Superconducting quantum bit reading method, system and device and storage medium
By acquiring the parameters of the readout resonant cavity, a high-order sinusoidal microwave pulse that satisfies the smoothness condition is generated, which solves the limitations of fidelity and speed in superconducting quantum bit readout methods, and realizes high-fidelity fast readout and reduces post-readout disturbances.
Patent Information
- Application Number
- CN202511788839.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-28
- Publication Date
- 2026-03-03
AI Technical Summary
Existing methods for reading superconducting qubits struggle to achieve high fidelity and fast reading speeds, and are also subject to post-reading perturbation issues, which limit reading speed and the efficiency of quantum computing.
By acquiring the attenuation rate, frequency, and dispersion coupling strength of the readout resonant cavity, the envelope waveform of the high-order sinusoidal waveform that satisfies the smoothness condition is determined, a readout microwave pulse is generated, and the readout frequency and pulse duration are optimized to achieve high fidelity and fast readout, avoiding post-readout disturbances.
High-fidelity fast readout of superconducting qubits was achieved, shortening the readout time and reducing post-readout perturbations, thus meeting the needs of large-scale quantum computing.
Smart Images
Figure CN121599148A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of quantum computing technology, and in particular to methods, systems, devices, and storage media for reading superconducting qubits. Background Technology
[0002] Superconducting quantum computing is a technological approach in the field of quantum computing. It utilizes the unique properties of superconducting materials at extremely low temperatures and constructs artificial atoms as superconducting qubits through Josephson junctions. By mapping the vacuum state and excited state of the superconducting qubits to the |0> state and the |1> state, respectively, it can be used to realize large-scale quantum computing.
[0003] Reading the state of a superconducting qubit is an indispensable and crucial step in superconducting quantum computing. Current methods for reading the state of a superconducting qubit generally involve injecting a microwave pulse of a specific frequency into a readout resonant cavity coupled to the qubit. The state of the qubit (|0> state or |1> state) affects the resonant frequency of the readout resonant cavity through dispersive coupling, causing a phase shift or amplitude shift in the microwave signal reflected or transmitted by the cavity. By measuring this microwave signal, the state of the superconducting qubit can be inferred.
[0004] Existing methods for achieving high fidelity during readout require accumulating more photons within the readout resonant cavity. However, excessive photons can lead to side effects, limiting the improvement of readout fidelity. Furthermore, the establishment and attenuation of photons in the readout resonant cavity during the injection of the readout microwave pulse are limited by the cavity's attenuation rate, resulting in slow readout speeds. Moreover, residual photons within the cavity after readout can easily interact with the superconducting qubit, potentially causing post-readout perturbations. These perturbations can negatively impact multiple readouts and quantum error correction algorithms. Therefore, there is an urgent need for a readout method for superconducting qubits that can achieve high fidelity and fast readout while effectively avoiding post-readout perturbations. Summary of the Invention
[0005] This application provides a method, system, device, and storage medium for reading superconducting qubits, which can achieve high fidelity and fast reading while resetting the reading state to effectively avoid post-reading disturbances.
[0006] This application provides a method for reading out superconducting qubits, including:
[0007] The attenuation rate of the readout resonant cavity, the frequency of the readout resonant cavity, and the dispersive coupling strength between the superconducting quantum bit and the readout resonant cavity are obtained.
[0008] Determine the envelope waveform that satisfies the smoothness condition: Where A is the amplitude, n is the waveform order, and n is a positive integer greater than or equal to 4; The pulse duration is determined based on the attenuation rate of the readout resonant cavity;
[0009] The frequency of the readout resonant cavity is adjusted based on the attenuation rate of the readout resonant cavity and the dispersive coupling strength to determine the readout frequency and obtain the microwave carrier corresponding to the readout frequency.
[0010] Based on the envelope waveform and the microwave carrier, a readout microwave pulse is generated to read the state of the superconducting quantum bit.
[0011] Furthermore, after obtaining the attenuation rate of the readout resonant cavity, the frequency of the readout resonant cavity, and the dispersive coupling strength between the superconducting quantum bit and the readout resonant cavity, the method further includes:
[0012] Based on a preset relation: =C / κ, determine the pulse duration Wherein, κ is the attenuation rate of the reading resonant cavity, and C is a proportionality coefficient within a preset range.
[0013] Furthermore, the preset value range is from 1.5 to 10.
[0014] Furthermore, after obtaining the attenuation rate of the readout resonant cavity, the frequency of the readout resonant cavity, and the dispersive coupling strength between the superconducting quantum bit and the readout resonant cavity, the method further includes:
[0015] The value of the waveform order n in the envelope waveform is determined based on the ratio of the attenuation rate of the readout resonant cavity to the dispersion coupling strength.
[0016] Furthermore, the envelope waveform that satisfies the smoothness condition is determined as follows: ,include:
[0017] If the envelope waveform and its first m derivatives are both zero at the start and end points, then the envelope waveform is determined to satisfy the smoothness condition; where m is less than n.
[0018] Furthermore, the order n of the waveform ranges from 6th to 14th.
[0019] Furthermore, the step of adjusting the frequency of the readout resonant cavity based on the attenuation rate of the readout resonant cavity and the dispersive coupling strength to determine the readout frequency includes:
[0020] Adjust the frequency of the readout resonant cavity until its attenuation rate is close to or meets the dispersion coupling strength. The adjusted frequency of the reading resonant cavity is taken as the reading frequency; where κ is the attenuation rate of the reading resonant cavity. The dispersion coupling strength is denoted as .
[0021] Furthermore, after generating the readout microwave pulse based on the envelope waveform and the microwave carrier, the method further includes:
[0022] The time-domain signals of the readout microwave pulse reflected by the readout resonant cavity are acquired when the superconducting quantum bit is in different states at the target acquisition time.
