arXiv subjects

Shyam Sridharan

Publications and source records attributed to Shyam Sridharan.

2 recordsLinked to original sources

arXiv2022

Gated InGaAs Detector Characterization with Sub-Picosecond Weak Coherent Pulses

We propose and demonstrate a method to characterize a gated InGaAs single-photon detector (SPD). Ultrashort weak coherent pulses, from a mode-locked sub-picosecond pulsed laser, were used to measure photon counts, at varying arrival times relative to the start of the SPD gate voltage. The uneven detection probabilities within the gate window were used to estimate the afterpulse probability with respect to various detector parameters: excess bias, width of gate window and hold-off time. We estimated a lifetime of 2.1 microseconds for the half-life of trapped carriers, using a power-law fit to the decay in afterpulse probability. Finally, we quantify the timing jitter of the SPD using a time to digital converter with a resolution of 55 ps.

quant-ph↗

arXiv2022

Equivalence of space and time-bins in DPS-QKD

Key generation efficiency, and security, in DPS-QKD improve with an increase in the number of path delays or time-bin superpositions. We demonstrate the implementation of super-position states using time-bins, and establish an equivalence with path-based superposition, thus yielding a simpler implementation of higher-order superposition states for differential phase-shift quantum key distribution (DPS-QKD). We set up DPS-QKD, over 105 km of single mode optical fiber, with a quantum bit error rate of less than 15% at a secure key rate of 2 kbps. With temporal guard bands, the QBER reduced to less than 10%, but with a 20% reduction in the key rate.

quant-ph↗