Optically multiplexed quantum control

Abstract

A qubit control system for a quantum computer includes a source of a plurality of optical carriers; an optical modulator that receives the plurality of optical carriers and modulates each optical carrier with a qubit control signal to provide a plurality of modulated optical signals; an optical multiplexer that receives the plurality of modulated optical signals and provides wavelength division multiplexed optical signals; optical waveguides through which the wavelength division multiplexed optical signals are received and transmitted; an optical demultiplexer that receives the wavelength division multiplexed optical signals and recovers each of the plurality of modulated optical signals; and a demodulator that receives each of the recovered plurality of modulated optical signals and outputs a corresponding plurality of recovered qubit control signals to control a subset of a plurality of qubits.

Description

Technical Field

[0001] Embodiments of the present invention currently claimed relate to quantum computing, and more specifically, to a qubit control system for a quantum computer and a method of controlling qubits within a quantum computer.

Background Art

[0002] One fundamental element in quantum computing is the ability to prepare qubits in specific quantum states. Qubits within a superconducting quantum computer are typically controlled using radio frequency energy. The radio frequency is sent to a resonator via a radio frequency line, and the resonator then interacts with the qubits to control the quantum states of the qubits.

[0003] The number of control radio frequency lines can correspond to the number of qubits within a quantum computer. For a very large number of qubits, the number of radio frequency lines can also become very large. To reduce the number of lines used, it may be desirable to utilize multiplexers and demultiplexers to send multiple radio frequency energy signals to multiple qubits. However, even when using multiplexers and demultiplexers to transmit radio frequency energy signals, these types of systems are bulky, and more importantly, the problem remains of introducing heat and associated noise into the superconducting environment of the qubits. Therefore, it is desirable to solve this and other problems of existing signal transmission technologies.

Summary of the Invention

[0004] One aspect of the present invention provides a qubit control system for a quantum computer. The qubit control system includes a source of a plurality of optical carrier waves, each optical carrier wave being light of a different wavelength; and an optical modulator configured to receive the plurality of optical carrier waves and modulate each optical carrier wave with a qubit control signal to provide a plurality of modulated optical signals. The qubit control system includes an optical multiplexer configured to receive the plurality of modulated optical signals and provide a wavelength division multiplexed optical signal; and an optical waveguide optically coupled to the optical multiplexer for receiving and transmitting the wavelength division multiplexed optical signal therethrough. The qubit control system further includes an optical demultiplexer optically coupled to the optical waveguide for receiving the wavelength division multiplexed optical signal after being transmitted through the optical waveguide to recover each of the plurality of modulated optical signals; a demodulator optically coupled to the optical demultiplexer for receiving each of the plurality of recovered modulated optical signals to output a corresponding plurality of recovered qubit control signals; and a plurality of spatially separated qubit control waveguides, each of the plurality of spatially separated qubit control waveguides being configured to receive at least one of the plurality of recovered qubit control signals such that an equal recovered qubit control signal is spatially divided into different spatially separated qubit control waveguides. Each of the plurality of spatially separated qubit control waveguides is configured to direct a qubit control signal to a different subset of a plurality of qubits, the plurality of qubits being configured to be controlled by the qubit control signal transmitted by the plurality of spatially separated qubit control waveguides.

[0005] In one embodiment, the plurality of qubit control signals and the corresponding plurality of recovered qubit control signals are in a radio frequency (RF) wavelength region corresponding to the excitation energy of the corresponding qubits to be controlled.

[0006] In one embodiment, the qubit control system further includes a radio frequency multiplexer configured to receive at least two recovered qubit control signals having different RF wavelengths from the demodulator and multiplex the at least two recovered qubit control signals into one of the plurality of spatially separated qubit control waveguides.

[0007] In one embodiment, the qubit control system further includes a plurality of radio frequency multiplexers, each configured to receive at least two recovered qubit control signals having different RF wavelengths from the demodulator and multiplex the at least two recovered qubit control signals into a corresponding one of the plurality of spatially separated qubit control waveguides.

[0008] In one embodiment, the radio frequency multiplexer includes a plurality of band - pass filters, each passing a corresponding one of the recovered qubit control signals while attenuating or substantially blocking all other recovered qubit control signals. In one embodiment, the demodulator includes a direct optical / electrical converter.