[0023] The current state of the superconducting quantum bit is determined by comparing the signal points of the time-domain signal on the IQ plane with the reference signal clusters of the superconducting quantum bit in different states on the IQ plane.
[0024] The read fidelity is determined based on the state of the superconducting quantum bit and the current state.
[0025] Based on the readout fidelity, the amplitude, waveform order, pulse duration, and acquisition time in the envelope waveform are adjusted until the readout fidelity reaches a preset fidelity threshold to obtain an optimized readout microwave pulse, which is then used to read the state of the superconducting quantum bit.
[0026] Furthermore, before acquiring the time-domain signal reflected by the readout microwave pulse through the readout resonant cavity when the superconducting quantum bit is in different states at the target acquisition time, the method further includes:
[0027] The target acquisition time is obtained by extracting the portion of the waveform whose relative intensity is greater than a preset intensity threshold within the pulse duration.
[0028] Furthermore, the preset intensity threshold is a relative intensity in the range of 0.001 to 0.000001.
[0029] Furthermore, the step of acquiring the time-domain signal of the readout microwave pulse reflected by the readout resonant cavity when the superconducting quantum bit is in different states at the target acquisition time further includes:
[0030] The time-domain signals corresponding to the superconducting quantum bits in different states are subtracted to obtain the readout signal;
[0031] Extract the envelope information of the read signal to obtain the envelope function;
[0032] Using the envelope function as the time-domain signal, the following steps are performed: comparing the signal point of the time-domain signal on the IQ plane with the reference signal cluster of the superconducting quantum bit in different states on the IQ plane to determine the current state of the superconducting quantum bit.
[0033] Furthermore, before comparing the signal points of the time-domain signal on the IQ plane with the reference signal clusters of the superconducting quantum bit in different states of the IQ plane to determine the current state of the superconducting quantum bit, the method further includes:
[0034] When the superconducting qubits are prepared in different states, the readout frequency is satisfied multiple times. The square wave is input to the reading resonant cavity;
[0035] Based on the time-domain signal reflected by the square wave through the readout resonant cavity, the reference signal clusters of the superconducting quantum bit in the IQ plane under different states are obtained.
[0036] This application also provides a superconducting quantum computing system, including: a superconducting quantum chip, a dilution refrigerator, a microwave transmitting module, and a signal receiving and processing module; the dilution refrigerator is used to provide a low-temperature environment for the superconducting quantum chip; the superconducting quantum chip includes: at least one superconducting quantum bit and a readout resonant cavity coupled to the superconducting quantum bit;
[0037] The microwave transmitting module is used to generate a readout microwave pulse by performing the readout method according to any one of claims 1 to 12, and to transmit the readout microwave pulse to the readout resonant cavity;
[0038] The signal receiving and processing module is used to receive and process the time-domain signal returned by the reading resonant cavity.
[0039] Furthermore, the microwave transmitting module includes: an acquisition unit, a determination unit, an execution unit, and a generation unit;
[0040] The acquisition unit is used to acquire the attenuation rate of the readout resonant cavity, the frequency of the readout resonant cavity, and the dispersive coupling strength between the superconducting quantum bit and the readout resonant cavity;
[0041] The determining unit is used to determine the envelope waveform that satisfies the smoothness condition: Where A is the amplitude, n is the waveform order, and n is a positive integer greater than or equal to 4; The pulse duration is determined based on the attenuation rate of the readout resonant cavity;
[0042] The execution unit is used to adjust the frequency of the read resonant cavity based on the attenuation rate of the read resonant cavity and the dispersion coupling strength, determine the read frequency, and obtain the microwave carrier corresponding to the read frequency;
[0043] The generation unit is used to generate a readout microwave pulse based on the envelope waveform and the microwave carrier, so as to read the state of the superconducting quantum bit using the readout microwave pulse.
[0044] This application also provides a superconducting quantum computing device, including the superconducting quantum computing system described above.
[0045] This application also provides a computer-readable storage medium storing computer instructions thereon, which, when executed by a processor, implement the reading method described above.
[0046] As can be seen from the above technical solutions, the embodiments of this application have the following advantages:
[0047] As can be seen, in this embodiment, the attenuation rate of the readout resonant cavity, the frequency of the readout resonant cavity, and the dispersive coupling strength between the superconducting quantum bit and the readout resonant cavity are obtained; the envelope waveform that satisfies the smoothness condition is determined. Where A is the amplitude, n is the waveform order, and n is a positive integer greater than or equal to 4; The pulse duration is determined based on the attenuation rate of the readout resonator; the frequency of the readout resonator is adjusted based on the attenuation rate and dispersion coupling strength to determine the readout frequency, and the microwave carrier corresponding to the readout frequency is obtained; a readout microwave pulse is generated based on the envelope waveform and the microwave carrier to read the state of the superconducting qubit.
[0048] Since the order of the envelope waveform is a positive integer greater than or equal to 4, the generated readout microwave pulse is a high-order sine wave. This allows for rapid accumulation of photons within the readout resonant cavity during the pulse duration, improving readout fidelity. Furthermore, the pulse duration in the high-order sine wave is determined by the attenuation rate of the readout resonant cavity, effectively shortening the pulse duration and thus reducing the readout time to the theoretical limit determined by the attenuation rate, thereby increasing readout speed. Additionally, because the envelope waveform in the readout microwave pulse satisfies the smoothness condition, the generated readout microwave pulse satisfies the smoothness condition, allowing for rapid attenuation of photons within the readout resonant cavity after readout, achieving rapid photon reset and effectively avoiding post-readout disturbances. In other words, the readout method of this application can achieve high fidelity and rapid readout while simultaneously resetting the readout state, effectively avoiding post-readout disturbances. Attached Figure Description
[0049] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings.
