Control device for a quantum computer

Abstract

A control device of a quantum computer capable of reducing the number of circuit components is provided. A signal processing unit (17) performs up-conversion processing on a first intermediate frequency signal using an up-converter (34), the first intermediate frequency signal being obtained by adding waveform data of each control signal using a digital combiner (30) to obtain synthesized waveform data, and then performing digital-to-analog conversion on the synthesized waveform data using a digital-to-analog converter (31). In addition, for an observation signal, a second intermediate frequency signal is obtained by performing digital-to-analog conversion on waveform data using a digital-to-analog converter (32), and then mixing the obtained second intermediate frequency signal with a second local oscillation signal using an up-converter (35). For an initialization signal, the initialization signal is directly generated by performing digital-to-analog conversion on waveform data using a digital-to-analog converter (33). When a response signal is down-converted, the response signal is input to a down-converter (41) together with the second intermediate frequency signal.

Description

Technical Field

[0001] This invention relates to a control device for a quantum computer. Background Technology

[0002] In recent years, research on quantum computers, which utilize quantum mechanical phenomena for computation, has attracted much attention. High-precision control of qubits is essential for realizing quantum computers, and various technologies related to quantum computer control have been proposed (e.g., see Patent Document 1, Patent Document 2, Non-Patent Document 1, and Non-Patent Document 2). Currently, superconducting qubits, which have become mainstream in quantum computers, are controlled by microwave pulses.

[0003] A quantum computer includes a qubit system consisting of multiple qubits and a control device for controlling the qubit system. The control device sends initialization signals to the qubit system to initialize the qubits, control signals to control the qubit states, and observation signals to read the qubit states. It also receives response signals from the qubit system in response to the input of the observation signals. The initialization signals, control signals, and observation signals convert the original waveform digital signals into analog signals via digital-to-analog converters (DACs), and then up-convert them to the frequency to be sent to the qubit system. When using multiple control signals, the multiple waveform digital signals corresponding to these control signals are first converted to analog signals, up-converted, and then the resulting analog signals are combined and sent to the qubit system. Furthermore, the response signal is first down-converted to a low-frequency signal before undergoing analog-to-digital conversion. Frequency conversion, i.e., up-conversion and down-conversion, is implemented by mixing the target signal with a local oscillation signal. Existing technical documents Patent documents

[0004] Patent Document 1: U.S. Patent Application Publication No. 2019 / 0049495 Patent Document 2: U.S. Patent Application Publication No. 2020 / 0065696 Non-patent literature

[0005] Non-patent literature 1: Colm A. Ryan, Blake R. Johnson, Diego Riste, Brian Donovan, Thomas A. Ohki, “Hardware for Dynamic Quantum Computing,” Review of Scientific Instruments 88 (10), 104703 (2017) Non-patent literature 2: Yilun Xu, Gang Huang, Jan Balewski, Ravi Naik, AlexisMorvan, Bradley Mitchell, Kasra Nowrouzi, David I. Santiago, Irfan Siddiqi, "QubiC: An open source FPGA-based control and measurement system for superconducting quantum information processors," IEEE Transactions on QuantumEngineering, vol. 2, pp. 1-11, 2021, Art no. 6003811 Summary of the Invention The problem that the invention aims to solve

[0006] However, in the control device of the quantum computer described above, each signal contained in the initialization signal, observation signal, and control signal requires a digital-to-analog converter, a local oscillation circuit, and an up-converter. Therefore, the following problems exist: the increased size of the circuit components in the control device hinders miniaturization and makes adjustments to ensure stable operation of each circuit difficult.

[0007] The present invention was made in view of the above-mentioned problems, and its object is to provide a control device for a quantum computer that can reduce the number of circuit components. Methods for solving problems

[0008] The control device for a quantum computer of the present invention includes a digital combiner, a control signal generation unit, an observation signal generation unit, and a receiving unit. The digital combiner adds first waveform data of multiple control signals with mutually staggered frequencies used for qubit control of a qubit system composed of multiple qubits in the digital domain to generate a composite waveform data. The control signal generation unit has a first digital-to-analog converter that performs analog-to-analog conversion on the composite waveform data to generate a combined control signal of a first frequency band. The observation signal generation unit has a second digital-to-analog converter that performs analog-to-analog conversion on second waveform data used for reading the state of qubits from the qubit system to generate an observation signal of a second frequency band different from the first frequency band. The receiving unit is input with a response signal output from the qubit system in response to the input of the observation signal to the qubit system, and has an analog-to-digital converter that performs digital-to-analog conversion on the response signal. The effects of the invention

