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arXiv:0801.3538 · Europhysics Letters (EPL)

Bose-Einstein condensation on a superconducting atom chip

Cédric Roux, Andreas Emmert, Adrian Lupaşcu, Thomas Nirrengarten, Gilles Nogues, M. Brune, J.-M. Raimond, S. Haroche

Published Feb 19, 2008• 67 citations
arXivHTMLPDF

Abstract

We have produced a Bose-Einstein condensate (BEC) on an atom chip using only superconducting wires in a cryogenic environment. We observe the onset of condensation for 1·10 4 atoms at a temperature of 100 nK. This result opens the way for studies of atom losses and decoherence in a BEC interacting with a superconducting surface. Studies of dipole-blockade with long-lived Rydberg atoms in a small and dense atomic sample are underway.

DOI
10.1209/0295-5075/81/56004

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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Mar 14, 2005•0 citations
We have produced a Bose-Einstein condensate (BEC) on an atom chip using only superconducting wires in a cryogenic environment. We observe the onset of condensation for 1·10 4 atoms at a temperature of 100 nK. This result opens the way for studies of atom losses and decoherence in a BEC interacting with a superconducting surface. Studies of dipole-blockade with long-lived Rydberg atoms in a small and dense atomic sample are underway.
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In this thesis I discuss work that has been carried out on the dynamics of a Bose Einstein condensate of Rb 87 produced near an atom chip. A Bose Einstein Condensate (BEC) is a quantum state of matter where a single quantum state becomes occupied by a macroscopic number of identical Bosons. In our case this is achieved by cooling a system of trapped identical rubidium 87 atoms to its ground state. To reach temperatures of condensation we initially laser cool atoms from room temperature, before loading them into a magnetic trap. The magnetic trap is produced through a combination of uniform magnetic fields from coils outside our vacuum chamber and currents running through wires on an atom chip. The atom chip is a microfabricated device, produced by a coating a silicon chip with a thin layer of gold and etching wires into it. Together, these fields create a magnetic field minimum 120μm from the surface of the chip which can be used to confine low field seeking hyperfine states of the atom in an elongated harmonic trap. Once the atoms are confined in the magnetic trap we used force evaporative cooling out to reach the phase space densities required for Bose Einstein condensation. The BEC is used to investigate the relative dynamics between the fraction of the atoms in the condensate to those not in the condensate. Our atom chip provided a suitable environment to investigate this due to fragmentation of the magnetic potential close to the chip. Small imperfections in the wires on our atom chip mean that the trapping potential isn’t smooth. Small regions of higher trapping frequency - or fragments - are formed. Due to the small size of these fragments it is possible to find a position where a condensate can form in the fragment, and see a potential of high frequency, whereas a non-condensed atom will see a lower frequency potential. We exploit this to set the condensed fraction moving relative to the non condensed part and investigate the subsequent damping of their motion relative to each other.
Atom chips are a reliable and versatile tool for the production and control of Bose-Einstein Condensates (BECs). They also offer the possibility of realising new, chip-based quantum devices. We have recently produced BECs on an atom chip fabricated with silver foil. Because of its high current capacity, our chip can produce moderately tight traps at distances further from the chip surface, avoiding losses and fragmentation of condensates seen on other experiments. We will also report on our progress towards efficient atom detection using a STIRAP based photoionisation scheme.
We describe the production of BECs on a new type of atom chip based on silver foil. Our atom chip is fabricated with thick wires capable of carrying currents of several amperes without overheating. The silver surface is highly reflective to light resonant with optical transitions used for Rb. The pattern on the chip consists of two parallel Z-trap wires, capable of producing two-wire guide, and two additional endcap wires for varying the axial confinement. Condensates are produced in magnetic microtraps formed within 1 mm of surface of the chip. We have observed the fragmentation of cold atom clouds when brought close to the chip surface. This results from a perturbed trapping potential caused by nanometer deviations of the current path through the wires on the chip. We present results of fragmentation of cold clouds at distances below 100 μm from the wires and investigate the origin of the deviating current. The fragmentation has different characteristics to those seen with copper conductors. The dynamics of atoms in these microtraps is also investigated.