Quantum device

Abstract

A quantum device includes: a filter having a plurality of trapped waves in a first frequency band lower than a second frequency band; a first qubit that resonates in a first frequency band; and a second qubit that resonates in a second frequency band. When single qubit gating is performed, a first qubit is input with a signal having a frequency of first qubit resonance via a filter to control a state of the first qubit, and when double qubit gating is performed, the first qubit is input with a signal having a frequency of first qubit resonance via a filter to control a state of the first qubit. The first qubit is input with a signal having a frequency at which the second qubit resonates via a filter to control a state of the second qubit according to a quantum state of the first qubit.

Description

Technical Field

[0001] The embodiments discussed herein relate to quantum devices. Background Art

[0002] In a quantum computer using superconducting qubits (hereinafter, also referred to as "qubits"), there is a known method for performing a dual-qubit gating operation. In order to control the qubit, the qubit is coupled to a waveguide, and a microwave pulse is irradiated from the waveguide. The stronger the coupling between the qubit and the waveguide, the shorter the time required to perform the qubit gating operation (or gate time) becomes. On the other hand, the stronger the coupling between the qubit and the waveguide, the shorter the quantum lifetime (or quantum coherence) of the qubit becomes. That is, increasing the quantum lifetime of the qubit and reducing the gate time are contradictory relationships, for example, as explained in International Publication Pamphlet No. WO2020 / 105732.

[0003] In two-qubit gating (also called cross-resonance gating), a signal having a frequency that resonates with the target qubit is input from a waveguide to the control qubit, causing the state of the target qubit to change depending on the state of the control qubit.

[0004] In the case of two-qubit gating, gating can be accelerated (i.e., gating time can be shortened) by increasing the strength of the signal input to the control qubit or increasing the coupling efficiency between the waveguide and the qubit. However, if the coupling between the control qubit and the input waveguide is too strong, the radiation loss from the control qubit to the input waveguide increases, and the coherence time (or data retention time) of the control qubit is shortened. Summary of the invention

[0005] Therefore, an object of one aspect of an embodiment is to provide a quantum device capable of ensuring quantum gating speed and coherence time.

[0006] According to one aspect of the embodiment, a quantum device includes: a filter having a plurality of notches in a first frequency band lower than a second frequency band; a first qubit that resonates in the first frequency band; and a second qubit that resonates in the second frequency band, wherein, when single-qubit gating is performed, the first qubit is input with a signal having a frequency at which the first qubit resonates via the filter to control a state of the first qubit, and when double-qubit gating is performed, the first qubit is input with a signal having a frequency at which the first qubit resonates via the filter to control a state of the second qubit according to a quantum state of the first qubit.

[0007] The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.

[0008] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a diagram showing a connection example of a qubit;

[0010] Figure 2 is a graph used to explain the frequency dependence of the coupling efficiency between the waveguide and the control qubit;

[0011] Figure 3 is a diagram for explaining a quantum device according to one embodiment;

[0012] Figure 4 is a diagram showing an example of frequency characteristics of coupling efficiency of a filter;

[0013] Figure 5 is a perspective view showing a configuration example of a quantum device according to a first embodiment;

[0014] Figure 6 is an equivalent circuit diagram of a quantum device according to the first embodiment;

[0015] Figure 7 is a plan view showing a configuration example of a quantum device according to a second embodiment;

[0016] Figure 8 is an equivalent circuit diagram of a quantum device according to the second embodiment; and

[0017] Fig. 9 It is a diagram for explaining the frequency characteristics of the resonance frequency of a quantum bit and the coupling efficiency of a filter. DETAILED DESCRIPTION

[0018] Preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0019] A quantum device according to an embodiment includes a filter for correcting the level difference between the signals required for single-qubit gating and double-qubit gating input to each qubit at each resonant frequency of a control qubit resonating in a low frequency band and a target qubit resonating in a high frequency band, so as to realize a quantum logic gate of a quantum computer. The quantum computer includes single-qubit logic gates such as Pauli gates and double-qubit logic gates such as controlled Pauli-X gates (or CNOT gates), and performs calculations using these qubit logic gates. The CNOT gate is used to generate quantum entangled states, etc.

