Photonic Readout of Superconducting Nanowire Single Photon Counting Detectors

Abstract

Scalable, low power, high speed data transfer between cryogenic (0.1-4 K) and room temperature environments is essential for the realization of practical, large-scale systems based on superconducting technologies. 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 (1,000-10,000 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. While promising, optical readout of cryogenic devices is challenging. First, we need semiconductor electro-optic devices operating at cryogenic temperatures, where effects such as carrier freeze-out (the incomplete ionization of p-and n-type dopants due to reduced thermal energy) can hinder device performance 1. Second, while superconducting devices have intrinsically low resistance, typical input impedances for electro-optic modulators are high (>100 kΩ). This impedance mismatch makes direct delivery of electrical signals from the superconducting device to the modulator challenging. Third, we need to operate with the mV-range electrical signals characteristic of superconducting electronics, while driving signals for conventional room temperature electro-optic modulators are in the 0.5 V-2 V range. To overcome these limitations, previous demonstrations have relied on the use of an interfacing device between the superconducting and the electro-optic devices. The use of semiconductor amplifiers is possible 2-7 , but its mW-scale power dissipation hinders its scalability. Another alternative is to use a nanocryotron 8 , but this requires actively resetting the device every time a pulse is generated. Recently, the use of a cryogenic thermal switch to drive a laser diode with low power dissipation has been reported 9 , but a slow turn-off time of 15 ns limits the achievable bandwidth of this approach. Here, we use a silicon optical modulator biased in the forward regime. Because of its high efficiency, modulation of the optical carrier is achieved with the small voltages generated by the SNSPD. Because of its low input impedance, direct delivery of the SNSPD signal to the modulator is possib...

Single-photon detection and cryogenic reconfigurability in lithium niobate nanophotonic circuits

“…Although these devices can now reach acceptable performance, including insertion loss <0.5 dB and a ~2 V driving voltage with a compact footprint 22 , they require a complex fabrication procedure and are prone to mechanical damage, making their use challenging for the realization of large-scale photonic integrated circuits. Moreover, optomechanical devices suffer from a maximum modulation bandwidth limited to the ~MHz range, which prevents their usage for a large number of important applications -such as spatial-and time-multiplexing schemes for scalable quantum computing 2,23,24 , fast feedforward operations for measurement-based quantum computation [25][26][27] , or optical read-out schemes for SNSPDs 28 -where a bandwidth in the ~GHz regime is mandatory. Electro-optic modulators (EOMs) based on the Pockels effect can overcome all the aforementioned limitations, and provide a simple and cryogenic-compatible [29][30][31][32] platform for on-chip reconfigurable photonics.…”

Advances in Silicon Quantum Photonics

“…Recently, ref. [175] demonstrated a modulator driven directly by a nearby integrated SNSPD-a powerful capability for signal multiplexing as well as high-speed multiplexing technologies.…”

Cryogenic electro-optic modulation in titanium in-diffused lithium niobate waveguides

“…An optimal photonic platform needs to combine the integrability of modulators and single photon detectors at cryogenic temperatures [7,16,8,17]. Titanium indiffused lithium niobate is an interesting platform to pursue this goal since it offers a large second order nonlinearity, low propagation loss, butt-coupling with single mode fibres, and integrability of SNSPDs [18,19].…”