Detection of small atom numbers through image processing

Ockeloen, C.F.; Tauschinsky, Atreju; Spreeuw, R. J. C.; Whitlock, S.

doi:10.1103/physreva.82.061606

Cited by 99 publications

(93 citation statements)

References 31 publications

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“…In order to reduce the shot noise in the absorption images, we use a ten times longer reference pulse. To further improve the quality of the absorption images, we apply a fringe removal algorithm [52].…”

Section: Absorption Imaging Parameters and Calibrationsmentioning

confidence: 99%

Observation of Pair Condensation in the Quasi-2D BEC-BCS Crossover

et al. 2015

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The condensation of fermion pairs lies at the heart of superfluidity. However, for strongly correlated systems with reduced dimensionality the mechanisms of pairing and condensation are still not fully understood. In our experiment we use ultracold atoms as a generic model system to study the phase transition from a normal to a condensed phase in a strongly interacting quasi-two-dimensional Fermi gas. Using a novel method, we obtain the in situ pair momentum distribution of the strongly interacting system and observe the emergence of a low-momentum condensate at low temperatures. By tuning temperature and interaction strength we map out the phase diagram of the quasi-2D BEC-BCS crossover.The characteristics of quantum many-body systems are strongly affected by their dimensionality and the strength of interparticle correlations. In particular, strongly correlated two-dimensional fermionic systems have been of interest because of their connection to high-T c superconductivity. Although they have been the subject of intense theoretical studies [1][2][3][4][5][6][7][8], a complete theoretical framework has not yet been established.Ultracold quantum gases are an ideal realization for exploring strongly interacting 2D Fermi gases, as they offer the possibility of independently tuning the dimensionality and the strength of interparticle interactions. Reducing the dimensionality [9] led to the observation of a Berezinskii-Kosterlitz-Thouless (BKT) type phase transition to a superfluid phase in weakly interacting 2D Bose gases [10,11]. Tuning the strength of interactions in a three-dimensional two-component Fermi gas made it possible to explore the crossover between a molecular Bose-Einstein Condensate (BEC) and a BCS superfluid [12][13][14][15].Recently, efforts have been made to combine reduced dimensionality with the tunability of interactions and to experimentally explore ultracold 2D Fermi gases [16][17][18][19][20][21]. However, the phase transition to a condensed phase has not yet been observed. Here, we report on the condensation of pairs of fermions in the quasi-2D BEC-BCS crossover.The BEC-BCS crossover smoothly links a bosonic superfluid of tightly bound diatomic molecules to a fermionic superfluid of Cooper pairs in 2D as well as 3D systems. However, changing the dimensionality leads to some inherent differences. In two dimensions, there is a two-body bound state for all values of the interparticle interaction. Furthermore, because of the enhanced role of * To whom correspondence should be addressed. E-mail: mries@physi.uni-heidelberg.de † These authors contributed equally to this work. ‡ Present address: MIT-Harvard Center for Ultracold Atoms, MIT, Cambridge, MA 02139, USA.fluctuations in 2D, true long-range order is forbidden for homogeneous systems at finite temperature [22,23]. Still, a low temperature superfluid phase with quasi-long-range order can emerge due to the BKT mechanism [24,25]. In a 2D gas with contact interactions, the interactions can be described by the 2D scattering length a 2D . Using th...

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Section: Absorption Imaging Parameters and Calibrationsmentioning

confidence: 99%

Observation of Pair Condensation in the Quasi-2D BEC-BCS Crossover

et al. 2015

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“…One straightforward application of this new capability is to image the spatial distribution of a molecular ensemble and, by taking images at different times, to access the phase-space distribution. Similar experiments have been used with ultracold atoms to measure their temperature [21][22][23][24]. In such experiments, the typical densities are high enough to guarantee thermalization of the ensemble, but in our experiments the densities are much too low, yet we nevertheless observe a nearly Maxwell-Boltzmann energy distribution.…”

Section: Introductionmentioning

confidence: 73%

“…In the atomic case, an atom cloud is illuminated with a laser beam tuned to a closed optical transition. To gain an image of the cloud, either the many scattered photons are imaged (fluorescence imaging), or the shadow cast in the laser beam is imaged (absorption imaging) [21][22][23][24]. The expansion of the gas over time is related to the temperature of the gas, and hence, this method is a relatively straightforward way of ascertaining the temperature.…”

Section: Measuring the Temperaturementioning

confidence: 99%

Measuring and manipulating the temperature of cold molecules trapped on a chip

et al. 2015

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Following Marx et al. [Phys. Rev. Lett. 111, 243007 (2013)], we discuss the measurement and manipulation of the temperature of cold CO molecules in a microchip environment. In particular, we present a model to explain the observed and calculated velocity distributions. We also show that a translational temperature can be extracted directly from the measurements. Finally, we discuss the conditions needed for an effective adiabatic cooling of the molecular ensemble trapped on the microchip.

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“…Between these two, a transverse laser beam blows away the F = 2 atoms. Numerical frame re-composition generates the respective reference images and largely reduces the effect of optical fringes [51]. Calculation of the optical density and correction for the high saturation [52] give access to the atom column density.…”

Section: Experimental Set-upmentioning

confidence: 99%

Stability of a trapped-atom clock on a chip

et al. 2015

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We present a compact atomic clock interrogating ultracold 87 Rb magnetically trapped on an atom chip. Very long coherence times sustained by spin self-rephasing allow us to interrogate the atomic transition with 85% contrast at 5 s Ramsey time. The clock exhibits a fractional frequency stability of 5.8 × 10 −13 at 1 s and is likely to integrate into the 10 −15 range in less than a day. A detailed analysis of 7 noise sources explains the measured frequency stability. Fluctuations in the atom temperature (0.4 nK shot-to-shot) and in the offset magnetic field (5 × 10 −6 relative fluctuations shot-to-shot) are the main noise sources together with the local oscillator, which is degraded by the 30% duty cycle. The analysis suggests technical improvements to be implemented in a future second generation set-up. The results demonstrate the remarkable degree of technical control that can be reached in an atom chip experiment.

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Detection of small atom numbers through image processing

Cited by 99 publications

References 31 publications

Observation of Pair Condensation in the Quasi-2D BEC-BCS Crossover

Observation of Pair Condensation in the Quasi-2D BEC-BCS Crossover

Measuring and manipulating the temperature of cold molecules trapped on a chip

Stability of a trapped-atom clock on a chip

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