Method for storing bit information, quantum circuit, quantum chip and electronic equipment

Abstract

The invention belongs to the technical field of quantum, and particularly relates to a method for storing bit information, a quantum circuit, a quantum chip and electronic equipment. A method for storing bit information comprises the following steps: mapping an initial energy level of a superconducting quantum device to a high excitation energy level, and defining an addressing position; applying a microwave pulse to the superconducting quantum device, and storing bit information of the superconducting quantum device to a storage unit corresponding to the addressing position; the high excitation energy level is an energy level greater than or equal to the second excitation energy level, and the high excitation energy level at least comprises two excitation energy levels. According to the method for storing the bit information, the high excitation energy level of the multi-energy-level superconducting quantum device is used as a storage unit and used for storing intermediate operation data and operation results participating in quantum operation, information storage is effectively achieved, and reading is convenient.

Description

Technical Field

[0001] The present invention belongs to the field of quantum technology, and specifically relates to a method for storing bit information, a quantum circuit, a quantum chip, and an electronic device. Background Art

[0002] The superconducting quantum platform is considered to be one of the most promising physical platforms for constructing large-scale general quantum computers because of its advantages of easy preparation and manipulation and strong scalability. However, at this stage, as the number of superconducting qubits increases, the architecture of the chip becomes increasingly complex. This brings two problems. One is that in the preparation of quantum chips, it is technically difficult to expand the number of qubits to a higher order of magnitude. The other is that in the measurement and control of qubits, more qubits mean more complex control circuits and more noise, which is an inevitable problem for high-fidelity measurement and control of superconducting qubits. Therefore, scientists believe that we will still explore on medium-scale quantum chips in the current stage and even in the next ten-odd years.

[0003] The multi-level superconducting quantum device (qudit) is a quantum system that expands the dimension of the two-level Hilbert space to a higher level. Compared with the two-level qubit, the multi-level superconducting quantum device can store and process more information. Using the multi-level superconducting quantum device, we can explore and process more complex physical problems on the existing qubit scale. The commonly used structure of superconducting qubits, such as the transmon qubit, is not a perfect two-level system, but a multi-level quantum system with weak anharmonicity. It is very convenient to use higher energy levels to achieve instant storage of bit information.

[0004] According to "Performing SU(d) Operations and Rudimentary Algorithms in a Superconducting Transmon Qudit for d = 3 and d = 4" published by Liu Pei et al. in "PHYSICAL REVIEW X" (translation: Physical Review X) 2023, 13(2): 021028, high-fidelity initialization, operation, and simultaneous reading of multi-level superconducting quantum devices (d = 3, d = 4), as well as quantum state tomography, quantum process tomography, random benchmark testing, etc. are disclosed. In addition, this technology also demonstrates the discrete Fourier transform, Grover algorithm, and variational quantum algorithm on multi-level superconducting quantum devices. However, the second and third excited states of the disclosed multi-level superconducting quantum device are usually regarded as computational processing units, which can improve processing efficiency, but new calculations will overwrite previous results, so it is not conducive to the storage and call of intermediate operation data.

[0005] Chinese Patent Application CN117616434A discloses a quantum computing method, which includes initializing a quantum emitter coupled to a resonator having at least four energy levels arranged in an N configuration, where the N configuration has a first ground state, a second ground state, a first excited state, and a second excited state; tuning the frequency of a first transition between the first ground state and the first excited state; tuning the frequency of a second transition between the second ground state and the second excited state; tuning the frequency of a third transition between the second ground state and the first excited state; feeding multiple photons at a frequency corresponding to the frequency of the second transition to entangle the multiple photons with the resonator-coupled quantum emitter; and feeding photons at a frequency corresponding to at least one of the first transition or the third transition to map the state of the resonator-coupled quantum emitter to the photons. However, the disclosed patent does not disclose how to store qubit information of the ground state and the excited state onto a higher excited state and apply corresponding timing waveform blocks to read the information on the superconducting quantum device.

