Optical multiplexed quantum control interface

Abstract

A qubit control system for a quantum computer, comprising: an optical waveguide configured to receive and transmit a wavelength division multiplexed optical signal therethrough, the wavelength division multiplexed optical signal having a plurality of modulated optical carriers each at a different optical wavelength and carrying a digital qubit control signal; an optical demultiplexer optically coupled to the optical waveguide to receive the multiplexed optical signal to recover the plurality of modulated optical carriers; a plurality of photodetectors in communication with the optical demultiplexer; a plurality of cryogenic filters in communication with the plurality of photodetectors, each cryogenic filter configured to filter a corresponding one of the plurality of digital qubit control signals to provide a corresponding one of a plurality of analog qubit control signals, wherein the plurality of analog qubit control signals are directed to a corresponding superconducting qubit and photodetector. The cryogenic filters are provided at cryogenic temperatures.

Description

TECHNICAL FIELD

[0001] The presently claimed embodiments relate to quantum computing, and more specifically to a method of controlling qubits in a quantum computer and a qubit control system for a quantum computer. BACKGROUND

[0002] One structural block in quantum computing is the ability to prepare qubits in specific quantum states. Qubits in superconducting quantum computers are typically controlled using radio frequency energy. The radio frequency energy is delivered via radio frequency lines to resonators, which in turn interact with the qubits to control the quantum states of the qubits.

[0003] The number of radio frequency lines can scale with the number of qubits in a quantum computer. On very large numbers of qubits, the number of radio frequency lines can also become very large. To reduce the number of lines used, it can be desirable to employ multiplexers and demultiplexers to enable multiple radio frequency energy signals to be sent to multiple qubits. However, even when multiplexers and demultiplexers are used to send radio frequency energy signals, the problem remains that these types of systems are bulky and more importantly only allow a limited number of qubit signals to be multiplexed (on the order of 8) because the qubit frequencies are reused on the quantum device by non-adjacent qubits. Thus, there is a need to address this and other problems with existing signal transmission techniques. SUMMARY

[0004] One aspect of the present invention is to provide a method of controlling qubits in a quantum computer. The method includes receiving a wavelength division multiplexed optical signal over an optical link, wherein the wavelength division multiplexed optical signal has a plurality of modulated optical carriers, each optical carrier of the plurality of modulated optical carriers having a different optical wavelength, and each carrier carrying a digital qubit control signal; demultiplexing the wavelength division multiplexed optical signal to recover the plurality of modulated optical carriers, each modulated optical carrier carrying the digital qubit control signal; detecting the digital qubit control signal of each modulated optical carrier of the plurality of modulated optical carriers using a corresponding photodetector; filtering the digital qubit control signal of each modulated optical carrier of the plurality of modulated optical carriers using a corresponding cryogenic filter to provide an analog qubit control signal; and directing the analog qubit control signal to a corresponding superconducting qubit of a plurality of superconducting qubits. The detecting and filtering are performed at cryogenic temperatures.

[0005] In an embodiment, filtering the digital qubit control signals in each of the plurality of modulated optical carriers using the corresponding cryogenic filter to provide the analog qubit control signals comprises filtering the digital qubit control signals in each of the plurality of modulated optical carriers using a superconducting LC bandpass cryogenic filter to provide the analog qubit control signals.

[0006] In an embodiment, the method further comprises, after filtering the digital qubit control signals in each of the plurality of modulated optical carriers using the corresponding cryogenic filter to provide the analog qubit control signals, and before directing the analog qubit control signals to the corresponding superconducting qubits, attenuating the analog qubit control signals using an attenuator to reduce external microwave energy present in the analog qubit control signals.

[0007] In an embodiment, the detecting and the filtering are performed at a first cryogenic temperature that is higher than a second cryogenic operating temperature of the corresponding superconducting qubits.

[0008] In an embodiment, the method further comprises electrically multiplexing each analog qubit control signal using an electrical multiplexer to output a single electrical control analog signal, thereby reducing a number of transmission lines required to transmit each analog qubit control signal to a corresponding superconducting qubit.

[0009] In an embodiment, receiving the wavelength division multiplexed optical signal over the optical link comprises transmitting the wavelength division multiplexed optical signal over an optical waveguide. In an embodiment, at least one of the detecting and the filtering is performed substantially at an operating temperature of the plurality of superconducting qubits. In an embodiment, each of the plurality of superconducting qubits has a control signal in a radio frequency (RF) frequency spectrum range.

