Quantum gate device, superconducting quantum gate device, quantum computer, and quantum gate operation method

Abstract

A quantum gate device 1 comprises: a quantum bit substrate unit 10 on which at least two data quantum bits, namely, a first data quantum bit 11 and a second data quantum bit 12, and a coupler quantum bit 13 disposed between the first data quantum bit 11 and the second data quantum bit 12 are mounted; and a pulse irradiation unit 20 that irradiates the coupler quantum bit 13 with a drive pulse. When the resonance frequency of the first data quantum bit 11 in a first excitation state is ω1, the resonance frequency of the second data quantum bit 12 in the first excitation state is ω2, and the resonance frequency of the coupler quantum bit 13 in the first excitation state is ωc, the pulse irradiation unit 20 irradiates the coupler quantum bit 13 with a first cross-Rabi transition drive pulse defined by the frequency ωc+|ω1-ω2|, and with a residual ZZ interaction-erasing drive pulse of the frequency ωc+|ω1-ω2|-δ that is shifted by a predetermined frequency δ from the first cross-Labi transition drive pulse. The predetermined frequency shift δ is a value that erases a residual ZZ interaction between the first data quantum bit 11 and the second data quantum bit 12.

Description

[Technical Field]

[0001] The present invention relates to a quantum gate device, a superconducting quantum gate device, a quantum computer, and a quantum gate operation method. [Background technology]

[0002] It is known that operations in a quantum computer can be realized by combining a set of quantum gates consisting of one quantum gate and two quantum gates, i.e., a "universal quantum gate set," with readout elements for individual quantum bits (e.g., Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] "Progress and Applications of Superconducting Qubit Research," Yasunobu Nakamura, Applied Physics, Vol. 90, No. 4 (2021) https: / / www.jstage.jst.go.jp / article / oubutsu / 90 / 4 / 90_209 / _pdf [Non-patent document 2] “A universal gate for fixed-frequency qubits via a tunable bus”, David C. McKay, etc. Phys. Rev. Applied 6, 064007 (2016)https: / / arxiv.org / pdf / 1604.03076.pdf Summary of the Invention [Problem to be solved by the invention]

[0004] Tunable interactions are a key element for building well-controlled superconducting quantum processors. A promising approach for this is to use frequency-locked superconducting qubits with high coherence. However, in frequency-locked qubits, always-on residual interactions have limited the control precision. Single-quantum gates are typically performed by inducing Rabi oscillations using microwave pulses resonating between two levels with a time width of approximately 10–20 ns. In contrast, two-quantum gates generally require longer gate operations than single-quantum gates and are therefore more susceptible to decoherence. In particular, in two-quantum gates, residual ZZ interactions exist even when gate operations are not being performed due to coupling between qubits. This is undesirable because it can cause errors that reduce the precision of gate control. Therefore, the challenge is how to eliminate the residual ZZ interactions.

[0005] One method proposed to eliminate the residual ZZ interaction is to use a DC-SQUID to change the resonant frequency of the coupling element or data quantum bit (for example, Non-Patent Document 2). However, this method has the problem that the quantum processor is responsive to external magnetic flux, which causes it to be affected by magnetic flux noise, shortening the coherence time.

[0006] The present invention has been made in view of these problems, and its purpose is to provide a technology that can eliminate the residual ZZ interaction and realize two-quantum gate operation without requiring an external magnetic flux. [Means for solving the problem]

[0007] In order to solve the above problems, a quantum gate device according to one embodiment of the present invention includes a qubit substrate unit that mounts at least two data qubits, i.e., a first data qubit and a second data qubit, and a coupler qubit disposed between the first data qubit and the second data qubit, and a pulse irradiation unit that irradiates the coupler qubits with a drive pulse, where ω1 is the resonant frequency of the first excited state of the first data qubit, ω2 is the resonant frequency of the first excited state of the second data qubit, and ω is the resonant frequency of the first excited state of the coupler qubit. c , the pulse irradiation unit has a frequency ω c + |ω1-ω2|, and the frequency ω, which is a predetermined frequency δ shift from the first cross Rabi transition drive pulse. c +|ω1-ω2|-δ, a residual ZZ interaction erasing drive pulse, and the predetermined frequency shift δ is a value that erases the residual ZZ interaction between the first data qubit and the second data qubit.

[0008] According to this embodiment, it is possible to provide a device that can eliminate residual ZZ interaction and realize two-quantum gate operation without requiring an external magnetic flux.

[0009] Another aspect of the present invention is a quantum gate device. This quantum gate device includes a qubit substrate unit that mounts at least two data qubits, i.e., a first data qubit and a second data qubit, and a coupler qubit disposed between the first data qubit and the second data qubit, and a pulse irradiation unit that irradiates the coupler qubit with a drive pulse. The resonant frequency of the first excited state of the first data qubit is ω1, the resonant frequency of the first excited state of the second data qubit is ω2, and the resonant frequency of the first excited state of the coupler qubit is ω. c , the pulse irradiation unit has a frequency ω c The second cross Rabi transition drive pulse defined by -|ω1-ω2| and the frequency ω shifted by a predetermined frequency δ from the second cross Rabi transition drive pulse. cand irradiating the coupler qubit with a residual ZZ interaction erasing drive pulse of −|ω1−ω2|−δ, where the predetermined frequency shift δ is a value that erases the residual ZZ interaction between the first data qubit and the second data qubit.

[0010] According to this embodiment, it is possible to provide a device that can eliminate residual ZZ interaction and realize two-quantum gate operation without requiring an external magnetic flux.

[0011] In an embodiment, the pulse irradiator may irradiate the coupler qubit with both the first crossed Rabi transition drive pulse and the second crossed Rabi transition drive pulse, and a residual ZZ interaction erasing drive pulse.

[0012] In an embodiment, the first cross-Rabi transition drive pulse may implement a controlled phase gate between the first data qubit and the second data qubit.

[0013] In an embodiment, the second cross-Rabi transition drive pulse may implement a controlled phase gate between the first data qubit and the second data qubit.

[0014] In an embodiment, the system may further include a capacitor coupling the first data qubit and the second data qubit. The predetermined frequency shift δ may be a value that eliminates residual ZZ interactions between the first data qubit and the second data qubit and cross-resonances between the first data qubit and the second data qubit.

[0015] In one embodiment, the quantum bit substrate portion may mount, on a two-dimensional plane, three or more data quantum bits, coupler quantum bits arranged between adjacent data quantum bits, coupler control ports for controlling the coupler quantum bits, and readout ports for reading out the data quantum bits.

[0016] In one embodiment, the quantum bit substrate portion may include data quantum bits arranged in a square lattice pattern, coupler quantum bits arranged in a square lattice pattern between adjacent data quantum bits, a coupler control port arranged at the center of the square lattice of the coupler quantum bits for controlling the coupler quantum bits, and a readout port arranged at the center of the square lattice of the data quantum bits for reading out the data quantum bits.

