Building Differential Phase-Shift Quantum Key Distribution (DPS-QKD) System

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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

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.