Quantum Optics and Continuous Variables (CV) Fundamentals

Mingfeng Wang, Nian-Quan Jiang, Yi-Zhuang Zheng

The continuous-variable (CV) quadratic phase gate is one of the most fundamental CV quantum gates for universal CV quantum computation, while its experimental realization still remains a challenge. Here we propose a novel and experimentally feasible scheme to realize optical CV quadratic phase gate via Faraday interaction in an atomic ensemble. The gate is performed by simply sending an optical beam three times through an atomic medium prepared in coherent spin state. The fidelity of the gate can ideally run up to one. We show that the scheme also works well as a device to generate optical polarization squeezing. Considering the noise effects due to atomic decoherence and light losses, we find that the observed fidelities of gate operation and the attainable degree of polarization squeezing are still quite high.

Ivan B. Djordjević

Kuanshou Zhang, Jinxia Feng, Yuanji Li

Metropolitan fiber quantum communication network is the key step to construct quantum communication network. Owing to continuous variable (CV) quantum entangled states of optical field can be generated unconditionally and deterministically, high-performance quantum information processing with continuous variables based on quantum states of optical field can be achieved. However, quantum information processing with continuous variable over optical fiber is a great challenge.

Jan Peřina, Z. Hradil, Branislav Jurčo

Z. Ficek, Mohamed Ridza Wahiddin

Youbin Yu, Huaijun Wang

Bright three-color continuous-variable (CV) entanglement generated by a cascaded sum-frequency process in an optical cavity is investigated. The second- and fourth-harmonic beams can be generated by two quasi-phase-matched cascaded sum-frequency processes in a quasi-periodic optical superlattice. Quantum correlations among the fundamental and second- and fourth-harmonic beams are calculated and discussed by applying a sufficient and necessary inseparability criterion for CV three-mode entanglement. Strong three-color CV entanglement beams with a double frequency interval can be produced in this simple system. It is experimentally feasible and may be very useful for applications in quantum communication and computation networks.