[0020] Cross-resonance gating is an example of a configuration for inducing quantum entanglement. Cross-resonance gating has a control qubit adjacent to the input terminal and a target qubit to be coupled to the control qubit. The control qubit and the target qubit have mutually different resonant frequencies.

[0021] Figure 1 2 is a diagram showing a connection example of a qubit. A control signal S for driving two-qubit gating (or cross-resonance gating) in which the control qubit 10 and the target qubit 20 are coupled is input to the control qubit 10 .

[0022] In cross-resonance gating, a control signal S having the same frequency as the resonant frequency (or resonance frequency) of the target qubit 20 is input to the control qubit 10 so as to induce quantum entanglement between the control qubit 10 and the target qubit 20 adjacent to each other. As a result, the state of the target qubit 20 changes according to the quantum state of the control qubit 10. The control signal S is, for example, a microwave.

[0023] In the case of cross-resonance gating in which the control qubit 10 resonating in the low frequency band and the target qubit 20 resonating in the high frequency band are coupled, gating can be accelerated (gating time can be shortened) by increasing the strength of the control signal S input from the waveguide 31 to the control qubit 10 or increasing the coupling efficiency of the control signal S from the waveguide 31 to the control qubit 10. However, if the coupling strength between the waveguide 31 and the control qubit 10 is too large, the coherence time (or data retention time) of the control qubit 10 is shortened.

[0024] Therefore, the quantum device according to the present embodiment includes a filter structure in which the coupling efficiency γ between the waveguide 31 and the control qubit 10 has Figure 2 The coupling efficiency γ represents the ratio of the intensity of the control signal S input from the waveguide 31 to the control qubit 10 to the intensity of the control signal S input to the waveguide 31. The intensity of the control signal S is represented by the amplitude of the power of the control signal S, for example. The filter structure according to the present embodiment has the coupling characteristics such that the coupling efficiency γ in the second frequency band including the frequency (resonance frequency ω2) at which the target qubit 20 resonates is higher than the coupling efficiency γ in the first frequency band including the frequency (resonance frequency ω1) at which the control qubit 10 resonates.

[0025] Since the coupling efficiency γ is high at the resonance frequency ω2, the control signal S having a relatively high intensity at the resonance frequency ω2 is input to the control qubit 10, and therefore, the two-qubit gating between the control qubit 10 and the target qubit 20 can be accelerated. On the other hand, since the coupling efficiency γ is low at the resonance frequency ω1, the radiation loss from the control qubit 10 to the waveguide 31 at the resonance frequency ω1 can be reduced, and the shortening of the coherence time of the control qubit 10 can be reduced. Therefore, two-qubit gating capable of ensuring quantum gating speed and coherence time can be provided.

[0026] For example, by adopting a filter structure having a high coupling efficiency γ at the resonance frequency ω2, the quantum gating speed can be ensured even if the power of the control signal S input to the waveguide 31 at the resonance frequency ω2 is reduced compared to the case where such a filter structure is not adopted. By reducing the power of the control signal S input to the waveguide 31 at the resonance frequency ω2, reduced power consumption can be achieved.

[0027] For example, the power of the control signal S at the resonance frequency ω2 can be reduced to the power of the control signal S at the resonance frequency ω1. When the power of the control signal S at the resonance frequency ω2 becomes equal to the power of the control signal S at the resonance frequency ω1, digital generation of the control signal S is advantageous. For example, if a signal with a large level difference is created using a single digital-to-analog converter (DAC), the dynamic range of the signal becomes narrower and the quality of the signal may deteriorate. On the other hand, if such a signal with a large level difference is created using multiple DACs, the number of required components or parts increases, and the size and cost of the device for generating the control signal S are increased. In contrast, when the power of the control signal S at the resonance frequency ω2 becomes equal to the power of the control signal S at the resonance frequency ω1, even when the control signal S is generated using a single DAC, the degradation of the signal quality caused by insufficient dynamic range can be reduced.

[0028] according to Figure 3 The quantum device 100 of the present embodiment shown includes a high pass filter 40 in a stage preceding the control qubit 10. The high pass filter has a coupling characteristic in which the coupling efficiency γ in the second frequency band including the resonance frequency ω2 is higher than the coupling efficiency γ in the first frequency band including the resonance frequency ω1.

