System and method for transmitting signals between cryogenic system and external environment

Abstract

A system and method for transmitting signals between internal and external environments of a cryogenic system. The system includes at least one light source (e.g., a laser) for generating an optical input signal and at least one optical fiber for transmitting a modulated optical signal into and receiving an optical output signal from the interior of the cryogenic system. A plurality of detectors located in the external environment are used to detect the optical output signal and are connected to the optical fiber. In the cryogenic system, the system further includes a plurality of first transducers for converting the modulated optical signal to a microwave input signal and a plurality of second transducers for converting the microwave input signal to an optical output signal. The first microwave impedance matching resonator is connected to the plurality of first transducers and the second microwave impedance matching resonator is connected to the plurality of second transducers.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of UK patent application No. GB ​​2209126.8 filed on 21 June 2022. Technical Field

[0003] The field of the invention relates to systems for transferring data between an interior of a cryogenic system and an external environment, and more particularly to controlling and / or reading out the state of a quantum processor. Background Art

[0004] Quantum computers are expected to solve complex problems that are difficult to solve with current classical computers. Quantum computers may form an important part of the future high-performance computing market. Many candidates for quantum computing, including superconducting qubits and spin qubits, need to operate at low temperatures and microwave frequency drive fields (between hundreds of MHz and hundreds of GHz). In order to surpass classical computers, it is crucial to expand the number of qubits in quantum computers from the current state-of-the-art technology of 100 to 1,000,000 or more. Expanding the number of qubits will require delivering microwave signals to and from cryogenic refrigerators such as dilution refrigerators and liquid helium systems.

[0005] Two challenges in scaling up the number of qubits are the heat load and the spatial requirements of the signal delivery mechanism, as the cryostat has limited substrate area and limited cooling capabilities.

[0006] The standard method of delivering microwave signals to the quantum processor of a quantum computer is through a coaxial radio frequency (RF) cable with a series of attenuators. One RF cable can deliver microwave signals via time and frequency multiplexing to drive multiple qubits or qubit readout resonators. The qubits are read out by taking signals from a cryogenic system or refrigerator (also called a cryostat) after amplification at high temperatures within a cryostat, with one coaxial RF line for each of the multiple qubits.

[0007] The delivery and acquisition of microwave signals is also used for several applications related to quantum computing, including powering amplifiers, shifting quantum states, magnetic field sensing, and cavity occupancy readout. Using current methods for acquiring microwave signals, it is impractical to increase the number of cables in the system to a sufficient scale to support the large number of qubits required for practical quantum processors.

[0008] This article outlines an alternative system for the delivery and acquisition of microwave signals based on optical fiber.Optical fiber is present in telecommunication networks, data centers, and supercomputers because it offers large bandwidth, small form factor, and low power consumption.

[0009] Information is often encoded in certain telecommunication bands due to the low losses of optical fibers. The advantages of optical fibers can also be applied to quantum computing systems to increase bandwidth, space requirements, efficiency and reduce thermal conductivity.

[0010] On a small scale, microwave signals have been delivered into cryostats via optical carriers, and superconducting qubits have been read out via optical carriers. For example, B. Van Zeghbroeck, "Optical data communication between Josephson-junction circuits and room-temperature electronics," IEEE Transactions on Applied Superconductivity, vol. 3, no. 1, 1993.3 (DOI: 10.1109 / 77234002), shows basic connections to Josephson junction circuits with photodiodes and laser diodes.

[0011] Lecocq et al., “Control and readout of a superconducting qubit using a photonic link,” Nature, 591, 575-579, 2021, (DOI: 10.1038 / s41586-021-03268-x), shows that control pulses for qubit manipulation and readout of drive tones can be delivered to the substrate of a dilution refrigerator. Lecocq et al. used an electro-optic modulator coupled to an optical fiber going into the dilution refrigerator and a commercial fiber-coupled photodiode. In this paper, it is proposed that the design can be extended by adding multiplexing, demultiplexing, and higher load resistors for the photodiode. However, how to implement such a system in a scalable way remains an open question.

[0012] One challenge outlined by Lecocq et al. is the power consumption in the dilution refrigerator. Lecocq et al. propose to address this challenge by reducing the reactive power consumption of the optical fiber relative to the coaxial RF cable. However, Lecocq et al. propose that if the drive pulse is applied for more than 2% of each switching cycle, the active power consumption in the coldest phase of the cryostat exceeds the power consumption of the coaxial RF cable. The excessive power consumption of the coaxial RF cable limits the duty cycle of the quantum processor.

[0013] The authors Lecocq et al. proposed that this limitation could be overcome by placing a higher load resistor (10kOhm) at the output of the photodiode. A higher load resistor would reduce power consumption, and Lecocq et al. suggested that the photodiode and load resistor could be connected directly to the quantum processor, reducing impedance mismatch. Lecocq et al. pointed out that the distance between the photodiode and the quantum processor should be much less than one centimeter to avoid standing waves. Therefore, a technical problem is known from Lecocq et al., that the distance between the photodiode and the quantum processor must be very small (much less than one centimeter) and must be accurately selected to reduce impedance mismatch.

[0014] However, close proximity of superconducting materials (such as those used in superconducting qubits) to visible light can lead to the generation of quasiparticles and the destruction of qubit states (as highlighted by Mirhosseini et al. in Nature, vol. 588, 2020.12.23, “Superconducting qubit to optical photon transduction”). For example, the close proximity of superconducting materials can be an optical chip wire-bonded to a superconducting qubit chip, or an optical fiber located in the same shield that can act as a superconducting qubit with a direct line of sight to the optical fiber. Longer connections can be used to separate the photodiode from the quantum processor to avoid the problem of quasiparticle generation and qubit state destruction, but the resulting impedance mismatch also leads to power consumption.

[0015] Another challenge raised by Lecocq et al. is shot noise. The authors Lecocq et al. identify shot noise as a fundamental limit to the noise generated by the photodiode. Lecocq et al. estimate that as the load resistance increases, the shot noise increases, and therefore the qubit control gate error rate also increases. For example, Lecocq et al. state that using a 50Ohm resistor, the probability of error due to shot noise is 8*10 -5 , but with a 10k Ohm resistor, the error probability increases to 10 -3 , which may limit the scalability of superconducting qubit processors.

[0016] U.S. Patent Application No. US2018 / 0003753 A1, “Read out of quantum states of microwave frequency qubits with optical frequency photons,” IBM, 2016, proposes using the presence or absence of an optical signal to read out the state of a superconducting qubit. The document outlines methods that include the possibility of multiplexing, but does not allow for recovery of arbitrary microwave states. Amplitude and phase quadratic readout is a more standard method for reading out superconducting qubits.

[0017] Delanay et al., "Non-destructive optical readout of a superconducting qubit", arXiv:2110.09539, 2021, (DOI:10.48550 / arXiv.2110.09539) show the readout of superconducting qubits via light fields, including reading out the amplitude and phase of microwave signals. This approach involves a large free-space optical cavity (occupying a large volume on a substrate) and free space, rather than fiber optic transmission out of a dilution refrigerator. However, it is not clear how this approach can be scalably combined with optical fibers and multiplexed.