[0010] Another aspect of the present disclosure is to provide a qubit control system for a quantum computer. The qubit control system includes an optical waveguide configured to receive and transmit a wavelength division multiplexed optical signal therethrough, wherein the wavelength division multiplexed optical signal has a plurality of modulated optical carriers each at a different optical wavelength and carrying a digital qubit control signal; and an optical demultiplexer optically coupled to the optical waveguide to receive the wavelength division multiplexed optical signal after transmission through the optical waveguide to recover the plurality of modulated optical carriers each carrying a corresponding digital qubit control signal of a plurality of digital qubit control signals. The qubit control system further includes a plurality of photodetectors in communication with the optical demultiplexer, each of the plurality of photodetectors configured to detect a corresponding digital qubit control signal of the plurality of digital qubit control signals; and a plurality of cryogenic filters in communication with the plurality of photodetectors, each of the plurality of cryogenic filters configured to filter the corresponding digital qubit control signal of the plurality of digital qubit control signals to provide a corresponding analog qubit control signal of a plurality of analog qubit control signals. The corresponding analog qubit control signal of the plurality of analog qubit control signals is directed to a corresponding superconducting qubit of a plurality of superconducting qubits. The plurality of photodetectors and the plurality of cryogenic filters are provided at a cryogenic temperature.

[0011] In an embodiment, each of the plurality of cryogenic filters includes a superconducting LC bandpass cryogenic filter.

[0012] In an embodiment, the qubit control system further includes a plurality of attenuators coupled to the plurality of cryogenic filters, each of the plurality of attenuators configured to reduce external microwave energy present in the corresponding analog qubit control signal of the plurality of analog qubit control signals.

[0013] In an embodiment, the plurality of photodetectors and the plurality of cryogenic filters are provided at a first temperature higher than a second cryogenic operating temperature of the plurality of superconducting qubits.

[0014] In an embodiment, each of the corresponding analog qubit control signals of the plurality of analog qubit control signals is in a radio frequency (RF) wavelength range corresponding to an excitation energy of the corresponding superconducting qubit to be controlled.

[0015] In an embodiment, the qubit control system further includes an electrical multiplexer coupled to the plurality of cryogenic filters, the electrical multiplexer configured to electrically multiplex each analog qubit control signal to output a single electrical control analog signal, thereby reducing a number of transmission lines required to transmit each analog qubit control signal to a corresponding superconducting qubit.

[0016] In an embodiment, each photodetector of the plurality of photodetectors is a silicon (Si)-based germanium (Ge) photodetector configured to operate in a photovoltaic mode of operation to minimize power consumption.

[0017] Yet another aspect of the present disclosure is to provide a quantum computer, the quantum computer comprising: a refrigeration system including a temperature-controlled container; a quantum processor disposed within the temperature-controlled container, the quantum processor including a plurality of qubits; and a qubit control system extending into the temperature-controlled container to provide control over the plurality of qubits. The qubit control system includes: an optical waveguide configured to receive and transmit a wavelength division multiplexed optical signal therethrough, wherein the wavelength division multiplexed optical signal has a plurality of modulated optical carriers, each of the plurality of optical carriers at a different optical wavelength and carrying a digital qubit control signal; and an optical demultiplexer optically coupled to the optical waveguide to receive the wavelength division multiplexed optical signal after transmission through the optical waveguide to recover the plurality of modulated optical carriers, each modulated optical carrier carrying a corresponding digital qubit control signal. The qubit control system further includes: a plurality of photodetectors in communication with the optical demultiplexer, each photodetector of the plurality of photodetectors configured to detect a corresponding digital qubit control signal; and a plurality of cryogenic filters in communication with the plurality of photodetectors, each cryogenic filter of the plurality of cryogenic filters configured to filter a corresponding digital qubit control signal to provide a corresponding analog qubit control signal. The corresponding analog qubit control signal is directed to a corresponding superconducting qubit of a plurality of superconducting qubits. The plurality of photodetectors and the plurality of cryogenic filters are provided at a cryogenic temperature within the temperature-controlled container.

[0018] In an embodiment, each cryogenic filter of the plurality of cryogenic filters includes a superconducting LC bandpass cryogenic filter.