[0006] Therefore, how to solve the contradiction between information storage and processing efficiency, provide a more flexible and efficient operation mode for quantum computing, and ensure the operational independence and stability of qubits is a problem that needs to be solved. Summary of the Invention

[0007] To solve the problem that the high excited energy level of the superconducting quantum device is used as a storage unit to save the intermediate results of the operation and effectively realize information storage, the present invention proposes a method for storing bit information. This solution only requires transverse microwave operation on a single superconducting quantum device, so only one XY microwave line is needed, and no additional drive lines and noise are introduced.

[0008] The first aspect of the present invention provides a method for storing bit information, including:

[0009] Mapping the initial energy level of the superconducting quantum device to a high excited energy level to clarify the addressing position;

[0010] Applying a microwave pulse to the superconducting quantum device to store the information of the qubit of the superconducting quantum device into the storage unit corresponding to the addressing position.

[0011] As a preferred embodiment, the high excited energy level at least includes a second excited energy level and a third excited energy level.

[0012] As a preferred embodiment, the high excited energy level includes a second excited energy level and a third excited energy level. The third energy level is higher than the second excited energy level.

[0013] As a preferred embodiment, the second excited energy level is higher than the initial energy level.

[0014] In some preferred embodiments, the addressing position is determined by obtaining the energy level difference of the high-excitation level of the transmission sub-quantum device and the energy level position of the transmission sub-quantum bit.

[0015] In some preferred embodiments, the determination of the energy level difference includes the following steps:

[0016] When the superconducting phase difference on both sides of the Josephson junction of the Hamiltonian of the transmission sub-quantum bit is 0, the energy level difference is obtained by determining the approximate value of the energy eigenvalue.

[0017] The Hamiltonian of the transmission sub-quantum bit can be expressed by the following relational expression (Ⅰ):

[0018]

[0019] In the formula:

[0020] E C : charging energy, the charging energy of the quantum bit, referring to the charging energy required for each electron in the Cooper pair to be added to the island;

[0021] n: Cooper pair number operator, representing the number of Cooper pairs on the superconducting island;

[0022] n g : bias charge, a dimensionless parameter, usually determined by the external environment;

[0023] E J : Josephson energy, reflecting the energy of Cooper pair tunneling in the Josephson junction.

[0024] A quantum operator, representing the superconducting phase difference on both sides of the Josephson junction.

[0025] For the above formula, expand near , and obtain the following approximate value of the energy eigenvalue by perturbation approximation to obtain the quartic term:

[0026]

[0027] In the formula:

[0028] E m : represents the energy of the m-th energy level of the quantum bit, where m is a quantum number (usually a non-negative integer, m = 0, 1, 2... )

[0029] E C : the charging energy of the quantum bit, referring to the charging energy required for each electron in the Cooper pair to be added to the island;

[0030] E J: Josephson energy, which reflects the energy of Cooper pair tunneling in a Josephson junction.

[0031] From this, the energy differences of each excitation level of the transmon quantum device can be further obtained as:

[0032]

[0033] In the formula:

[0034] E mn : represents the energy required for a qubit to transition from the m-th energy level to the n-th energy level;

[0035] E 01 : the energy difference between the ground state and the first excited state (the first excitation energy level);

[0036] E 12 : the energy difference between the first excited state (the first excitation energy level) and the second excited state (the second excitation energy level);

[0037] E 23 : the energy difference between the second excited state (the second excitation energy level) and the third excited state (the third excitation energy level).

[0038] Generally, the ground state of the transmon quantum device (corresponding to the ground state |0> in Figure 2 and the first excitation energy level (corresponding to the first excited state |1> in Figure 2 are the 0 state and 1 state of the qubit. The position information of the initial energy level mentioned in the present invention is known information. In this application, in order to store the intermediate information during the bit operation, the storage unit is defined as the second excitation energy level (corresponding to the second excited state |2> in Figure 2 and the third excitation energy level (corresponding to the third excited state |3> in Figure 2 of the superconducting quantum device. By mapping the information of the ground state and the first excitation energy level of the qubit to the second excitation energy level and the third excitation energy level respectively, the addressing position of the superconducting quantum device is further determined.

