Control device for quantum computer

Abstract

To provide a control device for a quantum computer that reduces the number of circuit components.SOLUTION: In the quantum computer including a control device and a quantum bit system consisting of multiple quantum bits, multiple signal processing units 17 of the control device each up-convert a first intermediate frequency signal obtained by a digital to analog conversion using a DA converter 31 of composite waveform data, generated by adding with a digital combiner 30 the waveform data of each control signal using an up-converter 34. For observation signals, a second intermediate frequency signal, obtained by digital-to-analog conversion of waveform data by a DA converter 32, is generated by mixing it with a second local oscillator signal using an up-converter 35. An initialization signal is generated directly by a digital-to-analog conversion of the waveform data using DA converter 33. When down-converting the response signal, the response signal and the second intermediate frequency signal are input to a down-converter 41.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a control device for a quantum computer. [Background technology]

[0002] In recent years, research into quantum computers, which perform calculations using quantum mechanical phenomena, has been attracting attention. To realize a quantum computer, it is essential to control quantum bits with high precision, and various technologies for controlling quantum computers have been proposed (see, for example, Patent Document 1, Patent Document 2, Non-Patent Document 1, and Non-Patent Document 2). Superconducting quantum bits, which are currently mainstream in quantum computers, are controlled by microwave pulses.

[0003] A quantum computer includes a quantum bit system consisting of multiple quantum bits and a control device that controls the quantum bit system. The control device transmits to the quantum bit system an initialization signal that initializes the quantum bits, a control signal that controls the quantum bit state, and an observation signal that reads the quantum bit state, and receives a response signal that the quantum bit system outputs in response to the input of the observation signal. The initialization signal, control signal, and observation signal are each converted from their original waveform digital signals into analog signals using a digital-to-analog converter and then upconverted to a frequency to be transmitted to the quantum bit system. When multiple control signals are used, multiple waveform digital signals corresponding to those control signals are converted to analog and upconverted, and the resulting analog signal is then combined and transmitted to the quantum bit system. The response signal is also downconverted to a lower frequency and then analog-to-digital converted. Frequency conversion, i.e., upconversion and downconversion, is performed by mixing the target signal with a local oscillator signal. [Prior art documents] [Patent documents]

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

[0005] [Non-Patent Document 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 document 2] Yilun Xu, Gang Huang, Jan Balewski, Ravi Naik, Alexis Morvan, 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 Quantum Engineering, vol. 2, pp. 1-11, 2021, Art no. 6003811 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the quantum computer control device described above requires a digital-to-analog converter, a local oscillator, and an up-converter for each of the signals included in the initialization signal, observation signal, and control signal. This increases the number of circuit components in the control device, hindering miniaturization of the control device and making it difficult to adjust each circuit for stable operation.

[0007] The present invention has been made in view of the above circumstances, and has an object to provide a quantum computer control device that can reduce the number of circuit components. [Means for solving the problem]

[0008] The quantum computer control device of the present invention includes a digital combiner that generates one composite waveform data by adding, in the digital domain, first waveform data of a plurality of control signals having frequencies shifted from each other for controlling quantum bits in a quantum bit system consisting of a plurality of quantum bits; a control signal generating unit that has a first digital-to-analog converter that converts the composite waveform data into analog and generates a combined control signal in a first frequency band; an observation signal generating unit that has a second digital-to-analog converter that converts, to analog, second waveform data for reading out a quantum bit state from the quantum bit system and generates an observation signal in a second frequency band different from the first frequency band; and a receiving unit that receives as input a response signal output from the quantum bit system in response to input of the observation signal to the quantum bit system and has an analog-to-digital converter that digitally converts the response signal. [Effects of the Invention]

[0009] According to the quantum computer control device of the present invention, waveform data corresponding to multiple control signals are combined by a digital combiner to generate composite waveform data, which is then digital-to-analog converted by a first digital-to-analog converter to generate a combined control signal, thereby reducing the number of circuit components. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a block diagram showing a configuration of a quantum computer according to an embodiment. [Figure 2] FIG. 2 is a block diagram showing the main configuration of a signal processing unit. DETAILED DESCRIPTION OF THE INVENTION

[0011] 1, quantum computer 10 includes control device 12 and quantum bit system 14 consisting of multiple quantum bits. Control device 12 includes server 16, multiple signal processing units 17, and clock generation unit 18. Qubit system 14 is disposed in an extremely low temperature refrigerator. Quantum computer 10 initializes and controls the quantum bits by sending (irradiating) microwave signals (electromagnetic wave signals) to quantum bit system 14 using control device 12, thereby causing quantum bit system 14 to perform calculations and reading the quantum bit states.

