Turbulence and 1/f Noise in Quantum Optics

F. T. Arecchi

Renzhi Yuan, Julian Cheng

The performance of free-space optical quantum communications deteriorates due to the presence of atmosphere turbulence. In this paper, the P-function of a coherent state passing through a turbulent atmosphere channel in the presence of thermal noise is derived using the additive property of the thermal noise channel. The analytical form of the density operator for this turbulent coherent state and its corresponding matrix representation in Fock basis is deducted. Using this matrix representation of density operator for turbulent coherent state, the error probability of optical quantum communication system for binary phase shift keying is analyzed.

F. T. Arecchi

Renzhi Yuan, Julian Cheng

An optical quantum communication system with receiver diversity is proposed for free-space communication using the optical combining technique and a generalized Kennedy receiver. The quantum channel model of the proposed system is established using the P -representation in the presence of both turbulence and thermal noise. A conditional dynamics based Kennedy receiver with threshold detection is proposed to mitigate the influence of both turbulence and thermal noise. The error probabilities for different types of generalized Kennedy receiver, i.e., the Kennedy receiver, the Type-II receiver, and the conditional dynamics based Kennedy receiver, are analytically studied and the lower bounds for these error probabilities are obtained. Numerical results show that both the Kennedy receiver and the Type-II receiver fail in the presence of either turbulence or thermal noise. The performance of the proposed conditional dynamics based Kennedy receiver with threshold detection can surpass the standard quantum limit given by the homodyne receiver in either weak turbulence or small thermal noise.

He Zhang, Santosh Kumar, Yu‐Ping Huang

We experimentally study a nonlinear optical approach to selective manipulation and detection of structured images mixed with turbulent noise. Unlike any existing adaptive-optics method by applying compensating modulation directly on the images, here we account for the turbulence indirectly, by modulating only the pump driving the nonlinear process but not the images themselves. This indirect approach eliminates any signal modulation loss or noise, while allowing more flexible and capable operations. Using specifically sum frequency generation in a lithium niobate crystal, we demonstrate selective upconversion of Laguerre-Gaussian spatial modes mixed with turbulent noise. The extinction reaches ~40 dB without turbulence, and maintains ~20 dB in the presence of strong turbulence. This technique could find utilities in classical and quantum communications, compressive imaging, pattern recognition, and so on.

F. T. Arecchi