Processing system, processing method, and program

Abstract

To provide a processing system, a processing method, and a program for accurately adjusting a resonance frequency in a quantum bit device.SOLUTION: The processing system 1 includes a calculation means 701 that calculates a first current value, which is a current value of a current flowing through a resonance circuit, based on a value of a residual magnetic flux in the resonance circuit included in a quantum bit device.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present disclosure relates to a processing system, a processing method, and a program. [Background technology]

[0002] Quantum computers are being developed as one way to speed up computer calculation processing. Patent Document 1 discloses a related technology, which is a technology relating to a quantum computing device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2023-554256 Summary of the Invention [Problem to be solved by the invention]

[0004] In technical fields related to quantum computers such as those described in Patent Document 1, there is a demand for a technique that can precisely adjust the resonant frequency in a quantum bit device.

[0005] One of the objectives of each aspect of the present disclosure is to provide a processing system, a processing method, and a program that can solve the above-mentioned problems. [Means for solving the problem]

[0006] According to one aspect of the present disclosure, a processing system includes a calculation means for calculating a first current value, which is a current value of a current to be passed through a resonant circuit included in a quantum bit device, based on a value of residual magnetic flux in the resonant circuit.

[0007] According to another aspect of the present disclosure, a processing method includes calculating a first current value, which is a current value of a current to be passed through a resonant circuit included in a quantum bit device, based on a value of residual magnetic flux in the resonant circuit.

[0008] According to another aspect of the present disclosure, a program causes a computer to calculate a first current value, which is the current value of a current to be passed through a resonant circuit included in a quantum bit device, based on a value of residual magnetic flux in the resonant circuit. [Effects of the Invention]

[0009] According to each aspect of the present disclosure, the resonant frequency can be adjusted with high precision. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 illustrates an example circuit according to some embodiments of the present disclosure. [Figure 2] FIG. 1 illustrates an example circuit according to some embodiments of the present disclosure. [Figure 3] FIG. 10 illustrates an example of the magnetic field dependence of the resonant frequency of a qubit device according to some embodiments of the present disclosure. [Figure 4] FIG. 1 illustrates an example of a configuration of a processing system according to some embodiments of the present disclosure. [Figure 5] FIG. 1 is a diagram illustrating an example of a processing flow of a processing system according to some embodiments of the present disclosure. [Figure 6] FIG. 10 is a diagram showing an example of measurement results obtained by a frequency measurement device according to some embodiments of the present disclosure. [Figure 7] FIG. 1 is a diagram illustrating an example of a processing flow of a processing system according to some embodiments of the present disclosure. [Figure 8] FIG. 1 illustrates an example circuit according to some embodiments of the present disclosure. [Figure 9] FIG. 1 illustrates an example of a configuration of a processing system according to some embodiments of the present disclosure. [Figure 10] FIG. 1 is a diagram illustrating an example of a processing flow of a processing system according to some embodiments of the present disclosure. [Figure 11] FIG. 1 is a schematic block diagram illustrating the configuration of a computer according to at least one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, the embodiments will be described in detail with reference to the drawings. <Embodiment> A processing system 1 according to an embodiment of the present disclosure will be described with reference to the drawings. The processing system 1 is a system that configures a superconducting quantum bit device using a superconducting quantum interference device (hereinafter referred to as "SQUID"). As described below, the processing system 1 calculates a current value to be passed through a bias line inductively coupled to the SQUID loop, taking into account the residual magnetic flux inside the SQUID loop, and sets the current value. Thereafter, the processing system 1 renormalizes the error between the desired resonant frequency and the resonant frequency observed by measurement as the residual magnetic flux, recalculates the current value, sets the current value, and confirms the resonant frequency by measurement. The processing system 1 adjusts the resonant frequency by repeating this operation.

[0012] (Method of adjusting the resonance frequency) A method for adjusting the resonant frequency in a processing system 1 according to an embodiment of the present disclosure will be described. To better understand the method for adjusting the resonant frequency in the processing system 1, a circuit 500 including a Josephson junction 501 and a capacitor 502 will first be described. FIG. 1 is a diagram illustrating an example of the circuit 500 according to some embodiments of the present disclosure. The circuit 500 includes a Josephson junction 501 and a capacitor 502. When a quantum bit device is configured using the circuit 500 as shown in FIG. 1, the resonant frequency determines the operating frequency. The resonant frequency of the circuit shown in FIG. 1 is 1 / (2π(Lj·C)^(1 / 2)) where "^" is the exponentiation operator. The inductance Lj is expressed as follows using the critical current value Ic of the Josephson junction 501 and the current I flowing through the Josephson junction 501:

[0013]

number

[0014] Here, Φ represents the magnitude of the magnetic flux quantum. Thus, the Josephson junction 501 has a nonlinear inductance Lj. However, when the current I flowing through the Josephson junction 501 is sufficiently small, the inductance Lj can be treated as an inductor with a magnitude of Φ / (2πIc).