[0009] Another aspect of the present invention provides a quantum computer including a cooling system including a temperature - controlled container; a quantum processor disposed within the temperature - controlled container, the quantum processor having a plurality of qubits; and a qubit control system having a portion outside the temperature - controlled container and a portion extending into the temperature - controlled container for providing control of the plurality of qubits.

[0010] The qubit control system includes: a source of a plurality of optical carrier waves, each optical carrier wave being light of a different wavelength; an optical modulator configured to receive the plurality of optical carrier waves and modulate each optical carrier wave with a qubit control signal to provide a plurality of modulated optical signals; an optical multiplexer configured to receive the plurality of modulated optical signals and provide a wavelength-division multiplexed optical signal; an optical waveguide optically coupled to the optical multiplexer for receiving and transmitting the wavelength-division multiplexed optical signal therethrough; an optical demultiplexer optically coupled to the optical waveguide for receiving the wavelength-division multiplexed optical signal after it has been transmitted through the optical waveguide to recover each of the plurality of modulated optical signals; a demodulator optically coupled to the optical demultiplexer for receiving each of the plurality of recovered modulated optical signals to output a corresponding plurality of recovered qubit control signals; and a plurality of spatially separated qubit control waveguides, each of the plurality of spatially separated qubit control waveguides being configured to receive at least one of the plurality of recovered qubit control signals such that an equal recovered qubit control signal is spatially divided into different spatially separated qubit control waveguides. Each of the plurality of spatially separated qubit control waveguides directs the qubit control signal to different subsets of the plurality of qubits, and the plurality of qubits are configured to be controlled by the qubit control signal transmitted by the plurality of spatially separated qubit control waveguides.

[0011] In one embodiment, the source of the plurality of optical carrier waves, the optical modulator, and the optical multiplexer are all disposed outside the temperature-controlled container. In one embodiment, the optical demultiplexer and the demodulator are disposed within the temperature-controlled container. In one embodiment, the optical waveguide extends from the optical multiplexer disposed outside the temperature-controlled container to the optical demultiplexer within the temperature-controlled container. In one embodiment, the plurality of qubit control signals and the corresponding plurality of recovered qubit control signals are within a radio frequency (RF) wavelength region corresponding to the excitation energy of the corresponding qubits to be controlled.

[0012] In one embodiment, the quantum computer further includes a radio frequency multiplexer configured to receive at least two recovered qubit control signals having different RF wavelengths from the demodulator and multiplex the at least two recovered qubit control signals into one of the plurality of spatially separated qubit control waveguides. In one embodiment, the quantum computer also includes a plurality of radio frequency multiplexers, each of which is configured to receive at least two recovered qubit control signals having different RF wavelengths from the demodulator and multiplex the at least two recovered qubit control signals into a corresponding one of the plurality of spatially separated qubit control waveguides.

[0013] In one embodiment, the radio frequency multiplexer includes a plurality of bandpass filters, each of the plurality of bandpass filters passing a corresponding one of the recovered qubit control signals while attenuating or substantially blocking all other recovered qubit control signals. In one embodiment, the demodulator includes a direct optical / electrical detector. In one embodiment, the cooling system further includes a second temperature-controlled container that should be controlled to a temperature higher than the temperature in the first-mentioned temperature-controlled container. At least one of the source of the plurality of optical carrier waves, the optical modulator, and the optical multiplexer is disposed within the second temperature-controlled container.

[0014] In one embodiment, the source of the plurality of optical carrier waves, the optical modulator, and the optical multiplexer are all disposed within the second temperature-controlled container. In one embodiment, the cooling system further includes a second temperature-controlled container that should be controlled to a temperature higher than the temperature in the first-mentioned temperature-controlled container. In one embodiment, the optical demultiplexer and at least one demodulator are disposed within the second temperature-controlled container. In one embodiment, the optical demultiplexer and all of the demodulators are all disposed within the second temperature-controlled container.

[0015] Another aspect of the present invention provides a method for controlling qubits in a quantum computer. The method includes modulating each of a plurality of qubit control signals onto a respective one of a plurality of optical carrier waves to provide a plurality of modulated optical signals, each optical carrier wave of the plurality of optical carrier waves being light of a different wavelength; multiplexing the plurality of modulated optical signals onto an optical waveguide to provide a wavelength-division multiplexed optical signal to be transmitted through the optical waveguide; demultiplexing the plurality of modulated optical signals from the wavelength-division multiplexed optical signal after transmission through the optical waveguide to recover the plurality of modulated optical signals; demodulating the recovered plurality of modulated optical signals to recover the plurality of qubit control signals; coupling each recovered qubit control signal from the plurality of recovered qubit control signals after the demodulation to at least one of a plurality of spatially separated qubit control waveguides such that equivalent qubit control signals are spatially separated into different qubit control waveguides; and directing the recovered qubit control signals from each spatially separated qubit control waveguide to different subsets of the plurality of qubits of the quantum computer to provide control thereof.

