Sep
2022
Name of the Speaker: Gautam shaw (EE15D047)
Guide: Dr. Anil Prabhakar
Venue/Online meeting link: ESB 244 (Seminar Hall)
Date/Time: September 19th, 4.00 pm
Abstract
Quantum key distribution (QKD) provides a means of generating secret random bits, or keys, for
cryptographic purposes, between two distant parties. QKD has drawn a lot of attention in last two
decades because of its unconditional security guaranteed by quantum mechanics, such as no-cloning
theorem. Experiments with 2-pulse Differential Phase-Shift Quantum Key Distribution (DPS-QKD)
with quantum bit error rate (QBER) of 21% and quantum random number generator (QRNG) with
two different entropies (arrival time of photon and path superposition) were presented in Seminar-I.
Key generation efficiency, and security, in DPS-QKD improve with an increase in the number
of optical delays or time-bin superpositions. We demonstrate the implementation of superposition
states using time-bins, with two different approaches. In Type-A, we use an optical pulse and create
superposition states with optical splitters and path delays. Similar superposition states are created, in
Type-B, by applying direct phase modulation within a single weak coherent pulse. In this talk, we will
discuss the equivalence between both the approaches, and implementation of higher-order
superposition states of Type-B in DPS-QKD. We have established 4-state DPS-QKD, over 105 km of
single mode optical fiber, with a QBER of less than 15% at a secure key rate of 2 kbps. To optimize
the performance of QKD test-bed, gated single photon detector (SPD) was characterized with sub-
picosecond weak coherent pulses. We have also shown that with temporal filtering, the QBER
reduced to less than 10%, but with a 20 % reduction in key rate.