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

Abstract

A quantum gate device (1) is provided with: a qubit substrate unit (10) on which at least two data qubits, i.e., a first data qubit (11) and a second data qubit (12), and a coupler qubit (13) disposed between the first data qubit (11) and the second data qubit (12), are mounted; and a pulse irradiation unit (20) that irradiates the coupler qubit (13) with a drive pulse. When the resonance frequency of the first excited state of the first data qubit (11) is set as [omega] 1, the resonance frequency of the first excited state of the second data qubit (12) is set as [omega] 2, and the resonance frequency of the first excited state of the coupler qubit (13) is set as [omega] c, [omega] 1, [omega] 2 and [omega] c are satisfied. A pulse irradiation unit (20) irradiates a coupler qubit (13) with a first cross-pull-ratio transition drive pulse defined by a frequency [omega] c + [omega] 1-[omega] 2, and a residual ZZ interaction cancellation drive pulse at a frequency [omega] c + [omega] 1-[omega] 2-[delta] shifted by a predetermined frequency [delta] from the first cross-pull-ratio transition drive pulse. The prescribed frequency offset [delta] is a value that cancels the residual ZZ interaction between the first data qubit (11) and the second data qubit (12).

Description

Technical Field

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

[0002] It is known that operations in a quantum computer can be realized by a combination of a set of quantum gates consisting of single quantum gates and double quantum gates, namely a "universal quantum gate set", and a readout element for each quantum bit (eg, Non-Patent Document 1).

[0003] Prior art literature

[0004] Non-patent literature

[0005] Non-Patent Literature 1: “Progress and Applications in Superconducting Quantum Bit Research” Yasunobu Nakamura, Applied Physics Vol. 90, No. 4 (2021) https: / / www.jstage.jst.go.jp / article / oubutsu / 90 / 4 / 90_209 / _pdf

[0006] Non-patent document 2: “A universal gate for fixed-frequency qubits via an unavailable bus”, David C. McKay, etc. Phys. Rev. Applied 6, 064007 (2016) https: / / arxiv.org / pdf / 1604.03076.pdf Summary of the invention

[0007] Problems to be solved by the invention

[0008] Variable interactions are an important element for building a well-controlled superconducting quantum processor. In this construction, the method of using frequency-fixed superconducting quantum bits with high coherence is a strong candidate. However, in the frequency-fixed method, the residual interaction that is always effective (ON) becomes the reason for limiting the control accuracy. Usually, a single quantum gate is executed by causing Rabi oscillations by a microwave pulse that resonates between two energy levels with a time width of about 10 to 20ns. In contrast, double quantum gates usually require time for gate operations compared to single quantum gates, and are accordingly susceptible to decoherence. In particular, in double quantum gates, due to the coupling between quantum bits, there is residual ZZ interaction even when the gate operation is not performed. This becomes the cause of errors that reduce the accuracy of gate control and is therefore undesirable. Therefore, how to remove the residual ZZ interaction becomes a topic.

[0009] As one of the methods for removing the residual ZZ interaction, a method of using a DC-SQUID to change the resonance frequency of the coupling element and the data qubit has been proposed (for example, non-patent document 2). However, in such a method, there is the following problem: since the quantum processor is responsive to the external magnetic flux and is affected by the magnetic flux noise, the coherence time becomes shorter.

[0010] The present invention has been made in view of such a problem, and an object of the present invention is to provide a technology for removing the residual ZZ interaction and realizing double quantum gate operation without requiring an external magnetic flux.

[0011] Solutions to Solve Problems

[0012] In order to solve the above-mentioned problems, a quantum gate device of a certain scheme of the present invention comprises: a quantum bit substrate unit, which carries at least two data quantum bits, namely a first data quantum bit and a second data quantum bit, and a coupler quantum bit arranged between the first data quantum bit and the second data quantum bit; and a pulse irradiation unit, which irradiates a driving pulse to the coupler quantum bit. The resonance frequency of the first excited state of the first data quantum bit is set to ω1, the resonance frequency of the first excited state of the second data quantum bit is set to ω2, and the resonance frequency of the first excited state of the coupler quantum bit is set to ω c At this time, the pulse irradiation unit irradiates the coupler quantum bit with a frequency ω c +|ω1-ω2| defined as the first cross-Rabi transition drive pulse, and the frequency ω shifted from the first cross-Rabi transition drive pulse by a predetermined frequency δ c The residual ZZ interaction of +|ω1-ω2|-δ cancels the driving pulse. The predetermined frequency shift δ is a value that cancels the residual ZZ interaction between the first data qubit and the second data qubit.

[0013] According to this embodiment, it is possible to provide a device that can achieve removal of residual ZZ interaction and double quantum gate operation without external magnetic flux.

[0014] Another embodiment of the present invention is also a quantum gate device. The quantum gate device comprises: a quantum bit substrate portion, which carries at least two data quantum bits, namely a first data quantum bit and a second data quantum bit, and a coupler quantum bit arranged between the first data quantum bit and the second data quantum bit; and a pulse irradiation portion, which irradiates a driving pulse to the coupler quantum bit. The resonance frequency of the first excited state of the first data quantum bit is set to ω1, the resonance frequency of the first excited state of the second data quantum bit is set to ω2, and the resonance frequency of the first excited state of the coupler quantum bit is set to ω c At this time, the pulse irradiation unit irradiates the coupler quantum bit with a frequency ω c- a second cross-Rabi transition driving pulse defined by |ω1-ω2|, and a frequency ω shifted from the second cross-Rabi transition driving pulse by a predetermined frequency δ c -|ω1-ω2|-δ residual ZZ interaction cancels the driving pulse. The predetermined frequency shift δ is a value that cancels the residual ZZ interaction between the first data qubit and the second data qubit.

[0015] According to this embodiment, it is possible to provide a device that can achieve removal of residual ZZ interaction and double quantum gate operation without external magnetic flux.

[0016] In one embodiment, the pulse irradiation unit may irradiate the coupler qubit with both the first cross-Rabi transition driving pulse and the second cross-Rabi transition driving pulse, as well as the residual ZZ interaction elimination driving pulse.

[0017] In a certain embodiment, the first cross-Rabi transition driving pulse may also perform a control phase gate between the first data qubit and the second data qubit.

[0018] In a certain embodiment, the second cross-Rabi transition driving pulse may also perform a control phase gate between the first data qubit and the second data qubit.

[0019] In one embodiment, a capacitor for coupling the first data qubit and the second data qubit may be further provided. The predetermined frequency shift δ may be a value that eliminates 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.

[0020] In a certain embodiment, the quantum bit substrate unit may also carry three or more data quantum bits, coupler quantum bits arranged between adjacent data quantum bits, a coupler control port for controlling the coupler quantum bits, and a readout port for reading out the data quantum bits on a two-dimensional plane.

[0021] In a certain embodiment, the quantum bit substrate portion may also be equipped with: data quantum bits, which are arranged in a square lattice; coupler quantum bits, which are arranged in a square lattice between adjacent data quantum bits; a coupler control port, which is arranged at the center of the square lattice of the coupler quantum bits to control the coupler quantum bits; and a readout port, which is arranged at the center of the square lattice of the data quantum bits to read out the data quantum bits.

