Jietai Jing

Quantum Dense Coding Exploiting a Bright Einstein-Podolsky-Rosen Beam

Highly efficient quantum dense coding for continuous variables has been experimentally accomplished by means of exploiting bright EPR beam with anticorrelation of amplitude quadratures and correlation of phase quadratures, which is generated from a nondegenerate optical parametric amplifier operating in the state of deamplification. Two bits of classical information are encoded on two quadratures of a half of bright EPR beam at the sender Alice and transmitted to the receiver Bob via one qubit of the shared quantum state after encoding. The amplitude and phase signals are simultaneously decoded with the other half of EPR beam by the direct measurement of the Bell-state at Bob. The signal to noise ratios of the simultaneously measured amplitude and phase signals are improved 5.4dB and 4.8dB with respect to that of the shot noise limit respectively. A high degree of immunity to unauthorized eavesdropping of the presented quantum communication scheme is experimentally demonstrated.

Dense-coding quantum key distribution based on continuous-variable entanglement

We proposed a scheme of continuous-variable quantum key distribution, in which the bright Einstein-Podolsky-Rosen entangled optical beams are utilized. The source of the entangled beams is placed inside the receiving station, where half of the entangled beams are transmitted with round trip and the other half are retained by the receiver. The amplitude and phase signals modulated on the signal beam by the sender are simultaneously extracted by the authorized receiver with the scheme of the dense-coding correlation measurement for continuous quantum variables, thus the channel capacity is significantly improved. Two kinds of possible eavesdropping are discussed. The mutual information and the secret key rates are calculated and compared with those of unidirectional transmission schemes.

LD pumped intracavity frequency-doubled and frequency-stabilized Nd:YAP/KTP laser with 1.1 W output at 540 nm

Abstract A compact LD pumped intracavity frequency-doubled and frequency-stabilized ring Nd:YAP/KTP laser with high output up to 1.1 W at 540 nm is achieved. In the design of the laser configuration, the anisotropic characteristics of Nd:YAP optical biaxial crystal are taken into account. A quarter-wave plate is placed between the Faraday rotator and the α-cut KTP to ensure the output fundamental wave from KTP in pure linear-polarization paralleling to that of the oscillating laser and unidirectional operation of laser. Due to rigorously temperature controlling on KTP crystals and optimizing design of resonator, the stable single-frequency green output is obtained. The intensity fluctuation is less than ±1.5%, and frequency stability is better than ±550 kHz by means of a standard frequency locking technology with F-P cavity.

EPR correlation and quantum noise squeezing of output light fields from a narrowband NOPA

Our calculation and experiment presented an indirect and undoubted path to demonstrate the quantum correlation between bright EPR beams, that bypassed the technical difficulty in these types of experiments. A system of nondegenerate optical parametric amplifiers (NOPA) in which the interconnected squeezed vacuum field, bright coherent-squeezed state light and EPR beams can be obtained simultaneously is also very interesting for practical applications.