Cavity-enabled spin squeezing for a quantum-enhanced atomic clock
Cavity-enabled spin squeezing for a quantum-enhanced atomic clock
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发表时间：
2011
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通讯作者：
M. Schleier-Smith
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作者：
M. Schleier-Smith
在过去的十年里，微波原子钟的稳定性一直处于标准量子极限，这是由测量不相关粒子集合时固有的投影噪声所决定的。在这里，我演示了一种原子钟，它通过在一种称为“压缩自旋态”的特定纠缠态中操作原子来超越这个限制。光学腔促进了稀原子云中非经典自旋相关的产生，它允许原子系综与单模光的强集体耦合。由于出腔的光与原子纠缠在一起，对光场进行适当的测量可以将原子系综投射到压缩自旋状态。用这种量子非拆除测量方法证明了3.0(8)dB的自旋压缩。本文进一步介绍了一种新的方法，即腔反馈压缩，它利用在谐振腔中循环的光场来介导原子之间的有效相互作用。光介导的相互作用模拟了单轴扭转哈密顿量的自旋动力学，其中相干自旋态确定性地演变为压缩自旋态。腔反馈制备的状态本质上被压缩了高达10(1)dB，可检测到被压缩了高达5.6(6)dB。应用于原子钟，它们产生的艾伦方差比标准量子极限低4.7(5)dB，平均时间长达50秒。在工程集体自旋动力学的迂回中，我提出了在腔冷却影响下原子集体运动动力学的直接观察。我演示了单个集体运动模式的协同增强冷却，其平均占用数为2.0（-0.3/+0.9）声子。用一个简单的解析量子光力学模型可以很好地定量描述冷却过程。论文导师：Vladan Vuletic职称：Lester Wolfe物理学副教授
For the past decade, the stability of microwave atomic clocks has stood at the standard quantum limit, set by the projection noise inherent in measurements on ensembles of uncorrelated particles. Here, I demonstrate an atomic clock that surpasses this limit by operating with atoms in a particular type of entangled state called a “squeezed spin state.” The generation of non-classical spin correlations in a dilute cloud of atoms is facilitated by an optical cavity, which allows for strong collective coupling of the atomic ensemble to a single mode of light. Since the light exiting the cavity is entangled with the atoms, an appropriate measurement performed on the light field can project the atomic ensemble into a squeezed spin state. I demonstrate 3.0(8) dB of spin squeezing by this method of quantum non-demolition measurement. I further introduce a new method, cavity feedback squeezing, which uses the light field circulating in the resonator to mediate an effective interaction among the atoms. The light-mediated interaction mimics the spin dynamics of the one-axis twisting Hamiltonian, under which a coherent spin state evolves deterministically into a squeezed spin state. The states prepared by cavity feedback are intrinsically squeezed by up to 10(1) dB and detectably squeezed by up to 5.6(6) dB. Applied in an atomic clock, they produce an Allan variance 4.7(5) dB below the standard quantum limit for averaging times of up to 50 s. In a detour from engineering collective spin dynamics, I present direct observations of collective motional dynamics of atoms under the influence of cavity cooling. I demonstrate cooperatively enhanced cooling of a single collective motional mode down to a mean occupation number of 2.0 (-0.3/+0.9) phonons. The cooling is quantitatively well described by a simple, analytic quantum optomechanical model. Thesis Supervisor: Vladan Vuletic Title: Lester Wolfe Associate Professor of Physics