82, 83, and 84 is a material that can become a superconductor, such as niobium or niobium nitride, etc. The material of the insulating layers 85, 86, and 87 is, for example, silicon oxide.

[0069] The Josephson element 88 has, for example, an aluminum film 88A, an aluminum oxide film 88B, and an aluminum film 88C. The aluminum film 88A is connected to the wiring layer 81. The aluminum oxide film 88B is provided on the aluminum film 88A. The aluminum film 88C is provided on the aluminum oxide film 88B, and the wiring layer 82 is in contact with the aluminum film 88C. The Josephson element 88 corresponds to the Josephson elements 321 and 322.

[0070] Quantum bit substrate 40 includes charge quantum bits 400, charge supply units 430, charge quantum bits 500, and charge supply units 530. Quantum bit substrate 40 has quantum bit regions 41 in which charge quantum bits 400 are arranged, and quantum bit regions 42 in which charge quantum bits 500 are arranged.

[0071] 25 is a cross-sectional view showing a portion of the quantum bit substrate 40. The quantum bit substrate 40 has, for example, a substrate 90, wiring layers 91 and 92, and an insulating layer 93. The wiring layer 91 is provided on the substrate 90, and the insulating layer 93 covers the surface of the wiring layer 91. The wiring layer 92 is provided on the insulating layer 93. The wiring layers 91 and 92 and the insulating layer 93 constitute Josephson junction elements corresponding to the Josephson junction elements 401 and 501.

[0072] Inductor 311 of coupling flux qubit 300 and inductor 403 of charge qubit 400 face each other and are inductively coupled to each other. Inductor 312 of coupling flux qubit 300 and inductor 503 of charge qubit 500 face each other and are inductively coupled to each other.

[0073] For example, inductors 311 and 312 of coupling flux qubit 300 are connected to wiring layer 84, a portion of wiring layer 84 and inductor 403 are inductively coupled to each other, and another portion of wiring layer 84 and inductor 503 are inductively coupled to each other.

[0074] (Second Example of the Configuration of the Quantum Device 22) Next, a second example of the configuration of the quantum device 22 will be described. Fig. 26 is a plan view showing the second example of the configuration of the quantum device 22. Fig. 27 is a cross-sectional view showing the second example of the configuration of the quantum device 22. Fig. 27 corresponds to a cross-sectional view taken along line XXVII-XXVII in Fig. 26 .

[0075] 26 and 27 , quantum device 22B of the second example has quantum bit substrate 30, quantum bit substrate 50, and quantum bit substrate 60. Quantum bit substrate 30 and quantum bit substrate 50 are bonded to each other via bump 26, and quantum bit substrate 30 and quantum bit substrate 60 are bonded to each other via bump 27. For example, quantum bit substrate 30 is flip-chip bonded to quantum bit substrates 50 and 60. For example, bump 26 is connected to a ground layer provided on quantum bit substrate 30 and a ground layer provided on quantum bit substrate 50, and bump 27 is connected to a ground layer provided on quantum bit substrate 30 and a ground layer provided on quantum bit substrate 60.

[0076] Quantum bit substrate 50 includes charge qubits 400 and charge supply units 430. Quantum bit substrate 50 has qubit regions 51 in which charge qubits 400 are arranged. Quantum bit substrate 60 includes charge qubits 500 and charge supply units 530. Quantum bit substrate 60 has qubit regions 61 in which charge qubits 500 are arranged.

[0077] Inductor 311 of coupling flux qubit 300 and inductor 403 of charge qubit 400 face each other and are inductively coupled to each other. Inductor 312 of coupling flux qubit 300 and inductor 503 of charge qubit 500 face each other and are inductively coupled to each other.

[0078] For example, inductors 311 and 312 of coupling flux qubit 300 are connected to wiring layer 84, a portion of wiring layer 83 or 84 is inductively coupled to inductor 403, and another portion of wiring layer 83 or 84 is inductively coupled to inductor 503.

