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European Quantum Electronics Conference (EQEC)

Maximum Contrast Interferometry and Coherence in Bose-Einstein Condensates

Victoria Henderson, Yueyang Zhai, Christopher Carson, Paul F. Griffin, Erling Riis, Aidan S. Arnold

Published Jun 21, 2015• 0 citations
OpenAlex

Abstract

Magnetic levitation is used to obtain clear spatial interference between two Bose-Einstein condensates which are initially axially separated. Fringes with periods of up to 85 µm are observed using standard (non-tomographic) resonant absorption imaging, utilising the `magnifying' effect of a weak axial inverted parabolic potential [1]. With 160ms levitation [2], and careful choice of probe detuning, single-shot interference contrast of > 95% is observed (Fig. 1a) - close to the theoretical limit caused by CCD camera pixellation of the sinusoidal fringes. In addition, we observe dramatic variation of the fringe contrast as a function of camera focal position due to the spatial Talbot effect.

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Magnetic levitation is used to obtain clear spatial interference between two Bose-Einstein condensates which are initially axially separated. Fringes with periods of up to 85 µm are observed using standard (non-tomographic) resonant absorption imaging, utilising the `magnifying' effect of a weak axial inverted parabolic potential [1]. With 160ms levitation [2], and careful choice of probe detuning, single-shot interference contrast of > 95% is observed (Fig. 1a) - close to the theoretical limit caused by CCD camera pixellation of the sinusoidal fringes. In addition, we observe dramatic variation of the fringe contrast as a function of camera focal position due to the spatial Talbot effect.
We use magnetic levitation and a variable-separation dual optical plug to obtain clear spatial interference between two condensates axially separated by up to 0.250.250.25 mm---the largest separation observed with this kind of interferometer. Clear planar fringes are observed using standard (i.e., nontomographic) resonant absorption imaging. The effect of a weak inverted parabola potential on fringe separation is observed and agrees well with theory.
We use magnetic levitation [1-3] and a variable-separation dual optical plug [4] to obtain clear spatial interference between two BECs axially separated by up to 0.25mm. Fringes are observed using standard (i.e. non-tomographic) resonant absorption imaging. The `magnifying' effect of a weak inverted parabola potential on fringe separation is observed and agrees well with theory [4]. With 160ms levitation we recently observed single-shot interference contrasts of 95% (see 1.5×0.75mm absorption image below), close to the theoretical limit due to pixellation of the sinusoidal fringes on our CCD camera. Interference patterns with fringe periods of 85microns (individual de Broglie wavelengths of 170microns) are possible with 200ms levitation.
Nearly two centuries ago Talbot first observed the fascinating effect whereby light propagating through a periodic structure generates a ‘carpet’ of image revivals in the near field. Here we report the first observation of the spatial Talbot effect for light interacting with periodic Bose-Einstein condensate interference fringes. The Talbot effect can lead to dramatic loss of fringe visibility in images, degrading precision interferometry, however we demonstrate how the effect can also be used as a tool to enhance visibility, as well as extend the useful focal range of matter wave detection systems by orders of magnitude. We show that negative optical densities arise from matter-wave induced lensing of detuned imaging light – yielding Talbot-enhanced single-shot interference visibility of > 135% compared to the ideal visibility for resonant light.
Nearly two centuries ago Talbot first observed the fascinating effect whereby light propagating through a periodic structure generates a `carpet' of image revivals in the near field. Here we report the first observation of the spatial Talbot effect for light interacting with periodic Bose-Einstein condensate interference fringes. The Talbot effect can lead to dramatic loss of fringe visibility in images, degrading precision interferometry, however we demonstrate how the effect can also be used as a tool to enhance visibility, as well as extend the useful focal range of matter wave detection systems by orders of magnitude. We show that negative optical densities arise from matter-wave induced lensing of detuned imaging light -- yielding Talbot-enhanced single-shot interference visibility of >135% compared to the ideal visibility for resonant light.
Interference between two freely expanding Bose-Einstein condensates has been observed. Two condensates separated by approximately 40 micrometers were created by evaporatively cooling sodium atoms in a double-well potential formed by magnetic and optical forces. High-contrast matter-wave interference fringes with a period of approximately 15 micrometers were observed after switching off the potential and letting the condensates expand for 40 milliseconds and overlap. This demonstrates that Bose condensed atoms are "laser-like"; that is, they are coherent and show long-range correlations. These results have direct implications for the atom laser and the Josephson effect for atoms.
This chapter describes the Bose--Einstein condensate (BEC) interferometry. We first introduce the optical interferometer, briefly discussing the role of fringe contrast in observing interference patterns. Next, we examine a BEC interferometer in a Michelson geometry that consists of a BEC in a trapping potential well. The BEC cloud in the potential well is put into a linear superposition of two clouds that travel along different paths in the trap and are recombined using the same light beams. By studying the population of atoms in the different motional states of the BEC clouds that emerge after recombination, we obtain information about the relative phase shift accumulated by the two traveling superposed condensates during the interferometry. We then characterize the atom distribution that is found in the output of the interferometer by finding the probability density distribution and calculating the features of the probability density such as the mean, the variance, and the interference fringe contrast. Finally, we parameterize the effect of two-body collisional interactions on the observed interference fringes in a way that can be directly controlled in an experiment.