[0017] In one embodiment, the quantum bit substrate portion may have mounted on a two-dimensional plane three or more data quantum bits, coupler quantum bits arranged between adjacent data quantum bits, coupler control ports for controlling the coupler quantum bits, readout ports for reading out the data quantum bits, and one-qubit control ports for controlling one quantum bit of the data quantum bits.

[0018] In one embodiment, the quantum bit substrate portion may include data quantum bits arranged in a square lattice pattern, coupler quantum bits arranged in a square lattice pattern between adjacent data quantum bits, a coupler control port arranged at the center of the square lattice of the coupler quantum bits and controlling the coupler quantum bits, a read port arranged at the center of the square lattice of the data quantum bits and reading out the data quantum bits, and a one-qubit control port arranged at the center of the square lattice of the data quantum bits and controlling one quantum bit of the data quantum bits.

[0019] In one embodiment, the quantum gate device may further include a one-qubit control port located at the center of the square lattice of data qubits for providing one-qubit control of the data qubits.

[0020] In an embodiment, the first data qubit, the second data qubit, and the coupler qubit may be superconducting qubits.

[0021] Another aspect of the present invention is a superconducting quantum gate device, which includes the quantum gate device described above and a refrigerator for cooling and operating the quantum bit substrate portion.

[0022] According to this embodiment, it is possible to realize a superconducting quantum gate device that enables removal of residual ZZ interaction and two-quantum gate operation without requiring an external magnetic flux.

[0023] Yet another aspect of the present invention is a quantum computer, which includes the above-described superconducting quantum gate device and a control unit that controls the superconducting quantum gate device.

[0024] According to this embodiment, it is possible to realize a quantum computer that enables removal of residual ZZ interaction and two-quantum gate operation without requiring an external magnetic flux.

[0025] Another aspect of the present invention is a quantum gate operation method for a qubit system including at least two data qubits, i.e., a first data qubit and a second data qubit, and a coupler qubit disposed between the first and second data qubits, wherein the resonant frequency of the first excited state of the first data qubit is ω1, the resonant frequency of the first excited state of the second data qubit is ω2, and the resonant frequency of the first excited state of the coupler qubit is ω c , this method can be used to c +|ω1-ω2| is irradiated onto the coupler qubit with a first cross Rabi transition drive pulse defined by the frequency ω that is shifted by a predetermined frequency δ from the first cross Rabi transition drive pulse. c and irradiating the coupler qubit with a residual ZZ interaction erasing drive pulse of +|ω1-ω2|-δ, where the predetermined frequency shift δ is a value that erases residual ZZ interaction between the first data qubit and the second data qubit.

[0026] According to this embodiment, it is possible to remove the residual ZZ interaction and perform two-quantum gate operation without requiring an external magnetic flux.

[0027] Another aspect of the present invention is also a quantum gate operation method for a qubit system including at least two data qubits, i.e., a first data qubit and a second data qubit, and a coupler qubit disposed between the first data qubit and the second data qubit, wherein the resonant frequency of the first excited state of the first data qubit is ω1, the resonant frequency of the first excited state of the second data qubit is ω2, and the resonant frequency of the first excited state of the coupler qubit is ω c , this method can be used to c - a step of irradiating a second cross Rabi transition drive pulse defined by |ω1-ω2| to the coupler qubit, and a frequency ω shifted by a predetermined frequency δ from the second cross Rabi transition drive pulse. c and irradiating the coupler qubit with a residual ZZ interaction erasing drive pulse of -|ω1-ω2|-δ, where the predetermined frequency shift δ is a value that erases residual ZZ interaction between the first data qubit and the second data qubit.

[0028] According to this embodiment, it is possible to remove the residual ZZ interaction and perform two-quantum gate operation without requiring an external magnetic flux.

[0029] Another aspect of the present invention is a quantum gate device. The quantum gate device includes a qubit substrate unit that mounts at least two data qubits, i.e., a first data qubit and a second data qubit, and a coupler qubit disposed between the first data qubit and the second data qubit, and a pulse irradiation unit that irradiates the coupler qubit with a drive pulse. When the resonant frequency of the first excited state of the first data qubit is ω1 and the resonant frequency of the first excited state of the second data qubit is ω2, the pulse irradiation unit performs a first quantum gate operation by irradiating the coupler qubit with microwaves defined by frequency ω1.

[0030] A quantum gate device according to one embodiment includes a qubit substrate unit that mounts at least two data qubits, i.e., a first data qubit and a second data qubit, and a coupler qubit disposed between the first data qubit and the second data qubit, and a pulse irradiation unit that irradiates the coupler qubit with a drive pulse. When the resonant frequency of the first excited state of the first data qubit is ω1 and the resonant frequency of the first excited state of the second data qubit is ω2, the pulse irradiation unit performs a second quantum gate operation by irradiating the coupler qubit with microwaves defined by a frequency ω2.

[0031] According to this embodiment, quantum gate operations can be performed on each data qubit simply by irradiating the coupler qubit with microwaves, without the need to directly control the data qubits.

[0032] Any combination of the above components, and conversion of the present disclosure into a method, device, system, recording medium, computer program, etc., are also valid aspects of the present disclosure. [Effects of the Invention]