[0022] In a certain embodiment, the quantum bit substrate unit may also carry three or more data quantum bits, coupler quantum bits arranged between adjacent data quantum bits, a coupler control port for controlling the coupler quantum bits, a readout port for reading out the data quantum bits, and a single quantum bit control port for single quantum bit control of the data quantum bits on a two-dimensional plane.

[0023] In a certain embodiment, the quantum bit substrate portion may also be equipped with: data quantum bits, which are configured in a square lattice; coupler quantum bits, which are configured in a square lattice between adjacent data quantum bits; a coupler control port, which is configured at the center of the square lattice of the coupler quantum bits to control the coupler quantum bits; a readout port, which is configured at the center of the square lattice of the data quantum bits to read out the data quantum bits; and a single quantum bit control port, which is configured at the center of the square lattice of the data quantum bits to perform single quantum bit control of the data quantum bits.

[0024] In a certain embodiment, the quantum gate device may also be equipped with a single-qubit control port, which is arranged at the center of the square grid of the data qubit to perform single-qubit control of the data qubit.

[0025] In a certain embodiment, the first data qubit, the second data qubit, and the coupler qubit may also be superconducting qubits.

[0026] Another embodiment of the present invention is a superconducting quantum gate device, which includes: the quantum gate device described above; and a refrigerator for cooling a quantum bit substrate portion to operate the quantum bit substrate.

[0027] According to this scheme, a superconducting quantum gate device capable of removing residual ZZ interaction and performing double quantum gate operation without external magnetic flux can be realized.

[0028] Still another embodiment of the present invention is a quantum computer comprising the above-mentioned superconducting quantum gate device and a control unit that controls the superconducting quantum gate device.

[0029] According to this scheme, a quantum computer capable of removing residual ZZ interactions and performing double quantum gate operations without the need for external magnetic flux can be realized.

[0030] Another embodiment of the present invention is a quantum gate operation method. The method is a quantum gate operation method for a quantum bit system, wherein the quantum bit system has at least two data quantum bits, namely a first data quantum bit and a second data quantum bit, and a coupler quantum bit configured between the first data quantum bit and the second data quantum bit. The resonance frequency of the first excited state of the first data quantum bit is set to ω1, the resonance frequency of the first excited state of the second data quantum bit is set to ω2, and the resonance frequency of the first excited state of the coupler quantum bit is set to ω c , then, the method comprises the following steps: irradiating the coupler quantum bit with a frequency ω c +|ω1-ω2| defined as a first cross-Rabi transition driving pulse; and irradiating the coupler quantum bit with a frequency ω shifted by a specified frequency δ from the first cross-Rabi transition driving pulse c The residual ZZ interaction of +|ω1-ω2|-δ cancels the driving pulse. The predetermined frequency shift δ is a value that cancels the residual ZZ interaction between the first data qubit and the second data qubit.

[0031] According to this scheme, it is possible to perform removal of residual ZZ interaction and double quantum gate operation without external magnetic flux.

[0032] Another solution of the present invention is also a quantum gate operation method. The method is a quantum gate operation method for a quantum bit system, wherein the quantum bit system has at least two data quantum bits, namely a first data quantum bit and a second data quantum bit, and a coupler quantum bit configured between the first data quantum bit and the second data quantum bit. The resonance frequency of the first excited state of the first data quantum bit is set to ω1, the resonance frequency of the first excited state of the second data quantum bit is set to ω2, and the resonance frequency of the first excited state of the coupler quantum bit is set to ω c , then, the method comprises the following steps: irradiating the coupler quantum bit with a frequency ω c -|ω1-ω2| defined as a second cross-Rabi transition driving pulse; and irradiating the coupler qubit with a frequency ω shifted by a predetermined frequency δ from the second cross-Rabi transition driving pulse c -|ω1-ω2|-δ residual ZZ interaction cancels the driving pulse. The predetermined frequency shift δ is a value that cancels the residual ZZ interaction between the first data qubit and the second data qubit.

[0033] According to this scheme, it is possible to perform removal of residual ZZ interaction and double quantum gate operation without external magnetic flux.

[0034] Another embodiment of the present invention is a quantum gate device. The quantum gate device comprises: a quantum bit substrate portion, which carries at least two data quantum bits, namely a first data quantum bit and a second data quantum bit, and a coupler quantum bit arranged between the first data quantum bit and the second data quantum bit; and a pulse irradiation portion, which irradiates a driving pulse to the coupler quantum bit. The resonance frequency of the first excited state of the first data quantum bit is set to ω1, and the resonance frequency of the first excited state of the second data quantum bit is set to ω2. At this time, the pulse irradiation portion performs a first quantum gate operation by irradiating a microwave defined by a frequency ω1 to the coupler quantum bit.

[0035] A quantum gate device of a certain embodiment includes: a quantum bit substrate unit carrying at least two data quantum bits, namely a first data quantum bit and a second data quantum bit, and a coupler quantum bit arranged between the first data quantum bit and the second data quantum bit; and a pulse irradiation unit irradiating a driving pulse to the coupler quantum bit. The resonance frequency of the first excited state of the first data quantum bit is set to ω1, and the resonance frequency of the first excited state of the second data quantum bit is set to ω2. At this time, the pulse irradiation unit performs a second quantum gate operation by irradiating a microwave defined by a frequency ω2 to the coupler quantum bit.

[0036] According to this scheme, there is no need to directly control the data qubits, and quantum gate operations can be performed on each data qubit simply by irradiating the coupler qubits with microwaves.

[0037] It should be noted that any combination of the above-mentioned constituent elements and any form of the expression of the present disclosure converted into a method, an apparatus, a system, a recording medium, a computer program, etc. may also be effective as forms of the present disclosure.

[0038] Effects of the Invention

[0039] According to the present invention, it is possible to provide a technology that can achieve removal of residual ZZ interaction and double quantum gate operation without requiring an external magnetic flux. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a functional block diagram of the quantum gate device involved in the first embodiment.

[0041] Figure 2 It is shown Figure 1 Energy level diagram of the energy transition of a system.

[0042] Figure 3 Schematic diagram of the geometric phase obtained through crossed Rabi transitions.

[0043] Figure 4is a schematic diagram showing a controlled phase gate functioning between a first data qubit and a second data qubit.

[0044] Figure 5 It shows the installation Figure 4 Schematic diagram of the pulse sequence when controlling the phase gate.

[0045] Figure 6 1 is a schematic diagram showing how, when microwaves detuned by δ from the cross-Rabi transition are applied, the transition frequency of a state related to the cross-Rabi transition is modulated by AC-stark shift.

[0046] Figure 7 It is a functional block diagram of the quantum gate device involved in the second embodiment.

[0047] Figure 8 is a graph showing the intensity η of the cross resonance and the residual ZZ interaction as a function of the coupling strength of the classical coupler.

[0048] Fig. 9 It is a top view of the quantum bit substrate portion involved in the third embodiment.

[0049] Fig.10 Show Fig. 9 A top view of a quantum bit substrate in which the quantum bits are further integrated and arranged in a square lattice.

[0050] Fig.11 It is a top view of the quantum bit substrate portion involved in the fourth embodiment.

[0051] Fig.12 yes Fig.11 A top view of a quantum bit substrate in which the quantum bits are further integrated and arranged in a square lattice.

[0052] Fig.13 is a graph showing the frequencies of data qubits and coupler qubits.

[0053] Fig.14 is a diagram showing qubits and frequencies around a coupler control port.

[0054] Fig.15 Shown in Fig. 9 The coupler controls port 1 around the used frequency and becomes the error frequency.