[0018] International patent application number WO 2022 / 120469 A1, "Hybridphotonics-solid state quantum computer", ANYON SYSTEMS INC, describes in detail a system that combines the use of optical fibers to send microwave signals to a quantum processor and / or obtain microwave signals from a quantum processor. This document uses a similar geometry to the multiplexer and signal delivery system described by Lecocq et al. (see above). In addition, WO 2022 / 120469 A1 points out that amplifiers (such as Josephson parametric amplifiers or traveling wave parametric amplifiers) can be used to reduce power consumption, but in this case, a strong pump signal needs to be delivered to the parametric amplifier.

[0019] A strong pump signal can be delivered to the parametric amplifier via an additional coaxial cable, along with a thermal load or a strong optical pump signal. Delivering a strong pump signal without excessive power consumption can be challenging. To obtain a microwave signal from a quantum processor, WO 2022 / 120469 Al uses a microwave to optical transducer and a multiplexer to generate a microwave signal outside the cryostat that is identical to the microwave signal input inside the cryostat.

[0020] An aspect of switching to optical fiber for delivering and acquiring microwave signals is low power consumption, which can be achieved by this method. This low power consumption must also be accompanied by low additive noise in the microwave signal delivered to the cryostat. WO 2022 / 120469 Al does not mention how to meet the requirements of low power consumption and low additive noise at the same time. A solution to these two challenges will significantly improve the optical cryogenic interface.

[0021] Another challenge known from WO 2022 / 120469 A1 is the detection of the optical signal returning from the cryostat. This document does not specify how phase and amplitude information can be derived from the optical signal returning from the cryostat. The phase and amplitude of the optical signal are elements obtained by reading out the state of the qubit. It should be noted that the cryogenic system is noisy and randomizes the phase information in the optical signal. How to reduce the additive phase noise of the cryogenic system to an acceptable level from the optical phase noise to fully reconstruct the qubit state remains an unsolved challenge.

[0022] There have been several demonstrations of cryogenic compatible electro-optic modulators. Eltes et al., "An integrated optical modulator operating at cryogenic temperatures" in Nat. Mater. 19, 1164-1168, 2020, (DOI: 10.1038 / s41563-020-0725-5), demonstrated electro-optical switching and modulation from room temperature to 4K by using the Pockels effect in an integrated barium titanate device.

[0023] Yousefi et al., “A cryogenic electro-optic interconnect for superconducting devices,” in Nat Electron 4, 326-332, 2021, DOI: 10.1038 / s41928-021-00570-4, demonstrated cryogenic electro-optical readout of superconducting electromechanical circuits using a commercially available titanium-doped lithium niobate modulator.

[0024] Pintus et al. demonstrated an integrated current-driven modulator based on the magneto-optic effect and can operate at temperatures as low as 4K in "An integrated magneto-optic modulator for cryogenic applications" in Nat Electron 5, 604-610, 2022 (DOI: 10.1038 / s41928-022-00823-w).

[0025] Gehl et al., “Operation of high-speed silicon photonic micro-disk modulators at cryogenic temperatures,” in Optica 4, 374-382, 2017, (DOI: 10.1364 / OPTICA.4.000374), demonstrated the operation of high-speed, CMOS-compatible silicon micro-disk modulators sending data at rates up to 10 Gb / s at temperatures as low as 4.8 K.

[0026] Lee et al., "High-performance integrated grapheme electro-optic modulator at cryogenic temperature" in Nanophotonics, vol. 10, no. 1, 2021, pp. 99-104. (DOI: 10.1015 / nanoph-2020-0363), demonstrated an integrated graphene-based electro-optic modulator with a bandwidth of 14.7 GHz at 4.9 K, exceeding the 12.6 GHz bandwidth at room temperature.

[0027] Chakraborty et al., “Cryogenic operation of silicon photonic modulators based on the DC Kerr effect” in Optica 7, 1385-1390 (2020), (DOI: 10.1364 / OPTICA.403178) shows modulation based on the DC Kerr effect at 5K and at GHz speeds in silicon photonic devices fabricated exclusively in CMOS-compatible processes. Summary of the invention

[0028] The document discloses a system for transmitting signals between the interior of a cryogenic system and an external environment. The system includes at least one light source (e.g., a laser) for generating an optical input signal and at least one optical fiber for transmitting a modulated optical signal to the interior of the cryogenic system and receiving an optical output signal from the interior of the cryogenic system. A plurality of detectors located in the external environment are used to detect the optical output signal and are connected to at least one optical fiber. In the cryogenic system, the system also includes a plurality of first transducers for converting the modulated optical signal into a microwave input signal; and a plurality of second transducers for converting the microwave output signal into an optical output signal. A first microwave impedance matching resonator is connected to the plurality of first transducers, and a second microwave impedance matching resonator is connected to the plurality of second transducers. The first microwave impedance matching resonator and the second microwave impedance matching resonator are, for example, superconducting microwave frequency resonators. High impedance input or high impedance output from the first transducer and the second transducer can result in higher conversion efficiency and lower power consumption. The first microwave impedance matching resonator and the second microwave impedance matching resonator allow low loss connection of the high impedance output from the first transducer and the high impedance input of the second transducer with channels having different impedances, such as 50 Ohm resistor lines, to enable signal delivery and acquisition from the cryogenic system.

[0029] In another aspect, the system includes a plurality of first multiplexers having first multiplexer inputs connected to a plurality of optical sources and first multiplexer outputs connected to one or more optical fibers. This enables the one or more optical fibers to carry multiple optical signals, thereby reducing the number of optical fibers.

[0030] Correspondingly, a plurality of first demultiplexers may be located inside the cryogenic system. The plurality of first demultiplexers have a first demultiplexer input connected to at least one optical fiber and a first demultiplexer output connected to the plurality of first transducers. The first demultiplexer may separate the optical signals carried on the optical fiber.

[0031] In another aspect, a plurality of second multiplexers are located inside the cryogenic system and have second multiplexer inputs connected to the plurality of second transducers and second multiplexer outputs connected to at least one optical fiber. Correspondingly, in the external environment, a plurality of second demultiplexers having second demultiplexer inputs are connected to at least one optical fiber, and second demultiplexer outputs are connected to a plurality of detectors.

[0032] In one aspect, the system further comprises an electro-optical converter configured to modulate the optical input signal. This enables information to be communicated into the cryogenic system. The electro-optical converter modulates at least one of the phase, amplitude or frequency of the optical input signal.

[0033] The first superconducting microwave impedance matching resonator and the second superconducting microwave resonator are configured to operate at a temperature below 20 K, and in one aspect, in the milliKelvin range.

[0034] The document also discloses a method for transmitting signals between an external environment and a cryogenic system. The method includes generating a plurality of optical input signals, multiplexing and transmitting the plurality of modulated optical signals to the interior of the cryogenic system through an optical fiber, converting the plurality of modulated optical signals into microwave input signals, and applying the microwave input signals to a set of first microwave impedance matching resonators. The quantum processor is coupled to the first microwave impedance matching resonator, which is capable of transmitting the microwave input signal to the quantum processor to control the state or drive the readout of a set of quantum bits from the quantum processor.

[0035] The method also includes causing the microwave input signal to interact with the quantum bit in the quantum processor, thereby forming a microwave output signal output from the quantum processor into a second microwave impedance matching resonator, and converting the microwave output signal into a plurality of optical output signals. The plurality of optical output signals are transmitted from the cryogenic system to an external environment along an optical fiber, and then the amplitude and phase of the plurality of optical output signals are detected. This enables the state of the quantum bit in the quantum processor to be determined.

