Development of innovative superconducting electronics for multiplexing quantum sensors arrays

A sensor capable of detecting single photons in the infrared (IR) wavelength range, with accurate timing and spatial information, is a crucial component that will unlock applications across strategic sectors such as communication, healthcare, environmental monitoring and defence. This key technology underpins for example the transfer of secure information (Quantum communication/cryptography), opens the path to dramatic enhancements in the speed and computational power of next generation computers (Quantum computing) and enables tremendous performance improvements in imaging and remote sensing techniques (LIDAR for environmental monitoring or imaging, deep space long distance communication, photodynamic therapy for cancer treatment).

The semiconductor based IR photon counters technology is still not adequate to play a significant role in the most demanding 21st Century aforementioned applications. Superconducting nanowire single photon detectors (SNSPDs) can offer unprecedented performance when detecting single infrared photon at 1550 nm wavelength but are limited to single pixels of 15x15 micrometer square area.

A large area array of SNSPDs will achieve the ultimate single-photon sensitivity and high temporal resolution, together with imaging capability. A major challenge in scaling up SNSPDs to large focal plane arrays arises from their operation at cryogenic temperatures and special care is needed in designing efficient signal readout.

The goal of this PhD project is the development of superconducting electronic readout scheme for the multiplexing of a large arrays of SNSPDs. This circuit will enable precision time stamping, spectral resolution and extraction of photon number information. In partnership with the UK National Physical Laboratory (NPL) we are exploring a readout method using single flux quantum (SFQ) circuits based on superconducting nanobridges instead of the traditional Josephson junction technology. In this approach, a single photon absorption event is converted into a single flux quantum that is processed via a superconducting circuit at low temperature. This project will investigate a range of novel nanobridge SFQ readout devices for multi-pixel readout. Our eventual goal is to combine for the first time the readout on-chip with the SNSPDs patterned by a single electron beam lithography step. This will offer easy fabrication on existing photonics platforms for straightforward integration with quantum technologies, high control on the single circuitry components and flexibility in tailoring the performance of sensors for specific applications.

This project will encompass circuit simulation, advanced nanofabrication (carried out using state-of-the-art electron beam lithography facilities in the James Watt Nanofabrication Centre JWNC at the University of Glasgow). Device testing will be mainly carried out using low temperature RF electrical and optical characterization facilities in laboratories at NPL where the PhD student will spend at least 1 year.

This project is perfectly aligned with the goals of QuantIC, the UK Quantum Technology Hub in quantum enhanced imaging (WP4 Superconducting detectors), and with a current Innovate UK Quantum Technology Feasibility Study grant (Integrated superconducting nanobridge fast readout electronics for single photon detector arrays led by Dr Jane Ireland at the NPL. NPL strongly support this project and are keen to strengthen links with QuantIC and the JWNC; the industrial studentship is an ideal mechanism to enable this.

The current proposal strongly resonates with the EPSRC's objectives in terms of delivery plan driven by the following prosperity outcomes: development and deployment of transformational technologies devoted to connect people in secure and trustworthy ways; improvement of the ability to predict, diagnose and treat disease; development of world-leading technology in information, computing and engineering.