Phase and Noise

Albert D. Wheelon

Hefei Cao

We present two different efficient quantum key distribution schemes over two different collective-noise channels. One is the phase noise, and the other is rotating noise. For the phase noise, we proposed a scheme of using GHZ state. Through the channel of the phase noise, the phase factor eiϕcan be put forward as a whole phase, with the purpose of resistance to phase noise. For the rotating noise, we proposed a scheme of using Bell state, when the noise through the rotating channel, the impact of the noise can be effectively against.

Yun Shao, Wei Huang, Yang Li +5 more

In continuous-variable quantum key distribution with a local local oscillator (LLO CV-QKD), the phase noise after phase compensation is mainly composed of three parts: the relative phase drift noise, the relative phase accumulated noise, and the phase-reference measurement noise. Here, we develop a practical phase noise model for LLO CV-QKD protocols, in which part of the phase-reference measurement noise that can be locally calibrated by Bob at the receiver side is considered to be trusted noise. It is reasonable to adopt this model because Bob”s apparatus is inaccessible to the eavesdropper. We show that the secret key rate and the transmission distance of the LLO CV-QKD system under the practical phase noise model is significantly improved in comparison to that under the conventional phase noise model. We show that the secret key rate is improved more than 65% and the transmission distance is increased more than 70% with some typical simulation parameters.

Peter Høyer

Ruixin Li, Nanjing Jiao, Bingnan An +5 more

The direct realization of a quantum-enhanced phase noise filter has remained a major challenge. Conventional techniques are not only plagued by substantial technical noise but also fundamentally constrained by inherent quantum penalty, precluding their direct application in quantum-enhanced noise filtering. This work has realized a practical approach to the first, to our knowledge, quantum-enhanced laser phase noise filter by confronting the key challenges that degrade phase noise extraction and quantum enhancement, specifically the technical noises in the laser’s amplitude and phase. Our strategy employs a detuned cavity to direct optical readout of phase noise combined with a hybrid stabilization scheme to suppress both amplitude and phase noises simultaneously. This allows us to circumvent the limitations imposed by quantum noise penalty and effectively enable quantum enhancement via squeezed vacuum injection. Experimentally, we have achieved up to 5 dB of quantum-enhanced phase noise suppression across Fourier frequencies ranging from 5 to 60 kHz. This scheme represents more than just a proof-of-principle—it unlocks the potential of squeezed-enhanced laser phase noise suppression for a broad spectrum of applications.