[0036] The systems and methods of the present document can reduce active and passive heat dissipation in delivering and acquiring signals to and from a quantum processor. Using optical fibers to deliver and acquire optical signals can reduce heat dissipation compared to known RF lines, RF amplifier chains, and RF attenuation chains currently used to transmit signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A system for signal transmission between an interior of a cryogenic system and an exterior environment is shown.

[0038] Figure 2 The correction of the path length of the microwave output signal caused by the cryogenic system dephasing is shown.

[0039] Figure 3 A detailed system for signal transmission between the interior of the cryogenic system and the external environment and signal detection in the external environment is shown.

[0040] Figure 4 A method for transmitting signals between an external environment and a cryogenic system is shown. DETAILED DESCRIPTION

[0041] The present invention will now be described based on the accompanying drawings. It should be understood that the embodiments and aspects of the present invention described herein are merely examples and do not limit the scope of protection of the claims in any way. The present invention is defined by the claims and their equivalents. It should be understood that the features of one aspect or embodiment of the present invention may be combined with the features of different aspects or multiple aspects and / or embodiments of the present invention.

[0042] Figure 1 A system 1 for transmitting a signal from an input 10 between an interior of a cryogenic system 130 and an external environment 110 is shown.

[0043] The system 1 includes at least one laser source 20 configured to generate N optical tones 26 in an optical input signal 21. The laser source 20 includes, but is not limited to, an optical pump, a laser (e.g., N laser sources 20), a semiconductor laser. The N optical tones 26 can be generated from the N laser sources 20, or alternatively, can be generated by phase modulation and using L sidebands generated by reducing the number of P laser sources 20. The number P is equal to the difference between N and L.

[0044] At the output of the one or more laser sources 20, the N optical tones 26 are split into two paths using, for example, a first beam splitter BS1: an optical input signal 21 and an optical pump. A second beam splitter BS2 also splits the optical pump into a pump signal 22i and a reference optical signal 27. The reference optical signal 27 is used for readout and is passed to a second electro-optical modulator 35, as will be described later. Figure 3 The optical input signal 21 from the first beam splitter BS1 is transmitted to the optical input 31 of the first electro-optic modulator 30. The first electro-optic modulator 30 receives the input signal 23 (microwave signal) as input 10 at the electro-optic modulator microwave signal input 32, and modulates the optical input signal 21 using the electro-optic effect, which allows the input signal 23 to modulate the optical tone 26 of the optical input signal 21. The input signal 23 is generated by up-converting the lower frequency I input signal and Q output signal from the arbitrary waveform generator using a first microwave IQ mixer (not shown) using a microwave source 24 as a local oscillator.

[0045] The first electro-optic modulator 30 modulates at least one of the phase, amplitude or frequency of the optical input signal 21 to produce a modulated optical signal 28 at the electro-optic modulator output 33. In an alternative aspect, the first electro-optic modulator 30 is not used, and the optical input signal 21 is modulated at the output of the laser source 20.

[0046] The modulated optical signal 28 is coupled to a first multiplexer input 41 of a first multiplexer 40 where it is multiplexed into one or more optical fibers 120. The one or more optical fibers 120 are connected to a first multiplexer output 42. The first multiplexer 40 includes at least one first optical resonator 49 coupled to M fiber modes (e.g., N optical resonators corresponding to the N optical tones 26). The M fiber modes are waveguide modes or another spatial mode for light transmission. The M collection modes are guided into at least one optical fiber 120. For example, in one aspect of the invention, there will be M optical fibers 120.

[0047] It should be understood that the first multiplexer 40 is an optional element of the system 1 , and the modulated optical signal 28 may be coupled directly to the optical fiber 120 .

[0048] The laser source 20, the first electro-optic modulator 30 and the first multiplexer 40 are located in the external environment 110 and are typically maintained at room temperature.

[0049] Optical fiber 120 carries modulated optical signal 28 via M optical carriers into cryogenic system 130. Cryogenic system 130 is a system that operates at a temperature below 20 K, for example, and in one aspect, at milliKelvin temperatures.

[0050] The optical fiber 120 transmits the modulated optical signal 28 to a first demultiplexer input 51 of at least one first demultiplexer 50. The first demultiplexer 50 may be, but is not limited to, a prism, a diffraction grating, a spectral filter, an optical cavity such as a whispering gallery mode resonator, a Bragg grating, or a ring resonator. The first demultiplexer 50 separates the M fiber modes (or optical carriers) carrying the modulated optical signal 28 on the optical fiber 120 and passes the modulated optical signal 28 from the first demultiplexer output 52 to one or more of the first transducers 60.

[0051] It should be noted that the first demultiplexer 50 is an optional element of the system 1 and that the output of the optical fiber 120 may be connected directly to the first transducer 60 .

[0052] The first transducer 60 is an optical-to-electrical converter that performs an optical-to-electrical conversion operation to deliver an electrical input signal 62 (e.g., a microwave input signal 62) at a first transducer output 63 of the first transducer 60. The first transducer 60 converts the modulated optical signal 28 from the M optical fibers 120 into the electrical input signal 62, as will be explained later. The first transducer 60 is, for example, a photodiode (made of, for example, InGaAs, InAsSb), a photodetector, a photosensor or a phototransistor, a microwave-to-optical converter, an optical-piezoelectric device, an electro-optical-mechanical device, but this list is not intended to limit the present invention.

[0053] An output electrode at a first transducer output 63 of the first transducer 60 is coupled directly or via wire bonding to at least one first microwave impedance matching resonator 70. As will be explained later, the first microwave impedance matching resonator 70 is coupled to the device 140 by a waveguide.

[0054] In one aspect, device 140 is a superconducting quantum processor, quantum sensor, or quantum array.

[0055] The output of the quantum processor 140 is coupled by a waveguide to at least one second microwave impedance matching resonator 75. The second microwave impedance matching resonator 75 receives the microwave output signal 141 (which has interacted with the quantum state) from the quantum processor 140 at the microwave resonator frequency and outputs the microwave output signal 141 representing the readout quantum state of the quantum processor 140. The microwave output signal 141 ranges from about 3 GHz to 12 GHz, but this is not limiting of the present invention.

[0056] The first microwave impedance matching resonator 70 and the second microwave impedance matching resonator 75 may be implemented as superconducting microwave LC resonators.

[0057] The second microwave impedance matching resonator 75 is coupled to at least one second transducer 65. For example, the second transducer 65 is an electro-optical converter that performs an electro-optical conversion operation to deliver an optical output signal 68 at the output of the second transducer 65, the optical output signal representing the microwave output signal 141 received from the second microwave impedance matching resonator 75. In one aspect, the electro-optical effect is a Pockels effect, and in another non-limiting aspect, the conversion of the microwave output signal 141 to the optical output signal 68 uses a piezoelectric optomechanical effect.

[0058] The second transducer 65 is a device selected from the group consisting of an electro-optical device, a microwave to optical converter, an opto-mechanical device, an opto-piezoelectric device, an electro-optical mechanical device, an electro-optical converter via a piezoelectric opto-mechanical effect, and a magneto-optical device.