[0016] In certain embodiments, the modulating and multiplexing are performed at a higher temperature than the demultiplexing, the demodulating, the coupling, and the directing. In certain embodiments, the plurality of qubits are a plurality of superconducting qubits, and at least one of the demultiplexing, the demodulating, the coupling, and the directing is performed at the operating temperature of the plurality of superconducting qubits. In certain embodiments, each of the plurality of superconducting qubits has a control signal in the radio frequency (RF) spectral region, and the qubit control waveguides are RF waveguides.

[0017] In certain embodiments, demultiplexing the plurality of modulated optical signals from the wavelength-division multiplexed optical signal includes bandpass filtering the wavelength-division multiplexed optical signal for each of a plurality of passbands to provide a plurality of demultiplexed modulated optical signals at each of a plurality of optical channels.

[0018] In one embodiment, demodulating the plurality of qubit control signals from the plurality of modulated optical signals includes direct optical detection of each of the plurality of demultiplexed, modulated optical signals to provide a corresponding plurality of demodulated electrical signals within the RF spectral region.

[0019] In one embodiment, demodulating the plurality of qubit control signals from the plurality of modulated optical signals includes direct optical detection to provide a corresponding plurality of demodulated electrical signals within the RF spectral region. In one embodiment, the demodulating, combining, and directing are performed at the operating superconducting temperature of the plurality of qubits.

Brief Description of the Drawings

[0020] The present disclosure, as well as the methods of operation and functions of related structural elements, and combinations of components, and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings. These all form a part of this specification, and like reference numerals represent corresponding parts in the various figures. However, it should be clearly understood that these drawings are for illustrative and explanatory purposes only and are not intended as a definition of the limitations of the present invention.

[0021]

Figure 1

[0022]

Figure 2

[0023]

Figure 3

Modes for Carrying Out the Invention

[0024] In the following paragraphs, the terms "light" and "optics" are intended to be general and include both visible and invisible portions of the electromagnetic spectrum, such as visible light, infrared light, near-infrared light, and ultraviolet light, although not limited thereto. The term "subset of a plurality of qubits" is intended to include any integer including a single qubit or any plurality of qubits.

[0025] FIG. 1 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 a light source 102 of a plurality of optical carriers 102A, and each optical carrier is light of a different wavelength. In an embodiment, the light source 102 can include a plurality of lasers, such as a Fabry-Perot gain medium laser. For example, a laser having a quantum dot active region can be used to generate appropriately spaced optical wavelengths within a single optical fiber. These sources are suitable for generating a plurality of laser lines (e.g., 8 to 32 laser lines) within a relatively narrow optical wavelength range. For example, a quantum dot-based diode laser operating as an optical frequency comb generator can be used. A quantum dot-based laser can be coupled to an optical fiber to provide, for example, several low-noise 80 GHz spaced optical modes at about 1310 nm.

[0026] The qubit control system 100 also includes an optical modulator 104 configured to receive the plurality of optical carriers 102A and modulate each optical carrier 102A with a qubit control signal 106A generated by a qubit control signal source 106 to provide a plurality of modulated optical signals 108A.

[0027] The qubit control system 100 also includes an optical multiplexer (MUX) 108 configured to receive a plurality of modulated optical signals 108A and provide a wavelength-division multiplexed optical signal 108B. The qubit control system 100 also includes an optical waveguide 109 optically coupled to the optical multiplexer for receiving and transmitting the wavelength-division multiplexed optical signal therethrough.

[0028] The qubit control system 100 further includes an optical demultiplexer (DEMUX) 110 optically coupled to the optical waveguide 109 for receiving the wavelength-division multiplexed optical signal 108B after being transmitted through the optical waveguide 109 to recover each of the plurality of modulated optical signals 108A.

[0029] The qubit control system 100 also includes a demodulator 112 optically coupled to the optical demultiplexer 110 for receiving each of the plurality of recovered modulated optical signals 108A to output a corresponding plurality of recovered qubit control signals 106B. In certain embodiments, the plurality of recovered qubit control signals 106B are substantially the same or equivalent to the qubit control signals 106A.