[0009] According to the quantum computer control device of the present invention, a digital combiner is used to synthesize waveform data corresponding to multiple control signals to obtain synthesized waveform data, and then a first digital-to-analog converter is used to convert the obtained synthesized waveform data into digital-to-analog data to generate a combined control signal, thereby reducing the number of circuit components. Attached Figure Description

[0010] Figure 1 This is a block diagram illustrating the configuration of a quantum computer in an implementation scheme. Figure 2 It is a block diagram showing the configuration of the main parts of the signal processing unit. Detailed Implementation

[0011] Figure 1 In this system, the quantum computer 10 includes a control unit 12 and a qubit system 14 consisting of multiple qubits. The control unit 12 includes a server 16, multiple signal processing units 17, and a clock generation unit 18. The qubit system 14 is housed within a cryogenic refrigerator. The quantum computer 10 sends (irradiates) microwave signals (electromagnetic wave signals) to the qubit system 14 via the control unit 12, thereby initializing and controlling the qubits, enabling the qubit system 14 to perform calculations, and reading the qubit states.

[0012] The microwave signals transmitted from control device 12 to qubit system 14 include: control signals for controlling the qubits, observation signals for reading the qubit states, and initialization signals for initializing the qubits. For the control signals, signal processing unit 17 combines multiple control signals (three in this example) with different center frequencies to obtain a combined control signal, which is then sent to qubit system 14. The frequency bands of each signal are different. In this example, the frequency band of the combined control signal is set in the range of 5.8 GHz to 7 GHz. Similarly, the observation signal is set in the range of 2 GHz to 2.8 GHz, and the initialization signal is set in the range of 3.2 GHz to 3.8 GHz.

[0013] Server 16 receives instruction input from the user, calculates waveform data for the control, reading, and initialization of the qubit states of each qubit in the qubit system 14, and outputs this data to signal processing unit 17. As described above, for the control signal, multiple control signals are combined to obtain a combined control signal, which is then sent to the qubit system 14. Therefore, server 16 calculates waveform data for each control signal and outputs it to signal processing unit 17. The center frequencies of the signals represented by the waveform data for each control signal are staggered. Server 16 reads the digitally processed response signals and analysis results from each signal processing unit 17 and performs predetermined processing. The response signal is obtained by modulating the observation signal illuminating the qubit according to its qubit state.

[0014] As detailed below, in order to reduce the specifications (sampling rate and bandwidth) required by the DA (digital-to-analog) converter, the frequency (bandwidth) of the signal represented by the waveform data of each control signal is lower than that of each control signal in the multiplexing control signal sent to the quantum bit system 14.

[0015] For the same reason, the frequency of the signal represented by the waveform data of the observed signal is lower than the frequency of the observed signal sent to the qubit system 14. For the initialization signal, because its frequency band is relatively low, the signal obtained by digital-to-analog conversion of its waveform data is directly sent to the qubit system 14 as the initialization signal.

[0016] The clock generator 18 generates a clock that serves as the operating reference for the control device 12. The clock generated by the clock generator 18 is provided to the server 16 and each signal processing unit 17.

[0017] Each signal processing unit 17 generates a microwave signal irradiated by the quantum bit system 14 based on the waveform data calculated by the server 16. In addition, the signal processing unit 17 receives the response signal (microwave signal) output by the quantum bit system 14 in response to the observation signal, which corresponds to the state of the quantum bits, and analyzes the response signal.

[0018] Figure 2This diagram illustrates the configuration of the main components of the signal processing unit 17. The signal processing unit 17 includes a high-bandwidth memory (HBM) 21, a transmitting circuit 22, a receiving circuit 23, and an interface (I / F) 24 for connecting the server 16 and the high-bandwidth memory 21. The high-bandwidth memory 21 stores waveform data from the server 16 and data from the receiving circuit 23. The server 16 transmits and receives data with the signal processing unit 17 via the high-bandwidth memory 21. Additionally, the signal processing unit 17 also includes circuitry for monitoring and correcting the internal timing of various signals transmitted to the quantum bit system 14, and circuitry for synchronizing the signal processing units 17 with each other.