[0059] The second transducer 65 is optionally coupled to a second multiplexer input 56 of at least one of the plurality of second multiplexers 55. An optical output signal 68 is addressed to the second multiplexer input 56 of the second multiplexer 55, and the optical output signal 68 is multiplexed from the second multiplexer output 57 into at least one optical fiber 120. The second multiplexer 55 includes at least one third optical resonator 58 coupled to the M optical carriers. The M optical carriers are guided into the at least one optical fiber 120 (e.g., M optical fibers).

[0060] It should be understood that the second multiplexer 55 is an optional element of the system and that the optical output signal 68 may be coupled directly to the optical fiber 120 .

[0061] The same optical fiber 120 may be used to deliver optical signals to and read out optical signals from the cryogenic system 130. The bandwidth of the optical fiber 120 is sufficient to allow the modulated optical signal 28 and the optical output signal 68 to propagate through the optical fiber 120 simultaneously.

[0062] At cryogenic temperature, the first multiplexer 50 , the first transducer 60 , the first microwave impedance matching resonator 70 , the quantum processor 140 , the second microwave impedance matching resonator 75 , the second transducer 65 , and the second multiplexer 55 are located within the cryogenic system 130 .

[0063] The optical fiber 120 is coupled to the second demultiplexer 45 through the first demultiplexer input 46 located in the external environment 110. The second demultiplexer 45 can be, but is not limited to, a prism, a diffraction grating, a spectral filter, an optical resonator, a ring optical resonator. The second demultiplexer 45 separates the M optical carriers carrying the optical output signal 68 from the interior of the cryogenic system 130, and transmits the optical output signal 68 from the second demultiplexer output 47 to the detection circuit 100.

[0064] The detection circuit 100 includes at least one detector 90, which detects the optical output signal 68 from the second transducer 65. The detector 90 is, for example, an optical sensor, a photodiode, or a photodetector. Figure 2 and Figure 3 The detection circuit 100 is explained in detail in FIG.

[0065] Now we will describe the electro-optical conversion inside the first electro-optical modulator 30. This electro-optical conversion can be implemented by two methods: a modular method and an integrated method.

[0066] In a modular approach, the light source 20, the first electro-optic modulator 30 and the first multiplexer 40 are connected together via optical fibers.

[0067] In the integrated approach, all components (except the light source 20) are integrated on the same chip. Examples of configurations of the integrated approach involve nonlinear optical media such as, but not limited to, lithium niobate, barium borate, potassium dihydrogen phosphate, potassium titanyl phosphate integrated on a silicon-on-insulator (SOI) stack.

[0068] The light source 20 is coupled into a first waveguide (eg, a ridge waveguide) in the nonlinear layer. The first waveguide is coupled to a ring resonator waveguide (ie, a first optical resonator 49) patterned into the nonlinear layer.

[0069] Metal electrodes are patterned around the first optical resonator 49 so that an applied voltage changes the resonant frequency of the first optical resonator 49 and modulates the amplitude of the optical input signal 21. The first optical resonator 49 is coupled to a second waveguide, which is coupled to a plurality of ring resonators. The plurality of ring resonators are coupled to a third waveguide. In this way, the out-coupled light (i.e., the modulated optical signal 28) from the plurality of ring resonators is combined and multiplexed.

[0070] The third waveguide is coupled into an optical fiber 120 which enters a cryogenic system 130. The multiplexing is wavelength division multiplexing, but is not limited to the given example. It should be understood that mode division multiplexing, dense wavelength division multiplexing, frequency division multiplexing, time division multiplexing and optical time division multiplexing may also be used.

[0071] Converting the input signal 23 to a modulated optical signal 28 carried in the optical fiber 120 enables many modulated optical signals 28 to be transmitted simultaneously or sequentially through the same optical fiber 120. Transmission of the modulated optical signal 28 through the optical fiber 120 allows the system to be more compact, more space-efficient, and also reduces thermal loads.

[0072] The output of the optical fiber 120 is coupled to the first demultiplexer input 51 in the cryogenic system 130. The conversion of the optical signal to an electrical signal in the cryogenic system 130 will now be described. This optical-to-electrical conversion can be implemented in two ways: an integrated approach and an on-chip approach.

[0073] The integration method is a configuration including a silicon on insulator (SOI) substrate and a nonlinear (e.g., lithium niobate) top layer. The first optical waveguide and the second optical resonator 53 are patterned into the oxide layer (SiO2) of the silicon on insulator substrate. If necessary, the electrodes patterned around the lithium niobate layer on top of the SOI substrate can tune the second optical resonator 53 to match the frequency at room temperature.

[0074] A second optical waveguide for the second optical resonator 53 is coupled to a first transducer 60. The first transducer 60 may be an on-chip photodiode junction, a silicon, germanium or gallium arsenide based (e.g., InGaAs), or a piezoelectric based optomechanical transducer, but this is not limiting of the present invention. A first transducer output 63 of the first transducer 60 is coupled to an input of a first microwave impedance matching resonator 70, the output of which is coupled to a connector for delivering a microwave input signal 62 to the quantum processor 140. Further details of the first microwave impedance matching resonator 70 are described in the modular description below.

[0075] The modular on-chip approach is a configuration comprising three chips: a first SOI chip (multiplexing / demultiplexing chip) as described above, which is used to demultiplex the modulated optical signal 28. The modulated optical signal 28 is coupled out of the output optical ridge waveguide of the first demultiplexer 50 via a coupling element (not shown). The coupling element is, but is not limited to, a grating coupler, an edge coupler, or a photonic wire bond.

[0076] The modulated optical signal 28 is coupled to the second chip (transducer chip) of the first transducer 60 via a coupling element. The transducer chip of the first transducer 60 is bonded to a third chip (microwave resonator chip) having a first microwave impedance matching resonator 70, for example, by wire bonding, flip chip or bump bonding. The first microwave impedance matching resonator 70 has a first input impedance IM1 and a first output impedance IM2. The value of the first input impedance IM1 may be different from the first output impedance IM2.

[0077] The electrodes are patterned onto the first transducer 60 and connected to an optional resistor and an on-chip first microwave impedance matching resonator 70. In the case of a photodiode (first transducer 60), the value of the resistor can be greater than the value of the output impedance of the first microwave impedance matching resonator 70 to reduce the photocurrent and thus the power consumption.

[0078] The output of the first microwave impedance matching resonator 70 is wire bonded to a connector for delivering the microwave input signal 62 to the quantum processor 140. The connection may be a coaxial cable or a microwave connection with a higher inductance, but such a connection is not limiting of the present invention.

[0079] The matching of the first input impedance IM1 and the first output impedance IM2 of the first microwave impedance matching resonator 70 with the source impedance of the first transducer output 63 and the load impedance of the input of the quantum processor 140 can reduce power consumption. The first input impedance IM1 can be from 1Ohm to 10000000Ohm, and in a specific example, can be from 10Ohm to 10000000Ohm. In a non-limiting example, the first output impedance IM2 can be from 10Ohm to 1kOhm, and the first output impedance IM2 can be from 10Ohm to 377Ohm. In one aspect, the first output impedance IM2 is 50Ohm, but this does not limit the present invention.

[0080] In one aspect, a flexible system is created that can be matched to the input impedance of the quantum processor 140. It will be appreciated that the high impedance of the first transducer output 63 or other opto-electrical converter will minimize power consumption. This mismatch between the first transducer output 63 and the input of the quantum processor 140 can be bridged by the first microwave impedance matching resonator 70.