[0055] Fig.16 Shown in Fig. 9 The coupler controls port 2 around the used frequency and becomes the error frequency.

[0056] Fig.17This is a functional block diagram of a superconducting quantum gate device according to the fifth embodiment.

[0057] Fig.18 This is a functional block diagram of a quantum computer according to the sixth embodiment.

[0058] Fig.19 : is a flowchart showing the processing of the quantum gate operation method involved in the seventh embodiment.

[0059] Fig. 20 This is a photo of the top of the quantum bit substrate used in the verification experiment.

[0060] Fig.21 It shows the observation and Figure 2 The thin solid arrows correspond to the experimental results obtained by the Rabi oscillations between states.

[0061] Fig. 22 It shows the observation and Figure 2 The thick solid arrows correspond to the experimental results obtained by Rabi oscillations between states.

[0062] Fig.23 The figure shows the results of evaluating the accuracy of controlling the phase gate by Interleaved randomized benchmarking.

[0063] Fig.24 This is a diagram showing the results of inducing ZZ interaction by AC Stark shift and canceling the residual ZZ interaction. DETAILED DESCRIPTION

[0064] Hereinafter, the present invention will be described based on a preferred embodiment and with reference to the accompanying drawings. The same reference numerals are used in the same or equivalent components, members, and processes shown in the various figures, and repeated descriptions are appropriately omitted. In addition, the scales and shapes of the various parts shown in the various figures are set for convenience in order to facilitate the description, and should not be interpreted restrictively unless otherwise mentioned. In the case of using terms such as "first" and "second" in this specification or technical solution, such terms do not indicate any order or importance unless otherwise mentioned, and are only used to distinguish a certain structure from other structures. In addition, a part of the components that are not important when describing the implementation method is omitted in each figure for display.

[0065] [First embodiment]

[0066] Figure 1 1 is a functional block diagram of the quantum gate device 1 according to the first embodiment. The quantum gate device 1 includes a quantum bit substrate unit 10 and a pulse irradiation unit 20 .

[0067] The qubit substrate 10 carries a first data qubit 11, a second data qubit 12, and a coupler qubit 13. 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. The first data qubit 11 is connected in parallel with the capacitor 1101 via a Josephson element 1001 to form a resonant circuit. The second data qubit 12 is connected in parallel with the capacitor 1102 via a Josephson element 1002 to form a resonant circuit. The coupler qubit 13 is connected in parallel with the capacitor 1103 via a Josephson element 1003 to form a resonant circuit. That is, in Figure 1 In the example, the first data qubit 11, the second data qubit 12 and the coupler qubit 13 are all composed of Transmon-type qubits with fixed frequencies.

[0068] The pulse irradiation unit 20 irradiates the coupler qubit 13 with a driving pulse. More specifically,

[0069] The resonance frequency of the first excited state of the first data quantum bit 11 is set to ω1,

[0070] The resonance frequency of the first excited state of the second data quantum bit 12 is set to ω2,

[0071] Set the resonance frequency of the first excited state of the coupler qubit 13 to ω c ,

[0072] hour,

[0073] The pulse irradiation unit 20 irradiates the coupler qubit 13 with a pulse of frequency ω c +|ω1-ω2| defined as the first cross-Rabi transition drive pulse, and the frequency ω shifted from the first cross-Rabi transition drive pulse by a predetermined frequency δ c The residual ZZ interaction of +|ω1-ω2|-δ eliminates the driving pulse.

[0074] Here, the predetermined frequency shift δ is a value that eliminates the 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.

[0075] [Cross-Rabi transition drive pulse]

[0076] Figure 1 The Hamiltonian of the system shown can be modeled by the following equation (1) in which anharmonic oscillators are coupled via the Jaynes-Cummings interaction.

[0077] [Formula 1]

[0078]

[0079] here

[0080] [Formula 2]

[0081]

[0082] It is the value obtained by dividing Planck's constant h by 2π. i (i∈{1, 2, c}) are the frequencies of the first excited states of the first data qubit 11 (i=1), the second data qubit 12 (i=2), and the coupler qubit 13 (i=c), respectively. i , (i∈{1, 2, c}) are the anharmonicity of the first data qubit 11 (i=1), the second data qubit 12 (i=2) and the coupler qubit 13 (i=c), respectively.

[0083] [Formula 3]

[0084]

[0085] are the generator and destroyer operators of each mode respectively. ic is a constant representing the strength of the Jaynes-Cummings interaction. For simplicity, the direct coupling between the first data qubit and the second data qubit is not considered here. It is assumed that the physical system modeled in this equation (1) is generated in a parameter region called the dispersion region. In this region,

[0086] [Formula 4]

[0087] |g ic / Δ ic |<<1,Δ ic =ω i -ω c

[0088] The relationship holds. In the system represented by equation (1) in the dispersion region, the new parameter resonance proposed below can be induced by applying microwaves to the coupler quantum bit 13. At this time, the microwave drive is driven at a driving frequency ω d In the rotating coordinate system, the Hamiltonian represented by equation (2) can be used for modeling.

[0089] [Formula 5]

[0090]

[0091] Here, Ω is a constant representing the driving strength.

[0092] Figure 2 It is shown Figure 1 The energy level diagram of the energy transition of the system. However, here, the state up to the excitation number 2 is extracted and shown. The Dirac symbol (bra-ket) shows the states of the first data qubit, the second data qubit, and the coupler qubit from the left. That is, |Q1Q2>|Q c > c The first data qubit is in the state of Q1, the second data qubit is in the state of Q2, and the coupler qubit is in the state of Q c The energy levels shown by the thick solid line are the energy levels used for calculation in the partial space where the coupler qubit is in the ground state. The energy levels shown by the thin solid line represent the partial space where the coupler qubit is in the first excited state.

[0093] In Figure 1 When the above microwave drive is applied to the system, Figure 2 The transitions are shown by the thick solid arrows or thin solid arrows. d In the rotating coordinate system, the driving frequencies are set so that the energy conservation laws shown in equations (3) and (4) hold true in the transitions indicated by the thick solid arrows and the thin solid arrows.

[0094] [Formula 6]

[0095]

[0096] [Formula 7]

[0097]

[0098] The thick solid arrows show the energy transition (ω) when microwaves are applied at a driving frequency that satisfies the energy conservation law of equation (3). d =ω c +Δ 12 , Δ 12 =ω1-ω2). At this time, the photon with frequency ω2 accumulated in the second data qubit and the photon with frequency ω provided by the microwave drive d The photons are converted into the four-wave mixing process caused by the third-order nonlinear effect of the Josephson junction of the coupler quantum bit and are accumulated at frequencies ω1 and ω c The first data qubit and the photon in the coupler qubit.

[0099] The thin solid arrows show the energy transition (ω) when microwaves are applied at a driving frequency that satisfies the energy conservation law of equation (4). d =ω c -Δ 12 , Δ 12=ω1-ω2). At this time, the photon with frequency ω1 accumulated in the first data qubit and the photon with frequency ω provided by the microwave drive d The photons are converted into the four-wave mixing process caused by the third-order nonlinear effect of the Josephson junction of the coupler quantum bit, which is accumulated at frequencies ω2 and ω c The second data qubit and the photon in the coupler qubit.

