Control device and control method

Abstract

The present invention reduces circuit mounting scale.　This control device (10) comprises a digital processing circuit (10a) and a DAC (30). The digital processing circuit (10a) generates: a control command group (g1) that includes a plurality of first control commands for controlling a plurality of first quantum bits; and a control command group (g2) that includes a plurality of second control commands for controlling a plurality of second quantum bits, wherein the second control commands have the same frequency as the first control commands. In addition, the digital processing circuit (10a) applies an offset to the control command groups (g1, g2) and performs frequency multiplexing of control command groups (g11, g12) in different frequency bands, thereby generating a digital multiplexed signal (dm1). The DAC (30) performs digital / analog conversion of the digital multiplexed signal (dm1) to generate an analog multiplexed signal (am1).

Description

Control device and control method

[0001] The present invention relates to a control device and a control method for a quantum computer.

[0002] The quantum computer control device has the function of controlling the operation of the quantum bits with a microwave control signal and reading out the operation result from the state of the quantum bits with a microwave. Related technologies, for example, have been proposed, such as a technology that combines a diplexer with a quantum bit signal distribution device and a readout signal distribution device to reduce the number of input lines. Another technology has been proposed for controlling a quantum processor with multiple digital-to-analog converters. Furthermore, a technology has been proposed for simultaneously controlling the amplitude and phase of pulses with different frequencies according to changes in the state of quantum bits coupled to a transmission line. Another technology has been proposed for realizing interaction between quantum bit circuits using multiple superconducting quantum bit circuits supplied with signals of the same frequency.

[0003] Patent Publication No. 2020-537396 Patent Publication No. 2022-536594 U.S. Patent Application Publication No. 2018 / 0013426 International Publication No. 2021 / 014889

[0004] The control device generates multiple control signals in the same frequency band based on commands issued from a host PC (Personal Computer), and uses a DAC (Digital to Analog Converter) that performs digital-to-analog conversion to generate the control signals.

[0005] However, when generating multiple control signals in the same frequency band, conventionally, a system is implemented in which the same number of DACs as the number of control signals to be generated are implemented, and a system is constructed for each DAC to generate an analog control signal from a digital command, which causes a problem in that the scale of circuit implementation increases as the scale of calculations for quantum bits increases.

[0006] In one aspect, the present invention aims to provide a control device and a control method that aim to reduce the circuit implementation scale.

[0007] To solve the above problem, a control device is provided, which includes: a digital processing circuit that generates a first control command group including a plurality of first control commands that control a plurality of first quantum bits, and a second control command group including a plurality of second control commands that have the same frequency as each of the first control commands and control a plurality of second quantum bits, and that performs frequency multiplexing with a third control command group having a first frequency band obtained by adding a first offset to the frequency band of the first control command group, and a fourth control command group having a second frequency band obtained by adding a second offset to the frequency band of the second control command group but different from the first frequency band, to generate a digital multiplexed signal, and a digital-to-analog converter that performs digital-to-analog conversion of the digital multiplexed signal to generate an analog multiplexed signal.

[0008] In order to solve the above problem, a control method for executing control similar to that of the above control device is also provided.

[0009] According to one aspect, the circuit packaging scale can be reduced. The above and other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings illustrating preferred embodiments of the present invention.

[0010] 1 is a diagram for explaining an example of a control device. FIG. 1 is a diagram for explaining an example of generation of a control signal. FIG. 2 is a diagram for explaining an example of processing of a readout signal. FIG. 2 is a diagram for explaining an example of control by cross resonance of a quantum computer. FIG. 3 is a diagram for explaining an example of a frequency band of a control signal. FIG. 4 is a diagram for explaining an example of readout control from a quantum computer. FIG. 4 is a diagram for explaining an example of a frequency band of a readout signal. FIG. 5 is a diagram for explaining an example of the configuration of a control device. FIG. 6 is a diagram for explaining an example of an operation of generating a control signal and processing a readout signal. FIG. 7 is a diagram for explaining an example of an operation of generating a control signal and processing a readout signal. FIG. 8 is a diagram for explaining an example of an operation of frequency conversion and frequency multiplexing. FIG. 9 is a diagram for explaining an example of extraction and up-conversion of a control command signal. FIG. 10 is a diagram for explaining an example of down-conversion and multiplexing of a readout signal. FIG. 11 is a diagram for explaining an example of frequency deviation detection of a resonant frequency of a control command. FIG. 12 is a diagram for explaining an example of frequency deviation correction of a resonant frequency of a control command. FIG. 13 is a diagram for explaining an example of an operation of up-conversion. FIG. 14 is a diagram for explaining an example of an operation of down-conversion. FIG. 15 is a diagram for explaining a modified example of a control device. FIG. 16 is a diagram for explaining a modified example of a control device.

[0011] The present embodiment will be described below with reference to the drawings. Fig. 1 is a diagram illustrating an example of a control device. The control device 10 is connected to a host PC 5 and a quantum computer 6, and includes a digital processing circuit 10a that processes digital signals, and a DAC (digital-to-analog converter) 30.