[0029] Figure 3 is a diagram showing a configuration example of a quantum device according to the present embodiment. Figure 3The quantum device 100 shown includes: a high pass filter 40 that transmits a control signal S in a first frequency band with a coupling efficiency γ lower than the coupling efficiency in a second frequency band; a control qubit 10 that resonates in the first frequency band; and a target qubit 20 that resonates in the second frequency band. The quantum device 100 is a cross-resonance gated device in which the control qubit 10 and the target qubit 20 are coupled, for example, via a transmission line 30.

[0030] High pass filter 40 is an example of a filter that transmits a signal in a first frequency band with a coupling efficiency γ lower than a coupling efficiency in a second frequency band. Control qubit 10 is an example of a first qubit that resonates in a first frequency band. Target qubit 20 is an example of a second qubit that resonates in a second frequency band.

[0031] When single-qubit gating is implemented, a signal having a frequency at which the control qubit 10 resonates is input to the control qubit 10 via the high-pass filter 40, thereby controlling the quantum state of the control qubit 10. When double-qubit gating is implemented, a control signal S having a frequency at which the target qubit 20 resonates is input to the control qubit 10 via the high-pass filter 40. As a result, the state of the target qubit 20 changes according to the quantum state of the control qubit 10.

[0032] The high-pass filter 40 included in the quantum device 100 according to the present embodiment has a plurality of notches in a low frequency band including the resonance frequency of the control qubit 10 (a first frequency band in which the coupling efficiency γ is reduced more than in the second frequency band). Therefore, it is possible to ensure that the first frequency band in which the coupling efficiency γ is reduced more than in the second frequency band has a width as wide as a certain range. Since the wide width of the first frequency band can be ensured, the coupling efficiency characteristics of the high-pass filter 40 in the first frequency band can be made close to a flat characteristic. As a result, even when the frequency of the control qubit 10 resonance is offset due to manufacturing deviation or the like, the operation (cross-resonance gating) of the quantum device 100 can be stabilized.

[0033] Figure 4 : is a diagram showing an example of the frequency characteristics of the coupling efficiency of the filter. The high-pass filter 40 has a coupling efficiency characteristic of transmitting the control signal S in the first frequency band W1 with a coupling coefficient γ lower than the coupling coefficient in the second frequency band W2. The high-pass filter 40 has a plurality of notches (in this example, a first notch 51 and a second notch 52) in the first frequency band W1 including the resonance frequency fq1 of the control qubit 10.

[0034] The first notch 51 is a frequency characteristic point at which the control signal S1 is minimized at the first notch frequency fn1 included in the first frequency band W1. The second notch 52 is a frequency characteristic point at which the control signal S1 is minimized at the second notch frequency fn2 included in the first frequency band W1. The second notch frequency fn2 is higher than the first notch frequency fn1.

[0035] The high-pass filter 40 has a frequency characteristic A1 having a first notch 51 and a second notch 52 in the first frequency band W1. Therefore, compared with the case of having a frequency characteristic A2 having one notch 53 having a notch frequency fn3 in the low frequency band, the width of the first frequency band W1 in which the control signal S input to the control qubit 10 is transmitted with a coupling coefficient γ lower than the coupling coefficient in the second frequency band W2 can be widened. Since the width of the first frequency band W1 in which the control signal S is transmitted with a coupling coefficient γ lower than the coupling coefficient in the second frequency band W2 can be widened, the coupling coefficient characteristic of the high-pass filter 40 in the first frequency band W1 can be made close to a flat characteristic. As a result, even when the frequency at which the control qubit 10 resonates is offset due to manufacturing deviation or the like, the operation (cross-resonance gating) of the quantum device 100 can be stabilized.

[0036] exist Figure 4 In the example shown, the high-pass filter 40 has a first notch 51 and a second notch 52 so that the resonance frequency fq1 of the control qubit 10 is between the first notch frequency fn1 and the second notch frequency fn2. In this case, the control qubit 10 resonates in a frequency band between the first notch frequency fn1 and the second notch frequency fn2. Therefore, by providing notches above and below the resonance frequency fq1 of the control qubit 10, the coupling efficiency γ at the resonance frequency fq1 can be prevented from becoming excessively reduced.