[0012] The microwave signals sent from control device 12 to quantum bit system 14 include a control signal for controlling the quantum bit, an observation signal for reading out the quantum bit state, and an initialization signal for initializing the quantum bit. Regarding the control signals, a multiplexed control signal obtained by multiplexing a plurality of control signals (three in this example) with different center frequencies in signal processing unit 17 is sent to quantum bit system 14. The frequency bands of the individual signals are different. In this example, the frequency band of the multiplexed control signal is set within the range of 5.8 GHz to 7 GHz. Similarly, the observation signal is set within the range of 2 GHz to 2.8 GHz, and the initialization signal is set within the range of 3.2 GHz to 3.8 GHz.

[0013] Upon receiving instructions from the user, the server 16 calculates waveform data indicating signal waveforms required for controlling, reading, and initializing the quantum bit state of each quantum bit in the quantum bit system 14, and outputs the waveform data to the signal processing unit 17. As described above, a combined control signal obtained by combining multiple control signals is sent to the quantum bit system 14. For this reason, the server 16 calculates waveform data for each control signal and outputs the waveform data to the signal processing unit 17. The center frequencies of the signals indicated by the waveform data for each control signal are shifted. The server 16 reads out the digitized response signals and analysis results from each signal processing unit 17 and performs predetermined processing. The response signals are signals obtained by modulating the observation signals irradiated to the quantum bits according to their quantum bit states.

[0014] As will be described in detail later, in order to lower the specifications (sampling rate and bandwidth) required of the DA (digital-analog) converter, the signals shown in the waveform data for each control signal have a lower frequency (frequency band) than each control signal in the combined control signal sent to the quantum bit system 14.

[0015] For the same reason, the signal shown in the waveform data for the observation signal has a lower frequency than the observation signal sent to quantum bit system 14. As the frequency band of the initialization signal is relatively low, the waveform data is digital-to-analog converted and sent directly to quantum bit system 14 as the initialization signal.

[0016] The clock generating unit 18 generates a clock that is the basis for the operation of the control device 12. The clock generated by the clock generating unit 18 is supplied to the server 16 and each signal processing unit 17.

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

[0018] 2 shows the main configuration of the signal processing unit 17. The signal processing unit 17 includes a high-bandwidth memory (HBM) 21, a transmission circuit 22, a reception circuit 23, and an interface (I / F) 24 that connects the server 16 to the high-bandwidth memory 21. The high-bandwidth memory 21 stores waveform data from the server 16 and also stores data from the reception circuit 23. The server 16 exchanges data with the signal processing unit 17 via the high-bandwidth memory 21. The signal processing unit 17 also includes a circuit that monitors various signals sent to the quantum bit system 14 and corrects the internal operation timing, a circuit for synchronizing the signal processing units 17, and the like.

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

[0020] The transmission logic unit 27 holds parameters related to control of the transmission timing for each of the control signal (combined control signal), observation signal, and initialization signal, and sends the waveform data held in the wide-bandwidth memory 21 to the digital combiner 30 and DA converters 32 and 33 at timings according to the parameters.

[0021] The combined control signal is generated by a digital combiner 30, a DA converter 31, an up-converter 34, and a local oscillator 36. In this example, the digital combiner 30, the DA converter 31, the up-converter 34, and the local oscillator 36 constitute a control signal generating unit. Waveform data of each control signal is input to the digital combiner 30 from the transmission logic unit 27. The digital combiner 30 adds the input waveform data in the digital domain to generate one combined waveform data. The digital combiner 30 is configured, for example, by a DSP (digital signal processor) that performs high-speed digital arithmetic processing.

[0022] The DA converter 31 receives the composite waveform data from the digital combiner 30. The DA converter 31 generates a first intermediate frequency (IF) signal by digital-to-analog converting the input composite waveform data. The local oscillator 36 generates a first local oscillation signal based on the clock from the clock generating unit 18 and inputs this to the upconverter 34. The upconverter 34 mixes the input first intermediate frequency signal and the first local oscillation signal to generate a combined control signal by upconverting the first intermediate frequency signal. The combined control signal generated by the upconverter 34 is input to the combiner 38.

