JP-7857014-B2 - Quantum logic gate manipulation device, quantum logic gate manipulation method, and program

Inventors

• 部谷 謙太郎
• 中村 泰信

Assignees

• 国立研究開発法人理化学研究所

Dates

Publication Date

20260512

Application Date

20220810

Claims (14)

1. A two-qubit system in which a control qubit and a target qubit are coupled, A cross-resonance drive pulse irradiation unit irradiates the control qubit with a cross-resonance drive pulse having the intrinsic frequency of the target qubit, The control qubit is irradiated with an echo pulse irradiating an echo pulse to invert the quantum state of the control qubit, Control unit and A quantum logic gate manipulation device equipped with, The control unit, During the first period of the quantum logic gate operation, the cross-resonance drive pulse of the first phase is irradiated, During the second period of the quantum logic gate operation, the cross-resonance drive pulse is irradiated while continuously changing the phase of the cross-resonance drive pulse from the first phase to the second phase, while maintaining the intensity of the cross-resonance drive pulse. During the third period of the quantum logic gate operation, the cross-resonance drive pulse irradiation unit is controlled to irradiate with the cross-resonance drive pulse of the second phase. A quantum logic gate manipulation device characterized by controlling the echo pulse irradiation unit to irradiate echo pulses during the second period.
2. The quantum logic gate manipulation device according to claim 1, characterized in that the control unit controls the echo pulse irradiation unit to frequency modulate the echo pulse.
3. The quantum logic gate manipulation device according to claim 2, characterized in that the frequency modulation is a frequency modulation that follows the modulation of the resonance frequency of the control qubit.
4. The quantum logic gate manipulation device according to claim 3, characterized in that the frequency modulation is further modified by adding the change in the anharmonicness of the control qubit.
5. The quantum logic gate manipulation device according to claim 1 or 2, characterized in that the first phase is 0 and the second phase is π.
6. A quantum logic gate manipulation device according to claim 1 or 2, characterized in that it is a CNOT gate.
7. A quantum logic gate manipulation device according to claim 1 or 2, characterized in that it is a root CNOT gate.
8. The quantum logic gate manipulation device according to claim 1 or 2, characterized in that the control qubit and the target qubit are superconducting qubits.
9. The quantum logic gate manipulation device according to claim 1 or 2, characterized in that the control unit includes an arbitrary waveform generator.
10. The quantum logic gate manipulation device according to claim 1 or 2, characterized in that the cross-resonance drive pulse irradiation unit and the echo pulse irradiation unit are integrated.
11. The quantum logic gate manipulation device according to claim 1 or 2, characterized in that the cross-resonance drive pulse irradiation unit and the echo pulse irradiation unit are separate components.
12. The quantum logic gate manipulation device according to claim 1 or 2, characterized in that the control unit controls the cross-resonance drive pulse irradiation unit and the echo pulse irradiation unit to repeatedly perform the phase change of the cross-resonance drive pulse and the irradiation of the echo pulse.
13. A quantum logic gate operation method that performs quantum logic gate operations using a two-qubit system in which a control qubit and a target qubit are coupled, A cross-resonance drive pulse irradiation step in which the control qubit is irradiated with a cross-resonance drive pulse having the intrinsic frequency of the target qubit, The steps include an echo pulse irradiation step in which an echo pulse is irradiated onto the control qubit to invert the quantum state of the control qubit, Includes, In the aforementioned cross-resonance drive pulse irradiation step, During the first period of the quantum logic gate operation, the cross-resonance drive pulse of the first phase is irradiated, During the second period of the quantum logic gate operation, the cross-resonance drive pulse is irradiated while continuously changing the phase of the cross-resonance drive pulse from the first phase to the second phase, while maintaining the intensity of the cross-resonance drive pulse. During the third period of the quantum logic gate operation, the cross-resonance drive pulse of the second phase is irradiated. The method is characterized in that the echo pulse irradiation step involves irradiating an echo pulse during the second period.
14. A program that causes a computer to perform quantum logic gate operations using a two-qubit system in which a control qubit and a target qubit are coupled, A cross-resonance drive pulse irradiation step in which the control qubit is irradiated with a cross-resonance drive pulse having the intrinsic frequency of the target qubit, The steps include an echo pulse irradiation step in which an echo pulse is irradiated onto the control qubit to invert the quantum state of the control qubit, Includes, In the aforementioned cross-resonance drive pulse irradiation step, During the first period of the quantum logic gate operation, the cross-resonance drive pulse of the first phase is irradiated, During the second period of the quantum logic gate operation, the cross-resonance drive pulse is irradiated while continuously changing the phase of the cross-resonance drive pulse from the first phase to the second phase, while maintaining the intensity of the cross-resonance drive pulse. During the third period of the quantum logic gate operation, the cross-resonance drive pulse of the second phase is irradiated. The program is characterized in that, in the echo pulse irradiation step, an echo pulse is irradiated during the second period.