[0050] Figure 1 This is a schematic diagram of signal transmission during a reading process disclosed in an embodiment of this application;
[0051] Figure 2 This is a flowchart of generating and reading microwave pulses disclosed in an embodiment of this application;
[0052] Figure 3 This is a flowchart of an optimized microwave pulse reading method disclosed in an embodiment of this application;
[0053] Figure 4 This is a schematic diagram of a time-domain signal acquired when reading a microwave pulse as a square wave, as disclosed in an embodiment of this application.
[0054] Figure 5 This application discloses an optimized microwave pulse waveform diagram based on a square wave.
[0055] Figure 6 This is a schematic diagram illustrating a different type of microwave pulse reading disclosed in an embodiment of this application;
[0056] Figure 7 This is a schematic diagram illustrating the extraction of the envelope function from the original time-domain signal, as disclosed in an embodiment of this application.
[0057] Figure 8 for Figure 3 A schematic diagram for determining read fidelity;
[0058] Figure 9 This is a schematic diagram of a superconducting quantum computing system disclosed in an embodiment of this application;
[0059] Figure 10 for Figure 9 A schematic diagram of the composition of a microwave transmitting module. Detailed Implementation
[0060] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.
[0061] In the description of the embodiments of this application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.
[0062] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application based on the specific circumstances.
[0063] In this embodiment of the application, the input and output process of the signal during the reading of the state of the superconducting quantum bit is as follows: Figure 1 As shown, read the input signal. Typically, a readout microwave pulse of about 6 to 8 gigahertz (GHz) with a duration of tens of nanoseconds (ns) to a few microseconds (µs) is generated by an arbitrary wave generator (AWG). Then, the readout microwave pulse at room temperature is processed into a weak signal that meets the low-temperature environment requirements of the superconducting quantum chip. Specifically, the readout microwave pulse is input to a dilution refrigerator through a room temperature microwave cable. After passing through cooling plates, coaxial lines and attenuators at different temperatures within the dilution refrigerator, the signal strength of the readout microwave pulse can be attenuated to about -150 dBm when it reaches the superconducting quantum chip.
[0064] The attenuated readout microwave pulse is capacitively coupled to linearly respond to the system convolution after a. The input microwave signal a is fed into the coplanar waveguide to read the resonant cavity. The frequency of the readout resonant cavity matches the resonant frequency of the readout cavity. At this point, the readout cavity and the superconducting quantum bit are also capacitively coupled. The state of the superconducting quantum bit changes the resonant frequency of the readout cavity through dispersive coupling, causing a phase or amplitude shift in the microwave signal. This microwave signal, after being reflected by the readout cavity, is output from the superconducting quantum chip via reflection or transmission through the output circuitry; the corresponding output signal... After the signal is amplified by the first-stage amplifier, coaxial cable, and second-stage amplifier (e.g., amplified by 90-110dB), it is transmitted to the analog-to-digital converter (ADC). The output signal is acquired in real time, and after data processing, the state of the superconducting quantum bit can be inferred.
[0065] The readout performance of superconducting qubits mainly includes readout fidelity, readout speed, and post-readout perturbation. However, traditional readout schemes struggle to optimize these performance aspects simultaneously. First, readout fidelity directly depends on the signal-to-noise ratio (SNR) of the output signal. To improve SNR and achieve high fidelity during readout, the amplitude or duration of the readout microwave pulse is typically increased to accumulate more photons within the readout resonant cavity. However, excessive photons can lead to side effects such as Stark shift, Purcell effect, and inelastic transitions, limiting the improvement in readout fidelity. Second, readout speed is limited by the decay rate κ of the readout resonant cavity. The establishment and decay of photons within the cavity require at least 1 / κ of time, a theoretical limit that traditional square waves or simple pulse shapes cannot reach. For example, when a square wave is used for the readout microwave pulse, its steep rising and falling edges contain rich spectral components, which can excite higher-order modes within the cavity, resulting in severe ring-down. This causes photon decay within the cavity to be much slower than the theoretical value of 1 / κ, leading to a slower readout speed. Furthermore, after the reading is completed, if the residual photons in the reading resonant cavity cannot decay to a vacuum state quickly... These residual photons continue to interact with the qubit, causing unnecessary energy level transitions or phase loss, i.e., read-out perturbations. These perturbations not only affect the coherence of the current qubit, but the slow photon decay also forces a longer dead time for the cavity to be fully reset, significantly reducing the speed and efficiency of quantum computing.
[0066] Therefore, this application provides a method for reading superconducting qubits, which can achieve high fidelity and fast reading while effectively avoiding post-reading disturbances. In this application embodiment, the main focus is on reading the input signal. Starting with the characteristics of the resonant cavity and superconducting qubits, by changing... The shape is used to optimize reading. For example... Figure 2 As shown, the specific steps include the following:
[0067] 201. Obtain the attenuation rate of the readout resonant cavity, the frequency of the readout resonant cavity, and the dispersive coupling strength between the superconducting quantum bit and the readout resonant cavity.
[0068] In this embodiment, before generating the readout microwave pulse, it is necessary to determine the key parameters of the superconducting quantum system. The superconducting quantum bit is coupled to the readout resonant cavity, and the state of the superconducting quantum bit (|0> state or |1> state) changes the resonant frequency of the readout resonant cavity through dispersive coupling. Specifically, it is necessary to obtain the attenuation rate of the readout resonant cavity, the frequency of the readout resonant cavity, and the dispersive coupling strength between the superconducting quantum bit and the readout resonant cavity.
