Continuous Quantum Measurement of Cold Alkali-Atom Spins
Continuous Quantum Measurement of Cold Alkali-Atom Spins
复制标题
冷碱原子自旋的连续量子测量
DOI：
10.7907/7ptx-ab16
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
John K. Stockton
中科院分区：
文献类型：
--
作者：
John K. Stockton
量子计量学领域涉及传感器的物理测量，其精度可与量子力学设定的基本极限相媲美。通过使用传感器系统的纠缠态，有可能超越这些限制的朴素解释。一个例子是自旋压缩态，其中一个变量的不确定性以另一个变量的不确定性为代价而降低，同时仍然遵循海森堡的不确定性原理，提高了沿选定轴的旋转灵敏度。这些状态在原子钟、惯性传感器和磁力计等设备中具有潜在的用途。任何量子计量装置的模型都必须尊重这样一个事实，即物理测量不是被动的，正如经典所想象的那样，而是必然的侵入性。完全不是一个消极的特征，充分理解的量子测量可以有条件地将系统驱动到理想的纠缠态，包括自旋压缩态。此外，该过程的基本随机性原则上可以通过实时反馈控制来消除，从而激发经典反馈概念对量子领域的适应。在这篇论文中，我在一个实验实例的背景下描述了这些想法。激光冷却的铯自旋云通过光泵浦沿一个轴极化，随后，线性极化的远谐振探针束穿过样品。由于相互作用的哈密顿量，光偏振旋转的量名义上与集体自旋态的一个自旋分量成正比，对集体变量进行弱的、连续的、非破坏的测量。这种光学法拉第旋转然后用偏振计测量，固有的噪声结果用于通过量子滤波器或随机主方程来调节集体原子状态。理想情况下，该过程能够通过测量本身产生自旋压缩态。对测量的细节进行了深入的研究，包括非理想极化率哈密顿量的推导，带控制的投影过程的分析，以及磁敏灵敏度的推导。在实验上，我们展示了用大的单次信噪比连续测量集体自旋态，并验证了该模型的许多预测。最后，我们描述了观察原子投影噪声的尝试，这将推断自旋压缩态的制备。
The field of quantum metrology concerns the physical measurement of sensors with a precision comparable to fundamental limits set by quantum mechanics. It is possible to outperform naive interpretations of these limits by using entangled states of the sensor system. One example is that of a spin-squeezed state, in which the uncertainty of one variable is decreased at the expense of another while still obeying Heisenberg's uncertainty principle, improving rotation sensitivity along a chosen axis. These states are potentially useful in devices including atomic clocks, inertial sensors, and magnetometers. Any model of a quantum metrology device must respect the fact that physical measurements are not passive, as imagined classically, but necessarily invasive. Far from being a negative feature, well-understood quantum measurement can conditionally drive a system into desirable entangled states, including spin-squeezed states. Furthermore, the fundamental randomness of this process can, in principle, be removed with real-time feedback control, motivating an adaptation of classical feedback concepts to the quantum realm. In this thesis, I describe these ideas in the context of one experimental example. A laser-cooled cloud of cesium spins is polarized along one axis via optical pumping and, subsequently, a linearly polarized far-off resonant probe beam traverses the sample. Due to the interaction Hamiltonian, the optical polarization rotates by an amount nominally proportional to one spin component of the collective spin state, enacting a weak, continuous, nondemolition measurement of that collective variable. This optical Faraday rotation is then measured with a polarimeter and the inherently noisy result used to condition the collective atomic state via a quantum filter, or stochastic master equation. Ideally, this process is capable of producing spin-squeezed states via the measurement itself. The details of this measurement are investigated in depth, including a derivation of the nonideal polarizability Hamiltonian, an analysis of the projection process with control, and a derivation of the magnetometry sensitivity. Experimentally, we demonstrate continuous measurement of the collective spin state with a large single-shot signal-to-noise ratio and verify many predictions of the model. Finally, we describe attempts to observe the atomic projection noise, which would infer the preparation of spin-squeezed states.
影响因子：
64.8
作者：
Sorensen, A;Duan, LM;Zoller, P
通讯作者：
Zoller, P