[0033] According to the present invention, it is possible to provide a technique for eliminating residual ZZ interactions and realizing two-quantum gate operation without requiring an external magnetic flux. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is a functional block diagram of a quantum gate device according to a first embodiment. [Figure 2] FIG. 2 is an energy level diagram illustrating the energy transitions of the system of FIG. 1. [Figure 3] 1 is a schematic diagram of the geometric phase obtained by cross-Rabi transitions. [Figure 4] FIG. 2 is a schematic diagram illustrating a controlled phase gate acting between a first data qubit and a second data qubit. [Figure 5]FIG. 5 is a schematic diagram showing a pulse sequence when implementing the controlled phase gate of FIG. 4. [Figure 6] FIG. 1 is a schematic diagram showing how the transition frequency of a state relating to a cross Rabi transition is modulated by an AC-Stark shift when a microwave detuned by δ from the cross Rabi transition is applied. [Figure 7] FIG. 10 is a functional block diagram of a quantum gate device according to a second embodiment. [Figure 8] FIG. 1 shows the cross-resonance strength η and residual ZZ interaction as a function of coupling strength for a classical coupler. [Figure 9] FIG. 10 is a plan view of a quantum bit substrate according to a third embodiment. [Figure 10] FIG. 10 is a plan view of a quantum bit substrate portion in which the quantum bits of FIG. 9 are further integrated and arranged in a square lattice pattern. [Figure 11] FIG. 10 is a plan view of a quantum bit substrate according to a fourth embodiment. [Figure 12] FIG. 12 is a plan view of a quantum bit substrate portion in which the quantum bits of FIG. 11 are further integrated and arranged in a square lattice pattern. [Figure 13] FIG. 1 illustrates the frequencies of data qubits and coupler qubits. [Figure 14] FIG. 1 illustrates qubits and frequencies around a coupler control port. [Figure 15] The frequencies used around coupler control port 1 in Figure 9 and the frequencies that cause errors are shown. [Figure 16] The frequencies used around coupler control port 2 in FIG. 9 and the frequencies that result in errors are shown. [Figure 17] FIG. 10 is a functional block diagram of a superconducting quantum gate device according to a fifth embodiment. [Figure 18] FIG. 10 is a functional block diagram of a quantum computer according to a sixth embodiment. [Figure 19] 13 is a flowchart showing the process of a quantum gate operation method according to a seventh embodiment. [Figure 20] This is a photograph of the quantum bit substrate used in the verification experiment. [Figure 21] FIG. 3 shows the experimental results of observing Rabi oscillations between states corresponding to the thin solid arrows in FIG. 2. [Figure 22] FIG. 3 shows the experimental results of observing Rabi oscillations between states corresponding to the thick solid arrows in FIG. 2. [Figure 23] FIG. 10 is a diagram showing the results of evaluating the accuracy of a controlled phase gate by interleaved randomized benchmarking. [Figure 24] This figure shows the results of inducing ZZ interaction by AC Stark shift and eliminating the residual ZZ interaction. DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, parts, and processes shown in each drawing are designated by the same reference numerals, and redundant descriptions will be omitted where appropriate. The scale and shape of each part shown in each drawing are set for convenience to facilitate explanation and should not be interpreted as limiting unless otherwise specified. When terms such as "first" and "second" are used in this specification or claims, unless otherwise specified, these terms do not indicate any order or importance, but are intended only to distinguish one configuration from another. Furthermore, some components that are not important for explaining the embodiments are omitted from each drawing.

[0036] [First embodiment] 1 is a functional block diagram of a quantum gate device 1 according to a first embodiment. The quantum gate device 1 includes a quantum bit substrate unit 10 and a pulse irradiation unit 20.

[0037] Quantum bit substrate unit 10 is equipped with first data qubit 11, second data qubit 12, and coupler qubit 13. Coupler qubit 13 is disposed between first data qubit 11 and second data qubit 12. Coupler qubit 13 is coupled to first data qubit 11 and second data qubit 12 via capacitor 101 and capacitor 102, respectively. First data qubit 11 is configured with Josephson junction 1001 and capacitor 1101 connected in parallel to form a resonant circuit. Second data qubit 12 is configured with Josephson junction 1002 and capacitor 1102 connected in parallel to form a resonant circuit. Coupler qubit 13 is configured with Josephson junction 1003 and capacitor 1103 connected in parallel to form a resonant circuit. That is, in the example of FIG. 1, first data qubit 11, second data qubit 12 and coupler qubit 13 are all configured as frequency-locked transmon qubits.

[0038] The pulse irradiation unit 20 irradiates the coupler qubit 13 with a drive pulse. More specifically, the pulse irradiation unit 20 The resonant frequency of the first excited state of the first data qubit 11 is ω1, The resonant frequency of the first excited state of the second data qubit 12 is ω2, Let ω be the resonance frequency of the first excited state of coupler qubit 13. c , When frequency ω c + the first cross-Rabi transition drive pulse defined by |ω1-ω2|, The frequency ω is shifted by a predetermined frequency δ from the first cross-Rabi transition drive pulse. c +|ω1-ω2|-δ residual ZZ interaction erase drive pulse, is irradiated onto the coupler qubit 13. Here, the predetermined frequency shift δ is a value that eliminates residual ZZ interaction between the first data qubit 11 and the second data qubit 12. The cross-Rabi transition drive pulse will be described in detail below.

[0039] [Cross Rabi Transition Drive Pulse] The Hamiltonian of the system shown in Figure 1 can be modeled by the following equation (1), in which anharmonic oscillators are coupled by the Jaynes-Cummings interaction:

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[0040] Figure 2 is an energy level diagram showing the energy transitions of the system in Figure 1. However, here, only the states up to the excitation number 2 are shown. The brackets indicate, from left to right, the states of the first data qubit, the second data qubit, and the coupler qubit. That is, |Q1Q2>|Q c > c is the first data qubit Q1, the second data qubit Q2, and the coupler qubit Q c The levels indicated by the thick solid lines are the levels used for calculations in the subspace where the coupler qubit is in the ground state. The levels indicated by the thin solid lines represent the subspace where the coupler qubit is in the first excited state.

[0041] When the microwave drive described above is applied to the system shown in Figure 1, the transitions shown by the thick solid arrows or thin solid arrows in Figure 2 are induced. d In the coordinate system rotating with , the drive frequency is set so that the energy conservation shown in equations (3) and (4) holds true in the transitions indicated by the thick solid arrows and the thin solid arrows, respectively.

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[0042] The thick solid arrows indicate the energy transitions when microwaves are applied at a drive frequency where the energy conservation in equation (3) is satisfied (ω d =ω c +Δ 12 , Δ 12 =ω1-ω2). At this point, the photon of frequency ω2 stored in the second data qubit and the photon of frequency ω provided by the microwave drive are dphotons of frequencies ω1 and ω2 are generated by a four-wave mixing process due to the third-order nonlinear effect of the Josephson junction of the coupler qubit. c is converted into a photon that is stored in the first data qubit and the coupler qubit.

[0043] The thin solid arrows indicate the energy transitions when microwaves are applied at a drive frequency where the energy conservation in equation (4) is satisfied (ω d =ω c -Δ 12 , Δ 12 =ω1-ω2). At this time, the photon of frequency ω1 stored in the first data qubit and the photon of frequency ω provided by the microwave drive are d photons of frequencies ω and ω are mixed by a four-wave mixing process due to the third-order nonlinear effect of the Josephson junction of the coupler qubit. c is converted into a photon that is stored in the second data qubit and the coupler qubit.

[0044] The above is a qualitative explanation of the parametric resonance proposed in this embodiment. As shown in FIG. 2, this resonance transitions from a state with one total excitation to a state with two total excitations while exchanging excitations between data qubits. Thus, by applying microwave drive to a frequency-fixed Transmon coupler qubit, parametric resonance resulting from the third-order nonlinear effect of the coupler qubit occurs, and the data qubits transition to a state with a different total excitation by one while exchanging excitations. This phenomenon and principle were previously unknown and were discovered by the inventors in the process of devising the present invention. Because this transition occurs between levels with a different excitation by one while exchanging excitations, the inventors have named this transition a "cross Rabi transition" or a "Coupler-Assisted Swap (CAS) transition." Hereinafter, the term "cross Rabi transition" will be used in this specification. Furthermore, the pulse that drives the cross Rabi transition will be referred to as a "cross Rabi transition drive pulse."