[0069] The attenuation rate of the readout resonant cavity can be obtained through AC stack shift measurement (also known as AC stack shift measurement). AC stack shift measurement involves applying a microwave pulse of a specific amplitude to the readout resonant cavity and observing the amplitude attenuation or phase drift of the cavity's response signal under the pulse. The energy loss rate of the resonant cavity is then deduced from the signal attenuation curve or phase change law, thus obtaining the attenuation rate. The frequency of the readout resonant cavity (its inherent frequency, i.e., cavity frequency) can be obtained through S21 measurement. S21 is a scattering parameter of the microwave measurement, characterizing the transmission characteristics of the microwave signal from the transmitting port to the receiving port. During measurement, microwave signals of different frequencies are input into the readout resonant cavity, and the amplitude and phase of the S21 signal at different frequencies are recorded. When the signal amplitude reaches its peak (or the phase undergoes a sudden change), the corresponding frequency is the frequency of the readout resonant cavity. The dispersive coupling strength between the superconducting quantum bit and the readout resonant cavity can be represented by the difference in the frequency of the readout resonant cavity when the superconducting quantum bit is in the |0> state and the |1> state.
[0070] For example, the frequency at which the resonant cavity is read can be obtained. =7GHz, read the attenuation rate of the resonant cavity. = The dispersive coupling strength between superconducting qubits and readout resonant cavities At this point, the characteristic time of reading the resonant cavity is... When the input signal is a square wave, the duration of the square wave can be set to 2µs. After inputting the square wave into the resonant cavity, the time it takes for the number of photons in the resonant cavity to increase to its maximum value is approximately 5µs. After the reading is completed, there is also a photon attenuation process within the reading resonant cavity, which also requires 5 seconds. Time causes the photon number to decay to 0.7% of its maximum value; the time-domain signal acquired by an analog-to-digital converter (ADC) at a sampling rate of 2.5 GHz is as follows: Figure 4 As shown in the figure, the horizontal axis represents the time sampling points, with each sampling point spaced 0.4 ns apart, and the vertical axis represents the relative intensity (representing the number of photons in the readout resonant cavity). It can be seen that when the readout speed is less than 1 μs (i.e., 2500 time sampling points), the readout fidelity decreases rapidly as the readout time shortens. And as... Figure 5 As shown, the vertical axis represents the relative intensity of the read waveform after normalization. Even with methods such as rapidly increasing the number of photons in the read resonant cavity by adding ringing to the square wave waveform and rapidly lowering the waist to balance the photons, achieving high-fidelity readout is difficult due to the theoretical limit determined by 1 / κ, which makes it hard to shorten the readout time. Therefore, in this embodiment, a higher-order sine wave that satisfies the smoothness condition is used to improve readout fidelity while shortening readout time. The specific steps are as follows:
[0071] 202. Determine the envelope waveform that satisfies the smoothness condition: .
[0072] In the embodiments of this application, the envelope waveform that satisfies the smoothness condition can be determined: Where A is the amplitude, n is the waveform order, and n is a positive integer greater than or equal to 4; The pulse duration is determined based on the attenuation rate of the readout resonant cavity. The envelope waveform satisfying the smoothness condition is determined as follows: if the envelope waveform and its first m derivatives are both zero at the start and end points, then the envelope waveform satisfies the smoothness condition; where m is less than n; that is, the envelope waveform... Envelope waveform The first m derivatives at t=0 and t= The time interval is zero. Here, m can be n-1, meaning the envelope waveform is zero at both the starting point t=0 and the ending point t= The derivatives within the (n-1)th order are all zero, resulting in very smooth on / off switching of the readout microwave pulses and a pure spectrum, thus avoiding the excitation of higher-order modes in the readout resonant cavity. After the readout microwave pulse ends, the number of photons in the readout resonant cavity drops exponentially, achieving rapid reset of photons within the cavity.
[0073] It is understandable that in this envelope waveform In this process, it is necessary to determine the relevant parameter, pulse duration. And the waveform order n. This can be based on a preset relation: =C / κ, determines the pulse duration. Where κ is the attenuation rate of the resonant cavity, and C is a proportionality coefficient within a preset range, i.e., the pulse duration. The attenuation rate κ of the reading resonant cavity satisfies a preset relationship: =C / κ. The preset value range can be from 1.5 to 10, and is not limited here; preferably, the proportionality coefficient C can be 2 or 3.
[0074] The waveform order *n* can be flexibly adjusted based on the attenuation rate *κ* of the readout resonator and the dispersion coupling strength *χ* of different superconducting quantum chips, exhibiting high versatility and applicability to various superconducting quantum bit architectures (such as Transmon, Fluxonium, etc.). Preferably, the waveform order *n* ranges from order 6 to 14. For example, when the attenuation rate of the readout resonator... = The dispersive coupling strength between superconducting qubits and readout resonant cavities At this point, by changing the order of the envelope waveform n, the highest read fidelity and the shortest read time can be obtained. Under these conditions, the preferred waveform order n is 12.
[0075] 203. Adjust the frequency of the readout resonant cavity based on the attenuation rate and dispersion coupling strength to determine the readout frequency and obtain the microwave carrier corresponding to the readout frequency.