[0030] The qubit control system 100 further includes a plurality of spatially separated qubit control waveguides 111, each of the plurality of spatially separated qubit control waveguides 111 being configured to receive at least one of the plurality of recovered qubit control signals 106B such that equivalent recovered qubit control signals 106B are spatially divided into different spatially separated qubit control waveguides 111.

[0031] The qubit control system 100 is configured to control a plurality of qubits 116 by qubit control signals 106A transmitted by a plurality of spatially separated qubit control waveguides 111. Each of the plurality of spatially separated qubit control waveguides 111 directs a qubit control signal 106B to a different subset 116A of the plurality of qubits 116. Although a single qubit is shown as a qubit subset 116A of the plurality of qubits 116, it should be understood that one, two, or more can form a qubit subset 116A of the plurality of qubits 116.

[0032] In certain embodiments, the qubit control system 100 further includes a radio frequency multiplexer / demultiplexer 114 having one or more bandpass filters 114B configured to receive a plurality of recovered qubit control signals 106B transmitted via the spatially separated qubit control waveguides 111 and output frequency-filtered recovered qubit control signals 114A used to control corresponding subsets 116A of the plurality of qubits 116.

[0033] In certain embodiments, the plurality of qubit control signals 106A and the corresponding plurality of recovered qubit control signals 106B are within a radio frequency (RF) wavelength region corresponding to the excitation energy of the corresponding qubits 116A to be controlled.

[0034] In certain embodiments, the qubit control system 100 further includes a radio frequency multiplexer / demultiplexer 114 configured to receive at least two recovered qubit control signals 106B at different RF wavelengths from a demodulator 112 and multiplex the at least two recovered qubit control signals 106B onto one of the plurality of spatially separated qubit control waveguides 111.

[0035] In one embodiment, the qubit control system 100 also includes a plurality of radio frequency multiplexers / demultiplexers 114, and each radio frequency multiplexer / demultiplexer 114 receives at least two recovered qubit control signals 106B having different RF wavelengths from the demodulator 112 and multiplexes the at least two recovered qubit control signals 106B into a corresponding one of a plurality of spatially separated qubit control waveguides 111.

[0036] In one embodiment, the radio frequency multiplexer 114 includes a plurality of bandpass filters 114B, and each of the plurality of bandpass filters 114B passes a corresponding one of the recovered qubit control signals 106B while attenuating or substantially blocking all other recovered qubit control signals 106B. In one embodiment, each bandpass filter 114B can include an LC circuit to provide an LC bandpass filter.

[0037] In one embodiment, the demodulator 112 includes a direct optical / electrical converter. In one embodiment, the optical / electrical converter can include an optical detector or photodetector such as, for example, a photodiode, a photomultiplier tube, or a bolometer scale (SC).

[0038] Another aspect of the present invention provides a quantum computer 200. FIG. 2 is a schematic diagram of a quantum computer according to an embodiment of the present invention. The quantum computer 200 includes a cooling system 202 including 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 also includes a qubit control system 210 having a portion 210A outside the temperature-controlled container 204 and a portion 210B extending into the temperature-controlled container 204 to provide control of the plurality of qubits 208.

[0039] The qubit control system 210 is similar to the qubit control system 100 described in the above paragraph with respect to FIG. 1. Therefore, when referring to the components of the qubit control system 210, the similar components of the qubit control system 100 are referred to instead. Therefore, referring further to FIG. 1, the qubit control system 210 includes a light source 102 for a plurality of optical carriers 102A, and each optical carrier 102A is light of a different wavelength. The qubit control system 210 also includes an optical modulator 104 configured to receive the plurality of optical carriers 102A and modulate each optical carrier 102A with a qubit control signal 106A to provide a plurality of modulated optical signals 108A.

[0040] The qubit control system 210 also has an optical multiplexer 108 configured to receive the plurality of modulated optical signals 108A and provide a wavelength division multiplexed optical signal 108B. The qubit control system 210 also includes an optical waveguide 109 optically coupled to the optical multiplexer for receiving and transmitting the wavelength division multiplexed optical signal therethrough.

[0041] The qubit control system 210 further includes an optical demultiplexer 110 optically coupled to the optical waveguide 109 for receiving the wavelength division multiplexed optical signal 108B after being transmitted through the optical waveguide 109 to recover each of the plurality of modulated optical signals 108A.

