A superconducting quantum chip reading and control method and device

Abstract

The present invention relates to the field of quantum computing technology, and specifically provides a superconducting quantum chip reading method, which has the following steps: S1, setting a quantum bit operation fidelity threshold a; S2, applying an H gate to the quantum bit, and performing quantum state tomography on the final state after applying the H gate to obtain a final state density matrix ρ; S3, comparing the final state density matrix ρ obtained in step S2 with the |+> state density matrix ρ+, and the comparison method is to calculate Tr(ρρ+); S4, comparing the size relationship between Tr(ρρ+) and a, and judging whether to replace a new quantum chip; S5, repeating steps S2 to S4 for the new quantum chip; S6, finding a quantum chip corresponding to Tr(ρρ+)≥a. Compared with the prior art, the present invention realizes the control and reading of different superconducting quantum chips by switching switches between different control circuits and chip connections.

Description

Technical Field

[0001] The present invention relates to the field of quantum computing technology, and specifically provides a superconducting quantum chip reading and control method and device. Background Art

[0002] Superconducting quantum computing is currently recognized as one of the most likely technical solutions to achieve commercial computing in a short period of time. However, superconducting quantum computing technology is far from mature and is still in the research stage, especially the research and development of superconducting quantum chips. Different bit structure designs and processing technology differences will have a great impact on the performance of superconducting quantum chips. In addition, there is often a problem of decreased fidelity of quantum chip operations as the use time increases, which will make it impossible to extract useful computing information from the state reading results of the quantum bits.

[0003] In order to check the fidelity of quantum bit operations, the commonly used method is the randomized benchmark (often abbreviated as RBM) scheme based on the Clifford group. However, this scheme has some shortcomings, such as its assumption that the errors of continuous gate operations are independent, which is inconsistent with the actual situation under certain non-Markov processes, and an RBM usually takes about several hours.

[0004] In addition, due to the limitations of the superconducting materials used in superconducting quantum chips and the characteristic frequency of superconducting quantum bits, superconducting quantum chips need to work in the ultra-low temperature environment provided by the dilution refrigerator. This means that every time a quantum chip is replaced, the dilution refrigerator needs to be heated up, disassembled, and cooled down again. The heating step alone takes about a day, which is time-consuming and labor-intensive. Summary of the invention

[0005] The present invention aims to overcome the above-mentioned deficiencies in the prior art and provides a highly practical method for reading a superconducting quantum chip.

[0006] A further technical task of the present invention is to provide a superconducting quantum chip control method.

[0007] A further technical task of the present invention is to provide a superconducting quantum chip control device that is rationally designed, safe and applicable.

[0008] The technical solution adopted by the present invention to solve its technical problem is:

[0009] A superconducting quantum chip reading method comprises the following steps:

[0010] S1. Set the quantum bit operation fidelity threshold a;

[0011] S2, applying the H gate to the quantum bit, and performing quantum state tomography on the final state after applying the H gate to obtain the final state density matrix ρ;

[0012] S3. Compare the final state density matrix ρ obtained in step S2 with the |+> state density matrix ρ+, and the comparison method is to calculate Tr(ρρ+).

[0013] S4. Compare the magnitude relationship between Tr(ρρ+) and a, and determine whether to replace the new quantum chip.

[0014] S5. For the new quantum chip, repeat steps S2 to S4.

[0015] S6. Find the quantum chip corresponding to Tr(ρρ+)≥a.

[0016] Furthermore, in step S3, if ρ = ρ+, at this time Tr(ρρ+) = 1, and the fidelity is 100%. In the case of errors, the CPTP condition of the density matrix limits 0 < Tr(ρρ+) < 1, and Tr(ρρ+) reflects the gap between the actual operation final state and the theoretical expected final state, which can be used as the judgment criterion for the qubit operation fidelity.

[0017] Furthermore, in step S4, if Tr(ρρ+)≥a, then keep the current quantum chip operation unchanged; if Tr(ρρ+) < a, then use the switch to connect to the control and reading lines of the new quantum chip.

[0018] Furthermore, in step S5, if the quantum chip corresponding to Tr(ρρ+)≥a cannot be found after traversing all the new quantum chips, then heat up the dilution refrigerator and replace a new batch of superconducting quantum chips.

[0019] A superconducting quantum chip control method, adding a switch on the Still disk of the dilution refrigerator, installing several superconducting quantum chips in the mK temperature range of the dilution refrigerator, and connecting the reading and control wires of all quantum chips to the corresponding connectors on the MXC cold disk.

[0020] Furthermore, directly connect the corresponding connectors of the MXC cold disk and the Still cold disk, add a switch at one end connector of the Still cold disk, directly connect the switch to the MXC cold disk, and through the switch switching of the sub - circuit connected by the switch, the switch of the sub - circuit controls the superconducting quantum chips on each line.

[0021] A superconducting quantum chip control device, adding a switch on the Still disk in the dilution refrigerator, installing several superconducting quantum chips in the mK temperature range of the dilution refrigerator, and connecting the reading and control wires of all quantum chips to the corresponding connectors on the MXC cold disk.

