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arXiv:1505.02654 · Physical Review A

Robust spatial coherence 5μm from a room-temperature atom chip

Shuyu Zhou, David Groswasser, Mark Keil, Yonathan Japha, R. Folman

Published Jun 13, 2016• 4 citations
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Abstract

We study spatial coherence near a classical environment by loading a Bose-Einstein condensate into a magnetic lattice potential and observing diffraction. Even very close to a surface ($5\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{m}$), and even when the surface is at room temperature, spatial coherence persists for a relatively long time ($\ensuremath{\ge}\phantom{\rule{0.16em}{0ex}}500\phantom{\rule{0.16em}{0ex}}\mathrm{ms}$). In addition, the observed spatial coherence extends over several lattice sites, a significantly greater distance than the atom-surface separation. This opens the door for atomic circuits, and may help elucidate the interplay between spatial dephasing, interatomic interactions, and external noise.

DOI
10.1103/physreva.93.063615

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We study spatial coherence near a classical environment by loading a Bose-Einstein condensate into a magnetic lattice potential and observing diffraction. Even very close to a surface (5\ensuremathμm5\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{m}5\ensuremathμm), and even when the surface is at room temperature, spatial coherence persists for a relatively long time (\ensuremath≥500ms\ensuremath{\ge}\phantom{\rule{0.16em}{0ex}}500\phantom{\rule{0.16em}{0ex}}\mathrm{ms}\ensuremath≥500ms). In addition, the observed spatial coherence extends over several lattice sites, a significantly greater distance than the atom-surface separation. This opens the door for atomic circuits, and may help elucidate the interplay between spatial dephasing, interatomic interactions, and external noise.
In quantum physics spatial coherence allows a massive object to be present in two locations at the same time. Such spatial coherence is easily lost in the presence of a classical environment, making it unobservable in our day-to-day experience. Here we report the persistence of spatial coherence for ultra-cold atoms held only 5 m from a room temperature surface, reducing substantially the distance previously achieved between trapped atoms exhibiting spatial coherence and their classical environment. At this distance, the environment would normally destroy spatial coherence over any length greater than a few micrometers, but we nevertheless observe coherence over a length of 30 m. We show that no observable dephasing is taking place, even on a time scale on the order of one second. From a technological point of view, this may enable quantum devices based on atomic circuits. A room temperature solid quantum circuit would have enormous potential and perhaps be as important a development as the long-sought room temperature superconductor. Atom chips [1{3] are a promising candidate but a true analogue of a solid atomic circuit remains beyond reach, although impressive progress towards clocks, acceleration sensors and quantum information processing on these chips is being made. Alongside this progress towards a technological breakthrough, numerous fundamental experiments have also been made with atom chips (e.g., [4{9]). To realize a complete \solid state device with isolated atoms, at least three milestones { adapted from electronic devices { need to be met: arbitrary (e.g., not periodic) guides and traps; single site addressability; and controlled interaction via tunneling barriers. The latter requirement demands that potentials must be sculptured with a resolution on the order of the de-Broglie wavelength of the atoms (about 1 m). To achieve these milestones in a scalable device, thereby forming circuits for matter-waves (e.g., [10, 11]), one must be able to trap the atoms and manipulate their external degree of freedom coherently a few micrometers or less from the surface used to generate the potential
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We have produced a Bose-Einstein condensate on a permanent-magnet atom chip based on periodically magnetized videotape. We observe the expansion and dynamics of the condensate in one of the microscopic waveguides close to the surface. The lifetime for atoms to remain trapped near this dielectric material is significantly longer than above a metal surface of the same thickness. These results illustrate the suitability of microscopic permanent-magnet structures for quantum-coherent preparation and manipulation of cold atoms.
We use supercomputer simulations to show that interatomic interactions can strongly affect the phase evolution of Bose-Einstein condensates that are diffracted from atom chips, thereby explaining recent experiments. Interactions broaden and depopulate noncentral diffraction orders and so, counterintuitively, they actually reduce the spatial width of the diffracted cloud. This means that the experiments cannot be fully described by noninteracting theories and, consequently, interferometers that use many interacting atoms to enhance sensitivity require complex calibration. We identify device geometries required to approximate noninteracting behavior.