[0019] In an embodiment, the qubit control system further includes a plurality of attenuators coupled to the plurality of cryogenic filters, each attenuator of the plurality of attenuators configured to attenuate external microwave energy present in a corresponding analog qubit control signal.

[0020] In an embodiment, the plurality of photodetectors and the plurality of cryogenic filters are provided at a first temperature higher than a second cryogenic operating temperature of the plurality of superconducting qubits.

[0021] In an embodiment, the qubit control system comprises an electrical multiplexer coupled to the plurality of cryogenic filters, the electrical multiplexer configured to electrically multiplex each analog qubit control signal to output a single electrical control analog signal, thereby reducing the number of transmission lines required to transmit each analog qubit control signal to the corresponding superconducting qubit. BRIEF DESCRIPTION OF DRAWINGS

[0022] The disclosure, together with the associated methods of operation of the related elements of structure and the combination and operation of its parts, according to the embodiments thereof, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for purposes of illustration only and are not intended as a definition of the limits of the application. As used in the description of the application and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a component" or "the component" can include

[0023] Figure 1 is a schematic diagram of a qubit control system for a quantum computer according to an embodiment of the application;

[0024] Figure 2A and 2B is a schematic diagram showing the connection type of a cryogenic filter according to an embodiment of the application;

[0025] Figure 3 is a schematic diagram showing the connection of the cryogenic filter to an attenuator before being connected to a qubit chip having a plurality of qubits according to an embodiment of the application;

[0026] Figure 4 is a schematic diagram of a quantum computer according to an embodiment of the application; and

[0027] Figure 5 is a flowchart of a method of controlling qubits in a quantum computer according to an embodiment of the application. DETAILED DESCRIPTION

[0028] In the following passages the terms "light" and "optical" are intended to be generic to include the visible and non-visible portions of the electromagnetic spectrum, such as but not limited to visible light, infrared light, near-infrared light, and ultraviolet light.

[0029] Figure 1This is a schematic diagram of a qubit control system 100 for a quantum computer (not shown) according to an embodiment of the present invention. The qubit control system 100 includes an optical waveguide 102 configured to receive and transmit wavelength division multiplexed optical signals 104. The wavelength division multiplexed signals 104 have a plurality of modulated optical carriers 104A. Each of the plurality of modulated optical carriers 104A is at a different optical wavelength (λ1, λ2, ...) and carries a digital qubit control signal. Figure 1 The example shown has eight optical carriers demultiplexed by a ring resonator 104A, each with eight different wavelengths (λ1, λ2, ..., λ8). However, the broad concept of the invention is not limited to any particular number of optical carriers or optical demultiplexing scheme. There can be more than eight or fewer than eight without limitation.

[0030] In the embodiment, the light source ( Figure 1 (Not shown) may include, for example, multiple lasers. These lasers may be, but are not limited to, Fabry-Perot gain medium lasers, which can be used to generate appropriately spaced optical wavelengths (λ1, λ2, ...) in the optical waveguide 102. For example, a quantum dot-based diode laser operating as an optical frequency comb generator can be used. The quantum dot-based laser can be coupled to the optical waveguide (e.g., optical fiber) to provide, for example, several low-noise 80 GHz spaced optical modes at approximately 1310 nm. However, any number of lasers (one, two, or more) can also be used, each configured to transmit one or more optical wavelengths. Regardless of how multiple optical wavelengths are generated, they are all modulated at room temperature with a specific qubit control signal.

[0031] The qubit control system 100 also includes an optical demultiplexer (DEMUX) 106 optically coupled to an optical waveguide 102 to receive a wavelength-division multiplexed optical signal 104 transmitted through the optical waveguide 102, to recover a plurality of modulated optical carriers 104A, each modulated optical carrier 104A carrying a corresponding digital qubit control signal from a plurality of digital qubit control signals. In some embodiments, the optical DEMUX 106 may comprise, for example, a ring resonator structure coupled to the optical waveguide 102 via evanescent radiation. However, the general concept of the invention is not limited to this embodiment.

