Adaptive phase estimation is more accurate than non-adaptive phase estimation for continuous beams of light

Adaptive phase measurements for narrowband squeezed beams

We have previously [Phys. Rev. A 65, 043803 (2002)] analyzed adaptive measurements for estimating the continuously varying phase of a coherent beam, and a broadband squeezed beam. A real squeezed beam must have finite photon flux N and hence can be significantly squeezed only over a limited frequency range. In this paper we analyze adaptive phase measurements of this type for a realistic model of a squeezed beam. We show that, provided it is possible to suitably choose the parameters of the beam, a mean-square phase uncertainty scaling as (N/kappa)^{-5/8} is possible, where kappa is the linewi…

Adaptive loop-based subtraction of a single photon from a traveling beam of light

Manipulating light by adding and subtracting individual photons is a powerful approach with a principal drawback: the operations are fundamentally probabilistic and the probability is often small. This limits not only the fundamental scalability but also the number of operations that can be applied in realistic experimental settings. We propose and analyze an adaptive technique which can significantly increase the probability of success while preserving the quality of the photon subtraction. We show the improvement both in single mode preparation and manipulation of non-Gaussian states with ne…

Adaptive Quantum Measurements of a Continuously Varying Phase

We analyze the problem of quantum-limited estimation of a stochastically varying phase of a continuous beam (rather than a pulse) of the electromagnetic field. We consider both non-adaptive and adaptive measurements, and both dyne detection (using a local oscillator) and interferometric detection. We take the phase variation to be \dotϕ= \sqrtκξ(t), where ξ(t) is δ-correlated Gaussian noise. For a beam of power P, the important dimensionless parameter is N=P/\hbarωκ, the number of photons per coherence time. For the case of dyne detection, both continuous-wave (cw) coherent beams and cw (broad…

Quantum Rotor Atoms in Light Beams with Orbital Angular Momentum: Highly Accurate Rotation Sensor

Atoms trapped in a red detuned retro-reflected Laguerre-Gaussian beam undergo orbital motion within rings whose centers are on the axis of the laser beam. We determine the wave functions, energies and degeneracies of such quantum rotors (QRs), and the microwave transitions between the energy levels are elucidated. We then show how such QR atoms can be used as high-accuracy rotation sensors when the rings are singly-occupied.

Quantum state engineering with twisted photons via adaptive shaping of the pump beam

High-dimensional entanglement is a valuable resource for quantum communication, and photon pairs entangled in orbital angular momentum are commonly used for encoding high-dimensional quantum states. However, methods for preparation of maximally entangled states of arbitrary dimensionality are still lacking, and currently used approaches essentially rely on filtering and entanglement concentration. Here we experimentally realize a method for generation of high-dimensional maximally entangled OAM states of photon pairs which does not require any of these procedures. Moreover, the prepared state …

基于无人机（UAV）的自由空间量子链路统一框架：光束整形与自适应视场（FoV）控制

A Unified Framework for UAV-Based Free-Space Quantum Links: Beam Shaping and Adaptive Field-of-View Control

本文提出一个用于无人机到地面量子通信链路的统一分析框架，结合多种物理损伤并引入基于网格的光子捕获概率近似，推导了量子密钥生成率和QBER的解析表达式，揭示了实现安全QKD所需的光束腰和跟踪精度条件，并提出自适应FoV调整策略。