[0012] [Step S1] Based on a control instruction from the host PC 5, the digital processing circuit 10a acquires a control command group g1 (first control command group) and a control command group g2 (second control command group).

[0013] The control command group g1 includes a plurality of first control commands that control a plurality of first quantum bits of the quantum computer 6. The control command group g2 includes a plurality of second control commands that have the same frequency as each of the first control commands and control a plurality of second quantum bits of the quantum computer 6.

[0014] 1, each of control command groups g1 and g2 includes a 5-qubit control command in a frequency band (f1 to f2) from frequency f1 to frequency f2. In the following description, the frequency band from frequency fa to frequency fb may be referred to as (fa-fb).

[0015] [Step S2] The digital processing circuit 10a performs frequency conversion by applying a first offset to the frequency band (f1-f2) of the control command group g1 to convert it into a first frequency band, thereby generating a control command group g11 (third control command group). Note that in the example of FIG. 1, the first offset is set to 0, and the first frequency band of the control command group g11 is the frequency band (f1-f2). If the offset is 0, the frequency conversion process may not be performed, and the first control command group may be used as the third control command group.

[0016] In addition, the digital processing circuit 10a performs frequency conversion to apply a second offset to the frequency band (f1-f2) of the control command group g2 to convert it into a second frequency band (f1+Δ-f2+Δ) different from the first frequency band (f1-f2), thereby acquiring the control command group g12 (fourth control command group).

[0017] [Step S3] The digital processing circuit 10a performs frequency multiplexing of the control command group g11 having the first frequency band (f1-f2) and the control command group g12 having the second frequency band (f1+Δ-f2+Δ) to generate a digital multiplexed signal (dm1).

[0018] [Step S4] The DAC 30 performs digital-to-analog conversion of the digital multiplexed signal dm1 to generate an analog multiplexed signal am1. In this way, the control device 10 applies frequency offsets to multiple control commands in the same frequency band to convert them to different frequency bands, and then digitally multiplexes them. The DAC 30 is then shared when used to generate multiple control signals in the same frequency band that control quantum bits from the control commands.

[0019] This eliminates the need to implement a system for generating analog control signals from digital control commands for each of multiple DACs when generating multiple control signals in the same frequency band, thereby reducing the circuit implementation scale of the control device and enabling the control device to be made more compact.

[0020] 2 is a diagram illustrating an example of generation of a control signal. The control device 10 further includes an analog processing circuit 10b1 (first analog processing circuit) that processes analog signals. [Step S5a] The analog processing circuit 10b1 extracts a control command signal sc1 (first control command signal) having a first frequency band (f1-f2) from the analog multiplexed signal am1 output from the DAC 30.

[0021] [Step S5b] The analog processing circuit 10b1 extracts from the analog multiplexed signal am1 output from the DAC 30 a control command signal sc2 (second control command signal) having a second frequency band (f1+Δ-f2+Δ).

[0022] [Step S6a] The analog processing circuit 10b1 modulates (up-converts) the first frequency band (f1-f2) of the control command signal sc1 to a third frequency band (f3-f4) to generate a control signal sd1 (first control signal), and outputs it to the quantum computer 6. The third frequency band (f3-f4) is the microwave frequency band required for quantum operations in the quantum computer 6.

[0023] [Step S6b] The analog processing circuit 10b1 modulates the second frequency band (f1+Δ-f2+Δ) of the control command signal sc2 into the third frequency band (f3-f4) to generate a control signal sd2 (second control signal), and outputs it to the quantum computer 6. In this way, the control command signals sc1 and sc2 having the same third frequency band (f3-f4) are output.

[0024] By providing the control device 10 with such an analog processing circuit 10b1, the frequency bands of the multiple control command signals extracted from the digital multiplexed signal are individually modulated to the frequency band required for transmission to the quantum computer 6. This makes it possible to generate multiple control signals in the same frequency band.

[0025] 3 is a diagram illustrating an example of read signal processing. The control device 10 further includes an analog processing circuit 10b2 (second analog processing circuit) that processes analog signals, and an ADC (Analog to Digital Converter) 40.

[0026] [Step S11] The analog processing circuit 10b2 acquires a read signal sr1 (first read signal) having a fourth frequency band (f5-f6) from the third quantum bits of the quantum computer 6.

[0027] The analog processing circuit 10b2 also acquires a read signal sr2 (second read signal) having a fourth frequency band (f5-f6) from the plurality of fourth quantum bits. [Step S12a] The analog processing circuit 10b2 demodulates (down-converts) the fourth frequency band (f5-f6) to a fifth frequency band (f7-f8) to generate a read signal sr11 (third read signal).

[0028] [Step S12b] The analog processing circuit 10b2 demodulates the fourth frequency band (f5-f6) into a sixth frequency band (f9-f10) different from the fifth frequency band (f7-f8) to generate a read signal sr12 (fourth read signal).

[0029] [Step S13] The analog processing circuit 10b2 combines the read signals sr11 and sr12 to generate an analog combined signal am2. [Step S14] The ADC 40 performs analog-to-digital conversion of the analog combined signal am2 to generate a digital combined signal dm2.