[0032] The qubit control system 100 further includes a plurality of photodetectors (PDs) 108 in communication with the optical demultiplexer (DEMUX) 106. Each photodetector of the plurality of photodetectors (PDs) 108 is configured to detect a corresponding digital qubit control signal of the plurality of digital qubit control signals. The qubit control system 100 also includes a plurality of cryogenic filters 110 in communication with the plurality of photodetectors (PDs) 108. Each cryogenic filter of the plurality of cryogenic filters 110 is configured to filter a corresponding digital qubit control signal of the plurality of digital qubit control signals to provide a corresponding analog qubit control signal of a plurality of analog qubit control signals (at frequencies vi, v2,...). The corresponding analog qubit control signal of the plurality of analog qubit control signals is directed to a corresponding superconducting qubit of a plurality of superconducting qubits (not shown in the middle). Figure 1 The plurality of photodetectors (PDs) 108 and the plurality of cryogenic filters 110 are provided at cryogenic temperatures.

[0033] In embodiments, the plurality of photodetectors (PDs) 108 are in communication with the optical demultiplexer (DEMUX) 106 via a plurality of optical fibers 107, each optical fiber carrying a corresponding modulated optical carrier 104A at a specific optical wavelength (λι, λ2,...). In embodiments, each photodetector (PD) 108 can be a silicon (Si)-based germanium (Ge) photodetector configured to operate in a photovoltaic mode of operation to minimize power consumption. In embodiments, the photodetector (PD) 108 can also be a photodiode, a photomultiplier, or a bolometer.

[0034] In embodiments, the plurality of cryogenic filters 110 are coupled to the plurality of photodetectors (PDs) 108 via a plurality of electromagnetic waveguides 109 (e.g., microwave or radio frequency waveguides). The plurality of electromagnetic waveguides 109 are configured to transport the digital qubit control signals to the plurality of cryogenic filters 110.

[0035] Figure 2A and 2B is a schematic diagram illustrating a connection type of a cryogenic filter 110 according to embodiments of the present application. In embodiments, each cryogenic filter of the plurality of cryogenic filters 110 includes a superconducting LC bandpass cryogenic filter. In embodiments, the LC bandpass cryogenic filter is connected to a photodetector 108 and receives a digital qubit control signal (e.g., including a plurality of voltage radio frequency pulses) and outputs an analog qubit control signal (e.g., a modulated sinusoidal curve).

[0036] Figure 3is a schematic diagram of an embodiment in accordance with the present invention, showing a cryogenic filter 110 connected to an attenuator 112 prior to being connected to a qubit chip 114 having a plurality of qubits. In an embodiment, the qubit control system 100 includes a plurality of attenuators 112 coupled to a plurality of cryogenic filters (e.g., LC cryogenic filters) 110 and a qubit chip 114. Each of the plurality of attenuators 112 is configured for reducing extraneous microwave (e.g., radio frequency) energy present in a corresponding analog qubit control signal output by the cryogenic filter 110 prior to inputting the analog qubit control signal to the qubit chip 114.

[0037] In an embodiment, the plurality of photodetectors 108 and the plurality of cryogenic filters 110 are provided at a first temperature that is higher than a second low temperature operating temperature of the plurality of superconducting qubits. For example, as shown in Figure 3 , the plurality of cryogenic filters 11 are provided at a first temperature of approximately 700 mK, and the plurality of superconducting qubits (qubit chip) 114 are provided at a lower second temperature of approximately 15 mK. In an embodiment, the attenuators 112 can be provided at an intermediate cryogenic temperature between the temperature of the cryogenic filters 110 and the temperature of the qubit chip 114. For example, as shown in Figure 3 , the attenuators 112 can be provided at a temperature of approximately 100 mK. In another embodiment, the attenuators 112 can be provided at the first temperature (e.g., 700 mK) of the cryogenic filters 110 or at the second temperature (e.g., 15 mK) of the plurality of superconducting qubits or at any temperature between the first and second temperatures. Further, if the photodetectors 108 and the cryogenic filters 110 are at a first temperature (e.g., 700 mK) level that is different from a second temperature (e.g., 15 mK) level of the plurality of superconducting qubits, the attenuators 112 can be provided at either or both of the cryogenic filter temperature level and the temperature level of the plurality of superconducting qubits.

[0038] In an embodiment, the corresponding analog qubit control signals are in a radio frequency (RF) wavelength range corresponding to an excitation energy of a corresponding qubit of the plurality of qubits in the qubit chip 114 to be controlled.