[0079] Although not shown in FIG. 27 , the quantum bit substrates 50 and 60 may have wiring or electrodes directly or indirectly connected to the quantum bits. The quantum bit substrates 50 and 60 may also have resonators for observing the quantum bit states and electrodes for manipulating the quantum bit states. Furthermore, paths for introducing signals for manipulating the quantum bit states may be formed from the edges of the quantum bit substrates 50 and 60 by wire bonding, or through-holes may be provided in the quantum bit substrates 40 and 60 to supply signals from the backside of the quantum bit substrates 50 and 60. The quantum bit substrate 30 may have a path for supplying signals at its edge or backside. Furthermore, the signal may be connected to a pattern provided on the quantum bit substrates 50 and 60 via a bump, and supplied from the backside via the edge or through-hole of the quantum bit substrates 50 and 60.

[0080] The other configurations are the same as those in the first example.

[0081] (Third Example of the Configuration of the Quantum Device 22) Next, a description will be given of a third example of the configuration of the quantum device 22. Fig. 28 is a plan view showing the third example of the configuration of the quantum device 22.

[0082] 28 , in the third example quantum device 22C, a region 52 in the quantum bit region 51 where the Josephson junction element 401 and the capacitor 402 are provided is spaced apart from the quantum bit substrate 30 in a planar view. Also, a region 62 in the quantum bit region 61 where the Josephson junction element 501 and the capacitor 502 are provided is spaced apart from the quantum bit substrate 30 in a planar view.

[0083] The other configurations are the same as those in the second example.

[0084] In the second example, the insulating layers 85, 86, and 87 included in the quantum bit substrate 30 can be a source of dielectric loss for the Josephson junction element 401 and the capacitor 402, and for the Josephson junction element 501 and the capacitor 502. In the third example, such dielectric loss can be reduced.

[0085] In the first or second example, a ground layer may be provided in the portion of the quantum bit substrate 30 corresponding to the Josephson junction device 401 and the capacitor 402, and the portion corresponding to the Josephson junction device 501 and the capacitor 502, in order to reduce dielectric loss.

[0086] The material of the bumps 25, 26, and 27 is preferably a material that can be bonded at low temperatures, such as indium or an indium alloy. The material of the bumps 25, 26, and 27 is preferably a material that can be bonded at 200°C or less, and more preferably a material that can be bonded at 180°C or less. The material of the bumps 25, 26, and 27 may also be a material that can improve adhesion, such as gold. An alloy of indium and gold may also be used. In this case, depending on the composition, it may be bondable at a temperature of 180°C or less and may be a superconducting material.

[0087] In the second and third examples, quantum bit substrate 30 and one of quantum bit substrates 50 and 60 may be coupled by a coaxial cable containing a superconducting material (hereinafter, a coaxial cable containing a superconducting material may be referred to as a superconducting cable.) The superconducting material used for the superconductor cable is, for example, an alloy of niobium and titanium.

[0088] For example, quantum bit substrate 30 and quantum bit substrate 50 are joined using bumps 26 as in the second example, and quantum bit substrate 30 and quantum bit substrate 60 are coupled by a superconducting cable. In this case, for example, inductor 312 of coupling flux qubit 300 and the superconducting cable are inductively coupled to each other, and the superconducting cable and inductor 503 of charge qubit 500 are inductively coupled to each other. For example, quantum bit substrate 30 may be flip-chip bonded to quantum bit substrate 50. The length of the superconducting cable may be several centimeters to several meters, typically 1 meter to 10 meters. The coupling state between charge qubit 400 and charge qubit 500 can be adjusted by controlling the energy potential of coupling flux qubit 300.

[0089] The coupling between the superconducting cable and charge qubit 400 or 500 may be capacitive, or the coupling between the superconducting cable and coupling flux qubit 300 may be capacitive. Furthermore, a superconducting circuit including a Josephson junction device may be further included in the coupling section, and direct, inductive, or capacitive coupling may be achieved.

[0090] The quantum bit substrates 30 and 60 may be joined using bumps 27 as in the second example, and the quantum bit substrates 30 and 50 may be coupled by superconducting cables. Alternatively, the quantum bit substrates 30 and 50 and 60 may be coupled by superconducting cables.

