Marco Avesani - Università di Padova and ThinkQuantum 

Low-Loss Integrated Photonics for Quantum-Secure Applications

Quantum key distribution and quantum random number generation are two fundamental building blocks of quantum-secure technologies. Their practical scalability, however, is limited by the complexity of the required optical hardware, stringent stability requirements, and the high detection performance needed to preserve security while achieving high rates. Photonic integration offers a promising route towards compact, stable, and scalable systems by reducing optical losses and component count while improving the robustness of coherent detection.

In this talk, we present continuous-variable QRNG and QKD experiments based on a common low-loss integrated heterodyne receiver. The polarization-insensitive device, fabricated in borosilicate glass by femtosecond laser writing, features insertion losses below 1.28 dB and a common-mode rejection ratio exceeding 73 dB.

Using this platform, we demonstrate source-device-independent quantum random number generation at a secure rate of 42.74 Gbit/s. We then extend randomness certification to an energy-constrained semi-device-independent protocol, which requires only an experimentally verifiable bound on the source energy and minimal assumptions on the devices. Under finite-size conditions and without assuming independent and identically distributed rounds, the protocol certifies 0.223 bit of randomness per measurement. We also employ the receiver in a QPSK continuous-variable QKD system, achieving a secret key rate of 3.2 Mbit/s.

These results demonstrate the potential of low-loss integrated coherent detection as a versatile platform for high-rate quantum communication and certified randomness generation across different device-trust models.