Mirror quiescence and high-sensitivity position measurements with feedback

Cooling of a mirror by radiation pressure

We describe an experiment in which a mirror is cooled by the radiation pressure of light. A high-finesse optical cavity with a mirror coated on a mechanical resonator is used as an optomechanical sensor of the Brownian motion of the mirror. A feedback mechanism controls this motion via the radiation pressure of a laser beam reflected on the mirror. We have observed either a cooling or a heating of the mirror, depending on the gain of the feedback loop.

Quantum locking of mirrors in interferometers

We show that quantum noise in very sensitive interferometric measurements such as gravitational-waves detectors can be drastically modified by quantum feedback. We present a new scheme based on active control to lock the motion of a mirror to a reference mirror at the quantum level. This simple technique allows to reduce quantum effects of radiation pressure and to greatly enhance the sensitivity of the detection.

Delayed Coherent Quantum Feedback from a Scattering Theory and a Matrix Product State Perspective

We study the scattering of photons propagating in a semi-infinite waveguide terminated by a mirror and interacting with a quantum emitter. This paradigm constitutes an example of coherent quantum feedback, where light emitted towards the mirror gets redirected back to the emitter. We derive an analytical solution for the scattering of two-photon states, which is based on an exact resummation of the perturbative expansion of the scattering matrix, in a regime where the time delay of the coherent feedback is comparable to the timescale of the quantum emitter's dynamics. We compare the results wi…

Macroscopic mechanical oscillators at the quantum limit using optomechanical cooling

We discuss how the optomechanical coupling provided by radiation pressure can be used to cool macroscopic collective degrees of freedom, as vibrational modes of movable mirrors. Cooling is achieved using a phase-sensitive feedback-loop which effectively overdamps the mirrors motion without increasing the thermal noise. Feedback results able to bring macroscopic objects down to the quantum limit. In particular, it is possible to achieve squeezing and entanglement.

Phase control of a longitudinal momentum entangled photon state by a deformable membrane mirror

We propose a paradigmatic demonstration of the potentialities of a deformable mirror for closed-loop control of a two-photon momentum-entangled state, subject to phase fluctuations. A custom-made membrane mirror is used to set a relative phase shift between the arms of an interferometric apparatus. The control algorithm estimates the phase of the quantum state, by measurements of the coincidence events at the output ports of the interferometer, and uses the measurements results to provide a feedback signal to the deformable mirror. Stabilization of the coincidence rate to within 1.5 standard d…

反馈控制诱导量子纠缠的涌现与增强

Emergence and enhancement of feedback control induced quantum entanglement

本文提出通过反馈控制增强量子纠缠的方案，展示在混合腔磁机械系统中增强双体和三体量子关联，并证明其对环境温度的鲁棒性。

Position measurement of a levitated nanoparticle via interference with its mirror image

Interferometric methods for detecting the motion of a levitated nanoparticle provide a route to the quantum ground state, but such methods are currently limited by mode mismatch between the reference beam and the dipolar field scattered by the particle. Here we demonstrate a self-interference method to detect the particle's motion that solves this problem. A Paul trap confines a charged dielectric nanoparticle in high vacuum, and a mirror retro-reflects the scattered light. We measure the particle's motion with a sensitivity of $1.7\times 10^{-12} \text{m}/\sqrt{\text{Hz}}$, corresponding to a…

Self-cooling of a micro-mirror by radiation pressure

We demonstrate passive feedback cooling of a mechanical resonator based on radiation pressure forces and assisted by photothermal forces in a high-finesse optical cavity. The resonator is a free-standing high-reflectance micro-mirror (of mass m=400ng and mechanical quality factor Q=10^4) that is used as back-mirror in a detuned Fabry-Perot cavity of optical finesse F=500. We observe an increased damping in the dynamics of the mechanical oscillator by a factor of 30 and a corresponding cooling of the oscillator modes below 10 K starting from room temperature. This effect is an important ingredi…

Back-action cancellation in interferometers by quantum locking

We show that back-action noise in interferometric measurements such as gravitational-waves detectors can be completely suppressed by a local control of mirrors motion. An optomechanical sensor with an optimized measurement strategy is used to monitor mirror displacements. A feedback loop then eliminates radiation-pressure effects without adding noise. This very efficient technique leads to an increased sensitivity for the interferometric measurement, which becomes only limited by phase noise. Back-action cancellation is furthermore insensitive to losses in the interferometer.

制备兼容高耦合效率的光纤腔镜基底

Fabricating fiber cavity mirror substrates compatible with high coupling efficiency

提出一种利用原位反射测量法在镀膜前评估光纤镜基底模式匹配能力的技术，通过预选光纤和CO2激光烧蚀，实现95%以上的模式匹配，提高了制备良率。

Creation of a quantum oscillator by classical control

As a pure quantum state is being approached via linear feedback, and the occupation number approaches and eventually goes below unity, optimal control becomes crucial. We obtain theoretically the optimal feedback controller that minimizes the uncertainty for a general linear measurement process, and show that even in the absence of classical noise, a pure quantum state is not always achievable via feedback. For Markovian measurements, the deviation from minimum Heisenberg Uncertainty is found to be closely related to the extent to which the device beats the free-mass Standard Quantum Limit for…

基于与半无限波导耦合原子的量子相干反馈控制与测量反馈控制

Quantum coherent and measurement feedback control based on atoms coupled with a semi-infinite waveguide

本文针对半无限波导耦合多二能级原子系统，提出量子相干与测量反馈控制方法，可生成目标量子态，利用随机图论解释演化，消除环境影响并处理零差检测噪声引发的振荡。