[0039] In some preferred embodiments, the specific steps of storing the information of the qubit of the superconducting quantum device into the storage unit corresponding to the addressing position include:

[0040] Represent the state of the transmon qubit with a density matrix;

[0041] Apply a microwave pulse to the transmon qubit so that the z information and x information of the transmon qubit are respectively stored into the corresponding storage units;

[0042] By obtaining the probabilities of the initial energy level and the high excitation energy level of the superconducting quantum device, the information of the qubit of the superconducting quantum device is stored into the storage unit.

[0043] More preferably, the density matrix is a 4-order density matrix; specifically, the 4-order density matrix is:

[0044]

[0045] In some preferred embodiments, the specific process of applying microwave pulses to the transmission sub-qubit is as follows:

[0046] H1: Apply pulses to store the information of the z of the qubit on the second excited energy level;

[0047] H2: Apply and pulses to store the x information of the qubit on the third excited energy level.

[0048] More preferably, the probabilities of the initial energy level and the highly excited energy level are specifically: the probabilities of the ground state, the first excited energy level, the second excited energy level, and the third excited energy level are respectively: and

[0049] In some preferred embodiments, when reading the information of the stored qubit, the following steps are performed:

[0050] Apply microwave pulses to the resonator coupled to the superconducting quantum device;

[0051] Determine the position information of the dispersive cavity that interacts with the superconducting quantum device in the resonator;

[0052] Obtain the response of the dispersive cavity to the superconducting quantum device, determine the probability of the highly excited energy level, and read the stored information in the storage unit.

[0053] According to the interaction relationship between the superconducting quantum device and the resonator, its Hamiltonian is shown in the following formula (Ⅱ):

[0054]

[0055] In the formula:

[0056] The energies of different quantum states, including the basic energy and the correction term ∑ j : Represents the summation over all states j; Reduced Planck constant; ω j : The frequency of the j-th quantum state; Λ j: The modulation or correction term related to the j-th state; |j><j|: Represents the projection operator, indicating the projection of the system onto the state |j>. Represents the energy of the harmonic oscillator, The particle number operator, representing the number of particles in the harmonic oscillator, ω r The frequency of the harmonic oscillator; Represents the interaction between the quantum state and the harmonic oscillator, χ j : Represents the interaction strength related to the j-th quantum state.

[0057] In some preferred embodiments, the qubit includes any one of a Transmon qubit and an Xmon qubit.

[0058] More preferably, the qubit includes a Transmon qubit.

[0059] In the present application, the applied microwave pulse is a microwave timing waveform block.

[0060] In a second aspect of the present invention, there is provided a quantum circuit, including: a target resonator and a qubit, wherein the qubit is coupled to a readout line through the target resonator, and the target resonator is coupled to the qubit, wherein the target resonator is the readout resonator of the qubit, and the qubit is the stored qubit.

[0061] In a third aspect of the present invention, there is provided a quantum chip including the above quantum circuit.

[0062] In a fourth aspect of the present invention, there is provided an electronic device, including: a quantum chip and a quantum memory; the quantum circuit described above is included in the quantum chip and / or the quantum memory.

[0063] The above technical solutions have the following advantages or beneficial effects:

[0064] 1. The method for storing qubit information proposed by the present invention uses the high-excitation energy level of a multi-level superconducting quantum device as a storage unit to store the intermediate operation data and operation results participating in quantum operations, effectively realizing information storage and facilitating reading;

[0065] 2. The method for storing qubit information proposed by the present invention only requires transverse microwave pulse operation on a single transmons quantum device, so only one XY microwave line is needed, and no additional drive lines and noise are introduced;

[0066] 3. The method for storing bit information proposed by the present invention not only solves the contradiction between information storage and processing efficiency, but also provides a more flexible and efficient operation mode for quantum computing, ensures the operational independence and stability of quantum bits, and significantly improves the overall performance of the quantum system. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 is a flowchart of the method for storing bit information proposed by the present invention;

[0068] Figure 2 is a schematic diagram of the addressing position of the method for storing bit information proposed by the present invention;

[0069] Figure 3 is a schematic diagram of bit information storage after applying a microwave pulse to the method for storing bit information proposed by the present invention;

[0070] Figure 4 is a schematic diagram of the quantum chip proposed by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0071] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0072] Refer to Figure 1 , an embodiment provided by the present invention:

[0073] A method for storing bit information, comprising:

[0074] Mapping the initial energy level of the superconducting quantum device to a high-excitation energy level to clarify the addressing position;

[0075] Applying a microwave pulse to the superconducting quantum device to store the information of the quantum bit of the superconducting quantum device in the storage unit corresponding to the addressing position;

[0076] The high-excitation energy level includes a second excitation energy level and a third excitation energy level.