[0081] Using a higher load resistance at the first transducer output 63 increases the voltage for the same photocurrent produced with the same optical power. Therefore, for a larger load resistance, the microwave to optical conversion efficiency is higher and the power consumption is reduced when delivering the microwave input signal 62. However, coupling the higher load resistance directly to the 50Ohm line will cause reflections and reduce power delivery, but the 50Ohm line facilitates modular connections within the cryogenic system 130.

[0082] The use of the first microwave impedance matching resonator 70 enables the use of a higher resistance at the first transducer 60 and a lower impedance connection channel to the microwave output at, for example, the quantum processor 140 .

[0083] When the modulated optical signal 28 is coupled to the first transducer 60, the first transducer 60 outputs a shot noise current. The shot noise current is typically "white" or spectrally flat, up to the bandwidth limit of the first transducer 60. Shot noise is not a limiting aspect of the present invention, and other implementations of the first transducer 60 may output other noise currents in addition to the shot noise current, such as due to thermal noise in the transducer.

[0084] One feature of the first impedance matching resonator 70 is that the first impedance matching resonator 70 transmits one frequency range and reflects or dissipates another frequency range. Thus, the first impedance matching resonator 70 can filter out frequencies from the transmitted signal (eg, the microwave input signal 62).

[0085] By matching the frequency of the first microwave impedance matching resonator 70 to the frequency of the microwave input signal 62, the bandwidth of the additive noise from the bandwidth of the first transducer 60 can be reduced. By reducing the bandwidth of the additive noise from the first transducer 60 to the bandwidth of the first microwave impedance matching resonator 70, the total additive shot noise from the first transducer 60 can also be reduced.

[0086] It will be appreciated that for the same amount of output voltage, a higher resistance of the first transducer output 63 will produce a lower photocurrent. Therefore, the ratio between the shot noise current and the signal current will be greater. A larger ratio increases the ratio of shot noise to microwave output power. The configuration of the first microwave impedance matching resonator 70 allows tuning to an optimal midpoint between low power consumption and high signal-to-noise ratio of the output signal (e.g., microwave input signal 62). The optimal value of the first input impedance IM1 of the first microwave impedance matching resonator 70 will depend on the power consumption and noise requirements of a particular application.

[0087] One embodiment will be described below. The output electrode of the first transducer 60 is coupled to the first microwave impedance matching resonator 70 directly or via wire bonding. The first microwave impedance matching resonator 70 can be, for example, a superconducting helical nanowire, a meander, or a ring nanowire. The first microwave impedance matching resonator 70 can also be frequency tuned via an applied magnetic field by patterning holes of the helical or ring nanowire within the wire path.

[0088] The first microwave impedance matching resonator 70 is connected to an external connector. The external connector can then be attached to a variable length microwave cable to conveniently deliver the electrical input signal 62 in the form of microwaves to different components of the quantum processor 140.

[0089] According to a fourth example of method implementation, a 500Ohm resistor is placed at the first transducer output 63. The 500Ohm resistor is coupled to the first microwave impedance matching resonator 70. The first microwave impedance matching resonator 70 is capacitively, inductively or galvanically coupled to the first transducer subcircuit and also coupled to the 50Ohm resistor line.

[0090] If the first microwave impedance matching resonator 70 comprises a superconducting material, the loss in the first microwave impedance matching resonator 70 can be made very small, and therefore the quality factor can be very large. Since the impedance at the first transducer output 63 is large, the voltage generated is 10 times the voltage generated in the case of a 50 Ohm resistor without using an impedance matching resonator.

[0091] In this case, the increase in voltage corresponds to a reduction by a factor of 3.2 in the optical power required to drive the microwave input signal 62. Another advantage of this embodiment is that the bandwidth of the shot noise output from the first microwave impedance matching resonator 70 is reduced compared to the case of a 50 Ohm resonator.

[0092] The bandwidth of the first transducer 60 may be, for example, between 300 MHz and 40 GHz. For example, the reduced noise bandwidth output may be between 3 MHz and 1 GHz, with a resonator quality factor of 100. Reduced shot noise levels and bandwidth will result in higher fidelity qubit control.

[0093] According to a fifth example of implementation of the method, a 50 kOhm resistor is placed at the first transducer output 63. The 50 kOhm resistor is coupled to the first microwave impedance matching resonator 70. The output of the first microwave impedance matching resonator 70 is connected to a microwave cable having an impedance of 50 Ohm.

[0094] Due to the large impedance at the first transducer output 63, the voltage generated is 1000 times larger than the case with a 50 Ohm resistor and no impedance resonator. This difference corresponds to a reduction of the optical power required to drive the microwave input signal 62 by a factor of 32. Another advantage of the 50 kOhm resistor is that the bandwidth of the shot noise output from the first microwave impedance matching resonator 70 is reduced compared to the case with a 50 Ohm resistor.

[0095] The bandwidth of the first transducer 60 may be, for example, between 300 MHz and 40 GHz. For example, the reduced noise bandwidth output may be between 9 MHz and 3 GHz, with a resonator quality factor of 32.

[0096] By using multiple multiplexing lines in parallel, a greater number of electrical input signals 62 may be delivered to the cryogenic system 130 .

[0097] According to a sixth example of the method implementation, a 1 Ohm resistor is placed at the first transducer output 63. The 1 Ohm resistor is coupled to the first microwave impedance matching resonator 70. The output of the first impedance matching resonator 70 is coupled to a microwave cable having an impedance of 50 Ohm. Due to the smaller resistance at the first transducer output 63, the current for a given voltage is 50 times greater than when a 50 Ohm resistor is used and no impedance resonator is used.

[0098] Therefore, the shot noise current at the input of the first microwave impedance matching resonator 70 is about 2.7 times larger than the case of the 50Ohm resistor. However, due to the reduced resistance, the shot noise power is about seven times smaller than the case of the 50Ohm resistor. Another advantage of this embodiment is that the shot noise bandwidth output from the microwave impedance matching resonator 70 is reduced compared to the case of the 50Ohm resistor.

[0099] The bandwidth of the first transducer 60 may be, for example, between 300 MHz and 40 GHz, with a resonator quality factor of 7. The reduced noise bandwidth output may be, for example, between 43 MHz and 15 GHz. The reduced shot noise level and bandwidth will result in high fidelity qubit control gate errors.

[0100] The acquisition of the amplitude and phase of the microwave signal from the N microwave channels within the cryogenic system 130 will now be described. The use of the second transducer 65 in conjunction with the optical fiber 120 eliminates the need for a traveling wave parametric amplifier or a high electron mobility transistor on a substrate or at higher temperatures within the cryogenic system 130. The use of one or more optical fibers 120 also eliminates the need for multiple RF cables, auxiliary amplifier cables, and multiple microwave filters to filter out room temperature noise.

[0101] One of the applications of the microwave output signal 141 from the cryogenic system 130 is for qubit readout, but this is not a limiting aspect of the invention and the signal readout may also be used for spectral characterization or as a local power meter.

[0102] Acquisition of cryogenic microwave output via optical fiber 120 includes three stages: using a reference signal to convert N microwave output signals 141 into N optical output signals 68 in M ​​optical fibers 120, sending the M optical fibers 120 out of the cryogenic system 130, and outputting the amplitude and phase of the N optical output signals 68 via a reference local oscillator.