[0100] The above is a qualitative description of the parametric resonance proposed in this embodiment. Figure 2 As shown, in this resonance, while excitations are exchanged between data qubits, a transition is made from a state where the total number of excitations is 1 to a state where the total number of excitations is 2. In this way, by applying microwave drive to the coupler qubit of the Transmon with a fixed frequency, a parametric resonance caused by the third-order nonlinear effect of the coupler qubit is generated, and while excitations are exchanged between data qubits, a transition is made to a state where the total number of excitations differs by one. Such phenomena and principles have been unknown so far and were discovered by the inventors in the process of conceiving the present invention. Since the transition is between energy levels with a difference of one in the number of excitations while exchanging excitations, the inventors named this transition "cross-Rabi transition" or "Coupler-Assisted Swap (CAS: coupling-assisted exchange) transition". Hereinafter, in this specification, the term "cross-Rabi transition" is used. In addition, the pulse that drives the cross-Rabi transition is referred to as a "cross-Rabi transition drive pulse".

[0101] Cross-Rabi transitions can be used to implement two functions of gate quantum devices. The first is quantum gate operation. This uses the geometric phase obtained by resonantly utilizing cross-Rabi transitions to induce Rabi oscillations between states outside the computation space. Figure 2 and Figure 3 The quantum gate operation is described.

[0102] Figure 3 Schematic diagram of the geometric phase obtained through cross-Rabi transitions. Figure 3 The Bloch sphere is shown as an example of two states associated with the cross-Rabi transition. Figure 2 The thick solid arrows correspond to the cross-Rabi transitions. In the starting state |01>|0> in the computation space c When the cross-Rabi transition is driven by microwaves as the starting point, the state indicated by the arrow is Figure 3 The surface of the Bloch sphere shown here develops along the dotted line with time. As a result of the time development, the end state is different from the start state |01>|0> c In consistent cases, Figure 3The dotted line becomes a closed curve. The geometric phase obtained at this time is proportional to the solid angle A enclosed by the closed curve. In this case, time development becomes a single process. Therefore, the initial state is phase-advanced by the amount of the obtained geometric phase compared to other states in the calculation space. By adjusting the length and frequency of the driven microwave to the appropriate length and frequency, quantum gate operation can be achieved.

[0103] For example, by adjusting the size of the geometric phase to π, such as Figure 4 As shown, a control phase gate can be implemented between the first data qubit 11 and the second data qubit 12. Here, Figure 4 is a schematic diagram showing a control phase gate that acts between the first data qubit 11 and the second data qubit 12 .

[0104] Figure 5 It shows the installation Figure 4 Schematic diagram of the pulse sequence when controlling the phase gate. As mentioned above, here, the coupler quantum bit 13 is applied with a frequency ω d =ω c +Δ 12 The microwaves vibrate. In addition, the microwaves weakly modulate the frequency of the data qubits and cause AC-stark shift. Therefore, a local phase gate for correcting the phase shift is applied to each data qubit. This phase gate is installed by a method called a virtual phase gate.

[0105] The second function of the quantum gate device is to modulate the ZZ interaction. This function is achieved by using cross-Rabi transitions in a dispersed manner to induce AC-stark shift in the energy levels in the computation space. This effectively eliminates the residual coupling called residual ZZ interaction that exists due to the coupling of data qubits. The magnitude of the residual coupling ξ can be expressed using the energy levels of the computation space as

[0106] ξ=ω 11 -ω 10 -ω 01 .

[0107] Figure 6 Schematic diagram showing that when microwaves detuned by δ from the cross-Rabi transition are applied, the transition frequency of the state related to the cross-Rabi transition is modulated by AC-stark shift. Figure 2 The thick solid arrows cross the Rabi transition case, ω 01 The frequency of Figure 6 Therefore, the residual coupling can be expressed as ξ(ω d , Ω) and can be expressed by the frequency ω of the microwave drivend and intensity Ω for modulation.

[0108] Next, the interaction is derived analytically. First, the Hamiltonian in the dispersion region represented by equation (1) is diagonalized to the coupling constant g by a perturbed method called Schrieffer-Wolff transformation. ic The second order. The Schrieffer-Wolff transform uses the skew Hermitian matrix

[0109] [Formula 8]

[0110]

[0111] It is represented by the following formula (5).

[0112] [Formula 9]

[0113]

[0114] Here, until the coupling constant g ic The second order is valid [Formula 10]

[0115]

[0116] It can be found by solving the following equations (6) and (7).

[0117] [Formula 11]

[0118]

[0119] [Formula 12]

[0120]

[0121] in,

[0122] [Formula 13]

[0123]

[0124] [Formula 14]

[0125]

[0126] Formula (1) uses the obtained [Formula 10]

[0127]

[0128] It can be approximated by the following formula (8).

[0129] [Formula 15]

[0130]

[0131] here,

[0132] [Formula 16]

[0133]

[0134] is the frequency of each mode after Lamb shift,

[0135] [Formula 17]

[0136]

[0137] is the effective anharmonicity.

[0138] In addition, when using this

[0139] [Formula 8]

[0140]

[0141] When the driving Hamiltonian equation (2) is expanded, it can be expressed by the following equation (9).

[0142] [Formula 18]

[0143]

[0144] By using formula (9), under the condition of microwave driving, Figure 2 The transition intensity corresponding to the thin solid arrow is expressed by the following formula (10).

[0145] [Formula 19]

[0146]

[0147] The transition intensity corresponding to the thick solid arrow is expressed by the following formula (11).

[0148] [Formula 20]

[0149]

[0150] As described above, according to this embodiment, by driving the coupler qubit at a specific frequency, quantum gate operation can be realized and residual ZZ interaction can be effectively eliminated. That is, a quantum gate device that can eliminate residual ZZ interaction and realize double quantum gate operation without external magnetic flux can be provided.

[0151] It should be noted that the pulse irradiation unit 20 may also irradiate the coupler qubit 13 with either the first cross Rabi transition drive pulse or the second cross Rabi transition drive pulse and the residual ZZ interaction elimination drive pulse in an overlapping manner. Alternatively, the pulse irradiation unit 20 may also irradiate the coupler qubit 13 with both the first cross Rabi transition drive pulse and the second cross Rabi transition drive pulse and the residual ZZ interaction elimination drive pulse.

[0152] [Second embodiment]

[0153] Figure 7 2 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.

[0154] The qubit substrate 10a carries the first data qubit 11, the second data qubit 12, the coupler qubit 13, and the capacitor 30. The coupler qubit 13 is arranged 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 the capacitor 101 and the capacitor 102, respectively. In addition, the first data qubit 11 and the second data qubit 12 are directly coupled via the capacitor 30. That is, the quantum gate device 2 is relatively Figure 1 The structure of the quantum gate device 1 is different in that the first data qubit 11 and the second data qubit 12 are coupled via the capacitor 30. The other structures of the quantum gate device 2 are the same as those of the quantum gate device 1.

[0155] The pulse irradiation unit 20a irradiates the first cross Rabi transition driving pulse or the second cross Rabi transition driving pulse and the residual ZZ interaction elimination driving pulse to the coupler quantum bit 13. At this time, the first cross Rabi transition driving pulse or the second cross Rabi transition driving pulse and Figure 1 The quantum gate device 1 is the same as that of the quantum gate device 2, but the predetermined frequency offset δ for eliminating the residual ZZ interaction driving pulse is different from that of the quantum gate device 1. That is, the frequency offset δ of the quantum gate device 2 is a value for eliminating 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 described in detail below.