[0022] Furthermore, the MXC cold plate is directly connected to the connector corresponding to the Still cold plate, and a conversion switch is added to the connector at one end of the Still cold plate. The conversion switch is directly connected to the MXC cold plate, and the switch of the sub-circuit connected to the conversion switch is switched, and the switch of the sub-circuit controls the superconducting quantum chip on each circuit.

[0023] Compared with the prior art, the superconducting quantum chip control and reading method and device of the present invention have the following outstanding beneficial effects:

[0024] In order to replace the existing random calibration scheme to detect the fidelity of bit gate operation, the present invention proposes to directly use the Hadamard gate to prepare the bit state from the initial |0> state to the |+> state, and apply quantum state tomography to |+>, and judge the fidelity of single-bit gate operation by comparing the quantum state tomography results with the theoretical expected results. A conversion switch is added to the Still disk of the dilution refrigerator. When the fidelity is lower than the threshold, the control and reading of different superconducting quantum chips are realized by switching the switches between different control circuits and chip connections. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Attached Figure 1 It is a schematic diagram of connecting multiple superconducting quantum chips with conversion switches in a superconducting quantum chip control method;

[0027] Attached Figure 2 This is a schematic diagram of the connection of a single superconducting quantum chip in a superconducting quantum chip control method. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the solution of the present invention, the present invention is further described in detail below in conjunction with specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] A best embodiment is given below:

[0030] Apply a Hadamard gate (H gate) to a qubit in the initial state |0>. The H gate is generally composed of consecutive Y / 2 gates and X gates. In theory, a perfect H gate will prepare the |0> state into the |+> state. However, due to the existence of noise, the final state will not be in the |+> state. Therefore, by comparing the density matrix of the actual final state with that of the |+> state, the fidelity of the H gate operation can be determined.

[0031] Also, since the H gate is composed of Y / 2 gates and X gates, this fidelity actually reflects the errors of two operations: rotation around the Y axis of the Bloch sphere and rotation around the X axis. And because the two operations are executed in series, this fidelity also includes the possible non-Markov process. In addition, it usually takes only a few minutes to apply the H gate to a single qubit and perform state tomography. Therefore, this invention can make up for the deficiencies of RBM and be applied to the rapid determination of the fidelity of quantum operations.

[0032] As Figure 1-2 shown, the specific implementation steps are as follows:

[0033] S1. Set the quantum bit operation fidelity threshold a.

[0034] S2. Apply the H gate to the qubit and perform quantum state tomography on the final state after applying the H gate to obtain the final state density matrix ρ.

[0035] S3. Compare the final state density matrix ρ obtained in step S2 with the density matrix ρ+ of the |+> state. The comparison method is to calculate Tr(ρρ+). In the ideal case, ρ = ρ+, and at this time Tr(ρρ+) = 1, that is, the fidelity is 100%; in the case of errors, due to the CPTP condition restriction of the density matrix, 0 < Tr(ρρ+) < 1, and Tr(ρρ+) reflects the gap between the actual operation final state and the theoretical expected final state, which can be used as the judgment criterion for the quantum bit operation fidelity.

[0036] S4. Compare the size relationship between Tr(ρρ+) and a to determine whether to replace the new quantum chip;

[0037] If Tr(ρρ+) ≥ a, then keep the current quantum chip operation unchanged; if Tr(ρρ+) < a, then use the switch to change the external control and reading circuit to be connected to the control and reading circuit of the new quantum chip.

[0038] S5. For the new quantum chip, repeat steps S2 to S4.

[0039] S6. For S5, if a quantum chip corresponding to Tr(ρρ+) ≥ a still cannot be found after traversing all new quantum chips, then heat up the dilution refrigerator and replace a new batch of superconducting quantum chips.

[0040] A dilution refrigerator is a refrigeration device with a large cooling capacity that can maintain a temperature in the mK range for a long time. In superconducting quantum computing, a dilution refrigerator is often used to provide the necessary superconducting low-temperature environment. A dilution refrigerator is composed of several cold plates, among which the MXC cold plate that can reach a temperature in the mK range has a cooling power of only more than ten microwatts. Therefore, the present invention proposes to add a conversion switch to the Still plate with a higher cooling power (about hundreds of microwatts) to provide a superconducting quantum chip control switching function while ensuring the normal cooling of the dilution refrigerator. Accordingly, the superconducting quantum chip control switching method proposed in the present invention is described as follows.

[0041] The current connection method for controlling and reading a single superconducting quantum chip is to directly connect the corresponding control or read line to the corresponding connector of the mxc cold plate, and then the mxc cold plate is directly connected to the corresponding connector of the Still cold plate, and this direct connection method is used to directly introduce external control signals or directly lead out read signals. The microwave devices such as attenuators and filters added to the cold plates at each level do not affect this direct connection method.

[0042] The present invention proposes a superconducting quantum chip control method, which includes adding a conversion switch on the Still plate of a dilution refrigerator, installing a number of superconducting quantum chips in the mK temperature zone of the dilution refrigerator, and connecting the reading and control lines of all quantum chips to the corresponding connectors of the MXC cold plate.