[0015] Next, a circuit 600 will be described, which includes an inductor 601 having a linear inductance Lk and a SQUID having a loop formed by two Josephson junctions 602a and 602b. The inductance Lk of the SQUID can be changed by changing the magnetic flux inside the loop. This change in inductance Lk changes the resonant frequency. The magnetic flux can be generated by passing a current through a bias line inductively coupled to the SQUID loop. In other words, passing a current through the bias line changes the inductance Lk of the SQUID, ultimately changing the resonant frequency. FIG. 2 illustrates an example of a circuit 600 according to some embodiments of the present disclosure. The circuit 600 includes an inductor 601 having a linear inductance Lk and a SQUID having a loop formed by two Josephson junctions 602a and 602b. As shown in FIG. 2, the circuit 600 also includes a capacitor 603 having a capacitance C. If the critical current values ​​of the Josephson junctions 602a and 602b are Ic1 and Ic2, respectively, the critical current value Ic_eff of the entire SQUID is expressed as in equation (2) using the magnetic flux Φext penetrating the inside of the SQUID.

[0016]

number

[0017] Here, d = |Ic1 - Ic2| / (Ic1 + Ic2). In this case, the inductance Ls(Φext) of the SQUID is Ls(Φext) = Φ0 / (2πIc_eff(Φext)) when the current flowing through the Josephson junctions 602a and 602b is sufficiently small. The resonant frequency f(Φext) is expressed as in equation (3).

[0018]

number

[0019] As shown in equation (3), the resonant frequency f(Φext) depends on the magnetic flux Φext. In other words, the resonant frequency f(Φext) can be adjusted by adjusting the magnetic flux Φext. When multiple quantum bit devices are present, the resonant frequency f(Φext) affects the interactions between the multiple quantum bit devices. Therefore, it is desirable to be able to adjust the resonant frequency f(Φext).

[0020] FIG. 3 illustrates an example of the magnetic field dependence of the resonant frequency of a quantum bit device according to some embodiments of the present disclosure. The magnetic field dependence of the resonant frequency of the quantum bit device illustrated in FIG. 3 is based on the assumed frequency of a SQUID in which the two Josephson junctions in the SQUID are asymmetric and different from each other. This asymmetric SQUID is characterized by a non-zero minimum resonant frequency. Therefore, when the measurement frequency is limited by the experimental equipment (e.g., 5 to 10 GHz), adjusting the frequency range of the asymmetric SQUID to match the frequency provides the advantage of ensuring accurate measurement without losing track of the frequency. As can be seen from Equation (2), the dependence of the resonant frequency on magnetic flux Φext is periodic with respect to Φext. The period is Φ0. The magnetic flux Φext penetrating a certain SQUID can be expressed as Equation (4) using the current i flowing through a port inductively coupled to the SQUID with magnitude M and the residual magnetic flux Φoff present within the SQUID loop when no current is flowing.

[0021]

number

[0022] The residual magnetic flux Φoff in equation (4) may change due to the influence of hysteresis when the current value i is changed, or due to the influence of the environment (for example, temperature change).

[0023] In the explanation so far, we have considered one quantum bit device, but in reality, there are multiple quantum bit devices in one quantum chip. In such a case, the magnetic flux Φext_a that passes through the SQUID in the a-th quantum bit device also changes depending on the current flowing through the port inductively coupled to the SQUID in another quantum bit device. This is called crosstalk. Here, we assume that the port inductively coupled to the SQUID in the b-th quantum bit device is coupled to the SQUID in the a-th quantum bit device with a magnitude M_ab, and a current ib is flowing through it. In this case, the value of the magnetic flux Φext_a is expressed as in equation (5).

[0024]

number

[0025] Here, Φoff_a represents the residual magnetic flux that penetrates the SQUID in the a-th quantum bit device. Based on this equation (5), the resonant frequency of the a-th quantum bit device can be changed by changing the value of the magnetic flux Φext_a. In this case, the configurable parameter is the current ib flowing through each port. Note that changing the value of the current ib affects not only one quantum bit device, but all quantum bit devices. Therefore, it is necessary to set the current value for all quantum bit devices taking these effects into account.

[0026] Here, in order to collectively express the magnetic fluxes for a chip having N quantum bit devices, variables such as those in equations (6) to (9) are defined. Note that Φextv, Mv, Φoffv, and iv are matrices and vectors, respectively.

[0027]

number

[0028]

number

[0029]

number

[0030]

number

[0031] Using equations (6) to (9), the magnetic flux Φextv when multiple quantum bit devices exist is expressed as in equation (10).

[0032]

number

[0033] Therefore, if the magnetic flux Φtargetv to be set for the magnetic flux Φext in order to set the resonant frequency to a desired value is known from equation (10), the value of the current iv to be set when there are multiple quantum bit devices can be calculated using equation (11). Note that the first term on the right-hand side of equation (11) represents the inverse matrix of the matrix Mv.

[0034]

number

[0035] (Configuration of the processing system of the present disclosure) 4 is a diagram illustrating an example of a configuration of a processing system 1 according to some embodiments of the present disclosure. As shown in FIG. 4, the processing system 1 according to one embodiment of the present disclosure includes a control and calculation device 10, a control and measurement device 20, and a quantum chip 30.