[0030] Here, when processing readout signals of the same frequency band obtained from the quantum computer 6, conventionally, ADCs corresponding to the number of obtained readout signals are implemented. Then, each ADC configures a system from the analog readout signal to generating digital readout data to be returned to the host PC 5, which increases the scale of circuit implementation.

[0031] In contrast, the control device 10 includes the analog processing circuit 10b2 and the ADC 40 described above, so that read signals of the same frequency band are demodulated into different frequency bands, and the read signals are multiplexed after being converted into different frequency bands. This allows the ADC 40 to be used in common when generating read data.

[0032] Therefore, when generating read data, the control device 10 does not need a configuration that implements a system for generating digital read data from analog read signals for each of a plurality of ADCs, which makes it possible to reduce the circuit implementation scale of the control device and make the control device more compact.

[0033] <Quantum Computer Control and Readout> The control device 10 controls quantum operations by sending control signals to the quantum bits of the quantum computer 6. When controlling each quantum bit individually, control signals are connected to all quantum bits. In contrast to this, there is a technique called cross resonance, which allows multiple quantum bits to be controlled with a single control signal by combining quantum logic gates.

[0034] 4 is a diagram showing an example of control by cross resonance of a quantum computer, in which white circles represent quantum bits, black circles represent readout ports, thin solid lines represent control signal lines, and dotted lines represent readout signal lines.

[0035] This shows an example of cross resonance using two sets of five quantum bits, where cross resonance CR1 controls up to five quantum bits with one control signal, and cross resonance CR2 controls up to five quantum bits with one control signal.

[0036] 5 is a diagram showing an example of the frequency band of the control signal. The frequency band of the control signal during cross resonance is the same for all of them. In this example, the frequency band of the control signal for cross resonance CR1 and the frequency band of the control signal for cross resonance CR2 are both 8 GHz to 9 GHz, and the control signal frequency (resonance frequency) for each quantum bit is included within this band.

[0037] 6 is a diagram showing an example of read control from a quantum computer. When a read signal is read from the quantum computer 6, readout is performed using a combination of quantum bits different from that controlled by cross resonance. In this example, readout is performed from six locations, and four quantum bits are multiplexed and read out in each read range RD1, ..., RD6.

[0038] 7 is a diagram showing an example of the frequency band of the readout signal. All of the readout signals have the same frequency band. In this example, the frequency band of the readout signals for the readout ranges RD1, ..., RD6 is a band from 10 GHz to 10.5 GHz, and the readout signal frequency of the quantum bit state falls within this band.

[0039] 8 and 9 are diagrams showing an example of the configuration of a control device. The control device 10 includes a digital processing circuit 10a, an analog processing circuit 10b, a DAC 30, and an ADC 40. The digital processing circuit 10a includes an I / F (interface) unit 11, a control command generation unit 12, a control command storage unit 13, a control command acquisition unit 14, a read data storage unit 15, a read data acquisition unit 16, a read data analysis unit 17, an offset frequency control unit 18, and a memory unit 19.

[0040] Analog processing circuit 10b has the functions of analog processing circuits 10b1 and 10b2 shown in FIGS. 2 and 3, and includes BPFs (Band Pass Filters) 21a and 21b, upconverters 22a and 22b, BPFs 23a and 23b, downconverters 24a and 24b, a multiplexing unit 25, variable PLLs (Phase Locked Loops) 26a, 26b, 26c, and 26d, a microwave oscillator 27, and up-down converters 28a, 28b, 28c, and 28d.

[0041] <Flow of Operation for Generating Control Signals and Processing Read Signals> FIGS. 10 and 11 are diagrams for explaining an example of the operation for generating control signals and processing read signals.

[0042] (Generation of Control Signal) [Step S21] The host PC 5 transmits a control instruction to the quantum computer 6 to cause the quantum computer 6 to execute a quantum operation.

[0043] [Step S22] When the control command generation unit 12 receives a control instruction via the I / F unit 11, it generates a control command and transmits the control command to the control command storage unit 13. [Step S23] The control command storage unit 13 stores the control command in the memory unit 19.

[0044] [Step S24] The control command acquisition unit 14 reads and acquires a plurality of control commands from the memory unit 19. For example, when controlling five quantum bits with one set of cross resonance, the control commands corresponding to each of the five quantum bits are read from the memory unit 19.

[0045] [Step S25] The control command acquisition unit 14 groups the read control commands into a set of control commands corresponding to a set of cross resonance, and converts the frequency bands of the control command groups into mutually different frequency bands.

[0046] Then, the control command acquisition unit 14 frequency multiplexes the plurality of control command groups (for example, frequency multiplexes the control command groups for each of the two sets of cross resonances), and generates and outputs a digital multiplexed signal.

[0047] [Step S26] The DAC 30 performs D / A conversion of the digital multiplexed signal to generate and output an analog multiplexed signal. [Step S27a] The BPF 21a performs band-pass filtering of a predetermined band from the analog multiplexed signal to extract and output control command signals (one set of control commands after being converted into analog signals) for generating the control signal sd1 to be output from the control device 10.