[0045] Crossed Rabi transitions can be used to realize two functions of gate quantum devices. The first is quantum gate operation. This uses the geometric phase obtained by inducing Rabi oscillations between states outside the computation space by resonantly utilizing crossed Rabi transitions. This quantum gate operation is explained using Figures 2 and 3.

[0046] Figure 3 is a schematic diagram of the geometric phase obtained by the crossed Rabi transition. Figure 3 shows the Bloch sphere spanned by two states related to the crossed Rabi transition. As an example, we will explain the crossed Rabi transition corresponding to the thick solid arrow in Figure 2 below. The initial state |01>|0> belonging to the computation space c Starting from the point where the cross-Rabi transition is driven by microwaves, the state indicated by the arrow evolves along the dotted line on the surface of the Bloch sphere shown in Figure 3. As a result of the time evolution, the final state becomes |initial state|01>|0> c When the dotted line in Figure 3 coincides with the solid angle A enclosed by this closed curve, the dotted line in Figure 3 becomes a closed curve. The geometric phase acquired at this time is proportional to the solid angle A enclosed by this closed curve. In this case, time evolution is a unitary process. Therefore, the initial state advances in phase compared to other states in the computational space by the amount of the geometric phase acquired. By appropriately adjusting the length and frequency of the driving microwave, quantum gate operation can be realized.

[0047] For example, by adjusting the magnitude of the geometric phase to π, a controlled phase gate can be realized between the first data qubit 11 and the second data qubit 12, as shown in Fig. 4. Here, Fig. 4 is a schematic diagram showing a controlled phase gate acting between the first data qubit 11 and the second data qubit 12.

[0048] Figure 5 is a schematic diagram showing a pulse sequence for implementing the controlled phase gate of Figure 4. As mentioned above, here we apply a pulse to coupler qubit 13 at frequency ω d =ω c +Δ 12This microwave weakly modulates the frequency of the data qubits, causing an AC-Stark shift. To compensate for this, a local phase gate is applied to each data qubit. This phase gate is implemented using a technique called a virtual phase gate.

[0049] The second function of the quantum gate device is modulation of the ZZ interaction. This is achieved by dispersively using cross-Rabi transitions to induce an AC-Stark shift in the levels in the computation space. This effectively eliminates the residual coupling, called the residual ZZ interaction, that exists due to the coupling of data qubits. The magnitude of the residual coupling, ξ, is calculated using each level in the computation space as follows: ξ=ω 11 -ω 10 -ω 01 It can be expressed as:

[0050] Figure 6 is a schematic diagram showing how the transition frequency of the state related to the cross Rabi transition is modulated by the AC-Stark shift when a microwave detuned by δ from the cross Rabi transition is applied. When the cross Rabi transition indicated by the thick solid arrow in Figure 2 is used dispersively, the ω 01 The frequency of the signal is shifted as shown in Figure 6. Therefore, the residual coupling is ξ(ω d ,Ω), and the microwave frequency ω d and can be modulated by the intensity Ω.

[0051] Next, we analytically derive this interaction. First, we use a method called the Schrieffer-Wolff transformation to transform the Hamiltonian in the dispersion region expressed by equation (1) into the coupling constant g ic The Schrieffer-Wolff transformation perturbatively diagonalizes up to second order.

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[0052] Equation (1) was found

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[0053] Also this

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[0054] Using equation (9), when microwave drive is applied, the transition intensity corresponding to the thin solid arrow in FIG. 2 is expressed by the following equation (10):

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[0055] As described above, according to this embodiment, by driving the coupler qubit at a specific frequency, it is possible to effectively eliminate the residual ZZ interaction while realizing quantum gate operation. In other words, it is possible to provide a quantum gate device that eliminates the residual ZZ interaction and realizes two-quantum gate operation without requiring an external magnetic flux.

[0056] Note that pulse irradiation unit 20 may superimpose either the first crossed Rabi transition drive pulse or the second crossed Rabi transition drive pulse on the residual ZZ interaction erasing drive pulse and irradiate the resulting pulse onto coupler qubit 13. Alternatively, pulse irradiation unit 20 may irradiate coupler qubit 13 with both the first crossed Rabi transition drive pulse and the second crossed Rabi transition drive pulse and the residual ZZ interaction erasing drive pulse.

[0057] [Second embodiment] 7 is a functional block diagram of a quantum gate device 2 according to the second embodiment. The quantum gate device 2 includes a quantum bit substrate unit 10a and a pulse irradiation unit 20a.

[0058] The quantum bit substrate unit 10a is mounted with a first data qubit 11, a second data qubit 12, a coupler qubit 13, and a capacitor 30. The coupler qubit 13 is disposed between the first data qubit 11 and the second data qubit 12. The coupler qubit 13 is coupled to the first data qubit 11 and the second data qubit 12 via capacitors 101 and 102, respectively. Furthermore, the first data qubit 11 and the second data qubit 12 are directly coupled via capacitor 30. That is, the quantum gate device 2 differs from the configuration of the quantum gate device 1 in FIG. 1 in that it further includes a coupling between the first data qubit 11 and the second data qubit 12 via capacitor 30. The other configuration of the quantum gate device 2 is the same as the configuration of the quantum gate device 1.

[0059] The pulse irradiation unit 20a irradiates the coupler qubit 13 with a first crossed Rabi transition drive pulse or a second crossed Rabi transition drive pulse and a residual ZZ interaction erasing drive pulse. Here, the first crossed Rabi transition drive pulse or the second crossed Rabi transition drive pulse is the same as that of the quantum gate device 1 of FIG. 1, but the predetermined frequency shift δ that defines the residual ZZ interaction erasing drive pulse is different from that of the quantum gate device 1. That is, the frequency shift δ of the quantum gate device 2 is a value that erases the residual ZZ interaction between the first data qubit and the second data qubit and the cross resonance between the first data qubit and the second data qubit. This point will be explained in detail below.

[0060] In the configuration shown in Figure 1, the XI gate and IX gate contain a small amount of two-quantum gate elements called crossover resonance. Crossover resonance causes errors in one-quantum gates, so it is desirable to eliminate it.

[0061] 7, first data qubit 11 and second data qubit 12 are not only coupled via coupler qubit 13, but also directly coupled using capacitor 30. Hereinafter, the coupling via coupler qubit 13 will be referred to as a "quantum coupler," and the direct coupling using capacitor 30 will be referred to as a "classical coupler." After extensive research, the inventors have found that cross resonance can be canceled out by appropriately adjusting the magnitude of the coupling of the classical coupler.