[0036] The control and calculation device 10 controls the control and measurement device 20. For example, the control and calculation device 10 outputs to the control and measurement device 20 the measurement conditions under which the control and measurement device 20 performs measurements. Furthermore, for example, the control and calculation device 10 outputs to the control and measurement device 20 the value of the current that the control and measurement device 20 outputs to the quantum chip 30. Furthermore, the control and calculation device 10 performs a predetermined calculation using the results of measurements by the control and measurement device 20. Details of the processing performed by the control and calculation device 10 will be described later.

[0037] As shown in FIG. 4 , the control and measurement device 20 includes current sources 201a1, 201a2, . . . , 201aN and a frequency measurement device 202. Hereinafter, current sources 201a1, 201a2, . . . , 201aN may be collectively referred to as current source 201. The control and measurement device 20 controls the quantum chip 30. For example, each of the current sources 201 of the control and measurement device 20 controls the oscillation frequency of a corresponding quantum bit device 301 (described later) included in the quantum chip 30 by passing a current through the corresponding quantum bit device 301. Specifically, current source 201a1 controls the oscillation frequency of quantum bit device 301a1 by passing a current through quantum bit device 301a1. Furthermore, current source 201a2 controls the oscillation frequency of quantum bit device 301a2 by passing a current through quantum bit device 301a2. Furthermore, current source 201aN controls the oscillation frequency of quantum bit device 301aN by supplying a current to quantum bit device 301aN.

[0038] Furthermore, the control and measurement device 20 performs measurements on the quantum chip 30. For example, the frequency measurement device 202 of the control and measurement device 20 performs measurements necessary to adjust the oscillation frequency of each quantum bit device 301 in the quantum chip 30. For example, the frequency measurement device 202 is a network analyzer. Details of the processing performed by the control and measurement device 20 will be described later.

[0039] As shown in Fig. 4, quantum chip 30 includes quantum bit devices 301a1, 301a2, ..., 301aN. Quantum bit devices 301a1, 301a2, ..., 301aN may be collectively referred to as quantum bit device 301. Each of quantum bit devices 301 resonates in response to a current supplied from current source 201. Quantum bit device 301 represents a quantum bit device. For example, quantum bit device 301 includes circuit 600 having a SQUID shown in Fig. 2.

[0040] The above-described processing performed by the processing system 1 according to the embodiment of the present disclosure is merely an example, and the processing system 1 is not limited to the above-described processing. For example, the processing system 1 may perform the processing described below.

[0041] (Processing performed by the processing system of the present disclosure) 5 is a diagram illustrating an example of a processing flow of the processing system 1 according to some embodiments of the present disclosure. Here, the processing of steps S1 to S7 for adjusting the oscillation frequency of the quantum bit device 301 performed by the processing system 1 illustrated in FIG. 5 will be described.

[0042] (Processing in step S1) Step S1 is a process for measuring the current value dependency of the resonance frequency f(Φext) In step S1, values ​​of the diagonal elements of the inductance matrix Mv are found.

[0043] The processing system 1 measures the current value dependency of the resonant frequency f(Φext) of each quantum bit device. Specifically, the control and calculation device 10 outputs the measurement conditions under which the frequency measurement device 202 of the control and measurement device 20 performs measurements to the frequency measurement device 202. Examples of the measurement conditions include the strength of the signal output to each quantum bit device 301, and measurement items such as reflection measurement and equivalent measurement. The control and calculation device 10 also outputs to the current source 201 the current value of the current that each current source 201 of the control and measurement device 20 outputs to the corresponding quantum bit device 301. The current source 201 changes the current value for each measurement of quantum bit devices 1 to N, ie, quantum bit devices 301a1 to 301aN.

[0044] Here, the current value of the current flowing through the a-th quantum bit device of quantum bit devices 301a1-301aN is denoted as ia. In this case, while current source 201 changes current value ia, frequency measurement device 202 measures the resonant frequency f(Φext) of the a-th quantum bit device in accordance with the measurement conditions. At this time, the current values ​​of quantum bit devices other than the a-th quantum bit device being measured are all set to a constant value, for example, 0. Note that current value ia and the measurement conditions are set in advance by a person in control / calculation device 10.

[0045] FIG. 6 illustrates an example of measurement results obtained by the frequency measurement device 202 according to some embodiments of the present disclosure. The example of the measurement results illustrated in FIG. 6 is a measurement result for an asymmetric SQUID in which the critical current values ​​of the two Josephson junctions of the SQUID are different, similar to the magnetic field dependence of the resonant frequency of the quantum bit device illustrated in FIG. 3 . In FIG. 6 , the horizontal axis represents the current value. The vertical axis represents the resonant frequency f(Φext). The frequency measurement device 202 obtains one resonant frequency as a measurement result for one current value ia. That is, the frequency measurement device 202 obtains one of the points illustrated in FIG. 6 by performing a reflection measurement or a transmission measurement on the a-th quantum bit device 301a1-301aN. Then, the frequency measurement device 202 performs similar measurements on all of the quantum bit devices 301a1-301aN to obtain N measurement results that can be used to plot a graph such as that illustrated in FIG. 6 . The frequency measurement device 202 outputs the N measurement results to the control and calculation device 10.

