Superconducting nanowire single-photon detectors (SNSPDs) offer significant improvement on detection efficiency (DE) compared to their semiconducting counterparts, having enabled many breakthrough applications in quantum information technologies.

The team headed by Prof. Lixing You from Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences (CAS) (also affiliated to CAS Center for Excellence in Superconducting Electronics (CENSE)) first demonstrated the fabrication and operation of a NbN-SNSPD with system detection efficiency over 90% at 2.1 K at a wavelength of 1550 nm, which paves the way for practical application of SNSPD (Figure 1).

The results were published recently on SCIENCE CHINA Physics, Mechanics and Astronomy [1] as a cover image story. Dr. Weijun Zhang is the first author and Dr. Lixing You is the corresponding author.

At 1550 nm, which is the most important wavelength for applications, the state of the art SNSPD made of WSi superconductor has reached a DE record of 93% [2], compared to InGaAs detector with DE ~30%. Unfortunately, WSi-SNSPD usually operates at sub-kelvin temperatures, requiring expensive and user unfriendly refrigeration equipment.

Extensive efforts are made on the development of SNSPDs based on NbN, targeted at operating temperature above 2K, accessible to inexpensive and user-friendly compact cryocoolers. With a decade research, the detection efficiency of NbN-SNSPDs were gradually increased to ~ 80%. However, further improvements are not reported. Achieving DE over 90% requires the simultaneous optimization of many different factors, including near perfect optical coupling, near perfect absorption, and near unity intrinsic quantum efficiency. Previous attempts at doing this have mostly been made through a process of trial and error.

This paper first reported a NbN-SNSPD system based on G-M cryocooler with system detection efficiency over 90% (at dark count rate of 10 Hz) at 2.1 K at a wavelength of 1550 nm. The efficiency of the device saturates to 92% when the temperature is lowered to 1.8 K.

The success of this device has been the result of using an integrated Distributed Bragg Reflector (DBR) cavity offering near unity refection at the interface, and through systematic optimization of the NbN nanowire's meandered geometry. The joint efforts enable researchers to simultaneously achieve the stringent requirements for coupling, absorption and intrinsic quantum efficiency.

What is more, the device exhibit timing jitters down to 79 ps, almost half that of previously reported WSi-SNSPD, promising additional advantages in applications requiring high timing precision. The devices have been applied to the quantum information frontier experiments in University of Science and Technology of China.

SNSPD with near unity detection efficiency operational on economical and user-friendly compact cryocooler will provide researchers a powerful and easy accessible tool, envisage further breakthrough in quantum information areas such as optical quantum computation/simulation, quantum key distribution etc., in a foreseeable near future.

Research paper

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