[0062] Figure 8 shows the cross-resonance strength η and the strength of the residual ZZ interaction as a function of the coupling strength of the classical coupler. At the coupling strength indicated by the arrow (approximately 9 MHz), the cross-resonance crosses zero and disappears. Under these conditions, the residual ZZ interaction is also effectively reduced. Therefore, the predetermined frequency shift δ, which defines the residual ZZ interaction elimination drive pulse irradiated by the pulse irradiation unit 20a of the quantum gate device 2, can be set to a value that achieves this coupling strength.

[0063] According to this embodiment, in the quantum gate device, it is possible to eliminate cross resonance in addition to reducing residual ZZ interactions.

[0064] [Third embodiment] Next, a description will be given of a configuration in which data qubits and coupler qubits are integrated in the quantum gate device of the above-described embodiment.

[0065] 9 is a plan view of a qubit substrate unit 10b according to a third embodiment. The qubit substrate unit 10b mounts, on a two-dimensional plane, three or more data qubits: a first data qubit 11, a second data qubit 12, a third data qubit 19, coupler qubits 13 disposed between adjacent data qubits, a coupler control port 14 for controlling the coupler qubits 13, and a readout port 15 for reading out the data qubits. As shown in the figure, the qubit substrate unit 10b specifically includes nine data qubits, twelve coupler qubits, two coupler control ports 14, and one readout port 15.

[0066] The coupler control ports 14 are wires for controlling the coupler qubits, and are connected to the adjacent coupler qubits above, below, left, and right. The readout ports 15 are wires for reading out the data qubits, and are connected to the four adjacent data qubits diagonally.

[0067] According to this embodiment, qubits can be integrated and the coupler control port and readout port can be used to control the coupler qubits and readout the data qubits.

[0068] Figure 10 is a plan view of a qubit substrate in which the qubits of Figure 9 are further integrated and arranged in a square lattice. In this example, there are 64 data qubits, 112 coupler qubits, 40 coupler control ports, and 16 readout ports. With this arrangement, n 2 If we arrange data qubits in a square lattice, the number of coupler qubits is 2n(n-1) and the number of coupler control ports is (n+1) 2 -(n / 2+1) 2 -n 2 / 4, the number of read ports is n 2 However, the arrangement of each quantum bit and each port is not limited to that shown in FIG. 10, and the number of each quantum bit and each port is not limited to that shown above.

[0069] According to this embodiment, the quantum bits to be mounted can be further highly integrated.

[0070] [Fourth embodiment] 11 is a plan view of a qubit substrate unit 10c according to a fourth embodiment. The qubit substrate unit 10c has three or more data qubits mounted on a two-dimensional plane: first data qubit 11, second data qubit 12, third data qubit 19, coupler qubits 13 arranged between adjacent data qubits, coupler control ports 14 for controlling coupler qubits 13, readout port 15 for reading out the data qubits, and one-qubit control port 16. As shown in the figure, the qubit substrate unit 10c specifically includes nine data qubits, twelve coupler qubits, two coupler control ports 14, one readout port 15, and one one-qubit control port 16.

[0071] Coupler control ports 14 are wiring for controlling coupler qubits, and are each connected to adjacent coupler qubits above, below, left, and right. Readout ports 15 are wiring for reading out data qubits, and are each connected to four adjacent diagonal data qubits. One-qubit control ports 16 are wiring for controlling one qubit of the quantum gate device, and are each connected to four adjacent diagonal data qubits.

[0072] According to this embodiment, it is possible to control one quantum bit of a quantum gate device.

[0073] Figure 12 is a plan view of a qubit substrate in which the qubits of Figure 11 are further integrated and arranged in a square lattice. In this example, there are 64 data qubits, 112 coupler qubits, 40 coupler control ports, 16 readout ports, and 25 1-qubit control ports. In this arrangement, n 2If we arrange data qubits in a square lattice, the number of coupler qubits is 2n(n-1) and the number of coupler control ports is (n+1) 2 -(n / 2+1) 2 -n 2 / 4, the number of read ports is n 2 / 4, the number of 1-qubit control ports is (n / 2+1) 2 However, the arrangement of each quantum bit and each port is not limited to that shown in FIG. 10, and the number of each quantum bit and each port is not limited to that shown above.

[0074] According to this embodiment, the quantum bits to be mounted can be further highly integrated.

[0075] Figure 13 shows the frequencies of the data qubits and coupler qubits. The ovals are data qubits, the rectangles are coupler qubits, the circles with diagonal lines downward to the right are coupler control ports, and the circles with diagonal lines downward to the left are readout ports. The numbers in the data qubits and coupler qubits are frequencies expressed in MHz. Since multiple qubits are excited from a single wiring, the frequencies used must be adjusted to prevent collisions. For example, by allocating frequencies as shown in Figure 13, the eight types of frequencies applied to each wiring (four types for 1-quantum gates + four types for 2-quantum gates) will all be different, thereby reducing crosstalk.

[0076] Furthermore, there is a transition called the Fogi transition, which may be crossed with the frequency ωc+|ω1-ω2|=ωc+|Δ12| (where ω1-ω2=Δ12, and so on below) that performs the ZZ gate operation. The resonant frequency of the Fogi transition must be different from the resonant frequency of the cross-Rabi transition that performs the ZZ gate operation (i.e., frequency collision does not occur). This frequency collision is explained below.

[0077] Figure 14 shows the qubits and frequencies around the coupler control ports. Figure 15 shows the frequencies used around coupler control port 1 in Figure 9 and the frequencies that result in errors. Figure 15 shows the frequencies used around coupler control port 2 in Figure 16 and the frequencies that result in errors. Here, α represents the nonlinearity of the qubit. For example, α represents the nonlinearity of the quantum coupler Qc12 between the first qubit and the second qubit. The black circles (ω1, ω2, ω3, ω4) and white circles (ωc12 + |Δ12|, ωc24 + |Δ24|, ωc13 + |Δ13|, ωc34 + |Δ34|) in Figures 15 and 16 represent the frequencies used. On the other hand, the circles with downward slanting left (ωc12, ωc24, ωc13, ωc34) and the circles with downward slanting right (2ωc12+αc12-ω1, 2ωc24+αc24-ω4, 2ωc13+αc13-ω1, 2ωc34+αc34-ω4, 2ωc12+αc12-ω2, 2ωc24+αc24-ω2, 2ωc13+αc13-ω3, 2ωc34+αc34-ω3) in Figures 15 and 16 represent frequencies where errors occur. In particular, the circles with downward slanting right are frequencies where Fogi transitions occur.