[0019] The transmitting circuit 22 includes a transmitting logic section 27, a digital combiner 30, digital-to-analog (DA) converters 31-33, up-converters 34 and 35, local oscillators 36 and 37, and a combiner 38. The receiving circuit 23 includes a down-converter 41, an analog-to-digital (AD) converter 42, and a receiving logic section 43. The transmitting logic section 27 and the receiving logic section 43 are configured as programmable logic devices, for example, using an FPGA.

[0020] The transmitting logic unit 27 stores parameters related to the transmission timing of each of the control signals (combination control signals), observation signals, and initialization signals, and outputs the waveform data stored in the high-bandwidth memory 21 to the digital combiner 30, digital-to-analog converters 32 and 33 according to the timing specified by the parameters.

[0021] The combined waveform control signal is generated by a digital combiner 30, a digital-to-analog converter 31, an up-converter 34, and a local oscillator 36. In this example, these components constitute the control signal generation unit. The waveform data of each control signal is input from the transmitting logic unit 27 to the digital combiner 30. The digital combiner 30 adds the multiple input waveform data in the digital domain to generate a composite waveform. The digital combiner 30 is, for example, constructed by a DSP (Digital Signal Processor) that performs high-speed digital arithmetic processing.

[0022] The synthesized waveform data from the digital combiner 30 is input to the digital-to-analog converter 31. The digital-to-analog converter 31 performs digital-to-analog conversion on the input synthesized waveform data to generate a first intermediate frequency (IF) signal. A local oscillator 36 generates a first local oscillation signal based on a clock from the clock generator 18 and inputs the first local oscillation signal to the up-converter 34. The up-converter 34 mixes the input first IF signal with the first local oscillation signal, thereby generating a multiplexing control signal obtained by up-converting the first IF signal. The multiplexing control signal generated by the up-converter 34 is input to the combiner 38.

[0023] The digital-to-analog converter 31 only needs to have a bandwidth and sampling rate corresponding to the first intermediate frequency signal, and does not need to be adapted to the multiplexing control signal. Therefore, the digital-to-analog converter 31 does not need to be a high-speed and high-bandwidth device corresponding to the multiplexing control signal itself. In addition, as mentioned above, the multiple control signals are first synthesized in the digital domain by the digital combiner 30 to obtain waveform data corresponding to the multiple control signals, and then digital-to-analog conversion is performed, and the first intermediate frequency signal obtained by the digital-to-analog conversion is up-converted. Thus, a single digital-to-analog converter 31 can be used to perform digital-to-analog conversion on multiple control signals, eliminating the need to set up a digital-to-analog converter for each control signal, thereby reducing the number of components and facilitating the miniaturization of the control device 12. Furthermore, only the digital-to-analog converter 31 needs to be adjusted for the digital-to-analog conversion of the control signals, thus simplifying the adjustment process.

[0024] After transmitting the multiplexing control signal to the vector bit system 14, for example, 100 nanoseconds later, the vector bit system 14 transmits the observation signal. This observation signal is generated by the digital-to-analog converter 32, the up-converter 35, and the local oscillator 37. In this example, these components constitute the observation signal generation unit. Waveform data corresponding to the observation signal from the transmitting logic unit 27 is input to the digital-to-analog converter 32. The digital-to-analog converter 32 generates a second intermediate frequency (IF) signal by performing digital-to-analog conversion on the input waveform data. Similar to the digital-to-analog converter 31, the digital-to-analog converter 32 used to generate the observation signal only needs to correspond to the second IF signal and does not need to be adapted to the observation signal itself; therefore, it is not necessary to select a high-speed and high-bandwidth device corresponding to the observation signal itself.

[0025] The local oscillator 37 generates a second local oscillation signal based on the clock from the clock generator 18, and inputs the second local oscillation signal to the up-converter 35. The up-converter 35 mixes the input second intermediate frequency signal with the second local oscillation signal to generate the observation signal obtained by up-converting the second intermediate frequency signal. The observation signal generated by the up-converter 35 is input to the combiner 38.