[0046] Each quantum bit device 301 includes a circuit 600 shown in FIG. 2. It is known that the resonant frequency f(Φext) is determined by the linear inductance Lk, capacitance C, and critical current values ​​Ic1 and Ic2 of the Josephson junction Jj of the circuit. Therefore, for example, the critical current values ​​Ic1 and Ic2 can be calculated by fitting data points (i.e., measurement results at N points measured by the frequency measurement device 202) to analytical formula (3). Furthermore, for example, the current value required to change the magnetic flux by Φ0 can be calculated based on the periodicity of the resonant frequency f(Φext). Note that any method may be used here as long as it can obtain a function that reproduces the magnetic field dependence of the resonant frequency f(Φext). Therefore, the critical current values ​​Ic1 and Ic2 are not limited to being calculated by fitting data points to formula (3). For example, parameters other than those described above may be used as the data points, and formulas other than formula (3) suitable for those parameters may be used. Furthermore, other methods may also be used.

[0047] The control and calculation device 10 calculates the critical current values ​​Ic1 and Ic2 of the Josephson junction Jj in the circuit 600 for each of the quantum bit devices 301 by fitting the measurement results at N points measured by the frequency measurement device 202 to equation (3). Then, for each of the quantum bit devices 301, the control and calculation device 10 calculates the dependency f(Φext_a)_a of the resonant frequency f(Φext) and the magnetic flux Φext, and the dependency Φext(ia)_a of the magnetic flux Φext and the current value ia for all of the quantum bit devices 301a1 to 301aN, as in equations (3) and (4).

[0048] Therefore, frequency measurement apparatus 202 performs reflection measurements, transmission measurements, etc. on all of quantum bit devices 301a1-301aN to determine the dependence f(Φext_a)_a between resonance frequency f(Φext) and magnetic flux Φext, and the dependence Φext(ia)_a between magnetic flux Φext(i) and current value i for the a-th quantum bit device of quantum bit device 301. Then, inductance component M_aa of the a-th bit in inductance matrix Mv shown in equation (7) is determined. Furthermore, residual magnetic flux component Φoff_a of the a-th bit in residual magnetic flux matrix Φoffv for the a-th quantum bit device 301 can also be determined using the magnetic flux at current value ia=0.

[0049] (Processing of step S2) Step S2 is a process for measuring the magnitude of mutual inductance. In step S2, values ​​of the non-diagonal elements of the inductance matrix Mv other than the diagonal elements calculated in step S1 are calculated.

[0050] To determine the mutual inductance M_ab between the a-th quantum bit device 301 and the port of the b-th quantum bit device 301, the frequency measurement apparatus 202 measures the resonant frequency f(Φext) of the a-th quantum bit device 301 according to the measurement conditions while changing the current value ib of the current passed by the current source 201 to the b-th quantum bit device 301. The measurement of the resonant frequency f(Φext) of the a-th quantum bit device 301 is performed by a reflection measurement, a transmission measurement, or the like. The current value ia and the measurement conditions are set in advance by a human in the control / computation apparatus 10. The b-th quantum bit device 301 is one of the quantum bit devices 301 other than the a-th quantum bit device 301. In this measurement, the current value passed to the quantum bit devices 301 other than the b-th quantum bit device 301 is set to a constant value. For example, the current value ia of the current passed to the a-th quantum bit device 301 is set so that the magnetic flux in the SQUID loop is Φ0 / 4, and the current values ​​passed to all the other quantum bit devices 301 are set to 0. By keeping the magnetic flux Φext inside the SQUID loop of the a-th quantum bit device 301 to be measured finite, it is possible to increase the amount of change in the resonant frequency f(Φext) when the magnetic flux Φext changes. Frequency measurement device 202 performs similar measurements on all of quantum bit devices 301a1 to 301aN. Frequency measurement device 202 then outputs the measurement results to control and calculation device 10.

[0051] When all current values ​​other than current values ​​ia and ib are 0, magnetic flux Φext_a of the a-th quantum bit device 301 is expressed as in equation (12).

[0052]

number

[0053] The control and calculation unit 10 calculates M_ab using the relationship between the resonant frequency f(Φext)_a of the a-th quantum bit device 301 measured in step S1 and the internal magnetic flux Φext_a, and equation (12).

[0054] (Processing of step S3) Step S3 is a process for calculating the magnetic flux to be set. The control / computation device 10 calculates the magnetic flux Φtarget_a to be set by solving ftarget_a=f(Φtarget_a)_a for the resonant frequency ftarget_a to be set for each quantum bit device 301.