[0042] The qubit control system 210 also includes a demodulator 112 optically coupled to the optical demultiplexer 110 for receiving each of the plurality of recovered modulated optical signals 108A to output a corresponding plurality of recovered qubit control signals 106B.

[0043] The qubit control system 100 further includes a plurality of spatially separated qubit control waveguides 111, and each of the plurality of spatially separated qubit control waveguides 111 is configured to receive at least one of the plurality of recovered qubit control signals 106B such that an equal recovered qubit control signal 106B is spatially split into different spatially separated qubit control waveguides 111.

[0044] The plurality of qubits 208 are configured to be controlled by qubit control signals transmitted by a plurality of spatially separated qubit control waveguides. Each of the plurality of spatially separated qubit control waveguides 111 directs the qubit control signal to a different subset 208A of the plurality of qubits 208. In certain embodiments, each of the plurality of spatially separated qubit control waveguides 111 directs the qubit control signal to a different subset of the plurality of qubits 208.

[0045] In certain embodiments, the light source 102, the optical modulator 104, and the optical multiplexer 108 of the plurality of optical carrier waves 102A are all disposed outside the temperature-controlled container 204. In certain embodiments, the optical demultiplexer 110 and the demodulator 112 are disposed within the temperature-controlled container 204. The optical waveguide 109 extends from the optical multiplexer 108 disposed outside the temperature-controlled container 204 to the optical demultiplexer 110 within the temperature-controlled container 204.

[0046] In certain embodiments, the plurality of qubit control signals 106A and the corresponding plurality of recovered qubit control signals 106B are within a radio frequency (RF) wavelength region corresponding to the excitation energy of the corresponding qubits 208A to be controlled.

[0047] In one embodiment, the quantum computer 200 further includes a radio frequency multiplexer 212 configured to receive at least two recovered qubit control signals 106B having different RF wavelengths from the demodulator 112 and multiplex the at least two recovered qubit control signals 106B onto one of a plurality of spatially separated qubit control waveguides 111. The radio frequency multiplexer 212 may be the same as the radio frequency multiplexer 114 shown in FIG. 1 and described in the previous paragraph.

[0048] The quantum computer 200 further includes a plurality of radio frequency multiplexers 212, each of the plurality of radio frequency multiplexers 212 being configured to receive at least two recovered qubit control signals 106B having different RF wavelengths from the demodulator 112 and multiplex the at least two recovered qubit control signals 106B onto a corresponding one of a plurality of spatially separated qubit control waveguides 111.

[0049] In one embodiment, the radio frequency multiplexer 212 includes a plurality of bandpass filters, such as the bandpass filter 114B of the radio frequency multiplexer 114, each of the plurality of bandpass filters passing a corresponding one of the recovered qubit control signals 106B while attenuating or substantially blocking all other recovered qubit control signals 106B. In one embodiment, the bandpass filter can include an LC circuit to form an LC bandpass filter.

[0050] In one embodiment, the cooling system 202 further includes a second temperature-controlled container 205 to be controlled to a temperature higher than the temperature in the initially described temperature-controlled container 204. In one embodiment, the inner portion 210B of the qubit control system 210 includes an optical multiplexer 108, an optical modulator 104, and an optical demultiplexer 110 and is disposed within the second temperature-controlled container 205.

[0051] In another embodiment, the light source 102, the optical modulator 104, and the optical multiplexer 108 of the plurality of optical carrier waves 102A may be disposed within a second temperature-controlled container 205. In certain embodiments, the second temperature-controlled container 205 is controlled to a temperature higher than the temperature within the first-mentioned temperature-controlled container 204 in which the quantum processor 206 is positioned. In certain embodiments, the optical demultiplexer 110 and at least one demodulator 112 may be disposed within the second temperature-controlled container 205 instead of the first-mentioned temperature-controlled container 204. In certain embodiments, all of the optical demultiplexer 110 and the demodulators 112 are disposed within the second temperature-controlled container 205.

[0052] The second temperature-controlled container 205 is shown inside the first-mentioned temperature-controlled container 204, but the second temperature-controlled container 205 may be positioned outside the first-mentioned temperature-controlled container 204. Additionally, in another embodiment, the second temperature-controlled container 205 may be a portion or zone of the first-mentioned temperature-controlled container 204 that is at a higher temperature than the portion or zone of the first-mentioned temperature-controlled container 204 in which the quantum processor 206 is positioned or disposed. In certain embodiments, the quantum processor 206 and associated qubits 208, 116 operate at a superconducting temperature, and thus, the qubits 116 and 208 are superconducting qubits.