[0039] As shown in Figure 1 , the qubit control system 100 can further include an electrical multiplexer 120 coupled to the plurality of cryogenic filters 110. The electrical multiplexer 120 is configured to electrically multiplex each analog qubit control signal output by the cryogenic filters 110 to output a single electrical control analog signal, thereby reducing a number of transmission lines required to transmit each analog qubit control signal to a corresponding superconducting qubit.

[0040] Another aspect of the present invention is to provide a quantum computer 200.Figure 4 is a schematic diagram of a quantum computer 200 according to an embodiment of the present application. The quantum computer 200 includes a cryogenic system 202 that includes a temperature-controlled container 204 and a quantum processor 206 disposed within the temperature-controlled container 204. The quantum processor 206 includes a plurality of qubits 208. The quantum computer 200 further includes a qubit control system 210 that extends into the temperature-controlled container 204 to provide control over the plurality of qubits 208. The qubit control system 210 is similar in many respects to the qubit control system 100 described in the paragraphs above. Thus, it must be recognized that many of the features described above with respect to the qubit control system 100 are also applicable to the qubit control system 210.

[0041] The qubit control system 210 includes an optical waveguide 212 that is configured to receive and transmit wavelength division multiplexed optical signals 214 therethrough. The wavelength division multiplexed signals 214 have a plurality of modulated optical carriers 214A. Each of the plurality of optical carriers 214A is at a different optical wavelength (λ1, λ2,...) and carries a digital qubit control signal.

[0042] In embodiments, an optical source 212A, e.g., including a plurality of lasers such as Fabry-Perot gain medium lasers, can be used to generate the appropriately spaced optical wavelengths (λ1, λ2,...) in the optical waveguide 212.

[0043] The qubit control system 100 also includes an optical demultiplexer (DEMUX) 216 that is optically coupled to the optical waveguide 212 to receive the wavelength division multiplexed signals 214 after transmission through the optical waveguide 212 to recover the plurality of modulated optical carriers 214A, each of which carries a corresponding one of the plurality of digital qubit control signals.

[0044] The qubit control system 210 further includes a plurality of photodetectors (PDs) 218 in communication with the optical demultiplexer 216. Each of the plurality of photodetectors (PDs) 218 is configured to detect a corresponding one of the plurality of digital qubit control signals. The qubit control system 210 also includes a plurality of cryogenic filters 220 in communication with the plurality of photodetectors (PDs) 218. Each of the plurality of cryogenic filters 220 is configured to condition a corresponding one of the plurality of corresponding digital qubit control signals to provide a corresponding one of a plurality of analog qubit control signals. The corresponding one of the plurality of analog qubit control signals is directed to a corresponding one of the plurality of superconducting qubits 208 in the quantum processor 206. The plurality of photodetectors (PDs) 218 and the plurality of cryogenic filters 220 are provided at cryogenic temperatures.

[0045] In embodiments, the plurality of photodetectors (PDs) 218 are in communication with the optical demultiplexer 216 via a plurality of optical waveguides 217, each carrying a corresponding modulated optical carrier 104A at a particular optical wavelength (l1, l2,...). In embodiments, each photodetector (PD) 218 can be a silicon (Si)-based germanium (Ge) photodetector configured to operate in a photovoltaic mode of operation to minimize power consumption. In embodiments, each photodetector 108 can also be a photodiode, a photomultiplier, or a bolometer.

[0046] In embodiments, the plurality of cryogenic filters 220 are coupled to the plurality of photodetectors (PDs) 218 via a plurality of electromagnetic waveguides (e.g., microwave or radio frequency waveguides) 219. The plurality of electromagnetic waveguides 219 are configured to transmit digital qubit control signals to the plurality of cryogenic filters 220.

[0047] Corresponding analog qubit control signals (at frequencies v1, v2,...) output by each of the plurality of cryogenic filters 220 are directed to a corresponding superconducting qubit of the plurality of superconducting qubits 208 in the quantum processor 206. The plurality of photodetectors (PDs) 218 and the plurality of cryogenic filters 220 are provided at cryogenic temperatures within the thermally controlled container 204.

[0048] In embodiments, the plurality of photodetectors 218 and the plurality of cryogenic filters 220 are provided at a first temperature that is higher than a second cryogenic operating temperature of the plurality of superconducting qubits 208 within the thermally controlled container 204. For example, the thermally controlled container 204 can be equipped with a plurality of compartments, and the plurality of qubits 208 can be placed in one compartment at one temperature, while the plurality of photodetectors 218 and the plurality of cryogenic filters 220 can be placed in another compartment at a different temperature. For example, the plurality of cryogenic filters 220 can be provided at a first temperature of approximately 700 mK, and the plurality of superconducting qubits 208 can be provided at a lower second temperature of approximately 15 mK.