[0055] The resonant frequency f(Φext_a)_a is generally an even function. Therefore, f(Φext_a) = f(-Φext_a)_a. Furthermore, taking into account the periodicity of the resonant frequency f(Φext_a)_a, the magnetic flux to be set is Φtarget_a + nΦ0 or -Φtarget_a + nΦ0, where n is an integer. Generating a large magnetic flux results in excessive current flow, which is undesirable for superconducting devices. Therefore, it is desirable to set the range of the magnetic flux Φtarget_a as -Φ0 / 2<Φtarget_a<Φ0 / 2. Furthermore, the required current value differs depending on the combination of the magnetic flux signs. For example, if there are N quantum bit devices 301, there are 2^N possible combinations. However, as the number N of quantum bit devices 301 increases, the number of calculations increases exponentially. Therefore, when there are many quantum bit devices 301, in order to reduce the number of calculations and to reduce changes in the current value of the current flowing from current source 201 to quantum bit devices 301, the sign of Φtarget_a to be set is determined according to the sign of the residual magnetic flux Φoff_a of each quantum bit device 301. For example, in the case of a quantum bit device 301 in which the magnetic flux Φ0 is affected in the positive direction due to crosstalk, the resonant frequency that exists in the range of magnetic flux Φ0 on the positive side within the range of -Φ0 / 2<Φtarget_a<Φ0 / 2 is set to Φtarget_a.

[0056] It is preferable that the control / calculation device 10 performs the calculation 2^N times to identify the smallest current and set the identified current value as the final current value. Therefore, the control / calculation device 10 may set all combinations of current values ​​to the current source 201, perform the calculation 2^N times to identify the smallest current, and set the identified current value as the final current value.

[0057] (Processing of step S4) Step S4 is a process for calculating the current value to be set. The control and calculation device 10 calculates the current value to be set according to equation (11). At this time, the control and calculation device 10 calculates the current value according to the sign of Φtarget_a determined in step S3 according to the sign of the residual magnetic flux Φoff_a of each quantum bit device 301. As another example, the control and calculation device 10 may calculate the current value for all combinations of the signs of the magnetic fluxes described above, and then redefine the sign combination that minimizes the sum of squares of the calculated current values ​​as the sign of each element of Φtarget.

[0058] (Processing in step S5) Step S5 is a process for measuring the resonant frequency f(Φext). The control and calculation device 10 sets the current value calculated in step S4 for each of the current sources 201. Each of the current sources 201 passes a current of the set current value through the corresponding quantum bit device 301. Then, similar to the measurement of the resonant frequency f(Φext) in step S1, the frequency measurement device 202 measures the resonant frequency f(Φext) by measuring the reflection or transmission of the a-th quantum bit device 301 according to the measurement conditions. The frequency measurement device 202 outputs the measurement result to the control and calculation device 10.

[0059] (Processing in step S6) Step S6 is a process for making a judgment. The control and calculation device 10 calculates Δf_a=fmeasure_a-ftarget_a, where fmeasure_a is the resonance frequency f(Φext) measured by the frequency measurement device 202 in step S5. The control and calculation device 10 judges whether the calculated Δf_a is within a predetermined allowable error range. If the control and calculation device 10 judges that Δf_a is within the predetermined allowable error range, it ends the process. On the other hand, if the control and calculation device 10 judges that Δf_a is outside the predetermined allowable error range, it proceeds to the process of step S7.

[0060] (Processing in step S7) Step S7 is a process for updating the residual magnetic flux. The control and calculation device 10 updates the value of the residual magnetic flux Φoff based on fmeasure_a, which is the resonance frequency f(Φext) measured by the frequency measurement device 202 in step S5. For example, the control and calculation device 10 solves fmeasure_a=f(Φmeasure_a)_a using the relationship f(Φext_a)_a obtained in step S1. This allows the control and calculation device 10 to obtain the current magnetic flux Φmeasure_a. Furthermore, using the current input value iv and inductance matrix Mv, a new residual magnetic flux [Φ]_offv can be expressed as in equation (13).

[0061]

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[0062] The control and calculation device 10 substitutes the new residual magnetic flux [Φ]_offv shown in equation (13) into Φoffv in equation (11) and calculates the current value in the same way as in step S4.

[0063] By going through the above process, it is possible to correct minute changes in residual magnetic flux caused by current flowing through the port of each quantum bit device 301, and to set the frequencies of all quantum bit devices simultaneously.

[0064] (advantage) The processing system 1 according to one embodiment of the present disclosure has been described above. The processing system 1 includes a control and calculation device 10 (an example of a calculation means) that calculates a first current value, which is the current value of a current to be passed through a circuit 600 (an example of a resonant circuit) included in a quantum bit device 301, based on the value of residual magnetic flux Φoff in the circuit 600. The processing system 1 can adjust the resonant frequency with high precision.

[0065] <Modifications of the embodiment> A processing system 1 according to a modified example of an embodiment of the present disclosure will be described. The processing system 1 according to a modified example of an embodiment of the present disclosure is a system that reuses the results of measurements of resonance frequencies that have been performed in the past. The results of measurements of resonance frequencies that have been performed in the past are, for example, the results of measurements of steps S1 and S2 performed by the processing system 1 in the embodiment of the present disclosure, and are measurement results that can exhibit the relationships shown in FIGS. 3 and 6. The inductance matrix Mv, the resonance frequency, and the magnetic flux dependency f(Φext_a)_a are determined by the structure of the quantum bit device 301. Therefore, the results of measurements that have been performed in the past can be reused.

