The Experimental Investigation Of Two-color Continuous Variable Entangled States At Rubidium Absorption Lines And Telecom Band

Quantum entangled state is the important source for quantum communication and quantum computation. Two-color quantum entangled state, which has non-degenerated carrying frequencies for the two parties, is potentially useful in quantum communication networks. For instance, the two-color quantum entangled states at fiber communication wavelength and alkaline atoms’absorbing line is very useful in quantum information. One of the light field which lies in the telecom band can be transferred with low losses over long distances by the fiber to achieve the distribution of entangled states, the other light field can utilize local alkaline atoms to perform quantum memory. This is of great significance for efficient construction and realization of quantum repeaters.In this paper, we make use of a two-end pumped OPO/OPA system to achieve the preparation of frequency-tunable two-color continuous variable entangled states. One beam of the entangled state (795nm) can be tuned continuously at a range of2.4GHz and the hyperfine transitions of rubidium D1line are successfully measured based on saturated absorption spectroscopy; The other beam (1560nm) is injected into a5-km single mode fiber to distribute the entanglement, and the entanglement evolution between the transmitted beam and its entangled counterpart is investigated. The system presented in this paper will find potential application in long-distance quantum information processing.This article consists of the following four parts:Chapter one:We introduce the research background of two-color continuous variable quantum entangled states, the basic concept and criteria of continuous variable quantum entanglement, and the technique of homodyne detection.Chapter two:We analyze theoretically the generation of bright two-color continuous variable entangled light field from a phase-insensitive optical parametric amplifier. In experiment, we prepare the two-color continuous variable entangled light field via the phase-insensitive optical parametric amplifier, both the amplitude quadrature difference and phase quadrature sum quantum correlation are greater than3dB.Chapter three:By tuning the temperature of the PPKTP crystal, adjusting the Optical Parametric Oscillator cavity length and varying the pump light frequency, the frequency of the795nm beam of the two-color entangled light field can be tuned continuously and we successfully observed the Rb atomic hyperfine transition line based on the saturated absorption spectrum technique. Furthermore, the distribution of the entanglement is obtained by injecting the1560nm light field into a5km single mode fiber, and the entanglement evolution between the transmitted beam and its entangled counterpart is investigated. It is found the entanglement is still preserved after the distribution with quadrature amplitude difference of1.1dB and quadrature phase sum of0.9dB.Chapter four:Summary and outlook.