Optimized absorption imaging of mesoscopic atomic clouds

Muessel, W.; Strobel, Helmut; Joos, Maxime; Nicklas, Eike; Stroescu, Ion; Tomkovič, Jiří; Hume, David; Oberthaler, Markus K.

doi:10.1007/s00340-013-5553-8

Cited by 46 publications

(51 citation statements)

References 11 publications

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“…This is facilitated by simultaneously preparing up to 30 independent condensates in a onedimensional optical lattice potential. Atom numbers are detected via state and lattice site resolved absorption imaging with an uncertainty of ±4 atoms [20]. A typical raw image is shown in Fig.…”

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confidence: 99%

Quantum-Enhanced Sensing Based on Time Reversal of Nonlinear Dynamics

et al. 2016

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We experimentally demonstrate a nonlinear detection scheme exploiting time-reversal dynamics that disentangles continuous variable entangled states for feasible readout. Spin-exchange dynamics of Bose-Einstein condensates is used as the nonlinear mechanism which not only generates entangled states but can also be time reversed by controlled phase imprinting. For demonstration of a quantumenhanced measurement we construct an active atom SU(1,1) interferometer, where entangled state preparation and nonlinear readout both consist of parametric amplification. This scheme is capable of exhausting the quantum resource by detecting solely mean atom numbers. Controlled nonlinear transformations widen the spectrum of useful entangled states for applied quantum technologies.Nonlinear dynamics is the basis of generating nonclassical states of many particles. These entangled states are capable of improving a large variety of operations, e.g., computational tasks [1], communication and measurements [2]. Unlocking their full potential for quantum technologies requires both the generation and detection at the fundamental quantum limit. The generation of such highly entangled states with many particles has witnessed tremendous advances [3,4]. However, to fully exploit this quantum resource, the complete correlations on the single particle level need to be accessed, which still limits current experiments.To address this challenge, nonlinear readout schemes have been proposed [5][6][7][8]. Most of these employ a time inversion sequence. For this the nonlinear evolution that is used to produce the entangled state is inverted and reapplied for readout. If the state remains unperturbed, the second period of nonlinear evolution counteracts the first. This time-reversed readout disentangles the probe state such that the known separable initial state is recovered. This reversibility is nonperfect if the state is changed in between, similar to an incomplete Loschmidt-Echo [9]. By this sensitive mechanism, minute state perturbations are mapped onto readily discernable quantities.Experimentally, we use spin-changing collisions [10] in a mesoscopic spinor Bose-Einstein condensate. This nonlinear mechanism is the atomic analogue of parametric amplification, which is the textbook example of entangled state generation in quantum optics. At the same time, both the sign and the strength of the nonlinear coupling are experimentally adjustable, which makes this system ideally suited for realizing time reversal readout schemes.Spin exchange is performed in an effective three-level system within the spin F = 2 manifold of 87 Rb. For this the external degrees of freedom are frozen out such that dynamics is restricted to the spin degree of freedom. We start with a pure |F = 2, m F = 0 condensate (pump mode). Population in any m F = 0 state is carefully cleaned. During spin mixing atoms of the pump mode are coherently and pairwise scattered into the signal |↑ ≡ |2, 1 and idler |↓ ≡ |2, −1 mode, which we refer to as side modes (see Fig. 1). For small p...

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confidence: 99%

Quantum-Enhanced Sensing Based on Time Reversal of Nonlinear Dynamics

et al. 2016

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“…Another example is interferometry with spin-squeezed atomic states [5], where experimental results have shown a reduction of atom number variance approaching a level at which single-atom resolution becomes relevant [6]. Similarly, such high resolution atom detection would allow the direct observation of twin atom pairs produced via spin-changing collisions [7][8][9] and enable their use for interferometry at the Heisenberg limit.The most common detection method for neutral atoms is absorption imaging, but the precision of such measurements on mesoscopic ensembles has thus far been limited to the level of a few atoms [10,11]. Single-atom resolution for small atom numbers (N ∼ 10) has been achieved by fluorescence detection of neutral atoms in free space [12] as well as in magneto-optical traps (MOTs) [13][14][15], optical dipole traps [16] and optical cavities [17][18][19].…”