[0048] [Step S27b] The BPF 21b performs bandpass filtering of a predetermined band of the analog multiplexed signal to extract and output the control command signal (the other set of control commands after being converted into analog signals) for generating the control signal sd2 to be output from the control device 10.

[0049] [Step S28a] The up-converter 22a up-converts the control command signal output from the BPF 21a to the microwave frequency band required for processing in the quantum computer 6 based on the frequency signal output from the up-down converter 28a, and outputs the up-converted signal.

[0050] [Step S28b] The upconverter 22b upconverts the control command signal output from the BPF 21b to the microwave frequency band required for processing in the quantum computer 6, based on the frequency signal output from the up / down converter 28b, and outputs the upconverted signal. Note that both the upconverters 22a and 22b perform upconversion to microwave frequency bands of the same frequency band.

[0051] [Step S29a] The BPF 23a performs bandpass filtering to remove frequency components such as noise outside the desired band from the output signal upconverted by the upconverter 22a, and outputs the filtered control signal sd1 to the quantum computer 6.

[0052] [Step S29b] The BPF 23b performs bandpass filtering to remove frequency components such as noise outside the desired band from the output signal upconverted by the upconverter 22b, and outputs the filtered control signal sd2 to the quantum computer 6.

[0053] (Processing of Readout Signal) [Step S31a] The downconverter 24a receives the readout signal sr1 read out from the quantum computer 6.

[0054] [Step S31b] The downconverter 24b receives the read signal sr2 read from the quantum computer 6. The read signals sr1 and sr2 have the same frequency band.

[0055] [Step S32a] Based on the frequency signal output from the up-down converter 28c, the down-converter 24a down-converts the read signal sr1 to a frequency band that can be processed by the downstream ADC 40, and outputs the down-converted read signal.

[0056] [Step S32b] Based on the frequency signal output from the up-down converter 28d, the down-converter 24b down-converts the read signal sr2 to a frequency band that can be processed by the downstream ADC 40, and outputs the down-converted read signal. Note that the down-conversion is performed in the down-converters 24a and 24b so that the frequencies of the down-converted read signals are different from each other.

[0057] [Step S33] The multiplexer 25 multiplexes the read signal output from the downconverter 24a and the read signal output from the downconverter 24b to generate and output an analog multiplexed signal.

[0058] [Step S34] The ADC 40 performs A / D conversion of the analog combined signal to generate and output a digital combined signal. [Step S35] The read data storage unit 15 extracts read data (e.g., each read data multiplexed and read out in groups of four quantum bits) from the digital combined signal and stores it in the memory unit 19.

[0059] [Step S36] The read data acquisition unit 16 acquires the read data from the memory unit 19. [Step S37] The read data acquisition unit 16 transmits the acquired read data to the read data analysis unit 17.

[0060] [Step S38] The read data analysis unit 17 analyzes the read data and transmits the analysis results or the read data to the I / F unit 11. [Step S39] Information such as the results of quantum operations performed by the quantum computer 6 is transmitted from the control device 10 to the host PC 5.

[0061] The detailed operation of the offset frequency control unit 18, the variable PLLs 26a, . . . , 26d, the microwave oscillator 27, and the up-down converters 28a, .

[0062] <Frequency Conversion and Frequency Multiplexing> Fig. 12 is a diagram for explaining an example of frequency conversion and frequency multiplexing. The control command acquisition unit 14 acquires multiple control commands of the same frequency from the memory unit 19 to generate multiple sets of control commands, and performs frequency conversion by offsetting the frequency bands of the control command sets. Then, after frequency conversion, digital frequency multiplexing is performed.

[0063] Here, a control command group including five control commands corresponding to five quantum bits is defined as one set of cross resonance, and the frequency band required for one set of cross resonance is defined as 1 GHz. For the first set of cross resonance control command group g1 for generating the control signal sd1, the control command acquisition unit 14 sets the offset of the control command group g1 to 0 GHz and the frequency band of the control command group g1 to 0 GHz to 1 GHz.

[0064] In addition, for the second set of cross-resonance control command group g2 for generating the control signal sd2, the control command acquisition unit 14 frequency converts the frequency band of the control command group g2 from 1.1 GHz to 2.1 GHz, for example, by setting the starting point at 0 GHz and offsetting it to 1.1 GHz.

[0065] By providing an offset so that the frequency bands are different from each other in this way, the frequencies of the control commands included in control command group g2 are converted to values ​​different from the frequencies of the control commands included in control command group g1.

[0066] The control command acquisition unit 14 then frequency-multiplexes the frequency-converted control command groups g11 and g12 to generate a digital multiplexed signal dm1. In this example, the control command groups g1 and g2, which have a frequency band of 1 GHz, are frequency-converted so that the frequency margin is 0.1 GHz to generate the control command groups g11 and g12, and the control command groups g11 and g12 are frequency-multiplexed to generate the digital multiplexed signal dm1.

[0067] In this way, by applying an offset to the frequency band of the control command group and performing frequency conversion so that the frequency bands are different from each other, it is possible to frequency multiplex multiple control command groups that were originally in the same frequency band.

