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Continuous monitoring or tracking of a quantum system is essential to high-sensitivity measurement of time-varying quantities. We estimate spin precession of a magnetically-sensitive atomic ensemble by measuring spin projectors Fα at different times. Such projectors do not commute, and thus quantum measurement back-action (QMBA) necessarily enters the spin measurement record, introducing errors and...
We demonstrate detection of radio-frequency fields and arbitrarily-shaped radio-frequency waveform components beyond the projection noise limit (PNL). Our work employs a measure-evolve-measure (MEM) sequence, in which a first stroboscopic quantum non-demolition (QND) measurement M1 produces a state with reduced projection noise, a period of free evolution accumulates signal, and a second stroboscopic...
We report an experimental study of a new technique for spin cooling an ensemble of ultracold atoms via quantum non-demolition (QND) measurement and incoherent feedback. We have demonstrated 12db spin noise reduction. This technique has direct application in generating highly entangled macroscopic singlet states.
We report certified quantum non-demolition measurement of atomic spins using criteria developed for continuous variable experiments in optics. We observe quantum state preparation and information-damage trade-off beyond classical limits by seven and twelve standard deviations.
We report on a fast, nondestructive and sensitive measurement technique that uses atomic spin precession and non-destructive Faraday rotation probing to measure all three components of the magnetic field with kHz bandwidth. In contrast to other vector magnetometer techniques that modulate an applied magnetic field [1, 2, 3] we modulate the initial atomic polarization and extract the magnetic field...
Techniques for making quantum-limited nonlinear measurements have attracted a great deal of recent attention because they allow a measurement sensitivity that improves as the number of measuring particles (e.g. photons) increases faster than an equivalent linear measurement. This super-Heisenberg scaling was recently demonstrated in a proof-of-principle experiment [1], in which a measurement Hamiltonian...
We report an experimental study of a new technique for spin cooling an ensemble of ultracold atoms via quantum non-demolition (QND) measurement and incoherent feedback. This is a form of entropie cooling of the spins that increases the phase space density, in contrast to coherent feedback schemes such as described in Refs.[l, 2]. Our technique has potential applications in quantum optics such as quantum...
We extend the covariance-matrix description of atom-light quantum interfaces to spin-1 systems including technical noise and decoherences. We use this description to predict and produce a planar squeezed state in a cold 87Rb ensemble.
We report a nonlinear alignment-to-orientation conversion measurement of atomic spins that simultaneously shows super-Heisenberg scaling and achieves projection-noise limited sensitivity of 990 spins, 20 dB more sensitive than the previous best nonlinear measurement. Using this technique, we have recently demonstrated conditional spin squeezing of the atomic ensemble, and entanglement-enhanced measurement...
We report an experimental study of a new technique for entropic cooling of the spin in an ensemble of ultracold atoms via quantum non-demolition (QND) measurement and incoherent feedback.
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