[0066] (Processing system configuration) A processing system 1 according to a modified embodiment of the present disclosure has a configuration similar to that of the processing system 1 shown in FIG. 4. For example, when a quantum chip 30 including a quantum bit device 301 is once returned to a non-cryogenic state and then returned to a cryogenic state, only the residual magnetic flux Φoff changes. Therefore, the processing system 1 can complete frequency adjustment in a short time by reusing the results of previous resonant frequency measurements and updating only the residual magnetic flux Φoff. Specifically, for example, reusing the results of previous resonant frequency measurements by the processing system 1 is useful when, for example, the quantum chip 30 is transferred to a cryogenic refrigerator installed for quantum computing after evaluating its characteristics in a cryogenic refrigerator installed for basic characteristic evaluation. Furthermore, when a cryogenic refrigerator is operated for a long period of time, it may be necessary to remove impurities from the circulating gas. In this way, reusing the results of previous resonant frequency measurements is useful even when the inside of the cryogenic refrigerator is no longer in a cryogenic state.

[0067] (Processing performed by the processing system) 7 is a diagram illustrating an example of a processing flow of the processing system 1 according to some embodiments of the present disclosure. Here, a description will be given of the processing of step S8 that the processing system 1 illustrated in FIG. 7 performs instead of the processing of step S1 and the processing of step S2 in the processing flow illustrated in FIG.

[0068] (Processing of step S8) Step S8 is a process for measuring the initial value of the residual magnetic flux. In the processing system 1, the control and calculation device 10 outputs to the frequency measurement device 202 the measurement conditions under which the frequency measurement device 202 of the control and measurement device 20 performs measurements. Examples of the measurement conditions include the strength of the signal output to each quantum bit device 301, and measurement items such as reflection measurement and equivalent measurement. The control and calculation device 10 also outputs to the current source 201 the current value of the current that each current source 201 of the control and measurement device 20 outputs to the corresponding quantum bit device 301. The current source 201 changes the current value for each measurement of quantum bit devices 1 to N, 301a1 to 301aN.

[0069] While current source 201 changes current value ia, frequency measurement apparatus 202 measures the resonant frequency f(Φext) for the a-th quantum bit device in accordance with the measurement conditions. At this time, the current values ​​of quantum bit devices other than the a-th quantum bit device being measured are all constant, for example, 0. Note that, unlike step S1, in step S8, the inductance matrix Mv determined by the structure of quantum bit device 301 and the dependence f(Φext_a)_a of the resonant frequency and magnetic flux are already known. Therefore, while current source 201 changes current value ia, frequency measurement apparatus 202 only needs to measure the resonant frequency f(Φext) for two or more a-th quantum bit devices in accordance with the measurement conditions.

[0070] If current source 201 varies current value ia while frequency measurement device 202 measures the resonant frequency f(Φext) of only one a-th quantum bit device according to the measurement conditions, it is possible to measure the absolute value of residual magnetic flux Φoff. However, in this case, it is impossible to determine the sign of residual magnetic flux Φoff. For example, let i(a, 1 / 10) be the current value that changes the magnetic flux in the SQUID of a-th quantum bit device 301 by Φ0 / 10. In this case, the sign of residual magnetic flux Φoff is determined from the resonant frequency f(Φext) when ia = 0 and the resonant frequency f(Φext) when ia = i(a, 1 / 10). However, if residual magnetic flux Φoff is approximately 0, it is difficult to distinguish whether the sign of residual magnetic flux Φoff is positive or negative. However, in such a case, regardless of the sign of residual magnetic flux Φoff, the residual magnetic flux can be set to the correct value in the process of updating the residual magnetic flux in step S7. This is not actually a problem. After performing the process of step S8, the processing system 1 performs the same processes as the processes of steps S3 to S7 described in the embodiment of the present disclosure.

[0071] (advantage) The processing system 1 according to a modified example of an embodiment of the present disclosure has been described above. In the processing system 1, the results of previous measurements of the resonant frequency are reused, and while the current source 201 changes the current value ia, the frequency measurement device 202 measures the resonant frequency f(Φext) for two or more a-th quantum bit devices according to the measurement conditions. This processing system 1 can reduce processing and complete adjustment of the resonant frequency in a short time.

[0072] <Another modified example of the embodiment> In one embodiment and a variation of the embodiment of the present disclosure, the circuit 600 has been described as including an inductor 601, Josephson junctions 602a and 602b, and a capacitor 603, as shown in FIG. 2 . However, the circuit 600 is not limited to the circuit shown in FIG. 2 . For example, the circuit 600 may include a SQUID having one or more Josephson junctions in series with parallel-connected Josephson junctions. FIG. 8 is a diagram illustrating an example of the circuit 600 according to some embodiments of the present disclosure. In another variation of the embodiment of the present disclosure, for example, the circuit 600 may include an inductor 601, Josephson junctions 602a, 602b, 602c, and 602d, and a capacitor 603, as shown in FIG. 8 . The circuit 600 shown in FIG. 8 includes a SQUID in which two Josephson junctions 602c and 602d are connected in series with the parallel-connected Josephson junctions 602a and 602b of the SQUID shown in FIG. 2 . In the case of the circuit 600 shown in FIG. 8, it is necessary to modify equation (3) by the amount of the two Josephson junctions 602c and 602d connected in series.