[0049] In embodiments, the qubit control system 210 can also include a plurality of attenuators 222 coupled to the plurality of cryogenic filters (e.g., LC cryogenic filters) 220 and to the plurality of qubits 208 in the quantum processor 206. Each of the plurality of attenuators 222 is configured to reduce external microwave (e.g., radio frequency) energy present in a corresponding analog qubit control signal output by the cryogenic filter 220 prior to input to the quantum processor 206. In embodiments, the attenuators 222 can be provided at an intermediate cryogenic temperature between the temperature of the cryogenic filters 220 and the temperature of the plurality of qubits 208 in the quantum processor 206, in another compartment or region within the thermally controlled container 204. For example, the attenuators 222 can be provided at a temperature of approximately 100 mK. In another embodiment, the attenuators 222 can be provided at the first temperature of the cryogenic filters 220 (e.g., 700 mK) or at the second temperature of the plurality of superconducting qubits 208 (e.g., 15 mK) or at any temperature between the first and second temperatures. Further, if the photodetector 218 and the cryogenic filters 220 are at the first temperature (e.g., 700 mK) level different from the second temperature (e.g., 15 mK) level of the plurality of superconducting qubits 208, the attenuators 222 can be provided at either or both of the cryogenic filter temperature level and the plurality of superconducting qubit temperature level.

[0050] In another embodiment, the attenuators 222 can be provided at the first temperature of the cryogenic filters 220 (e.g., 700 mK) or at the second temperature of the plurality of superconducting qubits 208 (e.g., 15 mK) or at any temperature between the first and second temperatures. Further, if the photodetector 218 and the cryogenic filters 220 are at the first temperature (e.g., 700 mK) level different from the second temperature (e.g., 15 mK) level of the plurality of superconducting qubits 208, the attenuators 222 can be provided at either or both of the cryogenic filter temperature level and the plurality of superconducting qubit temperature level.

[0051] Figure 5is a flowchart of a method of controlling qubits in a quantum computer according to embodiments of the present application. The method includes, at S300, receiving a wavelength division multiplexed optical signal over an optical link, where the wavelength division multiplexed optical signal has a plurality of modulated optical carriers, each of the plurality of modulated optical carriers has a different optical wavelength, and each modulated optical carrier carries a digital qubit control signal. The method further includes, at S302, demultiplexing the wavelength division multiplexed optical signal to recover a plurality of modulated optical signals, each carrying a digital qubit control signal. The method also includes, at S304, detecting the digital qubit control signal in each of the plurality of modulated optical carriers using a corresponding photodetector, and at S306, filtering the digital qubit control signal in each of the plurality of modulated optical carriers using a corresponding cryogenic filter to provide an analog qubit control signal. At S308, the method further includes directing the analog qubit control signal to a corresponding superconducting qubit of a plurality of superconducting qubits. The detecting and filtering are performed at a cryogenic temperature.

[0052] In embodiments, filtering the digital qubit control signal in each of the plurality of modulated optical carriers using a corresponding cryogenic filter to provide an analog qubit control signal includes filtering the digital qubit control signal in each of the plurality of modulated optical carriers using a superconducting LC bandpass cryogenic filter to provide an analog qubit control signal.

[0053] The method further includes, after filtering the digital qubit control signal in each of the plurality of modulated optical carriers using a corresponding cryogenic filter to provide an analog qubit control signal, and before directing the analog qubit control signal to the corresponding superconducting qubit, attenuating the analog qubit control signal using an attenuator to reduce external microwave energy present in the analog qubit control signal. In embodiments, the detecting and filtering are performed at a first cryogenic temperature that is higher than a second cryogenic operating temperature of the corresponding superconducting qubit.

[0054] In embodiments, the method further includes electrically multiplexing each analog qubit control signal using an electrical multiplexer to output a single electrical control analog signal, thereby reducing a number of transmission lines required to transmit each analog qubit control signal to the corresponding superconducting qubit.