[0076] In this embodiment, the frequency of the readout resonator can be adjusted based on its attenuation rate and dispersive coupling strength to determine the readout frequency and obtain the microwave carrier corresponding to that frequency. Specifically, the frequency of the readout resonator can be adjusted until its attenuation rate and dispersive coupling strength are close to or meet the requirements. The adjusted frequency of the reading resonant cavity is used as the reading frequency. Where κ is the attenuation rate of the readout resonant cavity. This represents the dispersive coupling strength. Based on this readout frequency... Microwave carriers can be generated It is understood that, in the embodiments of this application, the frequency of the readout resonant cavity is adjusted until the attenuation rate of the readout resonant cavity and the dispersive coupling strength satisfy... By using the adjusted frequency of the readout resonant cavity as the readout frequency, and reading the superconducting qubit using a microwave carrier wave based on that readout frequency, the readout of the superconducting qubit can achieve optimal fidelity. It is understandable that when adjusting the frequency of the readout resonant cavity, the attenuation rate and dispersion coupling strength of the readout resonant cavity are not limited to satisfying... Under the condition that the attenuation rate of the resonant cavity is close to the dispersive coupling strength... Alternatively, the adjusted frequency of the reading resonant cavity can be used as the reading frequency; no specific limitation is made here.
[0077] 204. Generate readout microwave pulses based on the envelope waveform and microwave carrier wave to read the state of superconducting qubits using the readout microwave pulses.
[0078] After obtaining the envelope waveform and microwave carrier Then, based on the envelope waveform and microwave carrier Generate and read microwave pulses That is, reading microwave pulses. = * After obtaining the readout microwave pulse, the state of the superconducting qubit can be read using the readout microwave pulse; that is, the readout microwave pulse is input into the readout resonant cavity, and the state of the superconducting qubit is determined based on the signal reflected by the readout resonant cavity. For example... Figure 6As shown in the figure, the waveform order n in this application is greater than or equal to 4, and the generated reading microwave pulse is mainly a sixth-order sine wave, a twelfth-order sine wave or a sixteenth-order sine wave as shown in the figure.
[0079] As can be seen, in this embodiment, the attenuation rate of the readout resonant cavity, the frequency of the readout resonant cavity, and the dispersive coupling strength between the superconducting quantum bit and the readout resonant cavity are obtained; the envelope waveform that satisfies the smoothness condition is determined. Where A is the amplitude, n is the waveform order, and n is a positive integer greater than or equal to 4; The pulse duration is determined based on the attenuation rate of the readout resonator; the frequency of the readout resonator is adjusted based on the attenuation rate and dispersion coupling strength to determine the readout frequency, and the microwave carrier corresponding to the readout frequency is obtained; a readout microwave pulse is generated based on the envelope waveform and the microwave carrier to read the state of the superconducting qubit.
[0080] Since the order of the envelope waveform is a positive integer greater than or equal to 4, the generated readout microwave pulse is a high-order sine wave. This allows for rapid accumulation of photons within the readout resonant cavity during the pulse duration, improving readout fidelity. Furthermore, the pulse duration in the high-order sine wave is determined by the attenuation rate of the readout resonant cavity, effectively shortening the pulse duration and thus reducing the readout time to the theoretical limit determined by the attenuation rate, thereby increasing readout speed. Additionally, because the envelope waveform in the readout microwave pulse satisfies the smoothness condition, the generated readout microwave pulse satisfies the smoothness condition, allowing for rapid attenuation of photons within the readout resonant cavity after readout, achieving rapid photon reset and effectively avoiding post-readout disturbances. In short, the readout method of this application can achieve high fidelity and fast readout while effectively avoiding post-readout disturbances. It can effectively meet the requirements of large-scale quantum computing for high-fidelity and low-latency measurements.
[0081] Understandably, this method for generating and reading microwave pulses can be implemented using an arbitrary waveform generator (AWG) or FPGA digital logic without requiring hardware system modifications, and is easily integrated into existing quantum measurement and control systems.
[0082] In this embodiment of the application, after generating the readout microwave pulse, the readout microwave pulse can be optimized. The optimized readout microwave pulse is then used to read the state of the superconducting quantum bit, further improving the readout fidelity. Figure 3 As shown, it is understood that the embodiments of this application do not limit the optimization of the readout microwave pulse, and not optimizing the readout microwave pulse does not affect the above. Figure 2 The effectiveness of the method for generating and reading microwave pulses in the above-mentioned method depends on the fact that... Figure 2 All related improvements to the method for generating and reading microwave pulses fall within the scope of protection of this application. Figure 3The specific steps for optimizing the reading of microwave pulses are as follows:
[0083] 301. Acquire the time-domain signal of the microwave pulse reflected by the readout resonant cavity when the superconducting quantum bit is in different states at the target acquisition time.
[0084] In this embodiment, the time-domain signal of the readout microwave pulse reflected by the readout resonant cavity can be acquired when the superconducting quantum bit is in different states at the target acquisition time. That is, the superconducting quantum bit can be prepared into the |0> state and the |1> state respectively, and the readout microwave pulse can be simultaneously acquired. The input is fed into the reading resonant cavity via an input line, and the time-domain signal returned from the output port of the reading resonant cavity is acquired.
[0085] Specifically, the target acquisition time T can be obtained by truncating the portion of the waveform with a relative intensity greater than a preset intensity threshold within the pulse duration; this target acquisition time is the corresponding reading time (reading duration). In other words, for the original time-domain signal, the effective time-domain signal with a relative intensity greater than zero can be truncated based on the target acquisition time. The preset intensity threshold is a relative intensity in the range of 0.001 to 0.000001, and the specific value is not limited here. That is, by truncating the portion of the waveform with a relative intensity greater than 10e-6 to 10e-3, the actual pulse transmission time can be further shortened, thereby shortening the reading time, which can be 2.75. This can further reduce the reading time to the theoretical limit corresponding to the reading resonant cavity. This improves reading speed.
[0086] 302. Compare the signal points of the time-domain signal on the IQ plane with the reference signal clusters of the superconducting quantum bit in different states of the IQ plane to determine the current state of the superconducting quantum bit.