[0037] Figure 4 An example is shown in which the high-pass filter 40 has a frequency characteristic A1 of two notches including a first notch 51 and a second notch 52 in the first frequency band W1. However, the high-pass filter 40 may have three or more notches in the first frequency band W1. Therefore, the width of the first frequency band W1 in which the coupling coefficient γ is reduced more than in the second frequency band W2 can be further widened.

[0038] The frequency characteristics of the high pass filter 40 may have one or more resonance points that resonate between the resonance frequency fq1 of the control qubit 10 and the resonance frequency fq2 of the target qubit 20 . Figure 4The example of frequency characteristic A1 shown has a first resonance point 54 with filter resonance frequency fr1 and a second resonance point 55 with filter resonance frequency fr2 between resonance frequency fq1 and resonance frequency fq2. Filter resonance frequency fr1 is higher than second notch frequency fn2. Filter resonance frequency fr2 is higher than filter resonance frequency fr1. Frequency characteristic A2 has a resonance point 56 with filter resonance frequency fr3 between resonance frequency fq1 and resonance frequency fq2.

[0039] Since the high-pass filter 40 has a frequency characteristic A1 that resonates between the resonant frequency fq1 and the resonant frequency fq2, the coupling efficiency difference D can be increased compared to the case where the high-pass filter 40 has a frequency characteristic that does not resonate between the resonant frequency fq1 and the resonant frequency fq2. The coupling efficiency difference D represents the difference between the coupling efficiency γ of the high-pass filter 40 in the first frequency band W1 and the coupling efficiency γ of the high-pass filter 40 in the second frequency band W2. By increasing the coupling efficiency difference D, even if the intensity of the control signal S in the second frequency band W2 increases, the intensity of the control signal S in the first frequency band W1 can be reduced. That is, the quantum gating speed can be increased and the reduction in coherence time can be reduced at the same time.

[0040] The high pass filter 40 can have a coupling efficiency characteristic of transmitting the control signal S in the first frequency band W1 with a coupling coefficient γ lower than the coupling coefficient in the second frequency band W2 by utilizing Fano resonance. By utilizing Fano resonance, a frequency characteristic A1 capable of ensuring a large coupling efficiency difference D can be easily obtained.

[0041] like Figure 3 As shown, the high-pass filter 40 may include a first filter 41 forming a first notch 51 and a second filter 42 forming a second notch 52. Since each notch is formed by a separate filter, the accuracy of the first notch frequency fn1 and the second notch frequency fn2 can be improved. For example, the first filter 41 can use Fano resonance to achieve a frequency characteristic having a first notch 51 and a first resonance point 54. The second filter 42 can use Fano resonance to achieve a frequency characteristic having a second notch 52 and a second resonance point 55. Figure 4 The frequency characteristic A1 shown can be realized by a combination of the frequency characteristic of the first filter 41 and the frequency characteristic of the second filter 42 .

[0042] Figure 5 is a diagram showing a configuration example of a quantum device according to the first embodiment. Figure 5 The quantum device 101 shown is an example of the quantum device 100 described above. Figure 5The quantum device 101 shown includes a substrate 70 having a first layer 71 facing a first direction and a second layer 72 facing a second direction opposite to the first direction. One of the first layer 71 and the second layer 72 is a front surface layer of the substrate 70, and the other of the first layer 71 and the second layer 72 is a rear surface layer of the substrate 70. The substrate 70 is a dielectric substrate on which a predetermined conductor pattern is formed.

[0043] A terminal 43 to which a control signal S is input is provided on the first layer 71. The terminal 43 is electrically connected to a coaxial line 60 that transmits the control signal S. The terminal 43 is, for example, an electrode such as a planar terminal pad or the like. The coaxial line 60 is, for example, an example of a transmission line such as a coaxial cable or the like. The coaxial line 60 is an example of the above-mentioned waveguide 31. The control signal S input to the terminal 43 via the coaxial line 60 passes through the inner layer of the substrate 70 and reaches the control qubit 10 provided on the second layer 72. Although Figure 5 Although not shown in the figure, the target qubit 20 coupled to the control qubit 10 is disposed on the second layer 72, for example.