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confidence: 99%

“…The most common detection method for neutral atoms is absorption imaging, but the precision of such measurements on mesoscopic ensembles has thus far been limited to the level of a few atoms [10,11]. Single-atom resolution for small atom numbers (N ∼ 10) has been achieved by fluorescence detection of neutral atoms in free space [12] as well as in magneto-optical traps (MOTs) [13][14][15], optical dipole traps [16] and optical cavities [17][18][19].…”

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Accurate Atom Counting in Mesoscopic Ensembles

et al. 2013

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Many cold atom experiments rely on precise atom number detection, especially in the context of quantum-enhanced metrology where effects at the single particle level are important. Here, we investigate the limits of atom number counting via resonant fluorescence detection for mesoscopic samples of trapped atoms. We characterize the precision of these fluorescence measurements beginning from the single-atom level up to more than one thousand. By investigating the primary noise sources, we obtain single-atom resolution for atom numbers as high as 1200. This capability is an essential prerequisite for future experiments with highly entangled states of mesoscopic atomic ensembles.The Heisenberg uncertainty principle sets a fundamental limit, ∆φ = 1/N , on the precision at which one can determine an interferometric phase φ using N particles [1]. A prerequisite for reaching the Heisenberglimited uncertainty in a real measurement is a particle detector with atom number variance σ 2 N 1, i.e. exact particle counting at the interferometer output. This capability is challenging to realize, particularly for large particle numbers. For example, single-photon detectors suffer from limited quantum efficiency (typically < 95 %), which prohibits resolving photon numbers for N 10 [2]. On the other hand, single atoms can be detected with near-unit efficiency by trapping them and observing their fluorescence [3]. Here, we extend this single-atom counting capability to mesoscopic atom numbers by high accuracy fluorescence measurements.One example where single-atom resolution becomes necessary is spectroscopy with maximally entangled states. Here, it has been shown that Heisenberg-limited precision requires measurement of the parity [4]. Another example is interferometry with spin-squeezed atomic states [5], where experimental results have shown a reduction of atom number variance approaching a level at which single-atom resolution becomes relevant [6]. Similarly, such high resolution atom detection would allow the direct observation of twin atom pairs produced via spin-changing collisions [7][8][9] and enable their use for interferometry at the Heisenberg limit.The most common detection method for neutral atoms is absorption imaging, but the precision of such measurements on mesoscopic ensembles has thus far been limited to the level of a few atoms [10,11]. Single-atom resolution for small atom numbers (N ∼ 10) has been achieved by fluorescence detection of neutral atoms in free space [12] as well as in magneto-optical traps (MOTs) [13][14][15], optical dipole traps [16] and optical cavities [17][18][19]. A recent experiment explored the detection of mesoscopic ensembles of atoms [20] in an optical cavity, and stability at the single-atom level was observed in repeated measurements for effective atom numbers as high as N = 150. In this case, however, accurate determination of the absolute atom number was not possible due to inhomogeneous coupling to the standing-wave probe light. On the other hand, spatially resolved fluorescence me...

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“…We calibrate the absorption imaging by the procedure described in [18], whereby a scaling factor for the effective saturation intensity of the imaging transition is empirically determined. An independent method to verify this calibration relies on measuring the scaling of the imaging noise as the atom number is varied [19].…”

Section: Faraday Image Processing and Accuracymentioning

confidence: 99%

Sub-atom shot noise Faraday imaging of ultracold atom clouds

Kristensen

Gajdacz

Pedersen

et al. 2017

J. Phys. B: At. Mol. Opt. Phys.

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We demonstrate that a dispersive imaging technique based on the Faraday effect can measure the atom number in a large, ultracold atom cloud with a precision below the atom shot noise level. The minimally destructive character of the technique allows us to take multiple images of the same cloud, which enables sub-atom shot noise measurement precision of the atom number and allows for an in situ determination of the measurement precision. We have developed a noise model that quantitatively describes the noise contributions due to photon shot noise in the detected light and the noise associated with single atom loss. This model contains no free parameters and is calculated through an analysis of the fluctuations in the acquired images. For clouds containing N ∼ 5 × 10 6 atoms, we achieve a precision more than a factor of two below the atom shot noise level.

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Optimized absorption imaging of mesoscopic atomic clouds

Cited by 46 publications

References 11 publications

Quantum-Enhanced Sensing Based on Time Reversal of Nonlinear Dynamics

Quantum-Enhanced Sensing Based on Time Reversal of Nonlinear Dynamics

Accurate Atom Counting in Mesoscopic Ensembles

Sub-atom shot noise Faraday imaging of ultracold atom clouds

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