[0103] In the cryogenic system 130 , the N microwave output signals 141 are routed to the N second microwave impedance matching resonators 75 . The N second microwave impedance matching resonators 75 match the impedance of the second transducer 65 with the impedance of the input line of the second microwave impedance matching resonator 75 .

[0104] The N second transducers 65 convert the N microwave output signals 141 into N optical output signals 68 imprinted as a modulation of the N optical tones 26. The N optical input signals 68 are routed to the N third optical resonators 58, which are coupled to the M output optical fibers 120.

[0105] No or very few RF lines, RF amplifiers, or RF attenuators are required to connect the cryogenic system 130 to the external environment 110. It should be understood that there will be many RF lines within the cryogenic system 130.

[0106] In one aspect, the second transducer 65 is an acousto-optic actuator and is made of a piezoelectric material on a SOI material stack. The piezoelectric material on the SOI stack can be, but is not limited to, lithium niobate, aluminum nitride, barium titanate. The microwave input of the second transducer 65 is coupled to N second microwave impedance matching resonators 75, which can have internal steps for magnetic field tuning. The N second microwave impedance matching resonators 75 can match the low output impedance of the source (from the qubit readout resonator and the 50Ohm waveguide) to the higher input impedance of the second transducer 65.

[0107] A higher input impedance of the second transducer 65 may be required, which may be 5 kOhm, for example, in order to impedance match the acoustic resonance or optical resonance of the second transducer 65. Such a high input impedance may allow a large transduction bandwidth and a high transduction efficiency.

[0108] The second input impedance IM3 may be from 10 to 1 kOhm. The second output impedance IM4 may be from 1 Ohm to 10000000 Ohm. In one aspect, the second input impedance IM3 is 50 Ohm, but this does not limit the present invention.

[0109] The second transducer 65 transforms the microwave output signal 141 into an acoustic signal. The acoustic signal is coupled to the second transducer optical cavity 69 (i.e., an optomechanical cavity), which transforms the acoustic signal into an optical output signal 68 as long as the optical pump signal 22i is input into the second transducer optical cavity 69 at a frequency different from the resonant frequency of the optical cavity. The second transducer optical cavity 69 is manufactured, for example, on a suspended silicon layer. The pump signal 22i comes from the pump laser source 20, via the second multiplexer 45 in the external environment 110 and the second multiplexer 55 in the cryostat 130. In a non-limiting example, the optical tone 26 can be used as the pump signal 22i and can be delivered to the second multiplexer 55 in the cryostat 130 via the first multiplexer 40 in the external environment 110.

[0110] The optomechanical cavity is either directly coupled to the M on-chip silicon waveguides or coupled to the N third optical resonators 58 (e.g., optical ring resonators). The N third optical resonators 58 are coupled to the M on-chip silicon waveguides. The M on-chip silicon waveguides are then coupled to the M optical fibers 120, which are led out of the cryogenic system 130 to the external environment 110.

[0111] One of the challenges of converting microwave signals to optical signals and back again is phase stability. Due to the short wavelength of the optical output signal 68, fluctuations in the length of the optical fiber driven by the cryogenic system 130 will shift the phase of the carried microwave output signal 141. Therefore, the phase accumulated in the optical fiber 120 must be passively stabilized or actively tracked.

[0112] Figure 2 and Figure 3 The correction of the path length of the optical output signal 68 caused by fluctuations of the cryogenic system 130 is shown.

[0113] The laser source 20 generates a laser pump signal 22i, which is transmitted to the cryogenic system 130 and incident on the electro-optical converter (i.e., the second transducer 65 having the second transducer optical cavity 69) in the cryogenic system 130 to read out the phase and amplitude of the microwave output signal 141. The laser pump signal 22i can be derived from the laser source 20 or generated separately.

[0114] The second transducer 65 outputs a portion 22r of the pump signal 22i (return pump signal) and an optically converted signal (optical output signal 68) which is detuned from the pump frequency by the frequency of the microwave output signal 141.

[0115] The return pump signal 22r can be obtained by collecting the reflected signal or the transmitted signal from the second transducer optical cavity 69 in the second transducer 65. The amplitude of the microwave output signal 141 is added to the amplitude of the optical output signal 68 (optical conversion signal), and the phase of the microwave output signal 141 is added to the phase difference between the return pump signal 22r and the converted optical output signal 68.

[0116] The optical output signal 68 and the return pump signal 22r are transmitted from the cryogenic system 130 to the N fourth optical resonators 48 of the second multiplexer 45 in the external environment 110 at room temperature by the M optical fibers 120. The optical resonance frequency matches the optical resonance frequency of the third optical resonator 58 in the cryogenic system 130. The second multiplexer 45 outputs the optical output signal 68.

[0117] Since the returning pump signal 22r and the optical output signal 68 travel along the same optical path, any differences in optical path lengths are cancelled.

[0118] The returned pump signal 22r and the optical output signal 68 interfere with the reference optical signal 27 at the first beam splitter BS3. The reference optical signal 27 follows another reference path 115 in the external environment 110.

[0119] The first branch of the second beam splitter BS2 generates a pump signal 22i which can be pulse modulated or frequency shifted using an acousto-optic modulator (AOM). The AOM is configured to achieve maximum extinction by collecting an optical output signal that is frequency shifted by a given drive frequency. The drive frequency is in the range of 1 MHz to 1 GHz, but this is not a limiting aspect of the invention. The second branch of the second beam splitter BS2 (i.e., reference path 115) carries a reference optical signal 27 which is directed to a second electro-optic modulator 35 (e.g., Figure 3 ). The second electro-optic modulator 35 is connected to the microwave source 24. The second electro-optic modulator 35 modulates the amplitude and frequency of the reference optical signal 27 at the microwave frequency.

[0120] The reference optical signal 27 has a known frequency and a known amplitude and is used to extract the amplitude and phase of the optical output signal 68 by comparing the phase of the optical output signal 68 with the reference optical signal 27 in the detection circuit 100. The amplitude and phase of the returned pump signal 22r are also measured in the same way.

[0121] The detector 90 generates two balanced electrical signals 95 having different frequencies corresponding to the frequency of the optical output signal 68 and the frequency of the returned pump signal 22r. The two balanced electrical signals 95 are derived from the optical output signal 68. The frequency of the balanced electrical signal 95 is different from the frequency of the microwave output signal 141. This frequency shift between the balanced electrical signal 95 and the optical output signal 68 may be caused by the frequency shift sent by the AOM on the pump signal 22i.

[0122] Using the detection circuit 100 , the amplitude of the optical output signal 68 and the phase difference between the two balanced electrical signals 95 can be measured.

[0123] In this way, the detection circuit 100 reads out the amplitude and phase quadrature of the microwave output signal 141 without significant phase noise. Then, the amplitude and phase quadrature of the microwave output signal 141 can be output in the external environment 110 at room temperature. Two detection methods can be used to detect the reference optical signal 27 and the optical output signal 68.

[0124] In the first method, the second electro-optic modulator 35 modulates the reference optical signal 27 with the drive signal from the microwave source 24. The microwave source 24 can be the same microwave source 24 used to generate the input signal 23, but this does not limit the present invention. By modulating the reference optical signal 27, the second electro-optic modulator 35 adds one or more sidebands at different optical frequencies. The one or more sidebands added to the reference optical signal 27 are separated in frequency from the original reference optical signal 27 by the drive frequency.

