Communication and Measurement with Squeezed States

Xiaowei Deng, Shuhong Hao, Caixing Tian +3 more

Squeezed state can increase the signal-to-noise ratio in quantum communication and quantum measurement. However, losses and noises existing in real communication channels will reduce or even totally destroy the squeezing. The phenomenon of disappearance of the squeezing will result in the failure of quantum communication. In this letter, we present the experimental demonstrations on the disappearance and revival of the squeezing in quantum communication with squeezed state. The experimental results show that the squeezed light is robust (squeezing never disappears) in a pure lossy but noiseless channel. While in a noisy channel, the excess noise will lead to the disappearance of the squeezing, and the squeezing can be revived by the use of a correlated noisy channel (non-Markovian environment). The channel capacity of quantum communication is increased after the squeezing is revived. The presented results provide useful technical references for quantum communication with squeezed light.

Horace P. Yuen

Brett A. Hooper

Masahiro Kitagawa, Y. Yamamoto

The origin of quantum noise is addressed and it can be eliminated when the quantum state is optimally prepared for the single measured observable. Minimum uncertainty states are reviewed using Q (α) -representation, which include squeezed states and number-phase minimum uncertainty states. Squeezing is a concept of trading quantum uncertainties between two conjugate observables to optimize the state for the measurement. Need for optical nonlinearity to achieve squeezing is induced. Principles and experimental results for squeezing quadrature amplitude and photon number are delineated. Applications to optical communications and optical precision measurement are briefly stated.

Xi-Zeng Li, Zhenfeng Hu, Lixin Li

If the idler photon flux is continuously measured in a photon-counting detector and the photocurrent fluctuations are fed back to control the pump intensity, the output signal state will be an amplitude-squeezed state (near-number state) at low frequencies and high feedback loop gain. Electromagnetic field in number-phase minimum-uncertainty states (amplitude- squeezed states), and its limit (photon-number states) have potential applications in optical communication, precision measurement, and atomic spectroscopy, and gravitational wave detection. These states have been the focus of considerable attention.

P. L. Knight, Vladimír Bužek