[0068] In the above, frequency conversion / frequency multiplexing of two sets of cross-resonance control commands is shown to generate two control signals sd1 and sd2, but when generating three or more control signals, frequency conversion / frequency multiplexing of three or more sets of cross-resonance control commands is performed.

[0069] For example, assume that the DAC 30 located downstream of the control command acquisition unit 14 has an operating performance bandwidth of up to 5 GHz. In this case, the frequency band of the first set of cross-resonance control commands is set to 0 GHz to 1 GHz, and the frequency band of the second set of cross-resonance control commands is set to 1.1 GHz to 2.1 GHz with an offset.

[0070] Furthermore, an offset is applied to the frequency band of the third set of cross resonance control commands, making it 2.2 GHz to 3.2 GHz, and an offset is applied to the frequency band of the fourth set of cross resonance control commands, making it 3.3 GHz to 4.3 GHz. In this way, frequency conversion / frequency multiplexing capable of generating four control signals can be performed for one DAC having an operating performance of 5 GHz bandwidth.

[0071] 13 is a diagram for explaining an example of extraction and up-conversion of a control command signal. The DAC 30 performs D / A conversion on the digital multiplexed signal dm1 output from the control command acquisition unit 14, and outputs an analog multiplexed signal am1.

[0072] The BPF 21a extracts the control command signal sc1 from the analog multiplexed signal am1 by band-pass filtering, and the BPF 21b extracts the control command signal sc2 from the analog multiplexed signal am1 by band-pass filtering.

[0073] The control command signal sc1 is an analog signal after D / A conversion of the control command group g11 in the frequency band from 0 GHz to 1 GHz, and the control command signal sc2 is an analog signal after D / A conversion of the control command group g12 in the frequency band from 1.1 GHz to 2.1 GHz.

[0074] The upconverters 22a and 22b upconvert the control command signals sc1 and sc2 to the frequency band (microwave frequency band) required for the processing in which quantum operations are performed by the quantum computer 6, and generate and output control signals sd1 and sd2 of the same frequency band.

[0075] If the frequency band of the microwaves is frequency band F1, the frequency band of the control signals sd1 and sd2 is up-converted to frequency band F1. In this case, up-converters 22a and 22b perform up-conversion using a frequency (F1-Δ) obtained by subtracting the offset Δ, which was added when the control commands were frequency-converted, from the frequency band F1 required for the control signals sd1 and sd2 to be output.

[0076] For example, suppose the frequency band F1 of the control signals sd1 and sd2 is 5 GHz to 6 GHz. Since the offset Δ of the first set of control command signals sc1 is 0 GHz, the upconverter 22a upconverts the control command signals sc1 having a frequency band of 0 GHz to 1 GHz to 5 GHz (=5 GHz-0 GHz) to generate the control signal sd1 in the frequency band of 5 GHz to 6 GHz.

[0077] Furthermore, since the offset Δ of the second set of control command signals sc2 is 1.1 GHz, the upconverter 22b upconverts the control command signals sc2, which have a frequency band of 1.1 GHz to 2.1 GHz, at 3.9 GHz (=5 GHz-1.1 GHz) to generate a control signal sd2 in the frequency band of 5 GHz to 6 GHz. By performing upconversion at different frequencies in this way, a single control device 10 can generate multiple control signals in the same frequency band.

[0078] 14 is a diagram illustrating an example of down-conversion and multiplexing of read signals. When the down-converters 24a and 24b receive the read signals sr1 and sr2 from the quantum computer 6, they perform down-conversion so that the frequencies are different from each other and within a frequency band that can be read by the ADC 40 at the downstream stage.

[0079] The read signals sr1 and sr2 are, for example, signals in which up to four quantum bits are multiplexed and read out from the quantum computer 6, and the frequencies of the read signals sr1 and sr2 are the same and fixed. For example, suppose the frequency band of the read signals sr1 and sr2 is 5 GHz to 5.5 GHz.

[0080] When the downconverter 24a receives the first set of read signals sr1, it performs downconversion at, for example, 5 GHz to generate and output a read signal sr11 in the frequency band from 0 GHz to 0.5 GHz.

[0081] The downconverter 24b performs downconversion at 4.4 GHz (= 5 GHz - 0.5 GHz - 0.1 GHz) with a margin of 0.1 GHz, for example, so that the read signal sr12 after downconversion does not overlap when combined with the read signal sr11, thereby generating and outputting a read signal sr12 in the frequency band from 0.6 GHz to 1.1 GHz.

[0082] Thereafter, the multiplexer 25 multiplexes the read signal sr11 having a frequency band of 0 GHz to 0.5 GHz with the read signal sr12 having a frequency band of 0.6 GHz to 1.1 GHz to generate an analog multiplexed signal am2.

[0083] <Correction of deviation in resonant frequency of control command> The control device 10 detects and corrects the frequency deviation of the resonant frequency of the quantum bit, which is the control command. When detecting the frequency deviation of the resonant frequency, the digital processing circuit 10a of the control device 10 generates a pilot control command and transmits it to the quantum computer 6 via the analog processing circuit 10b. Then, the digital processing circuit 10a detects the deviation in the resonant frequency from the read signal, which is a reply to the pilot control command.