[0125] The driving frequency of the driving signal may be, for example, between 300 MHz and 100 GHz. The reference optical signal 27 interferes with the optical output signal 68 on the third beam splitter BS3 and is detected by a detector 90. At the detector 90, at least two balanced electrical signals 95 may be generated.

[0126] The frequency of the first balanced electrical signal 95a is equal to the frequency difference between the returned pump signal 22r and the reference optical signal 27. Therefore, the frequency of the first balanced electrical signal 95a is equal to the driving frequency of the AOM, typically a radio frequency, for example in the frequency range between 1 MHz and 1 GHz.

[0127] The frequency of the second balanced electrical signal 95b is lower than the frequency of the microwave output signal 141. The frequency of the second balanced electrical signal 95b is equal to the frequency difference between the generated sideband added to the reference optical signal 27 and the optical output signal 68. The lower frequency of the second balanced electrical signal 95b may be a radio frequency in the range of, for example, between 1 MHz and 1 GHz.

[0128] Other balanced electrical signals 95 of different frequencies may also be generated. The different frequencies of the other balanced electrical signals 95 may be caused by the combination of different laser frequencies. However, the other different frequencies can be filtered out by spectral filtering. For example, spectral filtering can be performed by selecting a detector 90 with a bandwidth less than the drive frequency of the microwave source 24 and less than the bandwidth of the microwave output signal 141.

[0129] The detection circuit 100 measures the phase difference between the two balanced electrical signals 95 and the amplitudes of the two balanced electrical signals 95. Because the frequency of the balanced electrical signals 95 is lower than the frequency of the original microwave output signal 141, the two balanced electrical signals 95 are more easily detected.

[0130] Because the balanced electrical signal 95 has the frequency bandwidth of the analog-to-digital converter 105, it is easier to detect the frequency of the balanced electrical signal 95. In addition, typical microwave detection of the balanced electrical signal 95 involves down-converting the microwave circuit frequency to a lower frequency before electrical detection with, for example, the analog-to-digital converter 105. In this aspect of the invention, the lower frequency is generated in the optical domain before the detector 90. Because the frequencies of both signals 95 are lower, a lower bandwidth detector 90 can be used, which may be more efficient and less noisy. In addition, the use of a lower frequency and the absence of a mixer in the detection circuit 100 can reduce the noise of the detection circuit 100.

[0131] In the second method, the second electro-optic modulator 35 does not exist in the system, or the second electro-optic modulator 35 does not modulate the reference optical signal 27. The reference optical signal 27 interferes with the optical output signal 68 on the third beam splitter BS3 and is detected by the detector 90.

[0132] Thus, at least two balanced electrical signals 95a and 95b can be generated. The frequency of the first balanced electrical signal 95a is equal to the frequency difference between the returned pump signal 22r and the reference optical signal 27. The frequency of the first balanced electrical signal 95a is equal to the driving frequency of the AOM, which is typically a radio frequency, for example in the frequency range between 1 MHz and 1 GHz.

[0133] The second balanced electrical signal 95b has a higher frequency than the first balanced electrical signal 95a. The frequency of the second balanced electrical signal 95b is equal to the frequency difference between the reference optical signal 27 and the optical output signal 68.

[0134] The first balanced electrical signal 95a and the second balanced electrical signal 95b can be separated by a duplexer 92, and the high frequency component can be down-converted to a low frequency by mixing with a local oscillator (not shown). The local oscillator can be derived from the same microwave source 24 used to generate the input signal 23, but this does not limit the present invention.

[0135] This lower frequency may be a radio frequency, for example in the range between 1 MHz and 1 GHz. Because the frequencies of the two balanced electrical signals 95a and 95b are lower than the frequency bandwidth of the analog-to-digital converter 105, the frequencies of the two balanced electrical signals 95a and 95b may be more easily detected.

[0136] An example of how the room temperature stage is achieved is Figure 3 As shown, M second demultiplexers 45 are used, which are frequency matched to the N third optical resonators 58 in the cryogenic system 130. The M second demultiplexers 45 are configured to separate the N optical output signals 68 from the optical fiber 120 into N output optical fibers (not shown) connected to the second demultiplexer output 47.

[0137] Each of the N output fibers has an optical output signal 68 and a returned pump signal 22r separated by the microwave output signal frequency 141. The optical output signal 68 and the returned pump signal 22r interfere with the reference optical signal 27 at the first beam splitter BS3. The optical output signal 68 and the returned pump signal 22r are measured at at least one detector 90 (e.g., two detectors in a balanced heterodyne configuration using the reference optical signal 27 as a local oscillator).

[0138] The measured signals from the two detectors 90 are subtracted at a differential circuit element 91. The two signals forming the balanced electrical signal 95 comprise the optical output signal 68 separated by the duplexer 92 and the pump return signal 22r.

[0139] The second balanced electrical signal 95b derived from the electrical output signal 68 is mixed with a microwave local oscillator reference (not shown in the figure) and then mixed with the first balanced electrical signal 95a derived from the pump return reference optical signal 27 on the IQ mixer 101 to produce one or two output signals 102 carrying phase and amplitude information of the microwave output pulse 141.

[0140] The output signal 102 can be measured directly, or used to reconstruct the microwave output pulse 141 from the quantum processor 140 at room temperature using a second microwave IQ mixer (not shown). The output signal 102 is coupled to an analog-to-digital converter 105. The analog-to-digital converter (ADC) 105 is configured to convert the output signal 102 into a digital signal.

[0141] Figure 4 A flow chart of a method for transmitting signals between the external environment 110 and the cryogenic system 130 is shown.

[0142] In step S301, a plurality of optical input signals 21 are generated, for example, by a laser source 20. The plurality of optical output signals 21 are passed to a first electro-optical modulator 30 and modulated in step S302. As described above, the optical input signals 21 may alternatively be modulated directly within the laser source 20. The first electro-optical modulator 30 outputs a modulated optical signal 28.

[0143] In step S303 , the modulated optical signal 28 is transmitted to the inside of the cryogenic system 130 . The modulated optical signal 28 may be multiplexed by the first multiplexer 40 , and may be transmitted to the cryogenic system 130 through the optical fiber 120 .

[0144] In step S304, the modulated optical signal 28 is converted into a microwave input signal 62. The modulated optical signal 28 may be received by the first demultiplexer 50 to separate the modulated optical signal 28 into different lines. The modulated optical signal 28 may be directed to the first transducer 60.

[0145] In step S305 , the microwave input signal 62 is applied to the first impedance matching microwave resonator 70 .

[0146] In step S306 , the quantum processor 140 having the quantum bits is coupled to the first microwave impedance matching resonator 70 , and the microwave input signal 62 is transmitted to the quantum processor 140 .

[0147] In step S307 , the microwave output signal 141 is output from the quantum processor 140 to the second microwave impedance matching resonator 75 .

[0148] In step S308 , the microwave output signal 141 is converted into a plurality of optical output signals 68 . For example, the microwave output signal 141 is converted by the second transducer 65 .

[0149] In step S309, the optical output signal 68 is transmitted from the cryogenic system 130 to the external environment 110. The optical output signal 68 may be multiplexed on the second multiplexer 55 and directed to the optical fiber 120.

[0150] In step S310, the phase and amplitude of the optical output signal 68 are detected by the detector 90. The detection of the phase and amplitude can be accomplished by generating two signals: one derived from the return pump signal 22r and the other derived from the optical output signal 68. Neither of the generated signals has the frequency of the microwave output signal 141, but the phase of the optical output signal 68 can be reconstructed from the phase difference between the two generated signals. The optical output signal 68 is coupled from the optical fiber 120 to the second multiplexer 45.