[0055] In embodiments, receiving the wavelength division multiplexed optical signal over the optical link includes transmitting the wavelength division multiplexed optical signal over an optical waveguide. In embodiments, at least one of the detecting and filtering is performed substantially at an operating temperature of the plurality of superconducting qubits. In embodiments, each of the plurality of superconducting qubits has a control signal in a radio frequency (RF) spectral range.

[0056] The description of various embodiments of the application has been presented for purposes of illustration, but is not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technology found in the marketplace, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for controlling qubits in a quantum computer, comprising: An optical demultiplexer directly coupled to an optical link receives wavelength division multiplexed optical signals through the optical link. The wavelength division multiplexed optical signals have multiple modulated optical carriers, each of which has a different optical wavelength, and each optical carrier carries a corresponding digital qubit control signal. The corresponding digital qubit control signal corresponds to a corresponding superconducting qubit among multiple superconducting qubits. The wavelength division multiplexed optical signal is demultiplexed by the corresponding ring resonator of the optical demultiplexer to recover the plurality of modulated optical carriers, each of the modulated optical carriers carrying the corresponding digital quantum bit control signal; The corresponding digital quantum bit control signal of each of the plurality of modulated optical carriers is detected by a photodetector directly coupled to the ring resonator; The corresponding digital qubit control signal in each of the plurality of modulated optical carriers is filtered by a corresponding cryogenic filter directly coupled to the photodetector to provide an analog qubit control signal corresponding to the corresponding digital qubit control signal; and The control signal for each analog qubit is directed to the corresponding superconducting qubit among the plurality of superconducting qubits. The detection and filtering are performed at low temperatures.

2. The method according to claim 1, wherein, Each cryogenic filter includes a superconducting LC bandpass cryogenic filter.

3. The method according to any one of claims 1-2, further comprising: After the corresponding digital qubit control signal in each of the plurality of modulated optical carriers is filtered using the corresponding cryogenic filter to provide the analog qubit control signal, and before the analog qubit control signal is directed to the corresponding superconducting qubit, the analog qubit control signal is attenuated by a corresponding attenuator directly coupled to the cryogenic filter to reduce the external microwave energy present in the analog qubit control signal.

4. The method according to any one of claims 1-2, wherein, The detection and the filtering are performed at a first cryogenic temperature, which is higher than the second cryogenic operating temperature of the corresponding superconducting quantum bit.

5. The method according to any one of claims 1-2, further comprising: Using an electrical multiplexer to electrically multiplex the control signal of each analog qubit to output a single electrical control analog signal reduces the number of transmission lines required to transmit each analog qubit control signal to the corresponding superconducting qubit.

6. The method according to any one of claims 1-2, wherein, Receiving the wavelength division multiplexed optical signal through the optical link includes transmitting the wavelength division multiplexed optical signal through an optical waveguide.

7. The method according to any one of claims 1-2, wherein, At least one of the detection and the filtering is performed substantially at the operating temperature of the plurality of superconducting qubits.

8. The method according to any one of claims 1-2, wherein, Each of the plurality of superconducting quantum bits has a control signal in the radio frequency (RF) spectrum range.

9. A qubit control system for a quantum computer, comprising: An optical waveguide is configured to receive and transmit wavelength division multiplexed optical signals, wherein the wavelength division multiplexed optical signals have multiple modulated optical carriers, each of the multiple modulated optical carriers being at a different optical wavelength and carrying a corresponding digital qubit control signal, the corresponding digital qubit control signal being respectively corresponding to a corresponding superconducting qubit among a plurality of superconducting qubits; An optical demultiplexer is directly optically coupled to the optical waveguide to receive the wavelength division multiplexed optical signal transmitted through the optical waveguide, and uses a corresponding ring resonator of the optical demultiplexer to demultiplex the wavelength division multiplexed optical signal to recover the plurality of modulated optical carriers, each of the modulated optical carriers carrying a corresponding digital qubit control signal from a plurality of digital qubit control signals; A plurality of photodetectors, which communicate with the optical demultiplexer and are directly coupled to the ring resonator, are configured to detect a corresponding digital qubit control signal among the plurality of digital qubit control signals. Multiple cryogenic filters are directly coupled to the plurality of photodetectors, each of the plurality of cryogenic filters being configured to filter a corresponding digital qubit control signal from the plurality of digital qubit control signals to provide an analog qubit control signal from a plurality of analog qubit control signals corresponding to the corresponding digital qubit control signal. The corresponding analog qubit control signal among the plurality of analog qubit control signals is guided to the corresponding superconducting qubit among the plurality of superconducting qubits, and the plurality of photodetectors and the plurality of cryogenic filters are provided at cryogenic temperatures.