[0087] After acquiring the time-domain signal, the signal points of the time-domain signal on the IQ plane can be compared with the reference signal clusters of the superconducting quantum bit in different states of the IQ plane to determine the current state of the superconducting quantum bit.
[0088] This requires first obtaining reference signal clusters for the IQ plane of the superconducting quantum bit in different states. Specifically, this involves repeatedly preparing the superconducting quantum bit in different states (|0> state and |1> state) and then repeatedly setting the read frequency close to or satisfying the... A square wave is input to the readout resonant cavity to obtain the time-domain signal reflected by the cavity. Based on the time-domain signal reflected by the cavity, a reference signal cluster for the superconducting quantum bit in different states in the IQ plane is obtained. Specifically, by performing a Fourier transform on the time-domain signal reflected by the cavity, a reference signal point can be obtained in the IQ plane. By inputting the square wave into the cavity multiple times, multiple reference signal clusters corresponding to these signal points can be obtained, ensuring that the |0> and |1> states of the superconducting quantum bit are located at the positions with the highest discriminative power in the IQ plane.
[0089] For comparison, a signal point can be obtained on the IQ plane after performing a Fourier transform on the acquired time-domain signal. Based on the signal point on the IQ plane and the reference signal clusters on the IQ plane of the superconducting quantum bit in different states, the current state of the superconducting quantum bit can be determined by linear discriminant or machine learning classification algorithms. By comparing the signal point on the IQ plane with the reference signal clusters on the IQ plane of the superconducting quantum bit in different states, the current state of the superconducting quantum bit can be accurately determined.
[0090] Furthermore, the acquired time-domain signal may contain noise components. To eliminate these noise components and further improve readout fidelity, in this embodiment, the time-domain signals corresponding to the superconducting quantum bit in different states can be subtracted to obtain the readout signal; that is, the time-domain signals of the superconducting quantum bit in the |0> state and the |1> state can be subtracted to obtain the readout signal, which is the readout waveform corresponding to the effective photon signal. The envelope information of the readout signal is extracted to obtain the envelope function weight; as shown... Figure 7 As shown, the envelope function weight corresponding to the time-domain signal trace(XI) of the superconducting quantum bit in different states can be obtained, where I represents the signal read without any operation, and X refers to the signal read after exciting the superconducting quantum bit to the |1> state. Next, the envelope function can be used as the time-domain signal, and the following steps can be performed: compare the signal point of the time-domain signal on the IQ plane with the reference signal cluster of the superconducting quantum bit in different states on the IQ plane to determine the current state of the superconducting quantum bit.
[0091] 303. Determine the read fidelity based on the state of the superconducting quantum bit and its current state.
[0092] After determining the current state of the superconducting qubit, the readout fidelity can be determined based on the current state and the state of the superconducting qubit. The current state of the superconducting qubit can be obtained by repeatedly acquiring the time-domain signal reflected from the readout resonant cavity by the readout microwave pulse when the superconducting qubit is in different states. By repeatedly comparing the current state with the current state, the first probability that the superconducting qubit falls within its own classification region in the |0> state distribution, and the second probability that the superconducting qubit falls within its own classification region in the |1> state distribution, can be determined. The average of the first and second probabilities can be used to determine the readout fidelity.
[0093] like Figure 8 The diagram shows a schematic of the reference signal clusters for the |0> and |1> states in the IQ plane (left side). Blue represents the reference signal clusters for the |0> states, orange represents the reference signal clusters for the |1> states, and the dashed line represents the classification boundary, used to distinguish between the |0> and |1> state reference signal clusters. The diagram also shows a projection histogram (right side). Blue peaks represent the projection distribution of the |0> states, and orange peaks represent the projection distribution of the |1> states. The horizontal axis represents the projection value of the IQ plane signal onto the classification boundary, used to compress the two-dimensional IQ signal into a one-dimensional distribution, facilitating the statistical analysis of the signal overlap between different states. The vertical axis shows the signal quantity statistics, reflecting the number of times the signal appears under a certain projection value; the cumulative probability reflects the probability distribution, used to represent the probability that the superconducting quantum bit falls within its own classification region in the |0> and |1> state distributions, respectively. The readout fidelity can be determined by the projection histogram. In the projection histogram, the higher the separation and the smaller the overlap between the two peaks, the better the readout discrimination of the superconducting quantum bit, i.e., the higher the fidelity.
[0094] 304. Adjust the amplitude, waveform order, pulse duration, and acquisition time in the envelope waveform based on the read fidelity until the read fidelity reaches the preset fidelity threshold to obtain the optimized read microwave pulse.
[0095] After determining the readout fidelity based on the state of the superconducting qubit and its current state, the amplitude, waveform order, pulse duration, and acquisition time in the envelope waveform can be adjusted based on the readout fidelity until a preset fidelity threshold is reached, resulting in an optimized readout microwave pulse. This optimized readout microwave pulse is then used to read the state of the superconducting qubit. Specifically, after adjusting the amplitude, waveform order, pulse duration, and acquisition time in the envelope waveform, steps 301 to 304 can be repeatedly executed until the readout fidelity reaches the preset fidelity threshold, resulting in an optimized readout microwave pulse. Preferably, this preset fidelity threshold is 99%.