[0151] Reference numerals

[0152] 1-System

[0153] 10- Input

[0154] 20-Laser source

[0155] 21-Optical input signal

[0156] 22i-Pump signal

[0157] 22r - Return pump signal

[0158] 23-Input signal

[0159] 24-Microwave source

[0160] 26-Optical Tint

[0161] 27-Reference optical signal

[0162] 28- Modulated optical signal

[0163] 30-First electro-optic modulator

[0164] 31-Electro-optic modulator optical input

[0165] 32-Electro-optic modulator microwave signal input

[0166] 33-Electro-optic modulator output

[0167] 35-Second electro-optic modulator

[0168] 40-First Multiplexer

[0169] 41-1st multiplexer input

[0170] 42-1st multiplexer output

[0171] 45-Second Demultiplexer

[0172] 46-2nd Demultiplexer Input

[0173] 47- Second Demultiplexer Output

[0174] 48-Fourth optical resonator

[0175] 49-First optical resonator

[0176] 50-First Demultiplexer

[0177] 51-1st demultiplexer input

[0178] 52-1st demultiplexer output

[0179] 53-Second optical resonator

[0180] 55-Second multiplexer

[0181] 56- Second multiplexer input

[0182] 57- Second multiplexer output

[0183] 58-Third optical resonator

[0184] 60-First transducer

[0185] 62-Microwave input signal

[0186] 63-First transducer output

[0187] 65-Second transducer

[0188] 68-Optical output signal

[0189] 69-Second transducer optical cavity

[0190] 70-First microwave impedance matching resonator

[0191] 75-Second microwave impedance matching resonator

[0192] 76-Electrical output signal

[0193] 90-Detector

[0194] 91-Differential Circuit Elements

[0195] 92-Duplexer

[0196] 95-Balanced electrical signal

[0197] 95a-first balanced electrical signal

[0198] 95b-second balanced electrical signal

[0199] 100-Detection circuit

[0200] 101-IQ Mixer

[0201] 102-Output signal

[0202] 105-Analog-to-Digital Converter

[0203] 110-External Environment

[0204] 115-Reference Path

[0205] 120-Fiber

[0206] 130-Low Temperature System

[0207] 140-Quantum Processor

[0208] 141-Microwave output signal

[0209] IM1 - first input impedance

[0210] IM2-1st output impedance

[0211] IM3 - Second input impedance

[0212] IM4 - Second output impedance

[0213] BS1-First beam splitter

[0214] BS2 - Second beam splitter

[0215] BS3 - Third beam splitter

[0216] AOM - Acousto-Optic Modulator

Claims

1. A system for transmitting signals between an interior of a cryogenic system (130) and an external environment (110), comprising: at least one light source (20) for generating an optical input signal (21); at least one optical fiber (120) for transmitting a modulated optical signal (28) to an interior of the cryogenic system (130) and receiving an optical output signal (68) from an interior of the cryogenic system (30); a plurality of detectors (90) for detecting the optical output signal (68) and connected to the at least one optical fiber (120); a plurality of first transducers (60) for converting the modulated optical signal (28) into a microwave input signal (62); a plurality of second transducers (65) for converting the microwave output signal (141) into the optical output signal (68); a first microwave impedance matching resonator (70) connected to the plurality of first transducers; and A second microwave impedance matching resonator (75) is connected to the plurality of second transducers (65).

2. The system according to claim 1, further comprising a plurality of first multiplexers (40) having first multiplexer inputs (41) connected to the plurality of light sources (20) and first multiplexer outputs (42) connected to the at least one optical fiber (120).

3. The system according to claim 1 or 2 also includes a plurality of first demultiplexers (50) located inside the cryogenic system (130), which have a first demultiplexer input (51) connected to the at least one optical fiber (120) and a first demultiplexer output (52) connected to the plurality of first transducers (60).

4. The system according to any of the above claims, further comprising a plurality of second multiplexers (55) located inside the cryogenic system (130), having second multiplexer inputs (56) connected to the plurality of second transducers (65) and second multiplexer outputs (57) connected to the at least one optical fiber (120).

5. The system according to any of the above claims further comprises a plurality of second demultiplexers (45) having a first demultiplexer input (46) connected to the at least one optical fiber (120) and a second demultiplexer output (47) connected to the plurality of detectors (90).

6. The system of claim 1, further comprising a first electro-optic modulator (30) configured to modulate the optical input signal (21).

7. The system of claim 6, wherein the first electro-optic modulator (30) modulates at least one of the phase, amplitude or frequency of the optical input signal (21).

8. The system of claim 1, wherein the first microwave impedance matching resonator (70) and the second microwave impedance matching resonator (75) are configured to operate at a temperature below 20K.

9. The system of claim 1, wherein the optical-to-electrical conversion and the electrical-to-optical conversion of the signal are located in the cryogenic system (130).

10. A system according to any one of the preceding claims, wherein: The first input impedance (IM1) of the first microwave impedance matching resonator (70) ranges from about 1 to 1,000,000 Ohm.

11. The system according to any of the preceding claims, wherein a first output impedance (IM2) of the first microwave impedance matching resonator (70) is in the range of about 1 to 1 kOhm.

12. The system according to any of the preceding claims, wherein the second input impedance (IM3) of the second microwave impedance matching resonator (75) ranges from about 1 to 377 Ohm.

13. The system according to any of the preceding claims, wherein the second output impedance (IM4) of the second microwave impedance matching resonator (75) is in the range of about 10 to 1000000 Ohm.

14. The system according to any of the preceding claims, wherein the light source (20) is a laser.

15. The system according to any one of the preceding claims, wherein one of the first microwave impedance matching resonator (70) and the second microwave impedance matching resonator (75) is implemented as a superconducting microwave LC resonator.

16. A system according to any of the preceding claims, wherein the amplitude and / or phase of the cryogenic microwave output signal (141) is measured by detecting the returned pump signal (22r) and the optical output signal (68) on one or more detectors (90).

17. A method for transmitting a signal between an external environment (110) and a cryogenic system (130), comprising: generating a plurality of optical input signals (21); transmitting the plurality of modulated optical signals (28) to the interior of the cryogenic system (130) by at least one optical fiber (120); converting the plurality of modulated optical signals (28) into microwave input signals (62); applying the microwave input signal (62) to a first microwave impedance matching resonator (70); coupling a device (140) to the first microwave impedance matching resonator (70) and transmitting the microwave input signal (62) to the device (140); Outputting a microwave output signal (141) from the device (140) into a second microwave impedance matching resonator (75); converting the microwave output signal (141) into the plurality of optical output signals (68) preserving phase and amplitude information; transmitting the plurality of optical output signals (68) from the cryogenic system (130) to the external environment (110) by the at least one optical fiber (120); The amplitude and phase of the plurality of optical output signals (68) are detected.

18. The method of claim 17, wherein the device (140) is at least one of a quantum processor, a quantum sensor, or a quantum array.

19. The method according to claim 17, wherein: Transmitting a microwave input signal (62) to the quantum processor (140) and detecting the amplitude and phase of the optical output signal (68) are used to determine the state of a quantum bit in the quantum processor (14).

Images