Institute: CSIR-National Physical Laboratory (NPL), Delhi

Principal Investigator: Dr. R P Aloysius

Co-Principal Investigator: Dr. Sangeeta Sahoo

Co-Principal Investigator: Dr. Sudhir Husale

Co-Principal Investigator: Dr. Ajeet Kumar

Mentor: Prof. Venugopal Achanta, Director CSIR-NPL (Delhi)

The project is on the indigenous development of single photon detectors based on superconducting nanowires, or alternatively called the Superconducting Nanowire Single Photon Detectors (SNSPD). Among the single photon detection technologies, SNSPD has the unrivalled advantage in terms of many of the performance indicators such as the jitter timing, dark count rate and detection speed etc. Detection efficiencies of more than 90% are commercially demonstrated by a few companies across the world. The key to the SNSPD technology development is the optimization of superconducting properties of the chosen materials (such as NbTiN, NbN, W (FIB Fabricated) etc., well within the 2D regime, (dimensions with in the coherence length of the system). In order to increase the area of interaction of an incoming photon with the detector, the meander type of detector geometry is generally adopted. The work packages for the development of SNSPD includes the establishment of superconductivity in meander type of nanowire geometry of a chosen system, assessing its transport characteristics such as the critical temperature, critical current (both the switching current and depairing current and dependence of these parameters on externally applied magnetic field. Device fabrication for SNSPD is dependent on nanofabrication tools such as E-beam lithography and focussed ion beam (FIB) milling etc. Minimising edge irregularities on the fabricated devices will lead to better performance of the device. CSIR-NPL is in possession of a state-of-the-art FIB, and the same has been used to produce meander structures of W and Nb with well-defined superconducting properties with signature of quantum phase fluctuations. Once the quality of the superconducting nanowire is established to the level required for SNSPD, next package consists of integration of the detector to the low temperature environment, wherein the detector has to be coupled properly to receive time correlated single photons from a single photon source. Fibre coupled schemes or waveguide integrated schemes can be adopted depending on the wavelength range of the incident photon and type application wherein SNSPD is applied to. The detection of the output electrical signal from the SNSPD (a short voltage pulse decaying to the level prior to incident photon within a few nanoseconds time interval) requires low temperature amplification, filtering schemes and high-speed detector electronics, all working in a synchronised manner with respect to the incident photon. The operating temperature of SNSPD is well below the critical temperature of the system (~ 2-3 K), so cryogenic technology is an important part in the technology development. Detection and counting of photons to the singular level will enable the development of many of the correlated technologies such as quantum communications, quantum information processing, teleportation and to quantum key distributions (QKD) etc.

Publications from this project: