Quantum phase modulator

A.G. Tam, Kerry James Hinton, Peter M. Farrell +1 more

Osung Kwon, Min‐Soo Lee, Min Ki Woo +5 more

We characterized a polarization-independent phase modulation method, called double phase modulation, for a practical plug and play quantum key distribution (QKD) system. Following investigation of theoretical backgrounds, we applied the method to the practical QKD system and characterized the performance through comparing single phase modulation (SPM) and double phase modulation. Consequently, we obtained repeatable and accurate phase modulation confirmed by high visibility single photon interference even for input signals with arbitrary polarization. Further, the results show that only 80% of the bias voltage required in the case of single phase modulation is needed to obtain the target amount of phase modulation.

Z. Hradil

Peng Ye, Wei Chen, Ze-Hao Wang +9 more

In chip-based quantum key distribution (QKD) systems, the non-ideal quantum state preparation due to the imperfect electro-optic phase modulators (EOPM) decreases the secret key rate and introduces potential vulnerabilities. We propose and implement an on-chip transmittance-invariant phase modulator (TIPM) to solve this problem. Simulated and experimental results show that TIPM can eliminate the correlation between phase, intensity, and polarization of quantum states caused by phase-dependent loss. The design can tolerate a significant fabrication mismatch and is universal to multi-material platforms. Furthermore, TIPM increases the modulation depth achievable by EOPMs in standard process design kit (PDK). The proposal of TIPM can improve the practical security and performance of the chip-based QKD systems.

Stephen Mark Barnett, David Thomas Pegg

Konstantin V. Stepanov, A.V. Borisova, A. G. Vtyurina

Subject of study . A phase modulation device for encoding quantum states based on an electro-optical phase modulator asymmetrically located in a Sagnac interferometer is studied. Aim of study. An easily implemented and repeatable method for measuring the path difference to a phase modulator inside a Sagnac interferometer in quantum key distribution systems is developed. Method. A phase difference between the clockwise and counterclockwise continuous propagating light is introduced in the beamsplitter of a Sagnac interferometer when an electrical pulse is transmitted to a phase modulator. Moreover, the asymmetric location of the phase modulator means that this single electrical pulse introduces twice the optical phase difference. Main results. A technique for measuring the difference in propagation time for light traveling in opposite directions to reach the phase modulator in a Sagnac interferometer was proposed and experimentally tested; this technique can be used for simultaneous modulation of phase and intensity in quantum key distribution systems. Practical significance. Our results regarding this highly accurate and easily implementable technique for measuring the difference in propagation time for light traveling in opposite directions to reach the asymmetrically positioned phase modulator in a Sagnac interferometer are relevant for the production of optoelectronic modules used in quantum key distribution systems, where this time difference directly affects the system quality and overall performance.