[0084] Since the design value of the resonant frequency is known in advance, by observing the actual measured value of the resonant frequency of the read signal during operation of the quantum computer 6, which is the reply to the transmitted pilot control command, it is possible to detect how much the frequency deviates from the design value.

[0085] 15 is a diagram showing an example of detecting a frequency deviation of the resonant frequency of a control command. The vertical axis represents the current, and the horizontal axis represents the frequency of the readout signal (resonant frequency). This example shows how a deviation in the resonant frequency is detected by utilizing the fact that the resonant frequency of a resonator coupled to a quantum bit changes depending on the state of the quantum bit.

[0086] The frequency deviation of the resonant frequency is fed back to the control command acquisition unit 14 via the read data analysis unit 17, for example, and the control command acquisition unit 14 corrects the frequency deviation, which will be described later.

[0087] Here, as design values, for example, the resonant frequencies of four quantum bits are set to 5, 5.1, 5.2, and 5.3 GHz, in increments of 100 MHz from 5 GHz. To measure these actual frequencies, the resonant frequencies are measured by transmitting a pilot control command at a frequency around 5 GHz and observing the readout signal that is returned. For example, the resonant frequency of the resonator used to read the quantum bits is swept, the amplitude of the reflection from the resonator is observed, and the deviation from the phase change point of the resonant frequency is measured.

[0088] In the example of Figure 15, at change point p1, 4.998 GHz is observed, and a frequency deviation of -2 MHz from 5 GHz is detected. At change point p2, 5.080 GHz is observed, and a frequency deviation of -20 MHz from 5.1 GHz is detected. At change point p3, 5.190 GHz is observed, and a frequency deviation of -10 MHz from 5.2 GHz is detected. At change point p4, 5.215 GHz is observed, and a frequency deviation of -85 MHz from 5.3 GHz is detected.

[0089] 16 is a diagram illustrating an example of frequency deviation correction of the resonant frequency of a control command. As described above, the resonant frequency of each control command in the control command group may deviate from the design value. For this reason, the control command acquisition unit 14 provides an offset corresponding to the frequency deviation of the resonant frequency of the quantum bit, and corrects the frequency deviation when generating the control command group.

[0090] For example, if a quantum bit with a design value of 5 GHz has a resonance point that is actually measured at 5.01 GHz, an offset of 0.01 GHz (correction offset) is added to the offset that is imparted during frequency multiplexing.

[0091] If the offset applied during frequency conversion is 1.1 GHz and there is a frequency deviation of 0.01 GHz in the control command group g2, the offset is shifted to 1.11 GHz by 0.01 GHz.

[0092] When upconverting to 5 GHz, the upconversion is performed at 3.89 GHz, which is a frequency obtained by subtracting 1.11 GHz from 5 GHz. That is, when upconverting at 3.9 GHz without correcting the frequency shift, the upconverter 22b performs upconversion at 3.89 GHz when correcting the frequency shift.

[0093] Note that the frequency deviation correction is performed for each control command (quantum bit) rather than for each set of control commands, so that a correction offset is applied to the resonant frequency with a frequency deviation.

[0094] As described above, when a negative correction is required, a correction offset is applied to the positive side overall, and the positive correction offset is reduced during upconversion, making it possible to correct the frequency shift of the resonant frequency for each quantum bit.

[0095] In this way, the quantum bits used in the quantum computer 6 may experience a frequency shift in the resonant frequency during manufacturing, but by performing the above-mentioned control, it is possible to accurately correct the frequency shift in the resonant frequency.

[0096] 17 is a diagram illustrating an example of the up-conversion operation. The BPF 21a performs band-pass filtering of the analog multiplexed signal am1 in the frequency band from 0 GHz to 1 GHz, and outputs a control command signal sc1 in the frequency band from 0 GHz to 1 GHz from the BPF 21a.

[0097] Furthermore, the BPF 21b performs bandpass filtering of the analog multiplexed signal am1 in the frequency band from 1.1 GHz to 2.1 GHz, and a control command signal sc2 in the frequency band from 1.1 GHz to 2.1 GHz is output from the BPF 21b.

[0098] The upconverter 22a upconverts the frequency band of the control command signal sc1 from 5 GHz to 6 GHz, and the upconverter 22b upconverts the frequency band of the control command signal sc2 from 5 GHz to 6 GHz. Therefore, a 5 GHz frequency signal is input to the upconverter 22a, and a 3.9 GHz frequency signal is input to the upconverter 22b.

[0099] Assume that the output from microwave oscillator 27 is 4 GHz. A 5 GHz frequency signal obtained by up-converting the 4 GHz output from microwave oscillator 27 by 1 GHz is input in response to control command signal sc1. In this case, based on a frequency setting instruction from offset frequency control unit 18, variable PLL 26a outputs 1 GHz, and up-down converter 28a up-converts 4 GHz to 1 GHz, thereby generating a 5 GHz frequency signal.