[0077] The addressing position is determined by obtaining the energy level difference of the high-excitation energy level of the transmon quantum device and the energy level position of the transmon qubit. The determination of the energy level difference includes the following steps:

[0078] When the superconducting phase difference on both sides of the Josephson junction of the Hamiltonian of the transmon qubit is 0, the energy level difference is obtained by determining the approximate value of the energy eigenvalue;

[0079] The Hamiltonian of the transmon qubit is expressed by the following relation (I):

[0080]

[0081] Where:

[0082] E C : charging energy, the charging energy of the qubit, which refers to the charging energy required for each electron in the Cooper pair to be added to the island;

[0083] n: Cooper pair number operator, representing the number of Cooper pairs on the superconducting island;

[0084] n g : bias charge, a dimensionless parameter, usually determined by the external environment;

[0085] E J : Josephson energy, reflecting the energy of Cooper pair tunneling in the Josephson junction.

[0086] A quantum operator representing the superconducting phase difference across the Josephson junction.

[0087] Expanding the above equation around and obtaining the quartic term through perturbation approximation, an approximate value of the following energy eigenvalue can be obtained:

[0088]

[0089] Where:

[0090] E m : represents the energy of the m-th energy level of the qubit, where m is the quantum number (usually a non-negative integer, m = 0, 1, 2...)

[0091] E C : the charging energy of the qubit, which refers to the charging energy required for each electron in the Cooper pair to be added to the island;

[0092] E J : Josephson energy, reflecting the energy of Cooper pair tunneling in the Josephson junction.

[0093] Thus, the energy level difference of the transmon quantum device can be further obtained as:

[0094]

[0095] Where:

[0096] E 01 : the energy difference from the ground state to the first excited energy level;

[0097] E 12: The energy difference between the first excited energy level and the second excited energy level;

[0098] E 23 : The energy difference between the second excited energy level and the third excited energy level.

[0099] Since the position information of |0> and |1> is known, according to the obtained energy level difference of the transmons quantum device, the addressing position is determined, and further the position of the high excited energy level is obtained. For specific details, see Figure 2 ;

[0100] The specific steps of storing the information of the qubits of the superconducting quantum device into the storage unit corresponding to the addressing position include:

[0101] Use the 4th-order density matrix to represent the state of the transmons qubit;

[0102] Apply a microwave pulse to the transmons qubit to store the z information of the transmons qubit on the second excited energy level; store the x information of the transmons qubit on the third excited energy level;

[0103] As Figure 3 , the specific process of applying the microwave timing waveform block to the transmons qubit is as follows:

[0104] H1: Apply pulse to the transmons qubit to store the z information of the qubit on the second excited energy level (corresponding to Figure 2 the second excited state |2>);

[0105] H2: Apply and pulses to the transmons qubit to store the x information of the qubit on the third excited energy level (corresponding to Figure 2 the third excited state |3>).

[0106] S23: The probabilities of the initial energy level and the high excited energy level are specifically: the probabilities of the ground state, the first excited energy level, the second excited energy level, and the third excited energy level are respectively: and

[0107] Calculate the qubit quantum state information according to the z information and the x information to ensure that the information of the qubit is stored on |2> and |3>.

[0108] When reading the information of the stored qubit, the following steps are carried out:

[0109] Apply a microwave pulse to the resonator coupled to the superconducting quantum device;

[0110] Determine the position information of the dispersive cavity that interacts with the superconducting quantum device in the resonant cavity;

[0111] Obtain the response of the dispersive cavity to the superconducting quantum device, determine the probability of the high-excitation energy level, and read the stored information in the storage unit.