[0091] By connecting qubit substrates using superconducting cables, the flexibility of arranging qubit substrates on stages within the same dilution refrigerator can be improved. For example, when placing qubit substrates on the lowest-temperature stage of a dilution refrigerator, qubit substrates can be placed at distant locations and protected by different magnetic shields. Furthermore, by using long superconducting cables (5 m to 10 m), qubits on qubit substrates installed in different dilution refrigerators can be connected.

[0092] In the first embodiment, the coupling flux qubit 300 is provided with a magnetic flux application unit 330 having a Φ ０ It is preferable that when a magnetic flux of 2πLI is applied, no obvious unstable state appears in the shape of the energy potential of the coupling flux qubit 300 (see FIG. 6). Ｃ / Φ ０ The variable β is expressed as Ｌ It is preferable that the value of is between 1.2 and 8.0. Here, L is the total inductance of coupling flux qubit 300, and I Ｃ is the sum of the critical current values ​​of the Josephson junction elements 321 and 322. Ｌ It is more preferable that the value of is 1.2 to 6.0, since an inflection point, which is a sign that an unstable state appears in the energy potential, does not clearly appear.

[0093] For example, the critical current value I of the Josephson junction elements 321 and 322 is ＣThe critical current value I Ｃ The smaller the critical current value I Ｃ The larger the value of , the narrower the range of selection for the inductance L becomes, but the easier it is to form the Josephson junction elements 321 and 322 stably.

[0094] In order to make the ground state of the flux qubit one, the applied magnetic flux is 0.5Φ ０ However, strictly 0.5Φ ０ It does not have to be 0.4Φ ０ ~0.6Φ ０ may be.

[0095] Furthermore, coupling flux qubit 300 may have a plurality of SQUIDs 320 connected in parallel, which can reduce variations in characteristics.

[0096] Coupling flux qubit 300 does not necessarily have to include flux application section 340 .

[0097] Quantum computing systems and quantum devices according to the present disclosure can be used, for example, in quantum computing.

[0098] Although the preferred embodiments have been described above in detail, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims.

[0099] 1, 2: Quantum computing system 10: Control unit 21, 22, 22A, 22B, 22C: Quantum device 30, 40, 50, 60: Qubit substrate 31, 41, 42, 51, 61: Qubit region 100, 200: Flux qubit 110, 210, 310: Main loop 120, 220, 320: SQUID 130, 140, 230, 240, 330, 340: Flux application unit 300: Coupling flux qubit 400, 500: Charge qubit 430, 530: Charge supply unit

Claims

1. Quantum devices and a control unit that controls the quantum device; and The quantum device is a first qubit; and a second qubit; and a coupling flux qubit that is coupleable to the first qubit and the second qubit; a first magnetic flux applying unit that applies a magnetic flux to the coupling flux quantum bit; and The control unit is configured to: applying a first magnetic flux having a first time modulation during a first time period; A quantum computing system that applies a second magnetic flux having a second time modulation different from the first time modulation during a second time period different from the first time period.

2. the first qubit comprises a first flux qubit; the second qubit comprises a second flux qubit; The quantum device is a second magnetic flux applying unit that applies a magnetic flux to the first magnetic flux qubit; a third magnetic flux applying unit that applies a magnetic flux to the second magnetic flux qubit; and The control unit is configured to: applying a third magnetic flux having the first time modulation during the first period; applying a fourth magnetic flux having a third time modulation different from the second time modulation during the second time period; The control unit is configured to: applying a fifth magnetic flux having the first time modulation during the first period; The quantum computing system according to claim 1 , wherein a sixth magnetic flux having the third time modulation is applied during the second period.

3. application of the fourth magnetic flux results in two ground states of the first magnetic flux qubit; application of the sixth magnetic flux results in two ground states of the second magnetic flux qubit; 3. The quantum computing system of claim 2, wherein application of the second magnetic flux causes the coupling flux qubit to have one base state.

