Quantum key distribution (QKD) provides a way of sharing secret keys in cryptographic protocols. By leveraging the inherent qualities of quantum states, such as quantum entanglement, no-cloning, and uncertainty in the measurement of quantum states, it promises secure data transfer that is immune to eavesdropping. Data security is enhanced by adding this key distribution.

Currently, we are focusing on the differential-phase-shift (DPS) QKD protocol. The schematic representation is shown in Figure 1. In DPS-QKD, the key information is encoded in the relative phase difference between consecutive pulses of an attenuated coherent pulse train. The encoded phase values are randomly chosen, either ‘0’ or ‘π’. The receiver measures the phase difference between the consecutive pulses using a 1-bit delay line interferometer setup. Single-photon detector (SPD)-1 clicks for the 0-phase difference and SPD-2 for the π phase difference between consecutive pulses.

Apart from enhancing the security of communication networks, the DPS-QKD approach simplifies the hardware requirements and thereby facilitates practical and scalable QKD systems.

The microscopic image of the fabricated amPICQ-QKD-Rx chip is shown in figure2. The complete QKD-Tx-Rx design is expected to be fabricated by Q4-2024.