[0026] An initialization signal is sent to the quantum bit system 14 before the transmission of the multiplexing control signal (e.g., 100 nanoseconds prior). This initialization signal is generated by a digital-to-analog converter 33. Waveform data corresponding to the initialization signal is input from the transmitting logic unit 27 to the digital-to-analog converter 33. The digital-to-analog converter 33 generates a third intermediate frequency signal by performing digital-to-analog conversion on the input waveform data. The initialization signal generated by the digital-to-analog converter 33 is input to the combiner 38. Thus, for the relatively low-bandwidth initialization signal, an up-converter is not used, but it is directly generated by the digital-to-analog converter 33. Therefore, there is no need to set up an up-converter and a local oscillator for generating the initialization signal, which reduces the number of components and also facilitates the miniaturization of the control device 12.

[0027] The combination control signal, observation signal, and initialization signal are output to the quantum bit system 14 via combiner 38. Combiner 38 combines the input analog signals and outputs the results; it is a so-called analog combiner. Alternatively, the combination control signal, observation signal, and initialization signal can be output directly to the quantum bit system 14 without going through combiner 38; or any two of the combination control signal, observation signal, and initialization signal can be output via combiner 38.

[0028] The qubit system 14 responds to the input of an observation signal and outputs a response signal corresponding to the state of the qubits. In this example, the receiving unit consists of a downconverter 41 and an analog-to-digital converter 42. The response signal from the qubit system 14 is input to the downconverter 41. In addition to the response signal, a second local oscillation signal from the local oscillator 37 used to generate the observation signal during upconversion is also input to the downconverter 41. The downconverter 41 generates an analog received signal obtained by downconverting the response signal by mixing the input response signal with the second local oscillation signal. Thus, for the downconversion of the response signal, the second local oscillation signal used to generate the observation signal during upconversion is used, so no phase shift occurs during the frequency conversion between the observation signal and the response signal. The analog signal from the downconverter 41 is transmitted to the analog-to-digital converter 42.

[0029] The analog-to-digital converter 42 performs analog-to-digital conversion on the analog received signal from the down-converter 41 to obtain digital data, and outputs the obtained digital data to the receiving logic unit 43. The analog-to-digital converter 42 only needs to correspond to the frequency of the analog received signal obtained after down-converting the response signal; high-speed and high-bandwidth devices are not required. The receiving logic unit 43 acquires and parses the digital data, i.e., the digitized response signal, according to its stored parameters. The receiving logic unit 43 writes the digital data of the response signal and the parsing result into the HBM21.

[0030] In this example, the control signal generation unit, as described above, obtains the multiplexing control signal by up-converting the first intermediate frequency signal obtained from the digital-to-analog converter 31. However, it can also be configured, similar to the initialization signal, to directly generate the multiplexing control signal by performing digital-to-analog conversion on the waveform data using the digital-to-analog converter 31 without up-conversion. Similarly, the observation signal generation unit can also be configured to directly generate the observation signal by performing digital-to-analog conversion on the waveform data using the digital-to-analog converter 32 without up-conversion. Furthermore, the receiving unit can be configured to not perform down-conversion on the response signal from the quantum bit system 14, but instead directly perform analog-to-digital conversion on the response signal using the analog-to-digital converter 42. In this way, the up-converter and down-converter can be omitted. It should be noted that in the configuration where the observation signal is directly generated by the digital-to-analog converter 32 and the response signal is directly converted by the analog-to-digital converter 42, it is preferable that the digital-to-analog converter 32 and the analog-to-digital converter 42 operate using a clock signal from a common clock source.

[0031] As described above, the control device 12 can reduce the number of digital-to-analog converters, up-converters, and local oscillators, and can achieve miniaturization. In addition, since the number of digital-to-analog converters, up-converters, and local oscillators is smaller, adjustments for stable operation are also simpler.