[0100] On the other hand, for the control command signal sc2, a 3.9 GHz frequency signal is input, which is obtained by down-converting 0.1 GHz from the 4 GHz output of the microwave oscillator 27. In this case, based on a frequency setting instruction from the offset frequency control unit 18, 0.1 GHz is output from the variable PLL 26b, and the up-down converter 28b down-converts 4 GHz to 0.1 GHz, thereby generating a 3.9 GHz frequency signal.

[0101] 18 is a diagram for explaining an example of the down-conversion operation. A read signal sr1 of 5 GHz to 5.5 GHz is input to the down-converter 24a, and a read signal sr2 of 5 GHz to 5.5 GHz is input to the down-converter 24b.

[0102] The downconverter 24a downconverts the read signal sr1 to a frequency band of 0 GHz to 0.5 GHz, and the downconverter 24b downconverts the read signal sr2 to a frequency band of 0.6 GHz to 1.1 GHz.

[0103] Since both read signals sr1 and sr2 are in the frequency band from 5 GHz to 5.5 GHz, a 5 GHz frequency signal is input to the down converter 24a, and a 4.4 GHz frequency signal is input to the down converter 24b.

[0104] Assume that the output from microwave oscillator 27 is 4 GHz. A 5 GHz frequency signal obtained by up-converting the 4 GHz output from microwave oscillator 27 by 1 GHz is input to read signal sr1. In this case, based on a frequency setting instruction from offset frequency control unit 18, variable PLL 26c outputs 1 GHz, and up-down converter 28c up-converts 4 GHz to 1 GHz, thereby generating a 5 GHz frequency signal.

[0105] On the other hand, a 4.4 GHz frequency signal is input for the read signal sr2, which is obtained by up-converting the 4 GHz output from the microwave oscillator 27 by 0.4 GHz. In this case, based on a frequency setting instruction from the offset frequency control unit 18, the variable PLL 26d outputs 0.4 GHz, and the up-down converter 28d up-converts 4 GHz to 0.4 GHz, thereby generating a 4.4 GHz frequency signal.

[0106] 19 and 20 are diagrams showing modified examples of the control device. The modified control device 10-1 includes a digital processing circuit 10a, a DAC 30, and an ADC 40. The analog processing circuit 10b described above in FIG. 9 is placed on the dilution refrigerator 7 side that cools the quantum computer 6.

[0107] That is, the analog processing circuit 10b is placed inside or outside the dilution refrigerator 7. Then, wiring is provided between the DAC 30 in the control device 10-1 and the BPFs 21a and 21b placed in the dilution refrigerator 7, and between the offset frequency control unit 18 in the control device 10-1 and the variable PLLs 26a, ..., 26d. Note that the operation is the same as that of the control device 10 described above.

[0108] In this way, the analog processing circuit 10b that processes the signal output from the DAC 30 and the signal before input to the ADC 40 is placed on the dilution refrigerator 7 side. This allows communication between the control device 10-1 and the dilution refrigerator 7 using multiplexed signals, even if the number of control signals and readout signals increases, making it possible to reduce the number of signals (number of wiring) between the control device 10-1 and the dilution refrigerator 7 (quantum computer 6).

[0109] Although the embodiments have been described above, the configuration of each part shown in the embodiments can be replaced with other parts having similar functions. Also, any other components or processes may be added. Furthermore, any two or more configurations (features) of the above-described embodiments may be combined.

[0110] The foregoing merely illustrates the principles of the present invention. Further, since numerous modifications and changes will be apparent to those skilled in the art, the present invention is not limited to the exact construction and application shown and described above, and all corresponding modifications and equivalents are deemed to be within the scope of the present invention as defined by the appended claims and their equivalents.

[0111] 10 Control device 10a Digital processing circuit 30 DAC (digital / analog converter) 5 Host PC 6 Quantum computer g1, g2 Control command group g11, g12 Control command group after frequency conversion dm1 Digital multiplexed signal am1 Analog multiplexed signal f1, f2 Frequency f1+Δ, f2+Δ Offset-added frequency

Claims

1. A control device comprising: a digital processing circuit that generates a first control command group including a plurality of first control commands that control a plurality of first quantum bits, and a second control command group including a plurality of second control commands that have the same frequency as each of the first control commands and control a plurality of second quantum bits, and that performs frequency multiplexing with a third control command group having a first frequency band in which a first offset is added to the frequency band of the first control command group, and a fourth control command group having a second frequency band different from the first frequency band in which a second offset is added to the frequency band of the second control command group, to generate a digital multiplexed signal; and a digital / analog converter that performs digital / analog conversion of the digital multiplexed signal to generate an analog multiplexed signal.

2. The control device according to claim 1, further comprising a first analog processing circuit that extracts a first control command signal having the first frequency band from the analog multiplexed signal, extracts a second control command signal having the second frequency band from the analog multiplexed signal, modulates the first frequency band of the first control command signal to a third frequency band to generate a first control signal, and modulates the second frequency band of the second control command signal to the third frequency band to generate a second control signal, and outputs the first control signal and the second control signal of the same frequency band.

