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arXiv quant-ph/0503186quant-ph
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利用相干原子记忆介质产生非经典光子对的量子理论

Quantum Theory for Generation of Nonclassical Photon Pairs by a Medium with Coherent Atomic Memory

Narek Sisakyan, Yuri Malakyan

摘要:

我们提出了一个完整的量子力学处理最近的实验集体量子记忆和生成的非经典相关的光子对从一个原子系综通过协议的Duan等。[自然{ \bf 414,} 413(2001)]。通过求解原子自旋波激发的运动方程,得到了光子数、光子统计以及Stokes场和反Stokes场之间的互相关随时间的演化关系。我们考虑一个低精细腔模型与集体增强的信噪比,这仍然是相当大的自由空间的限制。我们的结果解析地描述了量子关联对自旋退相干时间和读写激光之间的时间延迟的依赖关系,并很好地再现了观测数据,包括产生的脉冲形状、对Cauchy-Schwarz不等式的强烈违反以及反Stokes单光子脉冲的条件产生。该理论为量子信息的存储和提取提供了一种基本的量子描述方法,特别是在研究非经典脉冲的统计特性时。

英文摘要:

We present a fully quantum mechanical treatment of recent experiments on creation of collective quantum memory and generation of non-classically correlated photon pairs from an atomic ensemble via the protocol of Duan et al. [Nature {\bf 414,} 413(2001)]. The temporal evolution of photon numbers, photon statistics and cross-correlation between the Stokes and anti-Stokes fields is found by solving the equation of motion for atomic spin-wave excitations. We consider a low-finesse cavity model with collectively enhanced signal-to-noise ratio, which remains still considerably large in the free-space limit. Our results describe analytically the dependence of quantum correlations on spin decoherence time and time-delay between the write and read lasers and reproduce the observed data very well including the generated pulse shapes, strong violation of Cauchy-Schwarz inequality and conditional generation of anti-Stokes single-photon pulse. The theory we developed may serve as a basic approach for quantum description of storage and retrieval of quantum information, especially when the statistical properties of non-classical pulses are studied.

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