[0156] exist Figure 1 In the case of the structure shown, a small amount of a double quantum gate element called cross resonance is mixed in the XI gate and the IX gate. Since the cross resonance causes errors in the single quantum gate, it is desirable to remove it.

[0157] Therefore, in this embodiment, if Figure 7 As shown, the first data qubit 11 and the second data qubit 12 are coupled not only via the coupler qubit 13 but also directly coupled using the capacitor 30. Hereinafter, the coupling via the coupler qubit 13 is referred to as a "quantum coupler", and the direct coupling using the capacitor 30 is referred to as a "classical coupler". The present inventors have conducted intensive research and have found that cross resonance can be eliminated by accurately adjusting the magnitude of the coupling of the classical coupler.

[0158] Figure 8 In FIG. 1 , the intensity η of the cross resonance and the intensity of the residual ZZ interaction are shown as a function of the coupling strength of the classical coupler. At the coupling strength indicated by the arrow (about 9 MHz), the cross resonance zero crosses and disappears. In addition, under this condition, the residual ZZ interaction is also sufficiently and effectively reduced. Therefore, the predetermined frequency shift δ of the residual ZZ interaction elimination driving pulse irradiated by the pulse irradiation unit 20a of the quantum gate device 2 becomes a value that achieves the coupling strength.

[0159] According to this embodiment, in the quantum gate device, in addition to being able to reduce the residual ZZ interaction, it is also possible to remove the cross resonance.

[0160] [Third Embodiment]

[0161] Next, a description will be given of a form in which the data qubits and the coupler qubits are integrated in the quantum gate device of the above-described embodiment.

[0162] Fig. 9 1 is a top view of the qubit substrate unit 10b involved in the third embodiment. The qubit substrate unit 10b carries three or more data qubits, namely the first data qubit 11, the second data qubit 12 and the third data qubit 19, a coupler qubit 13 arranged between adjacent data qubits, a coupler control port 14 for controlling the coupler qubit 13, and a readout port 15 for reading out the data qubit. As shown in the figure, specifically, the qubit substrate unit 10b has 9 data qubits, 12 coupler qubits, 2 coupler control ports 14, and 1 readout port 15.

[0163] The coupler control port 14 is a wiring for controlling the coupler qubit, and is connected to the adjacent upper, lower, left, and right coupler qubits, respectively. The readout port 15 is a wiring for reading out the data qubit, and is connected to the adjacent four tilted data qubits, respectively.

[0164] According to this embodiment, qubits can be integrated, and the coupler qubits can be controlled and the data qubits can be read using the coupler control port and the readout port.

[0165] Fig.10 Yes Fig. 9 A top view of the qubit substrate portion of the qubits further integrated and configured in a square grid. In this example, the number of data qubits is 64, the number of coupler qubits is 112, the number of coupler control ports is 40, and the number of readout ports is 16. 2 When the data qubits are arranged in a square grid, the number of coupler qubits becomes 2n(n-1), and the number of coupler control ports becomes (n+1). 2 -(n / 2+1) 2 -n 2 / 4, the number of read ports becomes n 2 / 4. However, the configuration method of each quantum bit and each port is not limited to Fig.10 methods, and their number is not limited to the above.

[0166] According to this embodiment, the quantum bits carried can be further highly integrated.

[0167] [Fourth Embodiment]

[0168] Fig.11 1 is a top view of the qubit substrate unit 10c involved in the fourth embodiment. The qubit substrate unit 10c carries three or more data qubits, namely, a first data qubit 11, a second data qubit 12, and a third data qubit 19, a coupler qubit 13 arranged between adjacent data qubits, a coupler control port 14 for controlling the coupler qubit 13, a readout port 15 for reading out the data qubit, and a single qubit control port 16 on a two-dimensional plane. As shown in the figure, specifically, the qubit substrate unit 10c has 9 data qubits, 12 coupler qubits, 2 coupler control ports 14, 1 readout port 15, and 1 single qubit control port 16.

[0169] The coupler control port 14 is used to control the wiring of the coupler qubit, and is respectively connected to the adjacent upper, lower, left, and right coupler qubits. The readout port 15 is used to read the wiring of the data qubit, and is respectively connected to the four adjacent tilted data qubits. The single qubit control port 16 is used to control the wiring of the single qubit of the quantum gate device, and is respectively connected to the four adjacent tilted data qubits.

[0170] According to this embodiment, a single quantum bit of a quantum gate device can be controlled.

[0171] Fig.12 Yes Fig.11A top view of a qubit substrate in which the qubits are further integrated and arranged in a square grid. In this example, the number of data qubits is 64, the number of coupler qubits is 112, the number of coupler control ports is 40, the number of readout ports is 16, and the number of single qubit control ports is 25. 2 When the data qubits are arranged in a square grid, the number of coupler qubits becomes 2n(n-1), and the number of coupler control ports becomes (n+1). 2 -(n / 2+1) 2 -n 2 / 4, the number of read ports becomes n 2 / 4, the number of single-qubit control ports becomes (n / 2+1) 2 However, the configuration method of each quantum bit and each port is not limited to Fig.10 methods, and their number is not limited to the above.

[0172] According to this embodiment, the quantum bits carried can be further highly integrated.

[0173] Fig.13 The frequency of the data qubit and the coupler qubit is shown. The ellipse is the data qubit, the rectangle is the coupler qubit, the circle with a right lower slash is the coupler control port, and the circle with a left lower slash is the readout port. The values ​​in the data qubit and coupler qubit are frequencies expressed in MHz. Since multiple qubits are excited from one wiring, adjustments need to be made to avoid conflicts in the frequencies used. For example, by Fig.13 By allocating the frequencies in this way, the eight frequencies (four for single quantum gates and four for double quantum gates) applied to the respective wirings are all different, and thus crosstalk can be reduced.

[0174] In addition, there is a transition called Fogi transition as a transition that may cause line mixing with the frequency ωc+|ω1-ω2|=ωc+|Δ12| (set as ω1-ω2=Δ12. The same applies below) of the ZZ gate operation. The resonant frequency of the Fogi transition needs to be different from the resonant frequency of the cross-Rabi transition for the ZZ gate operation (that is, there should be no frequency conflict). The frequency conflict is described below.

[0175] Fig.14 The qubits and frequencies around the coupler control port are shown. Fig.15 Shown in Fig. 9 The coupler controls port 1 around the used frequency and becomes the error frequency. Fig.16 Shown in Fig. 9The frequency used around the coupler control port 2 and the frequency that becomes an error. Here, α represents the nonlinearity of the quantum bit. For example, αc12 represents the nonlinearity of the quantum coupler Qc12 between the first quantum bit and the second quantum bit. Fig.15 and Fig.16 The black circles (ω1, ω2, ω3, ω4) and white circles (ωc12+|Δ12|, ωc24+|Δ24|, ωc13+|Δ13|, ωc34+|Δ34|) indicate the frequencies used. On the other hand, Fig.15 and Fig.16 The circles with downward slashes on the left (ωc12, ωc24, ωc13, ωc34) and circles with downward slashes on the 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) indicate the frequencies that become errors. In particular, the circles with downward slashes on the right indicate the frequencies at which Fogi transitions occur.