[0044] Since the quantum device 101 has a configuration in which the control signal S is transmitted from the first layer 71 to the second layer 72, the length of the transmission line for transmitting the control signal S from the terminal 43 to the control qubit 10 is relatively short (approximately equal to the thickness of the substrate 70). For this reason, according to the conventional technology, it is difficult to provide a high-pass filter having a coupling efficiency characteristic similar to the above-mentioned frequency characteristic A1 on the transmission line from the terminal 43 to the control qubit 10 due to space constraints.

[0045] Therefore, in the quantum device 101 according to the first embodiment, the high-pass filter 40 (more specifically, the first filter 41 and the second filter 42) utilizing the interference of the Fano resonance for the coupling efficiency characteristic is provided on the first layer 71. Therefore, even in the quantum device 101 having a configuration in which it is difficult to sufficiently ensure the length of the transmission line for transmitting the control signal S from the terminal 43 to the control qubit 10, it is easy to form the high-pass filter 40 having the above-described frequency characteristic A1.

[0046] The first filter 41 and the second filter 42 are arranged around the terminal 43. Therefore, it is easy to form the high-pass filter 40 having the above-mentioned frequency characteristic A1 that transmits the control signal Sin from the terminal 43 to the control qubit 10 with a low coupling coefficient γ. In this example, the second filter 42 is formed to be opposite to the first filter 41, with the terminal 43 interposed therebetween.

[0047] The first filter 41 includes a first resonator 44 adjacent to the terminal 43, and the second filter 42 includes a second resonator 45 adjacent to the terminal 43. The first resonator 44 is a high-frequency circuit that forms a first resonance point 54 of the frequency characteristic A1, and the second resonator 45 is a high-frequency circuit that forms a second resonance point 55 of the frequency characteristic A1. The second resonator 45 is formed to be opposite to the first resonator 44, and the terminal 43 is interposed between the second resonator 45 and the first resonator 44. The first resonator 44 is provided between the terminal 43 and the ground 73. The second resonator 45 is provided between the terminal 43 and the ground 73. The ground 73 is formed on the first layer 71.

[0048] The first resonator 44 includes a first conductor pattern 46 formed on the first layer 71. The second resonator 45 includes a second conductor pattern 47 formed on the first layer 71. For example, the first conductor pattern 46 and the second conductor pattern 47 are formed on Figure 4 A linear conductor is shown in the fan-shaped area and multiple turns.

[0049] The control qubit 10 includes a Josephson junction 11 that does not overlap with the first resonator 44 and the second resonator 45 in a plan view of the substrate 70. Therefore, the influence of the crosstalk of the first resonator 44 and the second resonator 45 on the Josephson junction 11 can be reduced, and thus the coherence time (the average time that the qubit maintains the excited state "1") of the control qubit 10 can be maintained.

[0050] Figure 6 is based on Figure 5 The equivalent circuit diagram of the quantum device of the first embodiment is shown in FIG. The substrate 70 has a substrate capacitance C between the terminal 43 and the control qubit 10. F . Substrate capacitance C F is a coupling capacitance between the terminal 43 and the control qubit 10 , and is included in the first filter 41 and the second filter 42 .

[0051] The first filter 41 includes a first capacitor C between the terminal 43 and the first conductor pattern 46 of the first resonator 44. k and a second capacitor C between the first conductor pattern 46 of the first resonator 44 and the control qubit 10 q That is, the first conductor pattern 46 forms a first capacitor C between the first conductor pattern 46 and the terminal 43. k , and a second capacitor C is formed between the first conductor pattern 46 and the control qubit 10 q The first notch 51 is formed by the first capacitor C k and the second capacitor C q The signal transmitted to the control qubit 10 via the first resonator 44 is connected to the substrate capacitor CF Destructive interference (Fanow resonance) between the signals transmitted directly from the waveguide to the control qubit 10 is formed.

[0052] The second filter 42 includes a third capacitor C between the terminal 43 and the second conductor pattern 47 of the second resonator 45. k2 and a fourth capacitor C between the second conductor pattern 47 of the second resonator 45 and the control qubit 10 q2 That is, the second conductor pattern 47 forms a third capacitor C between the second conductor pattern 47 and the terminal 43. k2 , and a fourth capacitor C is formed between the second conductor pattern 47 and the control qubit 10 q2 The second notch 52 is formed by the third capacitor C k2 and the fourth capacitor C q2 The signal transmitted to the control qubit 10 via the second resonator 45 is connected to the substrate capacitor C F Destructive interference between signals transmitted directly from the waveguide to the control qubit 10 is formed.