[0023] The DA converter 31 only needs to have a bandwidth and sampling rate corresponding to the first intermediate frequency signal, not the combined control signal. Therefore, the DA converter 31 does not need to be a high-speed, wide-band converter that corresponds to the combined control signal itself. Furthermore, as described above, the waveform data corresponding to the multiple control signals are digitally combined by the digital combiner 30, then digital-to-analog converted, and the first intermediate frequency signal obtained by this digital-to-analog conversion is upconverted. Therefore, multiple control signals can be digital-to-analog converted using a single DA converter 31, eliminating the need for a separate DA converter for each control signal. This reduces the number of components and contributes to the miniaturization of the control device 12. Furthermore, since only the DA converter 31 needs to be adjusted for the digital-to-analog conversion of the control signals, adjustments are easy.

[0024] After the combined control signal is sent to the quantum bit system 14, for example, 100 nanoseconds later, an observation signal is sent to the quantum bit system 14. This observation signal is generated by a DA converter 32, an upconverter 35, and a local oscillator 37. In this example, the DA converter 32, the upconverter 35, and the local oscillator 37 constitute an observation signal generating unit. Waveform data corresponding to the observation signal is input to the DA converter 32 from the transmission logic unit 27. This DA converter 32 generates a second intermediate frequency signal by digital-to-analog converting the input waveform data. Like the DA converter 31, the DA converter 32 for generating the observation signal only needs to be compatible with the second intermediate frequency signal rather than the observation signal, and therefore does not need to be a high-speed, wideband converter compatible with 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 this to the upconverter 35. The upconverter 35 mixes the input second intermediate frequency signal with the second local oscillation signal to generate an observation signal by upconverting the second intermediate frequency signal. The observation signal generated by the upconverter 35 is input to the combiner 38.

[0026] The initialization signal is sent to the quantum bit system 14 before (for example, 100 nanoseconds before) sending the multiplexing control signal. This initialization signal is generated by a DA converter 33. Waveform data corresponding to the initialization signal is input to the DA converter 33 from the transmission logic unit 27. The DA converter 33 generates a third intermediate frequency signal by digital-to-analog converting the input waveform data. The initialization signal generated by the DA converter 33 is input to a combiner 38. In this way, an initialization signal with a relatively low frequency band is generated directly by the DA converter 33 without using an up-converter. Therefore, there is no need to provide an up-converter or local oscillator for generating the initialization signal, which reduces the number of parts and is advantageous for miniaturizing the control device 12.

[0027] The combined control signal, the observation signal, and the initialization signal are output to the quantum bit system 14 via a combiner 38. This combiner 38 is a so-called analog combiner that combines and outputs input analog signals. Note that the combined control signal, the observation signal, and the initialization signal may be output to the quantum bit system 14 without going through the combiner 38, or only two of the combined control signal, the observation signal, and the initialization signal may be output via the combiner 38.

[0028] In response to an input of an observation signal, the quantum bit system 14 outputs a response signal corresponding to the quantum bit state. In this example, a receiver is configured with a downconverter 41 and an AD converter 42. The response signal from the quantum bit system 14 is input to the downconverter 41. In addition to the response signal, the downconverter 41 also receives a second local oscillator signal from the local oscillator 37, which was used when upconverting the response signal to generate the observation signal. The downconverter 41 mixes the input response signal with the second local oscillator signal to generate an analog received signal by downconverting the response signal. In this way, the downconversion of the response signal uses the second local oscillator signal used when upconverting the response signal to generate the observation signal, and there is no phase shift in the frequency conversion of the observation signal and the response signal. The analog signal from the downconverter 41 is sent to the AD converter 42.

[0029] The AD converter 42 converts the analog received signal from the downconverter 41 into digital data and outputs the resulting digital data to the receiving logic unit 43. The AD converter 42 need only be compatible with the frequency of the analog received signal obtained by downconverting the response signal, and does not need to be high-speed and wideband. The receiving logic unit 43 receives and analyzes the digital data, i.e., the digitized response signal, according to parameters stored therein. The receiving logic unit 43 writes the digital data of the response signal and the analysis results to the HBM 21.

[0030] In this example, the control signal generating unit generates the combined control signal by up-converting the first intermediate frequency signal obtained from the DA converter 31 as described above. However, as with the initialization signal, the combined control signal may be generated directly by digital-to-analog converting waveform data using the DA converter 31 without up-conversion. The observation signal generating unit may also be configured to generate the observation signal directly by digital-to-analog converting waveform data using the DA converter 32 without up-conversion. Furthermore, the receiving unit may be configured to directly analog-to-digital convert the response signal from the quantum bit system 14 using the AD converter 42 without down-converting it. This eliminates the need for an up-converter and a down-converter. In a configuration in which the DA converter 32 directly generates the observation signal and the AD converter 42 directly analog-to-digital converts the response signal, it is preferable to operate the DA converter 32 and the AD converter 42 using a clock signal from a common clock source.