[0096] Understandably, after obtaining the optimized readout microwave pulse, the photon count reset within the readout resonant cavity can be verified. First, the initial amplitude R1, i.e., the signal strength reference of the qubit, is measured using a Ramsey experiment. Next, after inputting the optimized readout microwave pulse into the readout resonant cavity, a Ramsey experiment is performed at regular intervals t to measure the amplitude R2, i.e., the change in signal strength after the readout operation. Finally, based on the difference between the initial amplitude R1 and the amplitude R2, the attenuation of the photon count within the readout resonant cavity is determined. The smaller the difference between the initial amplitude R1 and the amplitude R2, the greater the attenuation of the photon count within the readout resonant cavity. When the difference is less than 10e-3 (i.e., 0.001), it can be confirmed that the photon count has decreased to below 0.5, achieving rapid photon count reset.
[0097] For example, reading the frequency of the resonant cavity. =7GHz, read the attenuation rate of the resonant cavity. = The dispersive coupling strength between superconducting qubits and readout resonant cavities At this point, the characteristic time of reading the resonant cavity is... The corresponding envelope waveform In the process, based on the ratio of the attenuation rate of the resonant cavity to the dispersive coupling strength, the waveform order n is determined to be 12; based on the preset relationship: =C / κ, which determines the pulse duration. The acquisition time is 160 ns. By inputting the readout microwave pulse corresponding to this envelope waveform into the readout resonant cavity, the portion of the time-domain signal reflected from the cavity with a relative intensity greater than 0.0001 can be truncated. In this case, the target acquisition time is 110 ns. This readout microwave pulse can efficiently establish photons within the readout resonant cavity within an extremely short target acquisition time (integration time), enabling the output signal to achieve a sufficient signal-to-noise ratio, achieving a fidelity of over 99%. Simultaneously, with timing alignment, the corresponding readout duration is chosen as T = 110 ns ≈ 2.75. The read speed is close to the theoretical limit of the read resonant cavity. Under these conditions, the photon book in the readout resonant cavity can be attenuated to less than 0.5 units within 10 ns after readout, greatly reducing post-readout disturbances. This means that it is possible to achieve attenuation of the photon book within less than 3... Under these conditions, effective photon reading and rapid intracavity attenuation are achieved, enabling efficient photon resetting and high-fidelity rapid reading.
[0098] This application also provides a superconducting quantum computing system, such as... Figure 9As shown, the system includes: a superconducting quantum chip, a dilution refrigerator, a microwave transmitting module, and a signal receiving and processing module. The dilution refrigerator provides a low-temperature environment for the superconducting quantum chip. The superconducting quantum chip includes: at least one superconducting quantum bit and a readout resonant cavity coupled to the superconducting quantum bit. The microwave transmitting module generates a readout microwave pulse by executing the readout method described above and transmits the readout microwave pulse to the readout resonant cavity. The signal receiving and processing module receives and processes the time-domain signal returned by the readout resonant cavity to read the state of the superconducting quantum bit. This superconducting quantum computing system reads the state of the superconducting quantum bit through the readout microwave pulse, enabling high-fidelity and fast readout of the superconducting quantum bit while effectively avoiding post-readout disturbances and improving quantum computing speed.
[0099] Furthermore, such as Figure 10 As shown, in the superconducting quantum computing system, the microwave transmission module includes: an acquisition unit 1001, a determination unit 1002, an execution unit 1003, and a generation unit 1004; the acquisition unit 1001 is used to acquire the attenuation rate of the readout resonant cavity, the frequency of the readout resonant cavity, and the dispersive coupling strength between the superconducting quantum bit and the readout resonant cavity; the determination unit 1002 is used to determine the envelope waveform that satisfies the smoothness condition. Where A is the amplitude, n is the waveform order, and n is a positive integer greater than or equal to 4; The pulse duration is determined based on the attenuation rate of the readout resonant cavity; the execution unit 1003 is used to adjust the frequency of the readout resonant cavity based on the attenuation rate of the readout resonant cavity and the dispersion coupling strength to determine the readout frequency and obtain the microwave carrier corresponding to the readout frequency; the generation unit 1004 is used to generate a readout microwave pulse based on the envelope waveform and the microwave carrier to read the state of the superconducting quantum bit using the readout microwave pulse.
[0100] This application also provides a superconducting quantum computing device, including the superconducting quantum computing system described above. This superconducting quantum computing device reads the state of superconducting qubits through the superconducting quantum computing system, enabling high-fidelity and fast reading of the superconducting qubits while effectively avoiding post-reading disturbances and improving quantum computing speed.
[0101] This application also provides a computer-readable storage medium storing computer instructions thereon, which, when executed by a processor, implement the reading method as described above.
[0102] In this invention, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The term "multiple" refers to two or more unless otherwise expressly defined.
[0103] The above embodiments are only used to illustrate the technical solutions of the embodiments of this application, and are not intended to limit them. Although the embodiments of this application have been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of the embodiments of this application. If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage media include: USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, optical disks, and other media that can store program code.
Claims
1. A method for reading out superconducting qubits, characterized in that, include: The attenuation rate of the readout resonant cavity, the frequency of the readout resonant cavity, and the dispersive coupling strength between the superconducting quantum bit and the readout resonant cavity are obtained. Determine the envelope waveform that satisfies the smoothness condition: Where A is the amplitude, n is the waveform order, and n is a positive integer greater than or equal to 4; The pulse duration is determined based on the attenuation rate of the readout resonant cavity; The frequency of the readout resonant cavity is adjusted based on the attenuation rate of the readout resonant cavity and the dispersive coupling strength to determine the readout frequency and obtain the microwave carrier corresponding to the readout frequency. Based on the envelope waveform and the microwave carrier, a readout microwave pulse is generated to read the state of the superconducting quantum bit.
2. The reading method according to claim 1, characterized in that, After obtaining the attenuation rate of the readout resonant cavity, the frequency of the readout resonant cavity, and the dispersive coupling strength between the superconducting quantum bit and the readout resonant cavity, the method further includes: Based on a pre-defined relation: =C / κ, determine the pulse duration Wherein, κ is the attenuation rate of the reading resonant cavity, and C is a proportionality coefficient within a preset range.