[0176] Here, it is necessary to prevent conflicts between "used frequencies" and conflicts between "used frequencies" and "wrong frequencies". Fig.15 and Fig.16 In FIG. 1 , the drawing of the black circle and the drawing of the white circle do not conflict with each other. In addition, it can be seen that the black circle and the white circle are both deviated from the region (gray shaded region) containing the frequency that becomes an error, and the condition for avoiding the occurrence of frequency conflict is satisfied.

[0177] [Fifth Embodiment]

[0178] The above-described technology is expected to be applicable to various qubits. However, the first data qubit, the second data qubit, and the coupler qubit are particularly preferably superconducting qubits.

[0179] Fig.17 This is a functional block diagram of a superconducting quantum gate device 3 according to the fifth embodiment. The superconducting quantum gate device 3 includes the above-mentioned qubit substrate unit 10 formed using superconducting qubits, and a refrigerator 40 for cooling the qubit substrate unit 10 to operate it.

[0180] The refrigerator 40 is composed of a dilution refrigerator (cryostat) etc. The refrigerator 40 is kept at a low temperature of several K (Kelvin) to several tens of mK (milliKelvin). Devices other than the qubit substrate unit 10 such as the pulse irradiation unit 20 are placed outside the refrigerator 40 .

[0181] According to the present embodiment, a superconducting quantum gate device that can remove the residual ZZ interaction and perform double quantum gate operation without external magnetic flux can be provided.

[0182] [Sixth embodiment]

[0183] Fig.18 4 is a functional block diagram of a quantum computer 4 according to the sixth embodiment. The quantum computer 4 includes the above-mentioned superconducting quantum gate device formed using superconducting quantum bits, and a control unit 50 for controlling the superconducting quantum gate device 3. The control unit 50 performs, for example, syndrome extraction operations and logical quantum gate operations for quantum error correction processing, and is installed by a control device or PC placed outside the refrigerator 40.

[0184] According to this embodiment, a quantum computer that can remove the residual ZZ interaction and perform double quantum gate operation without external magnetic flux can be provided.

[0185] [Seventh Embodiment]

[0186] Fig.19 : is a flowchart showing the processing of the quantum gate operation method involved in the seventh embodiment. The method is a quantum gate operation method for a quantum bit system, the quantum bit system having at least two data quantum bits, namely a first data quantum bit and a second data quantum bit, and a coupler quantum bit configured between the first data quantum bit and the second data quantum bit, wherein the method includes steps S1 and S2. Here, the resonance frequency of the first excited state of the first data quantum bit is set to ω1, the resonance frequency of the first excited state of the second data quantum bit is set to ω2, and the resonance frequency of the first excited state of the coupler quantum bit is set to ω c Step S1: irradiate with a frequency ω c +|ω1-ω2| defined as the first cross-Rabi transition driving pulse. Step S2 irradiates the coupler qubit with a frequency ω shifted by a predetermined frequency δ from the first cross-Rabi transition driving pulse. c The residual ZZ interaction of +|ω1-ω2|-δ cancels the driving pulse. The predetermined frequency shift δ is a value that cancels the residual ZZ interaction between the first data qubit and the second data qubit.

[0187] Alternatively, step S1 may also replace the first cross Rabi transition driving pulse with a second cross Rabi transition driving pulse. Here, the frequency of the second cross Rabi transition driving pulse is ω c -|ω1-ω2| is defined. At this time, step S2 irradiates the coupler qubit with a frequency ω shifted by a predetermined frequency δ from the first cross-Rabi transition driving pulse. c -|ω1-ω2|-δ residual ZZ interaction cancels the driving pulse. In this case, the prescribed frequency shift δ is still a value that cancels the residual ZZ interaction between the first data qubit and the second data qubit.

[0188] According to the present embodiment, it is possible to perform removal of residual ZZ interaction and double quantum gate operation without external magnetic flux using a quantum gate device.

[0189] [Verification experiment]

[0190] Experiments were conducted to verify the techniques described above. Fig. 20 This is a photo of the top of the quantum bit substrate used in this experiment.

[0191] Fig.21 Shows observations and Figure 2 The thin solid arrows correspond to the experimental results obtained by the Rabi oscillations between states. Fig. 22 Shows observations and Figure 2 The thick solid arrows correspond to the experimental results of the Rabi oscillations between the states. Fig.21 and Fig. 22 In the graph, the horizontal axis represents the length of the microwave drive pulse used to induce the cross-Rabi interaction, and the vertical axis represents the detuning of the drive frequency from the frequency of the first excited state of the coupler qubit. The bars on the right side of the graph represent the transmission characteristics of the readout resonator coupled to the qubit, which is proportional to the occupancy of the qubit's first excited state.

[0192] Here, let the detuning of the driving frequency from the resonance of the coupler qubit be δ, and let the value obtained by converting the driving intensity into frequency be Ω. At this time, the resonance condition of the cross-Rabi transition becomes

[0193] √(δ 2 +4Ω 2 ),

[0194] In this embodiment, it is set to 140MHz. Therefore, δ is slightly offset from ±140MHz by the amount of Ω. Fig.19 In the case of Rabi oscillation, it is possible to observe δ=-100MHz near Fig. 20 Rabi oscillations can be observed near δ = 113.5 MHz.

[0195] Next, use Fig. 22 The parameters of the cross-Rabi transitions obtained in the experiment were used to install the control phase gates. The accuracy of the installed control phase gates was evaluated by a method called interleaved randomized benchmarking. Fig.23 The results are shown in the figure. The fidelity obtained by fitting is shown in the figure. As shown in the figure, it can be seen that a highly accurate control phase gate with a fidelity of about 99% is achieved.

[0196] Finally, by driving the Figure 2The transition shown by the thick solid arrow leads to the ZZ interaction based on AC Stark shift, which eliminates the residual ZZ interaction. Fig.24 The results are shown. The horizontal axis represents the detuning of the driving frequency from the coupler quantum bit transition frequency, and the vertical axis represents the magnitude of the residual ZZ interaction. The short vertical solid line represents the measurement result of the residual ZZ interaction, and the dotted line represents the fitting result of the measurement result.

[0197] The long vertical line near 125.6 MHz on the horizontal axis represents the detuning of the driving frequency from the coupler qubit when the residual ZZ interaction calculated from the fitting results becomes zero. That is, the data obtained by measuring the magnitude of the residual ZZ interaction can be fitted, and the detuning of the driving frequency from the coupler qubit is calculated from the fitting results. Fig.24 The driving frequency at which the residual interaction becomes zero (indicated by the arrow) is obtained. If the uncertainty of the fitting is taken into account, the residual ZZ interaction can be suppressed to a range of -150 Hz to 60 Hz. It should be noted that the magnitude of the residual ZZ interaction in the absence of microwave drive is about 2.5 kHz. In this way, the following result can be verified: the ZZ interaction becomes zero at an appropriate driving frequency, and the elimination of the residual ZZ interaction using the cross-Rabi transition in a dispersed manner is achieved as expected.

[0198] The technology disclosed in this specification has the two effects of eliminating the residual ZZ interaction that is the cause of quantum gate errors and realizing high-precision double quantum gates. The superconducting quantum circuit including the coupler quantum bits used can constitute all elements with frequency-fixed quantum bits. Therefore, no external magnetic flux is required, and it can become a noise-resistant structure. Thus, the optimization of interactions or subsequent functions such as gates that need to be corrected can all be performed only by the application of microwaves. Therefore, the number of microwave wiring for quantum bits can be reduced. The reduction of microwave wiring directly contributes to the increase in the number of quantum bits, and the control with less errors contributes to high-performance quantum computers. In addition, compared with existing methods, the problem of frequency conflict is also solved.