Description

This disclosure relates to a quantum logic gate manipulation device, a quantum logic gate manipulation method, and a program. Entangled quantum gates are a means of realizing the quantum logic gate operations necessary for quantum computers. Entangled quantum gates induce entanglement interactions between coupled qubits with different frequencies. This allows quantum information to be transmitted from one qubit to another. An example of a mechanism for manipulating entangled quantum gates is the cross-resonance gate (see, for example, Non-Patent Document 1). "Procedure for systematically tuning up crosstalk in the cross resonance gate", Sarah Sheldon, Easwar Magesan, Jerry M. Chow, and Jay M. Gambetta, Phys. Rev. A 93, 060302 (2016)“Cross-Cross Resonance Gate”, Kentaro Heya and Naoki Kanazawa, PRX Quantum 2, 040336 (2021) This is a schematic diagram illustrating the principle of a cross-resonance gate.This figure shows the temporal change of the cross-resonance drive pulse irradiated by DCX.This figure shows the temporal change of the cross-resonance drive pulse irradiated by TPCX.This figure shows the temporal change of the echo pulse irradiated by TPCX.This is a functional block diagram of a quantum logic gate manipulation device according to the first embodiment.This figure shows the temporal change of the cross-resonance drive pulse irradiated by OPCX.This figure shows the temporal change of the echo pulse irradiated by OPCX.This is an enlarged view of Figure 6 around the second period.This figure shows the phase change of the cross-resonance drive pulse of the OPCX on the complex plane.This figure shows the phase change of the TPCX cross-resonance drive pulse on the complex plane.This figure shows the relationship between the drive intensity and drive frequency of OPCX and TPCX.This figure shows the temporal change of the cross-resonance drive pulse irradiated by a two-pass OPCX.This figure shows the temporal change of the echo pulse irradiated by a two-pass OPCX.This is a processing flow diagram of the quantum logic gate manipulation method according to the second embodiment.This figure shows the changes in the main terms of the Cartan coefficient as gate operations are performed.This figure shows the changes in the secondary terms of the Cartan coefficient as a result of gate operations.This figure shows the change in the amount of leakage of the Kartan coefficient associated with the execution of gate operations. Before describing specific embodiments, let's refer to Figure 1 to explain the fundamental concepts. Figure 1 is a schematic diagram illustrating the principle of a cross-resonance gate. The two-qubit system 100 in Figure 1 is configured as a system in which a control qubit 101 and a target qubit 102 are coupled via a coupling resonator 103. In this example, both the control qubit 101 and the target qubit 102 are formed from superconducting qubits such as transmons, but this is not necessarily limited to this. The resonance frequency (also called the "natural frequency") f c of the control qubit 101 and the resonance frequency (also called the "natural frequency") f t of the target qubit 102 are different. For example, f c = 8.0 GHz and f t = 8.8 GHz, but these values are not limiting. In the two-qubit system 100 shown in Figure 1, the two qubits are coupled via a coupling resonator, but this is not necessarily limited to this. For example, the two-qubit system may be formed by direct coupling. What is important here is that qubits with different natural frequencies are coupled. The control qubit 101 and the target qubit 102 each have a state 0 (denoted as |0>) and a state 1 (denoted as |1>). Here, the states 0 and 1 of the control qubit 101 are denoted as |0> c and |1> c , respectively, and the states 0 and 1 of the target qubit 102 are denoted as |0> t and |1> t , respectively. In this system, a microwave pulse having the intrinsic frequency ft of the target qubit 102 is irradiated from the microwave source 104 to the control qubit 101. This microwave pulse is called a "cross-resonance drive pulse". At this time, the state of the control qubit 101 does not change before and after irradiation with the cross-resonance drive pulse. That is, |0> c → |0> c or |1> c → |1> c (the left side of the rightward arrow shows the state before irradiation with the cross-resonance drive pulse, and the right side shows the state after irradiation. The same applies below). On the other hand, the state of the target qubit 102 changes depending on the state of the control qubit 101. Specifically, when the state of the control qubit 101 is state 0 (|0> c ), the state of the target qubit 102 does not change. That is, if |0> c , then |0> t → |0> t or |1> t → |1> t . On the other hand, when the state of the control qubit 101 is state 1 (|1> c ), the state of the target qubit is reversed. That is, if |1> c , then |0> t → |1> t or |1> t → |0> t . In particular, a two-input, two-output cross-resonance gate that oper