Superconducting devices operate at speeds where coaxial copper cables can be a limiting factor. Coaxial cables can limit frequency response and impose significant thermal loading on a cyrogenic system. The high bandwidth of optical fibers and their low thermal conductivity make them good candidates for providing data into and out of superconducting circuits. In this paper, we present the results of our experience in operating photodetectors and laser diodes together with superconducting circuits in the same low temperature (4.2 K) environment. Using these photodetectors, we demonstrate the input of optical signals to an analog superconducting circuit at 6 GHz. Output from a superconducting circuit operating at 500 MHz is fed into a laser diode, and optically coupled to room temperature electronics. By combining these two techniques, we demonstrate a fully operational superconducting shift register with both input and output signals supplied by optical fiber.
Abstract Encoding information onto optical fields using electro-optical modulation is the backbone of modern telecommunication networks, offering vast bandwidth and low-loss transport via optical fibers. For these reasons, optical fibers are also replacing electrical cables for short range communications within data centers. Compared to electrical coaxial cables, optical fibers also introduce two orders of magnitude smaller heat load from room to milli-Kelvin temperatures, making optical interconnects based on electro-optical modulation an attractive candidate for interfacing superconducting quantum circuits and hybrid superconducting devices. Yet, little is known about optical modulation at cryogenic temperatures. Here we demonstrate a proof-of-principle cryogenic electro-optical interconnect, showing that currently employed Ti-doped lithium niobate phase modulators are compatible with operation down to 800mK ---below the typical operation temperature of conventional microwave amplifiers based on high electron mobility transistors (HEMTs)---and maintain their room temperature Pockels coefficient. We utilize cryogenic electro-optical modulation to perform spectroscopy of a superconducting circuit optomechanical system, measuring optomechanically induced transparency (OMIT). In addition, we encode thermomechanical sidebands from the microwave domain onto an optical signal processed at room temperature. Although the currently achieved noise figure is significantly higher than that of a typical HEMT, substantial noise reduction should be attainable by harnessing recent advances in integrated modulators, by increasing the modulator length, or by using materials with a higher electro-optic coefficient, leading to noise levels on par with HEMTs. Our work highlights the potential of electro-optical modulators for massively parallel readout for emerging quantum computing or cryogenic classical computing platforms.
The feasibility of optical data transmission to and from Josephson junction circuits, using metal-semiconductor-metal (MSM) photodiodes and GaAs/AlGaAs semiconductor laser diodes with sub-mA threshold current, is demonstrated. Standard devices can be used with the exception of a cooled GaAs detector. It is shown that silicon MSM detectors compatible with Josephson junction circuits can be fabricated. While these detectors show large photoconductive effects at room temperature they behave as good-quality photodiodes at low temperatures. Power dissipation in the laser diode scales with temperature while maintaining the modulation frequency. It is also shown that the combination of a laser diode and a photodiode provides the voltage gain needed to interface Josephson-junction circuits with room-temperature electronics. Experimental results on MSM detectors and laser diodes are presented. Expected power dissipation is below 1 mW per input/output (I/O) at a data rate of 1 Gb/s.>
Scalable, high speed data transfer between cryogenic (0.1-4 K) and room temperature environments is instrumental in a broad range of fields including quantum computing, superconducting electronics, single photon imaging and space-based communications. A promising approach to overcome the limitations of conventional wire-based readout is the use of optical fiber communication. Optical fiber presents a 100-1,000x lower heat load than conventional electrical wiring, relaxing the requirements for thermal anchoring, and is also immune to electromagnetic interference, which allows routing of sensitive signals with improved robustness to noise and crosstalk. Most importantly, optical fibers allow for very high bandwidth densities (in the Tbps/mm
2 range) by carrying multiple signals through the same physical fiber (Wavelength Division Multiplexing, WDM). Here, we demonstrate for the first time optical readout of a superconducting nanowire single-photon detector (SNSPD) directly coupled to a CMOS photonic modulator, without the need for an interfacing device. By operating the modulator in the forward bias regime at a temperature of 3.6 K, we achieve very high modulation efficiency (1000-10,000 pm/V) and a low input impedance of 500
Ω with a low power dissipation of 40
μW. This allows us to obtain optical modulation with the low, millivolt-level signal generated by the SNSPD. Optical communication is becoming the preferred I/O solution in modern, room temperature high performance systems, and this work demonstrates its suitability for scalable cryogenic readout, which could help achieve the full potential of superconducting technologies.
Superconducting nanowire single-photon detectors have become indispensable for experiments in quantum optics and photonic quantum information processing. Nevertheless, these detectors require temperatures below 4 K to operate. These devices typically require coaxial cables as electrical connections for biasing and readout. Replacing these electrical connections with optical fibers both isolates the SNSPD from noise in room-temperature control electronics and simultaneously achieves a connection with a low thermal load. Nevertheless, the optoelectronic interfaces required for this purpose must be fully compatible with the cryogenic operating conditions of the detector. Recently, optical readout of an SNSPD using an electro-optic modulator at cryogenic temperatures has been demonstrated [1]–[3]. In addition, we have shown an opto-electronic bias of an SNSPD by generating the bias current using a photodiode co-located on the cold stage of the cryostat [4]. Both methods replace elements of electrical connection for the SNSPD in the cryostat by an optical fiber. Here, we show the combination of the opto-electronic bias and optical read readout in a single device, which enables us to operate an SNSPD fully isolated from room temperature electronics.