[0053] In other embodiments, without limitation to a particular number, more than two temperature-controlled containers can be used. Further, in various embodiments, the components of the qubit control system that are distributed among these more than two temperature-controlled containers can be configured in many ways.

[0054] One advantage of using such qubit control systems 100, 210 is that wavelength division multiplexing (WDM) allows the same modulation frequency RF to be transmitted at different optical wavelengths, providing more signals / fibers than can be achieved when using radio frequency (RF) coaxial cables for the multiplexed signals. Another advantage is that high-frequency finite impulse response (FIR) and infinite impulse response (IIR) modulation can be performed at room temperature within the optical domain, or in an environment where the temperature is higher than that of the quantum processor / qubit. Another advantage is that the signal path at low temperature for the signal before filtering is relatively small, allowing the exclusion of active electronics within the cryostat, thus reducing heat dissipation. Instead, passive LC filters, photodetectors / converters can be used within the cryostat.

[0055] Another aspect of the present invention provides a method for controlling qubits within a quantum computer. FIG. 3 is a flowchart of a method for controlling qubits in a quantum computer according to an embodiment of the present invention. The method includes, at 300, modulating each of a plurality of qubit control signals onto a respective one of a plurality of optical carrier waves to provide a plurality of modulated optical signals, each of the plurality of optical carrier waves being light of a different wavelength; at 302, multiplexing the plurality of modulated optical signals onto an optical waveguide to provide a wavelength-division multiplexed optical signal to be transmitted through the optical waveguide; at 304, demultiplexing the plurality of modulated optical signals from the wavelength-division multiplexed optical signal after transmission through the optical waveguide to recover the plurality of modulated optical signals; at 306, demodulating the plurality of recovered modulated optical signals to recover the plurality of qubit control signals; at 308, coupling each recovered qubit control signal from the plurality of recovered qubit control signals after demodulation to at least one of a plurality of spatially separated qubit control waveguides such that equivalent qubit control signals are spatially separated into different qubit control waveguides; and at 310, directing the recovered qubit control signals from each spatially separated qubit control waveguide to different subsets of a plurality of qubits of the quantum computer to provide control thereof.

[0056] In one embodiment, modulation and multiplexing are performed at a higher temperature than demultiplexing, demodulation, coupling, and directing. In one embodiment, the plurality of qubits are a plurality of superconducting qubits, and at least one of demultiplexing, demodulation, coupling, and directing is performed at the operating temperature of the plurality of superconducting qubits. In one embodiment, each of the plurality of superconducting qubits has a control signal in the radio frequency (RF) spectral region, and the qubit control waveguides are RF waveguides.

[0057] In one embodiment, demultiplexing the plurality of modulated optical signals from the wavelength-division multiplexed optical signal includes bandpass filtering the wavelength-division multiplexed optical signal for each of a plurality of passbands to provide a plurality of demultiplexed modulated optical signals at each of a plurality of optical channels.

[0058] In one embodiment, the step of demodulating a plurality of qubit control signals from a plurality of modulated optical signals includes direct optical detection of each of the plurality of demultiplexed modulated optical signals to provide a corresponding plurality of demodulated electrical signals in the RF spectral region.

[0059] In one embodiment, the step of demodulating a plurality of qubit control signals from a plurality of modulated optical signals includes direct optical detection to provide a corresponding plurality of demodulated electrical signals in the RF spectral region.

