Intensity-Modulated DPS Quantum Key Distribution

Kyo Inoue

Hiroki Kawahara, Toru Oka, Kyo Inoue

Phase-modulated differential-phase-shift (DPS) quantum key distribution (QKD) is presented for combating sequential attacks that most severely restrict the DPS-QKD system distance. Slow phase modulation imposed onto the DPS signal obstructs the optimum unambiguous state discrimination measurement conducted in the sequential attack and improves the QKD distance as a result. The condition with which the phase modulation does not degrade the DPS-QKD system performance is also described.

Masahiro Takeoka

Kyo Inoue

The differential-phase-shift quantum key distribution (DPS-QKD) is a recently proposed QKD scheme in which a pulse train is transmitted through a quantum channel. This paper extends the ideal of the DPS-QKD to entanglement-based systems. Two schemes are presented. In one, an entanglement source sends pulse trains of signal and idler to two parties (Alice and Bob), respectively, who phase-modulate the incoming pulses and receive them after one-bit delay interferometers. In the other, two entanglement sources are prepared, one between Alice and a repeating node (Charlie) and one between Charlie and Bob, which send signal and idler pulse trains to Alice and Bob and Charlie, respectively. These schemes offer a longer distance between Alice and Bob than the conventional DPS-QKD.

Kyo Inoue, Yuuki Iwai

This paper presents a quantum key distribution (QKD) protocol named differential-quadrature-phase-shift (DQPS) QKD. A transmitter sends a coherent pulse train in which each pulse is phase modulated by ${0,\ensuremath{\pi}}$ ${\ensuremath{\pi}/2,3\ensuremath{\pi}/2}$, and a receiver measures it with either one of two asymmetric Mach-Zehnder interferometers having phase biases of 0 and $\ensuremath{\pi}/2$, respectively. This scheme is devised such that the idea of the conventional Bennett-Brassard 1984 protocol (BB84) is introduced to differential-phase-shift (DPS) QKD. Simulations show that the proposed scheme is robust against a sequential attack that is crucial eavesdropping to DPS-QKD.

Ivan B. Djordjević