[0078] Here, it is necessary to prevent collisions between "frequencies in use" and between "frequencies in use" and "frequencies that will cause errors." In both Figures 15 and 16, the plots of black and white circles do not collide with each other. Furthermore, both the black and white circles are outside the area that contains frequencies that will cause errors (the area hatched in gray), which shows that the conditions for preventing frequency collisions are met.

[0079] [Fifth embodiment] The techniques described above are expected to be applicable to a variety of qubits, but it is particularly desirable for the first data qubit, the second data qubit, and the coupler qubit to be superconducting qubits.

[0080] 17 is a functional block diagram of a superconducting quantum gate device 3 according to a fifth embodiment. The superconducting quantum gate device 3 includes the aforementioned quantum bit substrate unit 10 configured using superconducting quantum bits, and a refrigerator 40 for cooling and operating the quantum bit substrate unit 10.

[0081] Refrigerator 40 is composed of a dilution refrigerator (cryostat) or the like. The inside of refrigerator 40 is kept at a low temperature of several K (kelvin) to several tens of mK (millikelvin). Devices other than quantum bit substrate unit 10, such as pulse irradiation unit 20, are placed outside refrigerator 40.

[0082] According to this embodiment, it is possible to provide a superconducting quantum gate device that can eliminate residual ZZ interaction and realize two-quantum gate operation without requiring an external magnetic flux.

[0083] [Sixth embodiment] 18 is a functional block diagram of a quantum computer 4 according to a sixth embodiment. The quantum computer 4 includes the above-described superconducting quantum gate device configured using superconducting qubits, and a control unit 50 that controls the superconducting quantum gate device 3. The control unit 50 performs, for example, a syndrome extraction operation and a logical quantum gate operation for quantum error correction processing, and is implemented by a control device or a PC placed outside the refrigerator 40.

[0084] According to this embodiment, it is possible to provide a quantum computer that can eliminate residual ZZ interactions and realize two-quantum gate operations without requiring an external magnetic flux.

[0085] [Seventh embodiment] 19 is a flowchart showing the process of a quantum gate operation method according to a seventh embodiment. This method is a quantum gate operation method for a qubit system including at least two data qubits, i.e., a first data qubit and a second data qubit, and a coupler qubit disposed between the first data qubit and the second data qubit, and includes steps S1 and S2. Here, the resonant frequency of the first excited state of the first data qubit is ω1, the resonant frequency of the first excited state of the second data qubit is ω2, and the resonant frequency of the first excited state of the coupler qubit is ω c , Step S1 is the frequency ω c +|ω1-ω2|. Step S2 irradiates a first cross Rabi transition drive pulse defined by a predetermined frequency δ shifted from the first cross Rabi transition drive pulse. c +|ω1-ω2|-δ, a residual ZZ interaction erasing drive pulse, and the predetermined frequency shift δ is a value that erases the residual ZZ interaction between the first data qubit and the second data qubit.

[0086] Alternatively, in step S1, a second cross Rabi transition drive pulse may be irradiated instead of the first cross Rabi transition drive pulse. Here, the frequency of the second cross Rabi transition drive pulse is ω c At this time, step S2 is defined as a frequency ω that is shifted by a predetermined frequency δ from the first cross Rabi transition drive pulse. c and irradiating the coupler qubit with a residual ZZ interaction erasing drive pulse of −|ω1−ω2|−δ, again with a predetermined frequency shift δ that erases any residual ZZ interaction between the first data qubit and the second data qubit.

[0087] According to this embodiment, the quantum gate device can be used to remove the residual ZZ interaction and perform two-quantum gate operations without requiring an external magnetic flux.

[0088] [Verification experiment] An experiment was conducted to verify the technology described above. Figure 20 shows a photograph of the quantum bit substrate used in this experiment.

[0089] Figure 21 shows the experimental results of observing Rabi oscillations between states corresponding to the thin solid arrows in Figure 2. Figure 22 shows the experimental results of observing Rabi oscillations between states corresponding to the thick solid arrows in Figure 2. In both Figures 21 and 22, the horizontal axis indicates the length of the microwave drive pulse to induce cross-Rabi interactions, and the vertical axis indicates the detuning of the drive frequency from the frequency of the first excited state of the coupler qubit. The bar on the right of the graph represents the transmission characteristics of the readout resonator coupled to the qubit, which is proportional to the occupancy rate of the first excited state of the qubit.

[0090] Here, if the detuning of the drive frequency from the resonance of the coupler qubit is δ and the drive strength converted to frequency is Ω, then the resonance condition for the cross Rabi transition is √(δ 2 +4Ω 2 ) In this example, this was set to 140 MHz. Therefore, δ is slightly shifted from ±140 MHz by the amount of Ω. For this reason, Rabi oscillations can be observed near δ = -100 MHz in FIG. 19 and δ = 113.5 MHz in FIG. 20.

[0091] Next, we implemented a controlled phase gate using the cross Rabi transition parameters obtained in Figure 22. We evaluated the accuracy of the implemented controlled phase gate using a method called interleaved randomized benchmarking. The results are shown in Figure 23. The fidelity obtained by fitting is shown on the top of the figure. As shown in the figure, we can see that a highly accurate controlled phase gate has been realized with a fidelity of approximately 99%.

[0092] Finally, by driving the transition indicated by the thick solid arrow in Figure 2 slightly off-resonance, we induced a ZZ interaction via AC Stark shift and eliminated the residual ZZ interaction. The results are shown in Figure 24. The horizontal axis shows the detuning of the drive frequency from the coupler qubit transition frequency, and the vertical axis shows the magnitude of the residual ZZ interaction. The short vertical solid lines show the measured results of the residual ZZ interaction, and the dotted lines show the fitting results of the measured results.

[0093] The long vertical line near 125.6 MHz on the horizontal axis indicates the detuning of the drive frequency from the coupler qubit when the residual ZZ interaction calculated from the fitting results becomes zero. In other words, by fitting the measured data of the magnitude of the residual ZZ interaction, the drive frequency at which the residual interaction becomes zero (indicated by the arrow) can be determined from 24. Taking into account the uncertainty of the fitting, it is possible to suppress the residual ZZ interaction to a range from -150 Hz to 60 Hz. The magnitude of the residual ZZ interaction without microwave drive is approximately 2.5 kHz. Thus, the ZZ interaction becomes zero at the appropriate drive frequency, verifying that the residual ZZ interaction can be eliminated dispersively using cross-Rabi transitions as expected.

[0094] The technology disclosed herein achieves two advantages: it eliminates residual ZZ interactions, which cause errors in quantum gates, and it realizes highly accurate two-quantum gates. The superconducting quantum circuit, including the coupler qubits used, can be constructed entirely of frequency-locked qubits. Therefore, no external magnetic flux is required, making it robust against noise. This allows functions that require subsequent calibration, such as interaction optimization and gates, to be performed solely by applying microwaves. This reduces the number of microwave wirings required for the qubits. Fewer microwave wirings directly contribute to an increase in the number of qubits, and error-free control contributes to high-performance quantum computers. Furthermore, the problem of frequency collisions is resolved compared to existing methods.