[0060] The description of various embodiments of the present invention has been presented for purposes of illustration and is not intended to be exhaustive or limited to the disclosed embodiments. 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 of technology found in the marketplace, or technical improvements thereto, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A qubit control system for a quantum computer, comprising: Sources of a plurality of optical carrier waves, each optical carrier wave being light of a different wavelength; An optical modulator configured to receive the plurality of optical carrier waves and modulate each optical carrier wave with a qubit control signal to provide a plurality of modulated optical signals; An optical multiplexer configured to receive the plurality of modulated optical signals and provide a wavelength division multiplexed optical signal; An optical waveguide optically coupled to the optical multiplexer for receiving and transmitting the wavelength division multiplexed optical signal therethrough; An optical demultiplexer optically coupled to the optical waveguide for receiving the wavelength division multiplexed optical signal after transmission through the optical waveguide to recover each of the plurality of modulated optical signals; A demodulator optically coupled to the optical demultiplexer for receiving each of the plurality of recovered modulated optical signals and outputting a corresponding plurality of recovered qubit control signals; A plurality of spatially separated qubit control waveguides, each of the plurality of spatially separated qubit control waveguides being configured to receive at least one of the plurality of recovered qubit control signals such that an equal recovered qubit control signal is spatially divided into different spatially separated qubit control waveguides; Comprising: Each of the plurality of spatially separated qubit control waveguides directs a qubit control signal to a different subset of a plurality of qubits, and the plurality of qubits are configured to be controlled by the qubit control signal transmitted by the plurality of spatially separated qubit control waveguides. Qubit control system.

2. The qubit control system according to claim 1, wherein the plurality of qubit control signals and the corresponding plurality of recovered qubit control signals are in a radio frequency (RF) wavelength region corresponding to the excitation energy of the corresponding qubits to be controlled.

3. The qubit control system according to claim 2, further comprising a radio frequency multiplexer configured to receive at least two recovered qubit control signals having different RF wavelengths from the demodulator and multiplex the at least two recovered qubit control signals into one of the plurality of spatially separated qubit control waveguides.

4. The qubit control system according to claim 3, further comprising a plurality of radio frequency multiplexers, each of the plurality of radio frequency multiplexers being configured to receive at least two recovered qubit control signals having different RF wavelengths from the demodulator and multiplex the at least two recovered qubit control signals into a corresponding one of the plurality of spatially separated qubit control waveguides.

5. The qubit control system according to claim 3 or claim 4, wherein the radio frequency multiplexer has a plurality of bandpass filters, each of the plurality of bandpass filters passing a corresponding one of the recovered qubit control signals while attenuating or blocking all other recovered qubit control signals.

6. The qubit control system according to any one of claims 1 to 5, wherein the demodulator has a direct optical / electrical converter.

7. A cooling system having a temperature-controlled container; A quantum processor disposed within the temperature-controlled container, the quantum processor having a plurality of qubits; and A qubit control system having a portion outside the temperature-controlled container and a portion extending into the temperature-controlled container for providing control of the plurality of qubits comprising The qubit control system is a source of a plurality of optical carrier waves, each optical carrier wave being light of a different wavelength; an optical modulator configured to receive the plurality of optical carrier waves and modulate each optical carrier wave with a qubit control signal to provide a plurality of modulated optical signals; an optical multiplexer configured to receive the plurality of modulated optical signals and provide a wavelength division multiplexed optical signal; an optical waveguide optically coupled to the optical multiplexer for receiving and transmitting the wavelength division multiplexed optical signal therethrough; an optical demultiplexer optically coupled to the optical waveguide for receiving the wavelength division multiplexed optical signal after being transmitted through the optical waveguide to recover each of the plurality of modulated optical signals; a demodulator optically coupled to the optical demultiplexer for receiving each of the plurality of recovered modulated optical signals to output a corresponding plurality of recovered qubit control signals; A plurality of spatially separated qubit control waveguides, each of the plurality of spatially separated qubit control waveguides being configured to receive at least one of the plurality of recovered qubit control signals such that an equal recovered qubit control signal is spatially divided into different spatially separated qubit control waveguides. having Each of the plurality of spatially separated qubit control waveguides directs a qubit control signal to a different subset of the plurality of qubits, and the plurality of qubits are configured to be controlled by the qubit control signal transmitted by the plurality of spatially separated qubit control waveguides. A quantum computer. **Claim 8** The source of the plurality of optical carrier waves, the optical modulator, and the optical multiplexer are all disposed outside the temperature-controlled container. The optical demultiplexer and the demodulator are disposed inside the temperature-controlled container, and The optical waveguide extends from the optical multiplexer disposed outside the temperature-controlled container to the optical demultiplexer inside the temperature-controlled container. The quantum computer according to claim 7. **Claim 9** The plurality of qubit control signals and the corresponding plurality of recovered qubit control signals are within a radio frequency (RF) wavelength region corresponding to the excitation energy of the corresponding qubits to be controlled, for the quantum computer according to claim 8. **Claim 10** The quantum computer according to claim 9, further comprising a radio frequency multiplexer configured to receive at least two recovered qubit control signals having different RF wavelengths from the demodulator and multiplex the at least two recovered qubit control signals into one of the plurality of spatially separated qubit control waveguides. **Claim 11** The quantum computer according to claim 9, further comprising a plurality of radio frequency multiplexers, each of the plurality of radio frequency multiplexers being configured to receive at least two recovered qubit control signals having different RF wavelengths from the demodulator and multiplex the at least two recovered qubit control signals into a corresponding one of the plurality of spatially separated qubit control waveguides. **Claim 12** The radio frequency multiplexer has a plurality of band-pass filters, and each of the plurality of band-pass filters passes a corresponding one of the recovered qubit control signals while attenuating or blocking all other recovered qubit control signals. The quantum computer according to claim 11.

