Quantum communication and quantum metrology with coherent state of light

Lucia Caspani

Marcin Jarzyna

Hidehiro Yonezawa, Daisuke Nakane, Trevor A. Wheatley +10 more

Tracking a randomly varying optical phase is a key task in metrology, with applications in optical communication. The best precision for optical-phase tracking has until now been limited by the quantum vacuum fluctuations of coherent light. Here, we surpass this coherent-state limit by using a continuous-wave beam in a phase-squeezed quantum state. Unlike in previous squeezing-enhanced metrology, restricted to phases with very small variation, the best tracking precision (for a fixed light intensity) is achieved for a finite degree of squeezing because of Heisenberg's uncertainty principle. By optimizing the squeezing, we track the phase with a mean square error 15 ± 4% below the coherent-state limit.

Maria Luisa Rastello

Jiangrui Gao, Kui Liu, Shuzhen Cui +1 more

High quality light, whenever coherent light and nonclassical light, is more and more widely used in many filed.The coherent state behave minimum classical noise and better coherence, is mostly important light in quantum information, precise measurement and quantum metrology etc.In quantum information and quantum optics, a coherent light is used to entanglement generation (Ou, Z. et al. 1992), quantum teleportation (Furusawa, A. et al. 1998A.et al. ), quantum computation (Menicucci, N. et al. 2006) and quantum secret sharing (Lance, A. et al. 2004).The quiet laser beam, shot noise limited laser beam is important in above application.In the past 20 years there has been much interest in the generation and application of various nonclassical light sources, such as squeezed-state entanglement, quantum-correlated twin beams, and sub-poissonian light, for which improved signal-to-noise ratios and measurement precision beyond the quantum-noise limit are anticipated.In particular, subpoissonian light is a promising light source in quantum information and optical communication because of its communication capacity (

Osamu Hirota, Kentaro Kato, Dan Murakami

This Letter verifies the potential of several classes of entangled coherent state in well known quantum metrology which includes detection of classical external force, and shows that there is a class of entangled coherent state for the external force detection system without the quantum limit in the detection of the light. In the case of the precision measurement of continuos parameter like phase measurement, the entangled coherent state with perfect entanglement does not provide remarkable benefit, but we provide a concrete example that certain class of entangled coherent state gives a remarkable sensitive detection scheme in the discrimination of digital signal affected by external force.