10. The quantum bit control system according to claim 9, wherein, Each of the plurality of cryogenic filters includes a superconducting LC bandpass cryogenic filter.

11. The qubit control system according to any one of claims 9-10, further comprising: Multiple attenuators are directly coupled to the respective multiple cryogenic filters, each of the multiple attenuators being configured to reduce external microwave energy present in the corresponding analog qubit control signal in the multiple analog qubit control signals.

12. The qubit control system according to any one of claims 9-10, wherein, The plurality of photodetectors and the plurality of cryogenic filters are provided at a first temperature higher than the second cryogenic operating temperature of the plurality of superconducting qubits.

13. The qubit control system according to any one of claims 9-10, wherein, Each of the corresponding analog qubit control signals in the plurality of analog qubit control signals is in the radio frequency (RF) wavelength range corresponding to the excitation energy of the corresponding superconducting qubit to be controlled.

14. The qubit control system according to any one of claims 9-10, further comprising: An electrical multiplexer, coupled to the plurality of cryogenic filters, is configured to electrically multiplex each analog qubit control signal to output a single electrically controlled analog signal, thereby reducing the number of transmission lines required to transmit each analog qubit control signal to the corresponding superconducting qubit.

15. The quantum bit control system according to any one of claims 9-10, wherein, Each of the plurality of photodetectors is a silicon-based germanium photodetector configured to operate in photovoltaic mode to minimize power consumption.

16. A quantum computer, comprising: Refrigeration system, which includes a temperature-controlled container; A quantum processor, which is arranged inside the temperature-controlled container, includes a plurality of superconducting qubits; as well as A qubit control system extends into the temperature-controlled container to provide control over the plurality of superconducting qubits. The quantum bit control system includes: An optical waveguide is configured to receive and transmit wavelength division multiplexed optical signals, wherein the wavelength division multiplexed optical signals have multiple modulated optical carriers, each of the multiple modulated optical carriers being at a different optical wavelength and carrying a corresponding digital qubit control signal, the corresponding digital qubit control signal being respectively corresponding to a corresponding superconducting qubit among a plurality of superconducting qubits; An optical demultiplexer is directly optically coupled to the optical waveguide to receive the wavelength division multiplexed optical signal transmitted through the optical waveguide, and to demultiplex the wavelength division multiplexed optical signal using a corresponding ring resonator of the optical demultiplexer to recover the plurality of modulated optical carriers, each of the modulated optical carriers carrying a corresponding digital quantum bit control signal; A plurality of photodetectors, which communicate with the optical demultiplexer and are directly coupled to the ring resonator, are configured to detect a corresponding digital qubit control signal. Multiple cryogenic filters are directly coupled to the plurality of photodetectors. Each of the plurality of cryogenic filters is configured to filter a corresponding digital qubit control signal to provide an analog qubit control signal corresponding to the corresponding digital qubit control signal. The corresponding analog quantum bit control signal is guided to the corresponding superconducting quantum bit in the plurality of superconducting quantum bits, wherein the plurality of photodetectors and the plurality of cryogenic filters are provided within the temperature-controlled container at a cryogenic temperature.

17. The quantum computer according to claim 16, wherein, Each of the plurality of cryogenic filters includes a superconducting LC bandpass cryogenic filter.

18. The quantum computer according to any one of claims 16-17, further comprising: Multiple attenuators are directly coupled to the multiple cryogenic filters, each of the multiple attenuators being configured to attenuate external microwave energy present in the corresponding analog qubit control signal.

19. The quantum computer according to any one of claims 16-17, wherein, The plurality of photodetectors and the plurality of cryogenic filters are provided at a first temperature higher than the second cryogenic operating temperature of the plurality of superconducting qubits.

20. The quantum computer according to any one of claims 16-17, further comprising: An electrical multiplexer, coupled to the plurality of cryogenic filters, is configured to electrically multiplex each analog qubit control signal to output a single electrically controlled analog signal, thereby reducing the number of transmission lines required to transmit each analog qubit control signal to the corresponding superconducting qubit.

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