[0112] According to the interaction relationship between the superconducting quantum device and the resonant cavity, its Hamiltonian is shown in the following formula (Ⅱ):

[0113]

[0114] In the formula:

[0115] The energy of different quantum states, including the basic energy and the correction term ∑ j : Represents the summation over all states j; Reduced Planck constant; ω j : The frequency of the j-th quantum state; Λ j : The modulation or correction term related to the j-th state; |j><j| represents the projection operator, indicating the projection of the system onto the state |j>; Represents the energy of the harmonic oscillator, The particle number operator, representing the number of particles in the harmonic oscillator, ω r The frequency of the harmonic oscillator; Represents the interaction between the quantum state and the harmonic oscillator, χ j : Represents the interaction strength related to the j-th quantum state;

[0116] The resonant cavity interacts with the |j>-th energy level of the transmons qubit, and the dispersive frequency of the resonant cavity has a shift of χ j ;

[0117] Determine the dispersive cavity information (j = 2, 3); measure the response of the dispersive cavity to the superconducting quantum device, thereby measuring the probabilities of the second and third excitation energy levels, and read the stored information in the storage unit.

[0118] It should be noted that the qubit in this application is a Transmon qubit.

[0119] It further includes a quantum circuit, including: a target resonant cavity and a qubit, wherein the qubit is coupled to the reading line through the target resonant cavity, the target resonant cavity is coupled to the qubit, wherein the target resonant cavity is the reading resonant cavity of the qubit, and the qubit is the stored qubit.

[0120] Such as Figure 4As shown, it further includes a quantum chip, which includes the above-mentioned quantum circuit.

[0121] It further includes an electronic device, including: a quantum chip and a quantum memory; the quantum circuit is included in the quantum chip and the quantum memory.

[0122] Finally, it should be noted that: the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for storing bit information, characterized in that: include: Map the initial energy level of the superconducting quantum device to the high excited energy level and clearly define the addressing position; A microwave pulse is applied to the superconducting quantum device to store the information of the quantum bit of the superconducting quantum device in a storage unit corresponding to the addressing position.

2. The method for storing bit information according to claim 1, characterized in that: The high excitation energy level includes at least a second excitation energy level and a third excitation energy level, and the third energy level is an energy level higher than the second excitation energy level.

3. The method for storing bit information according to claim 2, characterized in that: The second excitation energy level is an energy level higher than the initial energy level.

4. The method for storing bit information according to claim 1, characterized in that: The addressing position is determined by obtaining the energy level difference of the high excitation energy level of the transmission sub-quantum device and the energy level position of the transmission sub-qubit.

5. The method for storing bit information according to claim 4, characterized in that: The method for determining the energy level difference includes: When the superconducting phase difference of the Hamiltonian of the transmission sub-qubit on both sides of the Josephson junction is 0, the energy level difference is obtained by determining the approximate value of the energy eigenvalue.

6. The method for storing bit information according to claim 1, characterized in that: The specific step of storing the information of the quantum bit of the superconducting quantum device into the storage unit corresponding to the addressing position comprises: Applying microwave pulses to the transmission sub-qubits so that the z information and the x information of the transmission sub-qubits are respectively stored in the corresponding storage units; By obtaining the probability of the initial energy level and the high excitation energy level of the superconducting quantum device, the information of the quantum bit of the superconducting quantum device is stored in the storage unit.

7. The method for storing bit information according to claim 1, characterized in that: The quantum bit includes any one of a Transmon quantum bit and an Xmon quantum bit.

8. A quantum circuit, characterized in that: include: A target resonant cavity and a quantum bit, wherein the quantum bit is coupled to a readout circuit via the target resonant cavity, the target resonant cavity is coupled to the quantum bit, wherein the target resonant cavity is a readout resonant cavity of the quantum bit, and the quantum bit is a stored quantum bit.

9. A quantum chip, characterized in that: Comprising the quantum circuit as claimed in claim 8.

10. An electronic device, characterized in that: include: Quantum chip and quantum memory; the quantum chip and / or quantum memory comprises the quantum circuit according to claim 8.

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