[0032] In the above embodiments, a digital combiner is used to merge the waveform data of multiple control signals into a single composite waveform, which is then converted from digital to analog. However, when using multiple observation signals with different frequencies, a digital combiner can also be used to merge the waveform data of these multiple observation signals into a single composite waveform, which is then converted from digital to analog to generate a signal that has been combined with multiple observation signals. Similarly, a digital combiner can also be used to merge the waveform data of multiple initialization signals with different frequencies into a single composite waveform, which is then converted from digital to analog to generate a signal that has been combined with multiple initialization signals.

[0033] Alternatively, waveform data of at least two of different types of signals—initialization signals, control signals, and observation signals—can be input to a digital combiner. The resulting composite waveform data output from the digital combiner can then be converted from digital to analog via a digital-to-analog converter (DAC), thereby generating different types of signals. By inputting waveform data of different types of signals at staggered times, the output timing of the signals can also be staggered. For example, if the waveform data of an initialization signal is input to the digital combiner, followed by the waveform data of multiple control signals, the composite waveform data generated from the initialization signal waveform data is input to the DAC. Then, the composite waveform data obtained from the waveform data of the multiple control signals is input to the DAC. Therefore, the initialization signal and the composite control signal can be output sequentially from a single output terminal. Thus, different types of signals can be generated using a shared circuit, simplifying the circuit structure.

[0034] Furthermore, this invention is not limited to the embodiments described above. Various modifications can be made without departing from the spirit of this invention, and other embodiments and variations implemented by those skilled in the art are also included in this invention. In addition to superconducting quantum computers, this invention can also be applied to the control of various quantum computers, such as: semiconductor quantum dot quantum computers controllable by microwaves, quantum computers with cooled atomic gas systems controllable by microwaves, and quantum computers that use molecular or nanotechnology to arrange electron spins. Furthermore, this invention can also be applied to the control of quantum simulators or quantum sensors using microwave-controlled qubits, as well as quantum repeaters. Explanation of reference numerals in the attached figures

[0035] 10: Quantum computers; 12: Control device; 14: Quantum bit system; 17: Signal processing unit; 30: Digital combiner; 31-33: Digital-to-analog converters; 34, 35: Upgraded frequency converter; 36, 37: Local oscillators; 38: Combiner; 41: Down-converter; 42: Analog-to-digital converter.

Claims

1. A control device for a quantum computer, characterized in that, include: A digital combiner, in the digital domain, adds together the first waveform data of multiple control signals with mutually staggered frequencies used to control a qubit system consisting of multiple qubits, to generate a composite waveform data. The control signal generation unit has a first digital-to-analog converter that performs analog-to-analog conversion on the synthesized waveform data and generates a multiplexing control signal for a first frequency band. The observation signal generation unit has a second digital-to-analog converter that performs analog-to-analog conversion on second waveform data used to read the state of qubits from the qubit system, and generates an observation signal in a second frequency band that is different from the first frequency band; as well as The receiving unit is input to a response signal output from the qubit system in response to the input of the observation signal to the qubit system, and has an analog-to-digital converter for digital conversion of the response signal.

2. The control device for a quantum computer according to claim 1, characterized in that, The control signal generation unit includes: A first local oscillator outputs a first local oscillation signal; and The first up-converter up-converts the first intermediate frequency signal to the first frequency band by mixing the first intermediate frequency signal obtained by the analog-to-digital converter converting the synthesized waveform data with the first local oscillation signal, thereby generating the multiplexing control signal. The observation signal generation unit includes: The second local oscillator outputs a second local oscillation signal; and The second upconverter upconverts the second intermediate frequency signal to the second frequency band by mixing the second intermediate frequency signal obtained from the analog-to-digital converter's analog-to-digital conversion of the second waveform data with the second local oscillation signal, thereby generating the observed signal. The receiving unit includes: The downconverter downconverts the response signal by mixing it with the second local oscillation signal.

3. The control device for a quantum computer according to claim 2, characterized in that, The control device of the quantum computer includes an analog combiner that combines multiple input analog signals. The combination control signal and the observation signal are output to the quantum bit system via the analog combiner.

4. The control device for a quantum computer according to claim 3, characterized in that, include: The third digital-to-analog converter performs analog-to-analog conversion on the third waveform data used to initialize the qubits, generating an initialization signal in a third frequency band that is lower than the first and second frequency bands. The combination control signal, the observation signal, and the initialization signal are output to the quantum bit system via the analog combiner.

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