3. The reading method according to claim 2, characterized in that, The preset value range is 1.5 to 10.
4. The reading method according to claim 1, characterized in that, After obtaining the attenuation rate of the readout resonant cavity, the frequency of the readout resonant cavity, and the dispersive coupling strength between the superconducting quantum bit and the readout resonant cavity, the method further includes: The value of the waveform order n in the envelope waveform is determined based on the ratio of the attenuation rate of the readout resonant cavity to the dispersion coupling strength.
5. The reading method according to claim 1, characterized in that, The envelope waveform that satisfies the smoothness condition is determined as follows: ,include: If the envelope waveform and its first m derivatives are both zero at the start and end points, then the envelope waveform is determined to satisfy the smoothness condition; where m is less than n.
6. The reading method according to claim 1, characterized in that, The order n of the waveform ranges from 6 to 14.
7. The reading method according to claim 1, characterized in that, The step of adjusting the frequency of the readout resonant cavity based on the attenuation rate and the dispersive coupling strength to determine the readout frequency includes: Adjust the frequency of the readout resonant cavity until its attenuation rate is close to or meets the dispersion coupling strength. The adjusted frequency of the reading resonant cavity is taken as the reading frequency; where κ is the attenuation rate of the reading resonant cavity. The dispersion coupling strength is denoted as .
8. The reading method according to claim 1, characterized in that, After generating the readout microwave pulse based on the envelope waveform and the microwave carrier, the process further includes: The time-domain signals of the readout microwave pulse reflected by the readout resonant cavity are acquired when the superconducting quantum bit is in different states at the target acquisition time. The current state of the superconducting quantum bit is determined by comparing the signal points of the time-domain signal on the IQ plane with the reference signal clusters of the superconducting quantum bit in different states on the IQ plane. The read fidelity is determined based on the state of the superconducting quantum bit and the current state. Based on the readout fidelity, the amplitude, waveform order, pulse duration, and acquisition time in the envelope waveform are adjusted until the readout fidelity reaches a preset fidelity threshold to obtain an optimized readout microwave pulse, which is then used to read the state of the superconducting quantum bit.
9. The reading method according to claim 8, characterized in that, Before acquiring the time-domain signal reflected by the readout microwave pulse through the readout resonant cavity when the superconducting quantum bit is in different states at the target acquisition time, the method further includes: The target acquisition time is obtained by extracting the portion of the waveform whose relative intensity is greater than a preset intensity threshold within the pulse duration.
10. The reading method according to claim 9, characterized in that, The preset intensity threshold is a relative intensity in the range of 0.001 to 0.000001.
11. The reading method according to claim 8, characterized in that, The process of acquiring the time-domain signal of the readout microwave pulse reflected by the readout resonant cavity when the superconducting quantum bit is in different states at the target acquisition time further includes: The time-domain signals corresponding to the superconducting quantum bits in different states are subtracted to obtain the readout signal; Extract the envelope information of the read signal to obtain the envelope function; Using the envelope function as the time-domain signal, the following steps are performed: comparing the signal point of the time-domain signal on the IQ plane with the reference signal cluster of the superconducting quantum bit in different states on the IQ plane to determine the current state of the superconducting quantum bit.
12. The reading method according to claim 8, characterized in that, Before comparing the signal points of the time-domain signal on the IQ plane with the reference signal clusters of the superconducting quantum bit in different states of the IQ plane to determine the current state of the superconducting quantum bit, the method further includes: When the superconducting qubits are prepared in different states, the readout frequency is satisfied multiple times. The square wave is input to the reading resonant cavity; Based on the time-domain signal reflected by the square wave through the readout resonant cavity, the reference signal clusters of the superconducting quantum bit in the IQ plane under different states are obtained.
13. A superconducting quantum computing system, characterized in that, include: Superconducting quantum chip, dilution refrigerator, microwave transmitting module, and signal receiving and processing module; The dilution refrigerator is used to provide a low-temperature environment for the superconducting quantum chip; The superconducting quantum chip includes: at least one superconducting quantum bit and a readout resonant cavity coupled to the superconducting quantum bit; The microwave transmitting module is used to generate a readout microwave pulse by performing the readout method according to any one of claims 1 to 12, and to transmit the readout microwave pulse to the readout resonant cavity; The signal receiving and processing module is used to receive and process the time-domain signal returned by the reading resonant cavity.
14. The superconducting quantum computing system according to claim 13, characterized in that, The microwave transmitting module includes: an acquisition unit, a determination unit, an execution unit, and a generation unit; The acquisition unit is used to acquire the attenuation rate of the readout resonant cavity, the frequency of the readout resonant cavity, and the dispersive coupling strength between the superconducting quantum bit and the readout resonant cavity; The determining unit is used to determine the envelope waveform that satisfies the smoothness condition: Where A is the amplitude, n is the waveform order, and n is a positive integer greater than or equal to 4; The pulse duration is determined based on the attenuation rate of the readout resonant cavity; The execution unit is used to adjust the frequency of the read resonant cavity based on the attenuation rate of the read resonant cavity and the dispersion coupling strength, determine the read frequency, and obtain the microwave carrier corresponding to the read frequency; The generation unit is used to generate a readout microwave pulse based on the envelope waveform and the microwave carrier, so as to read the state of the superconducting quantum bit using the readout microwave pulse.
15. A superconducting quantum computing device, characterized in that, The superconducting quantum computing system includes any one of claims 13 to 14.
16. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions that, when executed by a processor, implement the reading method as described in any one of claims 1 to 12.