3. The control device of claim 2, further comprising: a second analog processing circuit that acquires a first read signal having a fourth frequency band from a plurality of third quantum bits, acquires a second read signal having the fourth frequency band from a plurality of fourth quantum bits, demodulates the fourth frequency band to a fifth frequency band to generate a third read signal, and demodulates the fourth frequency band to a sixth frequency band different from the fifth frequency band to generate a fourth read signal, combines the third read signal and the fourth read signal to generate an analog combined signal, and an analog / digital converter that performs analog / digital conversion of the analog combined signal to generate a digital combined signal.

4. A first analog processing circuit further comprising an analog / digital converter, the first analog processing circuit being connected to an analog processing circuit disposed in a dilution refrigerator that cools a quantum computer, the analog processing circuit: extracting a first control command signal having the first frequency band from the analog multiplexed signal, extracting a second control command signal having the second frequency band from the analog multiplexed signal, modulating the first frequency band of the first control command signal to a third frequency band to generate a first control signal, and modulating the second frequency band of the second control command signal to the fifth frequency band to generate a second control signal, and outputting the first control signal and the second control signal of the same frequency band to the quantum computer; and obtaining from the quantum computer a first readout signal having a fourth frequency band from a plurality of third quantum bits, and a second readout signal having the fourth frequency band from a plurality of fourth quantum bits, 2. The control device according to claim 1, further comprising: a second analog processing circuit that demodulates the fourth frequency band to a fifth frequency band to generate a third read signal, and demodulates the fourth frequency band to a sixth frequency band different from the fifth frequency band to generate a fourth read signal; and combines the third read signal and the fourth read signal to generate an analog combined signal, wherein the analog / digital converter performs analog / digital conversion of the analog combined signal output from the analog processing circuit to generate a digital combined signal.

5. A control device as described in claim 2 or claim 4, wherein the first analog processing circuit generates the first control signal by modulating the first frequency band at a frequency obtained by subtracting the first offset from the value of the third frequency band, and generates the second control signal by modulating the second frequency band at a frequency obtained by subtracting the second offset from the value of the third frequency band.

6. When a first resonant frequency of the first control command included in the first control command group includes a first frequency deviation from a design value, the digital processing circuit applies the first offset and a first correction offset that corrects the first frequency deviation to the first resonant frequency to generate a first digital control command; the first analog processing circuit modulates the first resonant frequency with a frequency obtained by subtracting the first offset and the first correction offset from a frequency of a first analog control command signal obtained after the first digital control command is digital-to-analog converted by the digital-to-analog converter, to generate the first control signal in which the first frequency deviation has been corrected; and when a second resonant frequency of the second control command included in the second control command group includes a second frequency deviation from the design value, the digital processing circuit applies the second offset and a second correction offset that corrects the second frequency deviation to the second resonant frequency to generate a second digital control command; 6. The control device according to claim 5, wherein the first analog processing circuit modulates the second resonant frequency with a frequency obtained by subtracting the second offset and the second correction offset from a frequency of a second analog control command signal obtained after the second digital control command is digital-to-analog converted by the digital-to-analog converter, to generate the second control signal in which the second frequency deviation has been corrected.

7. The control device according to claim 6, wherein the digital processing circuit generates a pilot control command for a quantum computer, observes an actual measured value of the resonant frequency from a reply read signal that is a reply to the pilot control command during operation of the quantum computer, and detects a frequency deviation of the resonant frequency from the design value.

8. A control device comprising: an analog processing circuit that acquires a first readout signal having a first frequency band from a plurality of first quantum bits, acquires a second readout signal having the first frequency band from a plurality of second quantum bits, demodulates the first frequency band to a second frequency band to generate a third readout signal, and demodulates the first frequency band to a third frequency band different from the second frequency band to generate a fourth readout signal, combines the third readout signal and the fourth readout signal to generate an analog combined signal, and an analog / digital converter that performs analog / digital conversion of the analog combined signal to generate a digital combined signal.

9. A control method, comprising: a digital processing circuit implemented in a control device generates a first control command group including a plurality of first control commands controlling a plurality of first quantum bits, and a second control command group including a plurality of second control commands having the same frequency as each of the first control commands and controlling a plurality of second quantum bits; performing frequency multiplexing with a third control command group having a first frequency band in which a first offset is added to the frequency band of the first control command group, and a fourth control command group having a second frequency band different from the first frequency band in which a second offset is added to the frequency band of the second control command group, to generate a digital multiplexed signal; and a digital / analog converter implemented in the control device performs digital / analog conversion of the digital multiplexed signal to generate an analog multiplexed signal.

10. A control method, comprising: an analog processing circuit implemented in a control device: acquiring a first readout signal having a first frequency band from a plurality of first quantum bits; acquiring a second readout signal having the first frequency band from a plurality of second quantum bits; demodulating the first frequency band to a second frequency band to generate a third readout signal; demodulating the first frequency band to a third frequency band different from the second frequency band to generate a fourth readout signal; combining the third readout signal and the fourth readout signal to generate an analog combined signal; and an analog / digital converter implemented in the control device performs analog / digital conversion of the analog combined signal to generate a digital combined signal.

Images