[0199] As described above, in this technology, all corrections for quantum gates or residual interaction elimination are performed using microwaves. Since no tuning based on a DC magnetic field is performed, there is no performance degradation of quantum bits caused by magnetic field noise, and stable control can be achieved. As a result, a high-fidelity double quantum gate is achieved. As shown in the above experimental results, the world's highest level of performance, 99%, is achieved with the current performance.

[0200] In addition, in the above experiment, the double quantum gate and the elimination of residual ZZ interaction were achieved with a very low microwave intensity of about -87dBm. This is because the transition amplitude of the cross-Rabi transition is large, and compared with the existing microwave-controlled gate, it can be controlled with a weak intensity of about 10dB to 20dB. Such energy-saving quantum gates solve the heat problem when driving a large number of quantum bits, which contributes to high scalability.

[0201] On the other hand, most all-microwave-based methods require the application of high-intensity microwaves. However, such high-intensity microwaves cause thermal problems as the number of quantum bits increases, resulting in the limitation that they can only be expanded within the cooling capacity of the refrigerator. As shown in the above-mentioned experiments, according to this method, very low-intensity microwaves such as about -87dBm can be used to achieve the elimination of double quantum gates and residual ZZ interactions. This is because the transition amplitude of the cross-Rabi transition is large. In this way, the microwave control of this method is very efficient compared with existing methods, and energy savings of 10dB to 20dB are achieved in terms of gate and ZZ interaction correction. This means that in the same refrigerator, the integration of 10 to 100 times the number of quantum bits can be directly achieved, which is helpful to realize large-scale superconducting quantum computers.

[0202] As described above, the technology disclosed in this specification applies microwave drive to the coupler quantum bit, causing parameter resonance originating from the third-order nonlinear effect of the coupler that has not been discovered so far, thereby achieving the removal of residual ZZ interaction and double quantum gate operation, which is a very novel and industrially useful technology.

[0203] [Application to single-qubit gate operations]

[0204] In the above-mentioned embodiment, the elimination of residual ZZ interaction and the control phase gate operation using microwave irradiation to the coupler qubit are described. The technology disclosed in the present invention is not limited to this, and can also be applied to the usual quantum gate operation (single qubit gate operation) using microwave irradiation to the coupler qubit.

[0205] Consider two data qubits Q i (i = 1, 2) and a coupler qubit Q c The coupling constant g i Coupled system.

[0206] Coupler qubit Q c Illuminating the data qubit Q i The frequency ω i , strength Ω0 i In this way,

[0207] In g ic / Δ ic <<1、Ω0 i / Δ ic <<1、(Δ ic =ω i -ω c ), the Hamiltonian of the entire system is written as follows.

[0208] [Formula 21]

[0209]

[0210] The first two terms are the terms that drive the data Transmon qubit via the coupler (CR terms). The second two terms are the terms that directly drive the data Transmon qubit due to microwave crosstalk on the chip (CT terms). The coefficient corresponding to the driving strength based on crosstalk is set to ν i IX , ν i IY .

[0211] Among the parameters of this system, Ω0 is satisfied i / Δ ic <<1, so the coupler qubit can be treated as the ground state (g state). c =1, then equation (12) can be rewritten as equation (13).

[0212] [Formula 22]

[0213]

[0214] According to this formula, it is possible to keep the coupler quantum bit Q unchanged. c state and only the data qubit Q i Drive.

[0215] According to the above situation, by adding the coupler quantum bit Q c Irradiating the data qubits Q1 and Q2 with microwaves of frequency ω1 and frequency ω2 can realize single-qubit gates of these data qubits Q1 and Q2.

[0216] According to the above situation, by adding the coupler quantum bit Q c Irradiating the data qubits Q1 and Q2 with microwaves of frequency ω1 and frequency ω2 can realize single-qubit gates of these data qubits Q1 and Q2.

[0217] [Eighth Embodiment]

[0218] Reference Figure 1The eighth embodiment is described with reference to the quantum gate device 1. The quantum gate device 1 comprises: a quantum bit substrate unit 10, which carries a first data quantum bit 11, a second data quantum bit 12, and a coupler quantum bit 13 arranged between the first data quantum bit 11 and the second data quantum bit 12; and a pulse irradiation unit 20, which irradiates a driving pulse to the coupler quantum bit 13. The resonance frequency of the first excited state of the first data quantum bit 11 is set to ω1, and the resonance frequency of the first excited state of the second data quantum bit 12 is set to ω2. At this time, the pulse irradiation unit 13 irradiates the coupler quantum bit 13 with a microwave defined by a frequency ω1. Thus, the first quantum gate operation on the first quantum bit 11 can be performed.

[0219] Alternatively, in the above-mentioned configuration, the pulse irradiation unit 13 may irradiate microwaves defined by the frequency ω2 to the coupler qubit 13. In this case, the second quantum gate operation for the second qubit is performed.

[0220] According to the present embodiment, it is possible to perform quantum gate operations on each data qubit simply by irradiating the coupler qubit with microwaves, without directly controlling the data qubit.

[0221] The present invention has been described based on the embodiments. These embodiments are illustrative, and those skilled in the art will appreciate that various modifications are possible in the combination of their constituent elements or processing steps, and such modifications are also within the scope of the present invention.

[0222] The first data qubit, the second data qubit, and the coupler qubit are not limited to superconducting qubits, and may be any appropriate qubit such as a quantum dot or an ion trap.

[0223] According to this modification, the degree of freedom of the structure can be increased.

[0224] A new embodiment generated by the combination has the effects of each of the combined embodiments and modifications.

[0225] The above-mentioned embodiments and modified examples are only specific examples, and various design changes such as changing, adding, deleting, etc. of constituent elements can be made. In the embodiments, the content that can make such design changes is emphasized by marking the expression "embodiment". However, even if there is no such expression, design changes are allowed.

[0226] Industrial Applicability

[0227] 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.

[0228] Description of Reference Numerals

[0229] 1··Quantum gate device.

[0230] 2··Quantum gate device.

[0231] 3··Superconducting quantum gate device.

[0232] 4··Quantum computer.

[0233] 10··Qubit substrate part.

[0234] 10a··Qubit substrate part.

[0235] 10b··Quantum bit substrate part.

[0236] 10c··Quantum bit substrate part.

[0237] 11··First data qubit.

[0238] 12··Second data qubit.

[0239] 13··Coupler qubit.

[0240] 14··Coupler control port.

[0241] 15··Read port.

[0242] 16··Single qubit control port.

[0243] 20··Pulse irradiation unit.

[0244] 20a··Pulse irradiation unit.

[0245] 30··Capacitor.

[0246] 40··Refrigerator.

[0247] 50··Control Department.

[0248] 101··Capacitor.

[0249] 102··Capacitor.

[0250] 1001··Josephson element.

[0251] 1101··Capacitor.

[0252] 1002··Josephson element.

[0253] 1102··Capacitor.

[0254] 1003··Josephson element.

[0255] 1103··Capacitor.

[0256] S1: a step of irradiating a first cross-Rabi transition driving pulse to the coupler qubit. S2: a step of irradiating a residual ZZ interaction elimination driving pulse to the coupler qubit.