4. The magnetic flux quantum is Φ ０ When In the third time modulation, the fourth magnetic flux and the sixth magnetic flux are changed from 0 (Wb) to Φ ０ rises to In the second time modulation, the fourth magnetic flux and the sixth magnetic flux are Φ ０ During the period, the second magnetic flux is 0.4Φ ０ ~0.6Φ ０ 4. The quantum computing system according to claim 2 or 3, wherein:

5. The fourth magnetic flux and the sixth magnetic flux are Φ ０ Before the second magnetic flux reaches 0.4Φ ０ ~0.6Φ ０ The quantum computing system of claim 4 .

6. The fourth magnetic flux and the sixth magnetic flux are Φ ０ At the same time as the second magnetic flux reaches 0.4Φ ０ ~0.6Φ ０ The quantum computing system of claim 4 .

7. The first quantum bit has an Xmon; the second qubit comprises an Xmon; application of the first magnetic flux results in two ground states of the coupling flux qubit; application of the second magnetic flux results in a single ground state for the coupling flux qubit; The magnetic flux quantum is Φ ０ When In the first period, the first magnetic flux is 0 (Wb) or Φ ０ And During the second period, the second magnetic flux is 0.4Φ ０ ~0.6Φ ０ The quantum computing system of claim 1 , wherein

8. The total inductance of the coupling flux qubit is L, and the critical current value of the Josephson junction device included in the coupling flux qubit is I Ｃ , the magnetic flux quantum is Φ ０ When this is the case, 2πLI Ｃ / Φ ０ The quantum computing system according to claim 1, 2, 3 or 7, wherein the value of is 1.2 to 8.

0.

9. A method for controlling a quantum device, comprising: The quantum device is a first qubit; and a second qubit; and a coupling flux qubit that is coupleable to the first qubit and the second qubit; and applying a first magnetic flux having a first time modulation to the coupling flux qubit during a first time period; applying a second magnetic flux to the coupling flux qubit during a second time period different from the first time period and having a second time modulation different from the first time modulation; A method for controlling a quantum device comprising:

10. the first qubit comprises a first flux qubit; the second qubit comprises a second flux qubit; applying a third magnetic flux with the first time modulation to the first flux qubit and a fifth magnetic flux with the first time modulation to the second flux qubit during the first time period; during the second time period, applying a fourth magnetic flux having a third time modulation different from the second time modulation to the first flux qubit and applying a sixth magnetic flux having the third time modulation to the second flux qubit; The method for controlling a quantum device according to claim 9 , comprising:

11. application of the fourth magnetic flux results in two ground states of the first magnetic flux qubit; application of the sixth magnetic flux results in two ground states of the second magnetic flux qubit; 11. The method of claim 10, wherein application of the second magnetic flux causes the coupling flux qubit to have one ground state.

12. the first qubit comprises a first charge qubit; the second qubit comprises a second charge qubit; application of the first magnetic flux results in two ground states of the coupling flux qubit; 12. The method of claim 11, wherein application of the second magnetic flux causes the coupling flux qubit to have one ground state.

13. Quantum devices and a control unit that controls the quantum device; and The quantum device is a first charge qubit; and a second charge qubit; and a coupling flux qubit that is coupleable to the first charge qubit and the second charge qubit; a first magnetic flux applying unit that applies a magnetic flux to the coupling flux quantum bit; and The control unit is configured to: a first period during which the coupling flux qubit has one ground state of energy potential, and a second period during which the coupling flux qubit has two ground states of energy potential, the second period being different from the first period;

14. A method for controlling a quantum device, comprising: The quantum device is a first charge qubit; and a second charge qubit; and a coupling flux qubit that is coupleable to the first charge qubit and the second charge qubit; a first magnetic flux applying unit that applies a magnetic flux to the coupling flux quantum bit; and causing the first magnetic flux applying unit to apply a magnetic flux that brings the energy potential of the coupling flux qubit into a single ground state during a first period; a first magnetic flux application unit applying a magnetic flux that causes the coupling flux qubit to have two ground states of energy potential during a second period different from the first period;