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arXiv 1307.2913quant-phphysics.chem-ph
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偶极耦合分子阵列线性光谱中的集体效应

Collective Effects in Linear Spectroscopy of Dipole-Coupled Molecular Arrays

A. A. Kocherzhenko, J. Dawlaty, B. P. Abolins, F. Herrera, D. B. Abraham, K. B. Whaley

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12 pages, 7 figures main text
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摘要：

我们提出了一个一致的分析线性光谱阵列的最近邻偶极耦合的两个级别的分子，揭示了不同的签名的弱耦合和强耦合制度分开的无限大的阵列的量子临界点。在弱耦合区，分子阵列的基态是无序的，而在强耦合区，它具有（反）铁电有序。我们发现，多个分子激发（奇/偶在弱/强耦合制度）可以直接从基态。我们分析了吸收和发射随系统尺寸的标度，发现在有序相和无序相中振子强度都表现出增强的超辐射行为。随着耦合的增加，单激发振子强度迅速超过众所周知的Heitler-London值。在强耦合制度，我们表明存在一个独特的光谱过渡与激发能，可以通过改变系统的大小和渐近接近零的大系统进行调谐。这种转变的振子强度与系统大小成二次方关系，显示出异常的单光子超辐射。对于无限大的系统，我们发现了一个新的，奇异的光谱签名的量子相变之间的无序和有序的基态。我们概述了如何阵列的超冷偶极分子被困在一个光晶格可以用来访问强耦合制度，并观察与此制度相关的异常超辐射效应。

英文摘要：

We present a consistent analysis of linear spectroscopy for arrays of nearest neighbor dipole-coupled two-level molecules that reveals distinct signatures of weak and strong coupling regimes separated for infinite size arrays by a quantum critical point. In the weak coupling regime, the ground state of the molecular array is disordered, but in the strong coupling regime it has (anti)ferroelectric ordering. We show that multiple molecular excitations (odd/even in weak/strong coupling regime) can be accessed directly from the ground state. We analyze the scaling of absorption and emission with system size and find that the oscillator strengths show enhanced superradiant behavior in both ordered and disordered phases. As the coupling increases, the single excitation oscillator strength rapidly exceeds the well known Heitler-London value. In the strong coupling regime we show the existence of a unique spectral transition with excitation energy that can be tuned by varying the system size and that asymptotically approaches zero for large systems. The oscillator strength for this transition scales quadratically with system size, showing an anomalous one-photon superradiance. For systems of infinite size, we find a novel, singular spectroscopic signature of the quantum phase transition between disordered and ordered ground states. We outline how arrays of ultra cold dipolar molecules trapped in an optical lattice can be used to access the strong coupling regime and observe the anomalous superradiant effects associated with this regime.

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