Claims

1. A quantum gate device, characterized in that: The quantum gate device comprises: A qubit substrate portion, which carries at least two data qubits, namely a first data qubit and a second data qubit, and a coupler qubit disposed between the first data qubit and the second data qubit; as well as a pulse irradiation unit for irradiating a driving pulse to the coupler quantum bit, The resonance frequency of the first excited state of the first data quantum bit is set to ω1, The resonance frequency of the first excited state of the second data quantum bit is set to ω2, The resonant frequency of the first excited state of the coupler qubit is set to ω c , At this time, the pulse irradiation unit irradiates the coupler quantum bit with a frequency ω c +|ω1-ω2| defined as a first cross-Rabi transition drive pulse, and a frequency ω shifted from the first cross-Rabi transition drive pulse by a specified frequency δ c +|ω1-ω2|-δ residual ZZ interaction eliminates the driving pulse, The predetermined frequency offset δ is a value that eliminates residual ZZ interaction between the first data qubit and the second data qubit.

2. A quantum gate device, characterized in that: The quantum gate device comprises: A qubit substrate portion, which carries at least two data qubits, namely a first data qubit and a second data qubit, and a coupler qubit disposed between the first data qubit and the second data qubit; as well as a pulse irradiation unit for irradiating a driving pulse to the coupler quantum bit, The resonance frequency of the first excited state of the first data quantum bit is set to ω1, The resonance frequency of the first excited state of the second data quantum bit is set to ω2, The resonant frequency of the first excited state of the coupler qubit is set to ω c , At this time, the pulse irradiation unit irradiates the coupler quantum bit with a frequency ω c - a second cross-Rabi transition driving pulse defined by |ω1-ω2|, and a frequency ω shifted from the second cross-Rabi transition driving pulse by a predetermined frequency δ c - The residual ZZ interaction of |ω1-ω2|-δ eliminates the driving pulse, The predetermined frequency offset δ is a value that eliminates residual ZZ interaction between the first data qubit and the second data qubit.

3. The quantum gate device according to claim 1 or 2, characterized in that: The pulse irradiation unit irradiates the coupler qubit with both the first cross-Rabi transition drive pulse and the second cross-Rabi transition drive pulse, and a residual ZZ interaction elimination drive pulse.

4. The quantum gate device according to claim 1, characterized in that: The first cross-Rabi transition driving pulse performs a control phase gate between the first data qubit and the second data qubit.

5. The quantum gate device according to claim 2, characterized in that: The second cross-Rabi transition driving pulse performs a control phase gate between the first data qubit and the second data qubit.

6. The quantum gate device according to claim 1 or 2, characterized in that: The quantum gate device further includes a capacitor for coupling the first data qubit and the second data qubit. The predetermined frequency offset δ is a value that eliminates 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.

7. The quantum gate device according to claim 1 or 2, characterized in that: The qubit substrate unit carries on a two-dimensional plane: three or more data qubits, coupler qubits arranged between adjacent data qubits, a coupler control port for controlling the coupler qubits, and a readout port for reading out the data qubits.

8. The quantum gate device according to claim 7, characterized in that: The quantum bit substrate is equipped with: The data quantum bits are arranged in a square lattice; The coupler qubits are arranged in a square lattice between adjacent data qubits; A coupler control port, which is arranged at the center of the square grid of the coupler qubits and controls the coupler qubits; as well as A readout port is arranged at the center of the square grid of the data quantum bits and performs readout of the data quantum bits.

9. The quantum gate device according to claim 7, characterized in that: The qubit substrate unit is further equipped with a single qubit control port, which performs single qubit control of the data qubit.

10. The quantum gate device according to claim 8, characterized in that: The qubit substrate portion is further equipped with a single qubit control port, which is arranged at the center of the square grid of the data qubits to perform single qubit control of the data qubits.

11. The quantum gate device according to claim 1 or 2, characterized in that: The first data qubit, the second data qubit, and the coupler qubit are superconducting qubits.

12. A superconducting quantum gate device, characterized in that: The superconducting quantum gate device has: The quantum gate device of claim 11; and A refrigerator is used to cool the quantum bit substrate to enable it to operate.

13. A quantum computer, characterized in that: The quantum computer has: The superconducting quantum gate device according to claim 12; and A control unit controls the superconducting quantum gate device.

14. A quantum gate operation method is a quantum gate operation method for a quantum bit system, wherein the quantum bit system has: at least two data qubits, namely a first data qubit and a second data qubit; and a coupler qubit disposed between the first data qubit and the second data qubit, It is characterized in that The resonance frequency of the first excited state of the first data quantum bit is set to ω1, The resonance frequency of the first excited state of the second data quantum bit is set to ω2, The resonant frequency of the first excited state of the coupler qubit is set to ω c , At this time, the quantum gate operation method includes the following steps: The coupler qubit is irradiated with a frequency ω c + the first cross-Rabi transition drive pulse defined by |ω1-ω2|; and The coupler qubit is irradiated with a frequency ω shifted by a predetermined frequency δ from the first cross-Rabi transition driving pulse. c +|ω1-ω2|-δ residual ZZ interaction eliminates the driving pulse, The predetermined frequency offset δ is a value that eliminates residual ZZ interaction between the first data qubit and the second data qubit.

15. A quantum gate operation method is a quantum gate operation method for a quantum bit system, wherein the quantum bit system has: at least two data qubits, namely a first data qubit and a second data qubit; and a coupler qubit disposed between the first data qubit and the second data qubit, It is characterized in that The resonance frequency of the first excited state of the first data quantum bit is set to ω1, The resonance frequency of the first excited state of the second data quantum bit is set to ω2, The resonant frequency of the first excited state of the coupler qubit is set to ω c , At this time, the quantum gate operation method includes the following steps: The coupler qubit is irradiated with a frequency ω c - a second cross-Rabi transition drive pulse defined by |ω1-ω2|; and The coupler qubit is irradiated with a frequency ω shifted by a predetermined frequency δ from the second cross-Rabi transition driving pulse. c - The residual ZZ interaction of |ω1-ω2|-δ eliminates the driving pulse, The predetermined frequency offset δ is a value that eliminates residual ZZ interaction between the first data qubit and the second data qubit.

16. A quantum gate device, characterized in that: The quantum gate device comprises: A qubit substrate portion, which carries at least two data qubits, namely a first data qubit and a second data qubit, and a coupler qubit disposed between the first data qubit and the second data qubit; as well as a pulse irradiation unit for irradiating a driving pulse to the coupler quantum bit, The resonance frequency of the first excited state of the first data quantum bit is set to ω1, The resonance frequency of the first excited state of the second data quantum bit is set to ω2, At this time, the pulse irradiation unit performs the first quantum gate operation by irradiating the coupler quantum bit with microwaves defined by a frequency ω1.

17. A quantum gate device, characterized in that: The quantum gate device comprises: A qubit substrate portion, which carries at least two data qubits, namely a first data qubit and a second data qubit, and a coupler qubit disposed between the first data qubit and the second data qubit; as well as a pulse irradiation unit for irradiating a driving pulse to the coupler quantum bit, The resonance frequency of the first excited state of the first data quantum bit is set to ω1, The resonance frequency of the first excited state of the second data quantum bit is set to ω2, At this time, the pulse irradiation unit performs the second quantum gate operation by irradiating the coupler quantum bit with microwaves defined by a frequency ω2.

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