[0031] As described above, the control device 12 can be made smaller by reducing the number of DA converters, up-converters, and local oscillators. Furthermore, because the number of DA converters, up-converters, and local oscillators is small, adjustments for stable operation are easy.

[0032] In the above example, the digital combiner combines the waveform data of multiple control signals into one composite waveform data, and then digital-to-analog converts the composite waveform data, but when multiple observation signals with different frequencies are used, the digital combiner may combine the waveform data of the multiple observation signals into one composite waveform data, and then digital-to-analog convert the composite waveform data to generate a signal in which the multiple observation signals are combined. Similarly, the digital combiner may combine the waveform data of multiple initialization signals with different frequencies into one composite waveform data, and then digital-to-analog convert the composite waveform data to generate a signal in which the multiple initialization signals are combined.

[0033] Alternatively, different types of signals may be generated by inputting at least two waveform data of different types, i.e., an initialization signal, a control signal, and an observation signal, into a digital combiner and then digital-to-analog converting the composite waveform data output from the digital combiner using a digital-to-analog converter. By inputting the waveform data of different types of signals at different times, the output timing of the signals can also be shifted. For example, by inputting the waveform data of an initialization signal into the digital combiner and then inputting the waveform data of each of the multiple control signals, composite waveform data generated from the waveform data of the initialization signal is input into a digital-to-analog converter, and then the composite waveform data obtained from the waveform data of each of the multiple control signals is input into the digital-to-analog converter. This allows the initialization signal and the composite control signal to be output sequentially from a single output terminal. This simplifies the circuit configuration because different types of signals can be generated using a common circuit.

[0034] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the present invention, and other embodiments and modifications made by those skilled in the art are also included in the present invention. Furthermore, the present invention can be applied to the control of various quantum computers, such as semiconductor quantum dot quantum computers that can be controlled by microwaves, quantum computers using cooled atomic gas systems that can be controlled by microwaves, and quantum computers that arrange electron spins using molecular technology or nanotechnology, in addition to superconducting quantum computers. Furthermore, the present invention can also be applied to the control of quantum simulators, quantum sensors, and quantum repeaters that use quantum bits controlled by microwaves. [Explanation of symbols]

[0035] 10. Quantum Computers 12 Control device 14 qubit system 17 Signal Processing Unit 30 Digital Combiner 31~33 DA converter 34, 35 Upconverter 36, 37 Local oscillator 38 Combiner 41 Down Converter 42 AD converter

Claims

1. a digital combiner that generates one composite waveform data by adding, in a digital domain, first waveform data of a plurality of control signals having frequencies shifted from each other for controlling the quantum bits of a quantum bit system including the plurality of quantum bits; a control signal generating unit having a first digital-to-analog converter for converting the composite waveform data into analog form, and for generating a combined control signal of a first frequency band; an observation signal generator that includes a second digital-to-analog converter that converts second waveform data for reading out a quantum bit state from the quantum bit system into analog data, and that generates an observation signal in a second frequency band different from the first frequency band; a receiver that receives a response signal output from the quantum bit system in response to the input of the observation signal to the quantum bit system, and that has an analog-to-digital converter that converts the response signal into a digital signal; A quantum computer control device comprising:

2. The control signal generating unit a first local oscillator that outputs a first local oscillation signal; a first up-converter that mixes a first intermediate frequency signal obtained by analog-converting the composite waveform data by the first digital-to-analog converter with the first local oscillation signal to up-convert the first intermediate frequency signal to the first frequency band and generate the combined control signal; and The observation signal generating unit a second local oscillator that outputs a second local oscillation signal; a second up-converter that mixes a second intermediate frequency signal obtained by analog-converting the second waveform data by the second digital-to-analog converter with the second local oscillation signal to up-convert the second intermediate frequency signal to the second frequency band and generate the observation signal; and The receiving unit a downconverter that downconverts the response signal by mixing the response signal with the second local oscillation signal; have 2. The quantum computer control device according to claim 1 .

3. an analog combiner for combining a plurality of input analog signals; The combined control signal and the observation signal are output to the quantum bit system via the analog combiner.

3. The quantum computer control device according to claim 2.

4. a third digital-to-analog converter that converts third waveform data for initializing a quantum bit into an analog signal to generate an initialization signal in a third frequency band that is lower than the first frequency band and the second frequency band; The combined control signal, the observation signal, and the initialization signal are output to the quantum bit system via the analog combiner.

4. The quantum computer control device according to claim 3.

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