[0095] As mentioned above, in this technology, all calibration of quantum gates and residual interaction elimination is performed using microwaves. Because tuning using a DC magnetic field is not performed, there is no degradation of qubit performance due to magnetic field noise, enabling stable control. As a result, a high-fidelity two-quantum gate is realized. As shown in the first half of the experimental results, the current performance is the world's highest level, at around 99%.

[0096] Furthermore, in the above experiment, two quantum gates and the elimination of residual ZZ interactions were achieved with a very low microwave intensity of approximately -87 dBm. This is due to the large transition amplitude of the cross-Rabi transition, which allows control at an intensity approximately 10 dB to 20 dB weaker than existing microwave-controlled gates. Such energy-saving quantum gates solve the heat problem when driving a large number of quantum bits, leading to high scalability.

[0097] On the other hand, all-microwave methods often require the application of high-intensity microwaves. However, such high-intensity microwaves cause thermal problems as the number of qubits increases, limiting their scalability to the cooling capacity of the cryocooler. As shown in the above experiments, our method achieves two-quantum gates and the elimination of residual ZZ interactions using extremely low-intensity microwaves of approximately -87 dBm. This is due to the large transition amplitude of the cross-Rabi transition. Thus, our microwave control method is significantly more efficient than existing methods, achieving energy savings of approximately 10 to 20 dB for gates and ZZ interaction correction. This means that it is possible to integrate 10 to 100 times more qubits within the same cryocooler, contributing to the realization of large-scale superconducting quantum computers.

[0098] As explained above, the technology disclosed in this specification is extremely novel and industrially useful, as it applies microwave drive to a coupler quantum bit, induces parametric resonance derived from a previously undiscovered third-order nonlinear effect of the coupler, and thereby eliminates residual ZZ interactions and realizes two-quantum gate operation.

[0099] [Application to single-qubit gate operation] In the above-described embodiment, the elimination of residual ZZ interactions and controlled phase gate operation using microwave irradiation on a coupler qubit have been described. However, the technology of the present disclosure is not limited to this and can also be applied to ordinary quantum gate operation (single-qubit gate operation) using microwave irradiation on a coupler qubit.

[0100] Two data qubits Q i (i=1, 2) and one coupler qubit Q c and the coupling constant g i Consider the coupled system. Coupler Qubit Q c , the data qubit Q i The frequency ω i , strength Ω0 i When microwaves are applied, g ic / Δ ic <<1, Ω0 i / Δ ic <<1, (Δ ic =ω i -ω c ), the Hamiltonian of the whole system is as follows: It can be written as

number

[0101] The parameters of this system are Ω0 i / Δ ic Since the adiabatic condition of Z << 1 is satisfied, we can treat the coupler qubit as the ground state (g state).c = 1, equation (12) can be rewritten as equation (13).

number

[0102] From the above, we can see that the coupler qubit Q c By irradiating the data qubits Q1 and Q2 with microwaves at frequencies ω1 and ω2, respectively, a one-qubit gate for these data qubits Q1 and Q2 can be realized.

[0103] From the above, we can see that the coupler qubit Q c By irradiating the data qubits Q1 and Q2 with microwaves at frequencies ω1 and ω2, respectively, a one-qubit gate for these data qubits Q1 and Q2 can be realized.

[0104] [Eighth embodiment] An eighth embodiment will be described with reference to the quantum gate device 1 of Fig. 1. The quantum gate device 1 includes a quantum bit substrate unit 10 that mounts a first data quantum bit 11, a second data quantum bit 12, and a coupler quantum bit 13 disposed between the first data quantum bit 11 and the second data quantum bit 12, and a pulse irradiation unit 20 that irradiates the coupler quantum bit 13 with a drive pulse. When the resonant frequency of the first excited state of the first data quantum bit 11 is ω1 and the resonant frequency of the first excited state of the second data quantum bit 12 is ω2, the pulse irradiation unit 13 irradiates the coupler quantum bit 13 with microwaves defined by the frequency ω1. This causes a first quantum gate operation to be performed on the first quantum bit 11.

[0105] Alternatively, in the above configuration, pulse irradiator 13 may irradiate coupler qubit 13 with microwaves defined by frequency ω2. In this case, a second quantum gate operation is performed on the second qubit.

[0106] According to this embodiment, it is possible to perform quantum gate operations on each data qubit simply by irradiating the coupler qubit with microwaves, without the need to directly control the data qubits.

[0107] The present invention has been described based on the embodiments. These embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of the respective components and treatment processes, and that such modifications are also within the scope of the present invention.

[0108] The first data qubit, the second data qubit, and the coupler qubit are not limited to superconducting qubits, but may be any suitable qubits, such as quantum dots, ion traps, or the like.

[0109] According to this modification, the degree of freedom in the configuration can be increased.

[0110] A new embodiment resulting from a combination has the combined effects of each of the combined embodiments and modifications.

[0111] The above-described embodiments and modifications are merely illustrative examples, and many design changes are possible, such as changing, adding, or deleting components. In the embodiments, the content that allows such design changes is emphasized by adding the notation "embodiment." However, design changes are also permitted even in content that does not have such notation. [Industrial Applicability]

[0112] The present invention can be applied to a quantum gate device, a superconducting quantum gate device, a quantum computer, and a quantum gate operation method. [Explanation of symbols]

[0113] 1··Quantum gate device. 2··Quantum gate device. 3··Superconducting quantum gate device. 4··Quantum computers. 10··Quantum bit substrate section. 10a··Quantum bit substrate section. 10b: Quantum bit substrate. 10c··Quantum bit substrate section. 11··First data qubit. 12··Second data qubit. 13·· Coupler qubit. 14·· Coupler control port. 15··Read port. 16··1 qubit control port. 20··Pulse irradiation section. 20a··Pulse irradiation section. 30··Capacitor. 40··Freezer. 50··Control section. 101··Capacitor. 102··Capacitor. 1001··Josephson element. 1101··Capacitor. 1002··Josephson element. 1102··Capacitor. 1003··Josephson element. 1103··Capacitor. S1··The step of irradiating the coupler qubit with the first cross-Rabi transition drive pulse. S2: Irradiating the coupler qubit with a residual ZZ interaction erasing drive pulse.

