玻色-爱因斯坦凝聚体中存在粒子损失时的最优自旋压缩

Dynamical spin squeezing: combining fast one-axis twisting and deep two-axis counter-twisting

Based on the recent twisting-tensor approach [T. Opatrny, ArXiv:1408.3265 (2014)], a specific scenario for fast and deep spin squeezing is proposed. Initially the state is subjected to one-axis twisting under optimum orientation, enabling the maximum squeezing rate allowed by the system nonlinearity. Later on, when for highly squeezed states the one-axis twisting deforms the uncertainty ellipse and deteriorates the squeezing properties, the process is switched to an effective two-axis counter-twisting by a sequence of $π/2$ pulses. The squeezing rate then slows to 2/3 of the maximum value, but…

Twisting tensor and spin squeezing

A unified tensor description of quadratic spin squeezing interactions is proposed, covering the single- and two-axis twisting as special cases of a general scheme. A closed set of equations of motion of the first moments and variances is derived in Gaussian approximation and their solutions are discussed from the prospect of fastest squeezing generation. It turns out that the optimum rate of squeezing generation is governed by the difference between the largest and the smallest eigenvalues of the twisting tensor. A cascaded optical interferometer with Kerr nonlinear media is proposed as one of…

Nonlocal restoration of two-mode squeezing in the presence of strong optical loss

We present the experimental realization of a theoretical effect discovered by Olivares and Paris, in which a pair of entangled optical beams undergoing independent losses can see nonlocal correlations restored by the use of a nonlocal resource correlating the losses. Twin optical beams created in an entangled Einstein-Podolsky-Rosen (EPR) state by an optical parametric oscillator above threshold were subjected to 50% loss from beamsplitters in their paths. The resulting severe degradation of the signature quantum correlations observed between the two beams was then suppressed when another, ind…

基于内部单路径局域压缩操作改进SU(1,1)干涉仪的相位灵敏度

Improved phase sensitivity of an SU(1,1) interferometer based on the internal single-path local squeezing operation

本文提出在SU(1,1)干涉仪内部实施单路径局域压缩操作的理论方案，利用零差检测提高相位测量精度，有效增强了干涉仪对内外部光子损耗的鲁棒性。

Extreme spin squeezing for photons

We apply spin-squeezing techniques to identify and quantify highly multi-partite photonic entanglement in polarization-squeezed light. We consider a practical single-mode scenario, and find that Wineland-criterion polarization squeezing implies entanglement of a macroscopic fraction of the total photons. A Glauber-theory computation of the observable N-photon density matrix, with N up to 100, finds that N-partite entanglement is observable despite losses and without post-selection. We estimate that existing detectors could observe $\sim1000$-partite entanglement from a few dB of polarization s…

Characterizing the multipartite continuous-variable entanglement structure from squeezing coefficients and the Fisher information

Understanding the distribution of quantum entanglement over many parties is a fundamental challenge of quantum physics and is of practical relevance for several applications in the field of quantum information. Here we use methods from quantum metrology to microscopically characterize the entanglement structure of multimode continuous-variable states in all possible multi-partitions and in all reduced distributions. From experimentally measured covariance matrices of Gaussian states with 2, 3, and 4 photonic modes with controllable losses, we extract the metrological sensitivity as well as an …

光学压缩在基于微谐振器的光学传感器中的应用

Application of optical squeezing to microresonator based optical sensors

研究基于微谐振器的光学传感器量子灵敏度极限，利用腔内光压缩抑制光学损耗和自相位调制效应，实现超散粒噪声极限灵敏度，制备压缩量子态输入光可额外增益灵敏度。

Optical spin squeezing: bright beams as high-flux entangled photon sources

In analogy with the spin-squeezing inequality of Wang and Sanders [Physical Review A 68, 012101 (2003)], we find inequalities describing macroscopic polarization correlations that are obeyed by all classical fields, and whose violation implies entanglement of the photons that make up the optical beam. We consider a realistic and exactly-solvable experimental scenario employing polarization- squeezed light from an optical parametric oscillator (OPO) and find that any two photons separated by less than the OPO coherence time are polarization entangled. The polarization entanglement is robust aga…

Optimal detection of losses by thermal probes

We consider the discrimination of lossy bosonic channels and focus to the case when one of the values for the loss parameter is zero, i.e., we address the detection of a possible loss against the alternative hypothesis of an ideal lossless channel. This discrimination is performed by inputting one-mode or two-mode squeezed thermal states with fixed total energy. By optimizing over this class of states, we find that the optimal inputs are pure, thus corresponding to single- and two-mode squeezed vacuum states. In particular, we show that for any value of the damping rate smaller than a critical…

通过优化的单轴扭转和旋转实现极端自旋压缩

Extreme Spin Squeezing via Optimized One-Axis Twisting and Rotations

针对 Ramsey 干涉测量，本文提出交替使用单轴扭转脉冲与旋转来生成最优压缩态，在脉冲幅度受限和光子散射损耗下仍保持 Heisenberg 标度的计量增益。

有损多路径原子干涉仪中的压缩增强

Squeezing Enhancement in Lossy Multi-Path Atom Interferometers

本文通过引入广义输入-输出形式，研究了在包含速度选择性和散射损耗的多路径原子干涉仪中，利用自旋压缩态（特别是单轴扭曲态）提升相位灵敏度的方法，并展示了在优化布拉格分束器参数和压缩度后，即使存在实际损耗也能超越标准量子极限数分贝，同时指出了有限温度对纠缠优势的挑战。

频率依赖压缩在Einstein Telescope低频探测器中的方法

Approaches of frequency-dependent squeezing for the low frequency detector of Einstein Telescope

本文研究了在Einstein Telescope低频探测器中用耦合腔或EPR压缩替代滤波腔的可行性，发现EPR压缩可消除一个滤波腔并有望提升探测器灵敏度。

Quantum noise in three-dimensional BEC interferometry

We develop a theory of quantum fluctuations and squeezing in a three-dimensional Bose-Einstein condensate atom interferometer with nonlinear losses. We use stochastic equations in a truncated Wigner representation to treat quantum noise. Our approach includes the multi-mode spatial evolution of spinor components and describes the many-body dynamics of a mesoscopic quantum system.

Entanglement and spin-squeezing in a network of distant optical lattice clocks

We propose an approach for collective enhancement of precision for remotely located optical lattice clocks and a way of generation of the Einstein-Podolsky-Rosen state of remote clocks. Close to Heisenberg scaling of the clock precision with the number of clocks M can be achieved even for an optical channel connecting clocks with substantial losses. This scenario utilizes a collective quantum nondemolition measurement on clocks with parallel Bloch vectors for enhanced measurement precision. We provide an optimal network solution for distant clocks as well as for clocks positioned in close prox…