[0053] The first resonator 44 includes a fifth capacitor C between the first conductor pattern 46 and the ground 73. R and a first inductor L between the first conductor pattern 46 and the ground 73 R The first resonator 44 includes a fifth capacitor C R and the first inductor L R The first resonance point 54 is formed by the first resonator 44.

[0054] The second resonator 45 includes a sixth capacitor C between the second conductor pattern 47 and the ground 73. R2 and a second inductor L between the second conductor pattern 47 and the ground 73. R2 The second resonator 45 includes a sixth capacitor C R2 and the second inductor L R2 The second resonance point 55 is formed by the second resonator 45 .

[0055] Figure 7 is a plan view showing a configuration example of a quantum device according to the second embodiment. Figure 7 The quantum device 102 shown is an example of the quantum device 100 described above. Figure 7 The quantum device 102 shown includes a substrate 70 having an input line 75 for inputting a control signal S and an output line 76 connected to the control qubit 10. The quantum device 102 includes a high pass filter 40 including a plurality of filters (in this example, a first filter 41 and a second filter 42) connected in series between the input line 75 and the output line 76.

[0056] The first filter 41 includes a first resonator 44 adjacent to an input line 75, and the second filter 42 includes a second resonator 45 adjacent to an output line 76. The first resonator 44 is a high frequency circuit that forms a first resonance point 54 of a frequency characteristic A1, and the second resonator 45 is a high frequency circuit that forms a second resonance point 55 of the frequency characteristic A1. The second resonator 45 is formed to face the first resonator 44, and capacitive coupling is interposed between the second resonator 45 and the first resonator 44. The first resonator 44 is disposed between the input line 75 and the second resonator 45 so as to be surrounded by the ground 73. The second resonator 45 is disposed between the first resonator 44 and the output line 76 so as to be surrounded by the ground 73. The ground 73 is formed on the first layer 71.

[0057] The first resonator 44 includes a first conductor pattern 46 formed on a first layer 71. The second resonator 45 includes a second conductor pattern 47 formed on a first layer 71. The first conductor pattern 46 and the second conductor pattern 47 are linear conductors that are folded back and forth multiple times.

[0058] Figure 8 yes Figure 7 The equivalent circuit diagram of the quantum device of the second embodiment is shown in FIG. The quantum device 102 includes a capacitor C between the input line 75 and the first filter 41. RE1 and the capacitance C between the first filter 41 and the second filter 42 RE2 The quantum device 102 also includes a capacitor C between the input line 75 and the output line 76 or the control qubit 10. RE3 and the capacitance C between the second filter 42 and the output line 76 or the control qubit 10 QR The plurality of notches including the first notch 51 and the second notch 52 are formed by the capacitor C RE1 , capacitor C RE2 and capacitor C QR The signal transmitted from the input line 75 to the output line 76 via the first resonator 44 and the second resonator 45 is connected to the capacitor C RE3 Destructive interference occurs between signals transmitted directly from input line 75 to output line 76.

[0059] The first resonator 44 includes a capacitor C between the first conductor pattern 46 and the ground 73. R and a first inductor L between the first conductor pattern 46 and the ground 73 R The first resonator 44 is composed of a capacitor C R and the first inductor L R The first resonance point 54 is formed by the first resonator 44.

[0060] The second resonator 45 includes a capacitor C between the second conductor pattern 47 and the ground 73. R2and a second inductor L between the second conductor pattern 47 and the ground 73. R2 The second resonator 45 includes a capacitor C R2 and the second inductor L R2 The second resonance point 55 is formed by the second resonator 45 .

[0061] Fig. 9 is a diagram for explaining the frequency characteristics of the resonance frequency of each qubit and the coupling efficiency of the filter. The target qubit 20 may include a plurality of target qubits (in this example, four target qubits 20a, 20b, 20c, and 20d) resonating at mutually different frequencies in the second frequency band W2.

[0062] The control qubit 10 has a resonance frequency fq1 in the first frequency band W1. By providing a plurality of notches in the first frequency band W1, the control signal S input to the control qubit 10 is transmitted in a low frequency band including the resonance frequency fq1 with a coupling coefficient γ lower than that in the second frequency band W2.

