Equivalence of space and time-bins in DPS-QKD

TL;DR

This paper demonstrates that using time-bin superpositions in DPS-QKD is equivalent to path-based superpositions, simplifying implementation and maintaining high security over long distances.

Contribution

It establishes the equivalence between space and time-bin superpositions in DPS-QKD, enabling simpler higher-order superposition state implementation.

Findings

Secure key rate of 2 kbps over 105 km fiber

Quantum bit error rate below 15% without guard bands

QBER reduced to under 10% with temporal guard bands

Abstract

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.