[0073] The processing system 1 according to each of the above-described embodiments of the present disclosure has been described as having multiple quantum bit devices and performing processing using a matrix. However, a processing system 1 according to another embodiment of the present disclosure can perform processing even when there is only one quantum bit device. In this case, the processing system 1 according to another embodiment of the present disclosure simply treats Φextv, Mv, Φoffv, and iv in the above equations as one row and one column, and performs the same procedure as the processing system 1 according to each of the above-described embodiments of the present disclosure. However, the first term on the right side of equation (11) is not the inverse matrix of Mv but its reciprocal, and the processing system 1 according to another embodiment of the present disclosure skips step S2, which calculates the off-diagonal elements of the matrix. Note that residual magnetic flux can occur even when there is only one quantum bit device. Therefore, it is meaningful for a processing system 1 according to another embodiment of the present disclosure to perform the process of setting the residual magnetic flux to a correct value, as described in each of the above-described embodiments of the present disclosure, even when there is only one quantum bit device.

[0074] 9 is a diagram illustrating an example of a configuration of a processing system 1 according to some embodiments of the present disclosure. As shown in FIG.

[0075] The calculation means 701 calculates a first current value, which is the current value of the current to be passed through a resonant circuit, based on the value of the residual magnetic flux in the resonant circuit of the quantum bit device.

[0076] The calculation means 701 can be realized, for example, by using the functions of the control and calculation device 10 illustrated in FIG.

[0077] Next, processing performed by the processing system 1 according to some embodiments of the present disclosure will be described. Fig. 10 is a diagram showing an example of a processing flow of the processing system 1 according to some embodiments of the present disclosure. Here, the processing of the processing system 1 will be described with reference to Fig. 10.

[0078] The calculation means 701 calculates a first current value, which is the current value of a current to be passed through a resonant circuit, based on the value of residual magnetic flux in the resonant circuit of the quantum bit device (step S101).

[0079] The processing system 1 according to some embodiments of the present disclosure has been described above. The processing system 1 allows the resonant frequency to be adjusted with high precision.

[0080] The order of the processes in each embodiment of the present disclosure may be changed as long as the processes are performed appropriately.

[0081] Each embodiment of the present disclosure has been described, but the above-mentioned processing system 1, control and calculation device 10, control and measurement device 20, and other control devices may have a computer system inside. The above-mentioned processing steps are stored in the form of a program on a computer-readable recording medium, and the above processing is performed by reading and executing this program by a computer. Specific examples of computers are shown below.

[0082] 11 is a schematic block diagram showing the configuration of a computer according to at least one embodiment. As shown in FIG. 11, the computer 5 includes a CPU (Central Processing Unit) 6, a main memory 7, a storage 8, and an interface 9.

[0083] For example, the above-mentioned processing system 1, control and calculation device 10, control and measurement device 20, and other control devices are each implemented in a computer 5. The operations of each of the above-mentioned processing units are stored in the form of a program in a storage 8. A CPU 6 reads the program from the storage 8, loads it into the main memory 7, and executes the above-mentioned processing in accordance with the program. The CPU 6 also allocates storage areas in the main memory 7 corresponding to each of the above-mentioned storage units in accordance with the program.

[0084] Examples of storage 8 include a hard disk drive (HDD), a solid state drive (SSD), a magnetic disk, a magneto-optical disk, a compact disc read-only memory (CD-ROM), a digital versatile disc read-only memory (DVD-ROM), and a semiconductor memory. Storage 8 may be an internal medium directly connected to the bus of computer 5, or an external medium connected to computer 5 via interface 9 or a communication line. In addition, when this program is distributed to computer 5 via a communication line, computer 5 that receives the program may load the program into main memory 7 and execute the above-mentioned processing. In at least one embodiment, storage 8 is a non-transitory tangible storage medium.

[0085] The program may also implement some of the functions described above. Furthermore, the program may be a file that can implement the functions described above in combination with a program already recorded in the computer system, a so-called differential file (differential program).

[0086] Although several embodiments of the present disclosure have been described, these embodiments are merely examples and do not limit the scope of the disclosure. Various additions, omissions, substitutions, and modifications may be made to these embodiments without departing from the spirit of the disclosure.

[0087] Note that part or all of the above-described embodiments can be described as, but are not limited to, the following supplementary notes.

[0088] (Appendix 1) a calculation means for calculating a first current value, which is a current value of a current to be passed through a resonant circuit included in the quantum bit device, based on a value of residual magnetic flux in the resonant circuit; A processing system comprising:

[0089] (Appendix 2) The calculation means calculating the first current value based on a matrix having elements determined based on a measurement result of the resonant frequency of the resonant circuit; 10. The processing system of claim 1.

[0090] (Appendix 3) a first setting means for setting the first current value as a current value of a current source that supplies a current to the resonant circuit; 3. The processing system of claim 1 or 2, comprising:

[0091] (Appendix 4) The calculation means calculating the first current value using the corrected value of the residual magnetic flux as the value of the residual magnetic flux in the resonant circuit; 4. The processing system of any one of claims 1 to 3.