Claims

1. at least two data qubits, a first data qubit and a second data qubit; a coupler qubit disposed between the first data qubit and the second data qubit; a quantum bit substrate unit equipped with the a pulse irradiation unit that irradiates the coupler quantum bit with a drive pulse; The resonant frequency of the first excited state of the first data qubit is defined as ω １ , The resonant frequency of the first excited state of the second data qubit is defined as ω ２ , The resonant frequency of the first excited state of the coupler qubit is denoted by ω ｃ , and then, The pulse irradiation unit frequency ω ｃ + | ω １ -ω ２ a first cross-Rabi transition drive pulse defined by |; A frequency ω shifted by a predetermined frequency δ from the first cross-Rabi transition drive pulse ｃ + | ω １ -ω ２ a residual ZZ interaction erase drive pulse of |-δ to the coupler qubit; The quantum gate device, wherein the predetermined frequency shift δ is a value that eliminates residual ZZ interaction between the first data quantum bit and the second data quantum bit.

2. at least two data qubits, a first data qubit and a second data qubit; a coupler qubit disposed between the first data qubit and the second data qubit; a quantum bit substrate unit equipped with the a pulse irradiation unit that irradiates the coupler quantum bit with a drive pulse; The resonant frequency of the first excited state of the first data qubit is defined as ω １ , The resonant frequency of the first excited state of the second data qubit is defined as ω ２ , The resonant frequency of the first excited state of the coupler qubit is denoted by ω ｃ , and then, The pulse irradiation unit frequency ω ｃ - | ω １ -ω ２ a second cross-Rabi transition drive pulse defined by | A frequency ω shifted by a predetermined frequency δ from the second cross-Rabi transition drive pulse ｃ - | ω １ -ω ２ a residual ZZ interaction erase drive pulse of |-δ to the coupler qubit; The quantum gate device, wherein the predetermined frequency shift δ is a value that eliminates residual ZZ interaction between the first data quantum bit and the second data quantum bit.

3. The pulse irradiation unit 3. The quantum gate device according to claim 1, wherein both the first crossed Rabi transition drive pulse and the second crossed Rabi transition drive pulse and a residual ZZ interaction erasing drive pulse are irradiated onto the coupler quantum bit.

4. 2. The quantum gate device of claim 1, wherein the first cross-Rabi transition drive pulse executes a controlled phase gate between the first data qubit and the second data qubit.

5. 3. The quantum gate device of claim 2, wherein the second cross-Rabi transition drive pulse executes a controlled phase gate between the first data qubit and the second data qubit.

6. a capacitor coupling the first data qubit and the second data qubit; 3. The quantum gate device according to claim 1, wherein the predetermined frequency shift δ is a value that eliminates residual ZZ interaction between the first data quantum bit and the second data quantum bit and cross resonance between the first data quantum bit and the second data quantum bit.

7. The quantum bit substrate unit includes: three or more data qubits; a coupler qubit disposed between adjacent data qubits; a coupler control port for controlling the coupler qubit; a read port for reading the data qubits; and 3. The quantum gate device according to claim 1, wherein the first and second gates are mounted on a two-dimensional plane.

8. The quantum bit substrate unit includes: the data qubits arranged in a square lattice; the coupler qubits arranged in a square lattice between adjacent data qubits; a coupler control port located at the center of the square lattice of coupler qubits and controlling the coupler qubits; a readout port disposed at the center of the square lattice of data qubits for reading out the data qubits; 8. The quantum gate device according to claim 7, wherein:

9. The quantum bit substrate unit includes: The quantum gate device according to claim 7, further comprising a one-qubit control port for controlling one qubit of the data qubit.

10. The quantum bit substrate unit includes:

9. The quantum gate device according to claim 8, further comprising a one-qubit control port that is arranged at the center of the square lattice of the data qubits and performs one-qubit control of the data qubits.

11. 3. The quantum gate device according to claim 1, wherein the first data qubit, the second data qubit, and the coupler qubit are superconducting qubits.

12. The quantum gate device according to claim 11; a refrigerator for cooling and operating the quantum bit substrate portion.

13. A quantum computer comprising: the superconducting quantum gate device according to claim 12; and a control unit that controls the superconducting quantum gate device.

14. at least two data qubits, a first data qubit and a second data qubit; a coupler qubit disposed between the first data qubit and the second data qubit, The resonant frequency of the first excited state of the first data qubit is defined as ω １ , The resonant frequency of the first excited state of the second data qubit is defined as ω ２ , The resonant frequency of the first excited state of the coupler qubit is denoted by ω ｃ , and then, frequency ω ｃ + | ω １ -ω ２ irradiating the coupler qubit with a first cross-Rabi transition drive pulse defined by | A frequency ω shifted by a predetermined frequency δ from the first cross-Rabi transition drive pulse ｃ + | ω １ -ω ２ and irradiating the coupler qubit with a residual ZZ interaction erase drive pulse of |-δ; The quantum gate operation method, wherein the predetermined frequency shift δ is a value that eliminates residual ZZ interaction between the first data quantum bit and the second data quantum bit.

15. at least two data qubits, a first data qubit and a second data qubit; a coupler qubit disposed between the first data qubit and the second data qubit, The resonant frequency of the first excited state of the first data qubit is defined as ω １ , The resonant frequency of the first excited state of the second data qubit is defined as ω ２ , The resonant frequency of the first excited state of the coupler qubit is denoted by ω ｃ , and then, frequency ω ｃ - | ω １ -ω ２ irradiating the coupler qubit with a second cross-Rabi transition drive pulse defined by | A frequency ω shifted by a predetermined frequency δ from the second cross-Rabi transition drive pulse ｃ - | ω １ -ω ２ and irradiating the coupler qubit with a residual ZZ interaction erase drive pulse of |-δ; The quantum gate operation method, wherein the predetermined frequency shift δ is a value that eliminates residual ZZ interaction between the first data quantum bit and the second data quantum bit.

16. at least two data qubits, a first data qubit and a second data qubit; a coupler qubit disposed between the first data qubit and the second data qubit; a quantum bit substrate unit equipped with the a pulse irradiation unit that irradiates the coupler quantum bit with a drive pulse; The resonant frequency of the first excited state of the first data qubit is defined as ω １ , The resonant frequency of the first excited state of the second data qubit is defined as ω ２ , and then, The pulse irradiation unit has a frequency ω １ and performing a first quantum gate operation by irradiating the coupler quantum bit with microwaves defined as:

17. at least two data qubits, a first data qubit and a second data qubit; a coupler qubit disposed between the first data qubit and the second data qubit; a quantum bit substrate unit equipped with the a pulse irradiation unit that irradiates the coupler quantum bit with a drive pulse; The resonant frequency of the first excited state of the first data qubit is defined as ω １ , The resonant frequency of the first excited state of the second data qubit is defined as ω ２ , and then, The pulse irradiation unit has a frequency ω ２ and performing a second quantum gate operation by irradiating the coupler qubit with microwaves defined by:

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