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arXiv 1908.00422cond-mat.quant-gascond-mat.stat-mechquant-ph
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隧道耦合一维玻色气体的关联和动力学

Correlations and dynamics of tunnel-coupled one-dimensional Bose gases

Thomas Schweigler

摘要:

我们提出了一系列的实验进行了两个超冷一维玻色气体(铷原子)在双阱势。采用物质波干涉,我们可以测量两种气体之间的空间分辨相位差,从而研究空间相关性。通过研究高阶关联函数能否分解为低阶关联函数,我们可以研究系统的相互作用性质。对于非相互作用系统,所有阶数大于2的关联函数都是因式分解的,其中一个观测到高斯涨落。在这里,我们提出了非因式分解的四阶相关函数的测量,导致量子多体系统的集体激发之间的相互作用的实验表征。非因式分解的程度,即,相位波动的非高斯性程度取决于阱之间的可调隧穿强度。从这样一个非高斯态开始,我们能够观察到向一个具有因子分解关联函数(高斯波动)的状态的动力学演化。我们从一个双阱开始,然后突然将两个子系统解耦。随后,我们观察到最初的非高斯相位波动如何变成高斯。此外,我们还讨论了双势阱隧穿过程中相位相干的动力学产生。我们实验研究了从两个不同的初始状态开始的演化。在一种情况下,我们将一团原子一分为二,并在它们的相对相位中引发全局振荡。振荡随后衰减,相位相干开始。在另一种情况下,两个独立的云突然通过隧道耦合。在两个子系统之间再次出现相位相干。

英文摘要:

We present a series of experiments performed with two ultracold one-dimensional Bose gases (rubidium atoms) in a double well potential. Employing matter-wave interference, we can measure the spatially resolved phase difference between the two gases and consequently investigate spatial correlations. By investigating whether higher order correlation functions can be factorized into correlations of lower order, we can investigate the interaction properties of the system. For a non-interacting system, all correlation functions with orders greater than two factorize and one observes Gaussian fluctuations. Here, we present the measurement of non-factorizing fourth-order correlation functions, leading to an experimental characterization of the interactions between the collective excitations of the quantum many-body system. The degree of non-factorizibility, i.e., the degree of non-Gaussianity of the phase fluctuations, depends on the tuneable tunneling strength between the wells. Starting from such a non-Gaussian state, we are able to observe the dynamical evolution towards a state with factorizing correlation functions (Gaussian fluctuations). We start in a double well with tunneling and then abruptly decouple the two subsystems. Subsequently, we observe how the initially non-Gaussian phase fluctuations become Gaussian. Moreover, we discuss the dynamical emergence of phase coherence in a double well potential with tunneling. We experimentally investigate the evolution starting from two different initial states. In one case, we split a cloud of atoms into two and trigger global oscillations in their relative phase. The oscillations subsequently damp and phase coherence sets in. In the other case, two independent clouds are suddenly coupled by tunneling. Again, phase coherence emerges between the two subsystems.

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