[0092] (Appendix 5) a second setting means for setting the first current value calculated by the calculation means as a current value of a current source that supplies a current to the resonant circuit; 5. The processing system of claim 4, comprising:

[0093] (Appendix 6) a first measuring means for measuring the resonant frequency of the resonant circuit; 6. The processing system of any one of appendices 2 to 5, comprising:

[0094] (Appendix 7) a second measuring means for measuring the initial value of the residual magnetic flux; 7. The processing system of any one of claims 1 to 6, comprising:

[0095] (Appendix 8) calculating a first current value, which is a current value of a current to be passed through a resonant circuit, based on a matrix having elements determined based on a measurement result of a resonant frequency of the resonant circuit included in the quantum bit device and a value of residual magnetic flux in the resonant circuit; A processing method comprising:

[0096] (Appendix 9) calculating the first current value based on a matrix having elements determined based on a measurement result of a resonant frequency of the resonant circuit; Attachment 8, a processing method comprising:

[0097] (Appendix 10) setting the first current value as a current value of a current source that supplies a current to the resonant circuit; 10. The method of claim 8 or 9,

[0098] (Appendix 11) calculating the first current value using the corrected value of the residual magnetic flux as the value of the residual magnetic flux in the resonant circuit; 11. The processing method according to any one of appendices 8 to 10,

[0099] (Appendix 12) setting the calculated first current value as a current value of a current source that supplies a current to the resonant circuit; 12. The method of claim 11, comprising:

[0100] (Appendix 13) measuring the resonant frequency of the resonant circuit; 13. The processing method according to any one of appendices 9 to 12, including:

[0101] (Appendix 14) measuring an initial value of the residual magnetic flux; 14. The processing method according to any one of claims 8 to 13,

[0102] (Appendix 15) On the computer, calculating a first current value, which is a current value of a current to be passed through a resonant circuit, based on a matrix having elements determined based on a measurement result of a resonant frequency of the resonant circuit included in the quantum bit device and a value of residual magnetic flux in the resonant circuit; A program that executes the following.

[0103] (Appendix 16) calculating the first current value based on a matrix having elements determined based on a measurement result of a resonant frequency of the resonant circuit; 16. The program according to claim 15, which causes the computer to execute the above steps.

[0104] (Appendix 17) setting the first current value as a current value of a current source that supplies a current to the resonant circuit; 17. The program according to claim 15 or 16, which causes the computer to execute the above.

[0105] (Appendix 18) calculating the first current value using the corrected value of the residual magnetic flux as the value of the residual magnetic flux in the resonant circuit; 18. The program according to any one of appendices 15 to 17, which causes the computer to execute the above.

[0106] (Appendix 19) setting the calculated first current value as a current value of a current source that supplies a current to the resonant circuit; 19. The program according to claim 18, which causes the computer to execute the above steps.

[0107] (Appendix 20) measuring the resonant frequency of the resonant circuit; 20. The program according to any one of appendices 16 to 19, which causes the computer to execute the above.

[0108] (Appendix 21) measuring an initial value of the residual magnetic flux; 21. The program according to any one of appendices 15 to 20, which causes the computer to execute the above. [Explanation of symbols]

[0109] 1. Processing System 5. Computer 6 CPU 7. Main memory 8. Storage 9. Interface 10. Control and computing device 20. Control and measurement equipment 30. Quantum chip 201, 201a1, 201a2, 201aN...Current source 301, 301a1, 301a2, 301aN···Qubit device 500, 600... circuits 501, 602a, 602b Josephson junction 502, 603... Capacitor 601···Inductor

Claims

1. a calculation means for calculating a first current value, which is a current value of a current to be passed through a resonant circuit included in the quantum bit device, based on a value of residual magnetic flux in the resonant circuit; A processing system comprising:

2. The calculation means calculating the first current value based on a matrix having elements determined based on a measurement result of the resonant frequency of the resonant circuit; The processing system of claim 1 .

3. a first setting means for setting the first current value as a current value of a current source that supplies a current to the resonant circuit; The processing system of claim 1 , comprising:

4. The calculation means calculating the first current value using the corrected value of the residual magnetic flux as the value of the residual magnetic flux in the resonant circuit; The processing system of claim 1 .

5. a second setting means for setting the first current value calculated by the calculation means as a current value of a current source that supplies a current to the resonant circuit; The processing system of claim 4 , comprising:

6. a first measuring means for measuring the resonant frequency of the resonant circuit; The processing system of claim 2 , comprising:

7. a second measuring means for measuring the initial value of the residual magnetic flux; The processing system of claim 1 , comprising:

8. calculating a first current value, which is a current value of a current to be passed through a resonant circuit included in the quantum bit device, based on a value of residual magnetic flux in the resonant circuit; A processing method comprising:

9. On the computer, calculating a first current value, which is a current value of a current to be passed through a resonant circuit included in the quantum bit device, based on a value of residual magnetic flux in the resonant circuit; A program that executes the following.

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