[0063] On the other hand, the plurality of target qubits 20a, 20b, 20c, and 20d have resonance frequencies fq2a, fq2b, fq2c, and fq2d within the second frequency band W2. The high-pass filter 40 has a coupling coefficient γ in the first frequency band W1 that is lower than the coupling coefficient γ in the second frequency band W2. The plurality of target qubits 20a, 20b, 20c, and 20d resonate at frequencies included in a high frequency band having a flat characteristic in the frequency characteristics of the high-pass filter 40.

[0064] According to the present disclosure, quantum gating speed and coherence time can be ensured.

[0065] Although the embodiments are numbered, for example, "first" or "second," the ordinal number does not imply priority of the embodiments. Many other variations and modifications will be apparent to those skilled in the art.

[0066] All examples and conditional language described herein are intended for teaching purposes to help readers understand the present invention and the concepts contributed by the inventor to promote the art, and should be interpreted as not limited to such specific examples and conditions, and the organization of such examples in the specification is not intended to show the advantages and disadvantages of the present invention. Although the embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions and modifications can be made thereto without departing from the spirit and scope of the present invention.

Claims

1. A quantum device, comprising: a filter having a plurality of notches in a first frequency band below a second frequency band; a first qubit that resonates in the first frequency band; as well as a second qubit that resonates in said second frequency band, Wherein, when single-qubit gating is performed, the first qubit is input with a signal having a frequency resonating with the first qubit via the filter to control the state of the first qubit, and when double-qubit gating is performed, the first qubit is input with a signal having a frequency resonating with the second qubit via the filter to control the state of the second qubit according to the quantum state of the first qubit.

2. The quantum device according to claim 1, wherein: The filter resonates between a resonant frequency of the first qubit and a resonant frequency of the second qubit.

3. The quantum device according to claim 1, wherein: The plurality of notches include a first notch having a first notch frequency and a second notch having a second notch frequency that is higher than the first notch frequency and lower than a resonant frequency of the filter.

4. The quantum device according to claim 3, wherein: The filter includes a first filter forming the first notch and a second filter forming the second notch.

5. The quantum device according to claim 4, further comprising: A substrate includes a first layer provided with the first filter and the second filter and a second layer provided with the first qubit.

6. The quantum device according to claim 5, wherein: The first layer is provided with a terminal to which a signal having a frequency resonating with the first qubit or the second qubit is input, and The first filter and the second filter are disposed around the terminal.

7. The quantum device according to claim 6, wherein: The second filter is opposed to the first filter via the terminal interposed between the first filter and the second filter.

8. The quantum device according to claim 6, wherein: The first filter includes a first resonator proximate to the terminal, and The second filter includes a second resonator proximate to the terminal.

9. The quantum device according to claim 8, wherein: The first qubit includes a Josephson junction that does not overlap with the first resonator and the second resonator in a plan view of the substrate.

10. The quantum device according to claim 8, wherein: The first filter includes a first capacitance between the terminal and the first resonator and a second capacitance between the first resonator and the first qubit, and The second filter includes a third capacitance between the terminal and the second resonator and a fourth capacitance between the second resonator and the first qubit.

11. The quantum device according to claim 8, wherein: Each of the first filter and the second filter includes a coupling capacitor between the terminal and the first qubit, and The first notch is formed by interference between a signal passing through the first resonator and a signal passing through the coupling capacitor, and the second notch is formed by interference between a signal passing through the second resonator and a signal passing through the coupling capacitor.

12. The quantum device according to claim 10, wherein: The first resonator includes a first conductor pattern forming the first capacitance and the second capacitance, a fifth capacitance between the first conductor pattern and ground, and a first inductor between the first conductor pattern and the ground, and The second resonator includes a second conductor pattern forming the third capacitance and the fourth capacitance, a sixth capacitance between the second conductor pattern and the ground, and a second inductor between the second conductor pattern and the ground.

13. The quantum device according to any one of claims 1 to 12, wherein: The first qubit resonates in a frequency band between the plurality of notches.

14. The quantum device according to any one of claims 1 to 12, wherein: The second qubit includes a plurality of qubits that resonate at frequencies different from one another in the second frequency band.

15. The quantum device according to any one of claims 1 to 12, wherein: The filter utilizes Fano resonance.

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