13. The quantum computer according to any one of claims 8 to 12, wherein the demodulator includes a direct optical / electrical detector.

14. The cooling system further has a second temperature-controlled container that should be controlled to a temperature higher than the temperature in the initially described temperature-controlled container, and at least one of the source of the plurality of optical carrier waves, the optical modulator, and the optical multiplexer is disposed in the second temperature-controlled container. The quantum computer according to any one of claims 8 to 13.

15. The quantum computer according to claim 14, wherein the source of the plurality of optical carrier waves, the optical modulator, and the optical multiplexer are all disposed in the second temperature-controlled container.

16. The cooling system further has a second temperature-controlled container that should be controlled to a temperature higher than the temperature in the initially described temperature-controlled container, and the optical demultiplexer and at least one demodulator are disposed in the second temperature-controlled container. The quantum computer according to any one of claims 8 to 15.

17. The quantum computer according to claim 16, wherein the optical demultiplexer and all of the demodulators are all disposed in the second temperature-controlled container.

18. A method for controlling qubits in a quantum computer, comprising: modulating each of a plurality of qubit control signals onto a respective one of a plurality of optical carrier waves to provide a plurality of modulated optical signals, each optical carrier wave of the plurality of optical carrier waves being light of a different wavelength; multiplexing the plurality of modulated optical signals onto an optical waveguide to provide a wavelength-division multiplexed optical signal to be transmitted through the optical waveguide; demultiplexing the plurality of modulated optical signals from the wavelength-division multiplexed optical signal after transmission through the optical waveguide to recover the plurality of modulated optical signals; demodulating the plurality of recovered modulated optical signals to recover the plurality of qubit control signals; coupling each of the recovered qubit control signals from the plurality of recovered qubit control signals after the demodulation to at least one of a plurality of spatially separated qubit control waveguides such that equivalent qubit control signals are spatially separated into different qubit control waveguides; and directing the recovered qubit control signals from each of the spatially separated qubit control waveguides to different subsets of the plurality of qubits of the quantum computer to provide control thereof A method comprising the steps of: **Claim 19** The method according to claim 18, wherein the modulation and the multiplexing are performed at a temperature higher than the demultiplexing, the demodulation, the coupling, and the directing. **Claim 20** The method according to claim 18 or 19, wherein the plurality of qubits are a plurality of superconducting qubits, and at least one of the demultiplexing, the demodulation, the coupling, and the directing is performed at an operating temperature of the plurality of superconducting qubits. **Claim 21** The method according to claim 20, wherein each of the plurality of superconducting qubits has a control signal in a radio frequency spectrum region (RF spectrum region), and the qubit control waveguide is an RF waveguide. **Claim 22** The method according to claim 21, wherein the demultiplexing the plurality of modulated optical signals from the wavelength division multiplexed optical signal comprises bandpass filtering the wavelength division multiplexed optical signal for each of a plurality of passbands to provide a plurality of demultiplexed modulated optical signals for each of a plurality of optical channels. **Claim 23** The method according to claim 21 or 22, wherein the demodulating the plurality of qubit control signals from the plurality of modulated optical signals includes direct optical detection of each of the plurality of demultiplexed modulated optical signals to provide corresponding demodulated electrical signals in the RF spectrum region. **Claim 24** The method according to claim 22 or 23, wherein the demodulating the plurality of qubit control signals from the plurality of modulated optical signals includes direct optical detection to provide corresponding demodulated electrical signals in the RF spectrum region. **Claim 25** The method according to any one of claims 21 to 24, wherein the demodulation, the coupling, and the directing are performed at an operating superconducting temperature of the plurality of qubits.

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