Igor Teper, Geert Vrijsen, Jongmin Lee, Mark A. Kasevich
We use a quantum nondemolition measurement to probe the collective pseudospin of an atomic ensemble in a high-finesse optical cavity. We analyze the backaction antisqueezing produced by the measurement process to show that our protocol could create conditional spin squeezing in the atomic ensemble.
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We use a reservoir engineering technique based on two-tone driving to generate and stabilize a quantum squeezed state of a micron-scale mechanical oscillator in a microwave optomechanical system. Using an independent backaction evading measurement to directly quantify the squeezing, we observe $4.7\pm0.9$ dB of squeezing below the zero-point level, surpassing the 3 dB limit of standard parametric squeezing techniques. Our measurements also reveal evidence for an additional mechanical parametric effect. The interplay between this effect and the optomechanical interaction enhances the amount of …
Characterization of Linear Measurements in Cavity Optomechanics: Examples and Applications
本文提出一套基于品质因数的腔光机械线性测量表征形式体系，分析位移探测、相干量子噪声消除与量子非破坏测量，并据此设计悬浮动力学中的相干散射QND方案。
A general approach to backaction-evading receivers with magnetomechanical and electromechanical sensors
本文提出利用传统电磁换能器实现规避反作用的直接速度测量理论模型，通过构建玩具模型评估测量噪声，发现读出方案选择决定对机械子系统位置或速度的获取，为暗物质粒子直接探测等基础物理实验指明了方向。
Impressive pictures of moving Bose-Einstein condensates have been taken using phase-contrast imaging M. R. Andrews et al., Science 273, 84 (1996). We calculate the quantum backaction of this measurement technique. We find that phase-contrast imaging is not a quantum nondemolition measurement of the atomic density. Instead, the condensate gets gradually depleted at a rate that is proportional to the light intensity and to the inverse cube of the optical wave length. The fewer atoms are condensed the higher is the required intensity to see a picture, and, consequently, the higher is the induced …
It is shown that the quantum jumps in the photon number n from zero to one or more photons induced by backaction evasion quantum nondemolition measurements of a quadrature component x of the vacuum light field state are strongly correlated with the quadrature component measurement results. This correlation corresponds to the operator expectation value <xnx> which is equal to one fourth for the vacuum even though the photon number eigenvalue is zero. Quantum nondemolition measurements of a quadrature component can thus provide experimental evidence of the nonclassical operator ordering dependen…
We present a detailed theoretical description of an atomic scanning microscope in a cavity QED setup proposed in Phys. Rev. Lett. 120, 133601 (2018). The microscope continuously observes atomic densities with optical subwavelength resolution in a nondestructive way. The super-resolution is achieved by engineering an internal atomic dark state with a sharp spatial variation of population of a ground level dispersively coupled to the cavity field. Thus, the atomic position encoded in the internal state is revealed as a phase shift of the light reflected from the cavity in a homodyne experiment. …
A kicked quantum nondemolition measurement is introduced, where a qubit is weakly measured by pumping current. Measurement statistics are derived for weak measurements combined with single qubit unitary operations. These results are applied to violate a generalization of Leggett and Garg's inequality. The violation is related to the failure of the noninvasive detector assumption, and may be interpreted as either intrinsic detector backaction, or the qubit entangling the microscopic detector excitations. The results are discussed in terms of a quantum point contact kicked by a pulse generator, …
In this review, we study how a hybrid optomechanical system (OMS), in which a quantum micro- or nano-mechanical oscillator (MO) is coupled to the electromagnetic (EM) radiation pressure, consisting of an ensemble of ultracold atoms or an atomic Bose-Einstein condensate (BEC), can be used as an ultra precision quantum sensor for measuring very weak signals. As is well-known in any precise quantum measurement the competition between the shot noise (SN) and the backaction noise of measurement executes a limitation on the measurement precision which is the so-called standard quantum limit (SQL). I…
With the advent of gravitational wave detectors employing squeezed light, quantum waveform estimation---estimating a time-dependent signal by means of a quantum-mechanical probe---is of increasing importance. As is well known, backaction of quantum measurement limits the precision with which the waveform can be estimated, though these limits can in principle be overcome by "quantum nondemolition" (QND) measurement setups found in the literature. Strictly speaking, however, their implementation would require infinite energy, as their mathematical description involves Hamiltonians unbounded from…
This article reviews recent research towards a universal light-matter interface. Such an interface is an important prerequisite for long distance quantum communication, entanglement assisted sensing and measurement, as well as for scalable photonic quantum computation. We review the developments in light-matter interfaces based on room temperature atomic vapors interacting with propagating pulses via the Faraday effect. This interaction has long been used as a tool for quantum nondemolition detections of atomic spins via light. It was discovered recently that this type of light-matter interact…
We study the three-dimensional nature of the quantum interface between an ensemble of cold, trapped atomic spins and a paraxial laser beam, coupled through a dispersive interaction. To achieve strong entanglement between the collective atomic spin and the photons, one must match the spatial mode of the collective radiation of the ensemble with the mode of the laser beam while minimizing the effects of decoherence due to optical pumping. For ensembles coupling to a probe field that varies over the extent of the cloud, the set of atoms that indistinguishably radiates into a desired mode of the f…
Monitoring the energy of a cavity by observing the emission of a repeatedly excited qubit
本研究利用色散耦合量子比特的荧光测量，实现了单次光子计数与腔内光子数跟踪，观察到光子逐一离开腔时的量子跃迁，为玻色子码量子纠错提供了新方法。
Quantum enhanced sensing is a powerful technique in which nonclassical states are used to improve the sensitivity of a measurement. For enhanced mechanical displacement sensing, squeezed states of light have been shown to reduce the photon counting noise that limits the measurement noise floor. It has long been predicted, however, that suppressing the noise floor with squeezed light should produce an unavoidable increase in radiation pressure noise that drives the mechanical system. Such nonclassical radiation pressure forces have thus far been hidden by insufficient measurement strengths and …
Squeezing of collective atomic spins has been shown to improve the sensitivity of atomic clocks and magnetometers to levels significantly below the standard quantum limit. In most cases the requisite atom-atom entanglement has been generated by dispersive interaction with a quantized probe field, or by state dependent collisions in a quantum gas. Such experiments typically use complex multilevel atoms like Rb or Cs, with the relevant interactions designed so atoms behave like pseudo-spin-$1/2$ particles. We demonstrate the viability of spin squeezing for collective spins composed of the physic…
Noise-Canceling Quantum Feedback: non-Hermitian Dynamics with Applications to State Preparation and Magic State Distillation
本文研究了通过连续量子测量实现噪声消除反馈控制，展示了非厄米特哈密顿量在量子态制备和魔态提纯中的应用，证明了在理想条件下噪声消除反馈能确定性地产生非厄米特动力学。
Multi-Shot Quantum Sensing for RF Signal Detection with MIMO Rydberg-Atom Receivers
本文提出了一种基于瑞利德原子接收器的多 shot 量子传感方法，通过相平均检验和非相干能量检测，实现了对弱场 RF 信号的高效检测，优于传统方法。
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