[0043] The MXC cold plate is directly connected to the corresponding connectors of the Still cold plate, and a conversion switch is added to the connector at one end of the Still cold plate. The conversion switch is directly connected to the MXC cold plate. The switch of the sub-circuit connected to the conversion switch is switched, and the switch of the sub-circuit controls the superconducting quantum chip on each circuit.

[0044] Based on the above method, a superconducting quantum chip control device adds a conversion switch on the Still disk in the dilution refrigerator, installs several superconducting quantum chips in the mK temperature zone of the dilution refrigerator, and connects the reading and control lines of all quantum chips to the corresponding connectors of the MXC cold disk.

[0045] The MXC cold plate is directly connected to the connector corresponding to the Still cold plate, and a conversion switch is added to the connector at one end of the Still cold plate. The conversion switch is directly connected to the MXC cold plate. The switch of the sub-circuit connected to the conversion switch is switched, and the switch of the sub-circuit controls the superconducting quantum chip on each circuit.

[0046] The above-mentioned specific implementations are only specific cases of the present invention. The patent protection scope of the present invention includes but is not limited to the above-mentioned specific implementations. Any appropriate changes or substitutions made by a person of ordinary skill in the art to a superconducting quantum chip reading, controlling method and device that conform to the claims of the present invention shall fall within the patent protection scope of the present invention.

[0047] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A superconducting quantum chip reading method, characterized in that: Add a changeover switch on the Still disk of the dilution refrigerator, install several superconducting quantum chips in the mK temperature range of the dilution refrigerator, and connect the readout and control wires of all quantum chips to the corresponding connectors on the MXC cold plate. The specific control and readout logic is as follows: S1. Set the quantum bit operation fidelity threshold a; S2. Apply the H gate to the quantum bit and perform quantum state tomography on the final state after applying the H gate to obtain the final state density matrix ρ; S3. Compare the final state density matrix ρ obtained in step S2 with the |+> state density matrix ρ+, and the comparison method is to calculate Tr(ρρ+); S4. Compare the magnitude relationship between Tr(ρρ+) and a to determine whether to replace the quantum chip with a new one; If Tr(ρρ+) ≥ a, then keep the current quantum chip operation unchanged; if Tr(ρρ+) < a, then use the changeover switch to connect to the control and readout lines of the new quantum chip; S5. For the new quantum chip, repeat steps S2 to S4; S6. Find the quantum chip corresponding to Tr(ρρ+) ≥ a.

2. A superconducting quantum chip reading method according to claim 1, characterized in that: In step S3, if ρ = ρ+, at this time Tr(ρρ+) = 1 and the fidelity is 100%. Under the condition of errors, the CPTP condition of the density matrix restricts 0 < Tr(ρρ+) < 1, and Tr(ρρ+) reflects the gap between the actual operation final state and the theoretical expected final state, which can be used as the judgment criterion for the quantum bit operation fidelity.

3. A superconducting quantum chip reading method according to claim 2, characterized in that: In step S5, if a quantum chip corresponding to Tr(ρρ+) ≥ a cannot be found after traversing all new quantum chips, then heat up the dilution refrigerator and replace it with a new batch of superconducting quantum chips.

4. A superconducting quantum chip reading method according to claim 1, characterized in that: Directly connect the corresponding connectors of the MXC cold plate and the Still cold plate, add a changeover switch at one end connector of the Still cold plate, the changeover switch is directly connected to the MXC cold plate, and through the switch switching of the sub-circuits connected by the changeover switch, the switch of the sub-circuit controls the superconducting quantum chips on each line.

5. A superconducting quantum chip control device, characterized in that: Add a changeover switch on the Still disk in the dilution refrigerator, install several superconducting quantum chips in the mK temperature range of the dilution refrigerator, and connect the readout and control wires of all quantum chips to the corresponding connectors on the MXC cold plate; The specific control and readout logic is as follows: S1. Set the quantum bit operation fidelity threshold a; S2. Apply the H gate to the quantum bit and perform quantum state tomography on the final state after applying the H gate to obtain the final state density matrix ρ; S3. Compare the final state density matrix ρ obtained in step S2 with the |+> state density matrix ρ+, and the comparison method is to calculate Tr(ρρ+); S4. Compare the magnitude relationship between Tr(ρρ+) and a to determine whether to replace the quantum chip with a new one; If Tr(ρρ+) ≥ a, then keep the current quantum chip operation unchanged; if Tr(ρρ+) < a, then use the changeover switch to connect to the control and readout lines of the new quantum chip; S5. For the new quantum chip, repeat steps S2 to S4; S6. Find the quantum chip corresponding to Tr(ρρ+) ≥ a.

6. A superconducting quantum chip control device according to claim 5, characterized in that: The MXC cold plate is directly connected to the connector corresponding to the Still cold plate, and a conversion switch is added to the connector at one end of the Still cold plate. The conversion switch is directly connected to the MXC cold plate, and the switch of the sub-circuit connected to the conversion switch is switched, and the switch of the sub-circuit controls the superconducting quantum chip on each circuit.

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