Coherence in Microchip Traps

Philipp Treutlein, Peter Hommelhoff, Tilo Steinmetz, Theodor W. Hänsch, Jakob Reichel
2004 Physical Review Letters  
We report the coherent manipulation of internal states of neutral atoms in a magnetic microchip trap. Coherence lifetimes exceeding 1 s are observed with atoms at distances of 5-130 m from the microchip surface. The coherence lifetime in the chip trap is independent of atom-surface distance within our measurement accuracy and agrees well with the results of similar measurements in macroscopic magnetic traps. Because of the absence of surface-induced decoherence, a miniaturized atomic clock with
more » ... a relative stability in the 10 ÿ13 range can be realized. For applications in quantum information processing, we propose to use microwave near fields in the proximity of chip wires to create potentials that depend on the internal state of the atoms. Magnetic microchip traps provide one of the few available techniques for manipulating neutral atoms on the micrometer scale and the only technique so far that enables nonperiodic, built-to-purpose micron-sized potentials [1]. The on-chip creation of Bose-Einstein condensates [2,3] and the highly controlled manipulation of atomic motion in "atomic conveyor belts," waveguides, and thermal beam splitters [1] are examples of the versatility of such "atom chips." Because of these possibilities, chip traps are promising candidates for the implementation of quantum gates [4], quantum simulations [5] , and interferometric sensors [6] . The ability to manipulate superpositions of internal states of the trapped atoms is essential for most of these applications. In quantum information processing (QIP), two internal states, j0i and j1i, of the atom serve as qubit states. To perform gate operations, long coherence lifetimes of the superposition states j0i j1i are required, and therefore decoherence processes have to be avoided. Atoms in chip traps, however, can potentially suffer from a reduction of the coherence lifetime due to interaction with the surface of the chip [7] in addition to other decoherence mechanisms which are also present in macroscopic traps [8] . In this Letter, we demonstrate coherent manipulation of internal atomic states in a magnetic microchip trap. We create superpositions of two hyperfine ground states of 87 Rb atoms in a thermal ensemble close to quantum degeneracy and perform Ramsey spectroscopy to determine the coherence lifetime (Fig. 1) . With atoms at distances of 5-130 m from the surface of the chip, we observe coherence lifetimes exceeding 1 s. These lifetimes are independent of the atom-surface distance and agree well with those observed in macroscopic magnetic traps [8] . The observed robustness of the superposition states is an extremely encouraging result for atom chip applications in QIP and opens a new perspective on applications in precision metrology. We demonstrate an atomic clock in the chip trap and measure the relative stability of its transition frequency. Our measurements show that a portable atom chip clock with a relative stability in the 10 ÿ13 ÿ1=2 = Hz p range is a realistic goal. To realize the collisional phase gate proposed in [4], a state-selective potential is needed. We point out that stateselectivity for our state pair can be provided by microwave potentials. These potentials, considered in the early 1990s [9,10] but abandoned later, gain new actuality as near-field traps on atom chips. To achieve long coherence lifetimes with magnetically trapped atoms in the proximity of the chip surface, we choose the jF 1;m F ÿ1i j0i and jF 2;m F 1i j1i hyperfine levels of the 5S 1=2 ground state of 87 Rb. The magnetic moments of the two states are approximately equal. At a magnetic field of B 0 3:23 G, both states experience the same first-order Zeeman shift, and the remaining magnetic field dependence of the transition frequency 10 is minimized [8] . In all of our experiments, we therefore adjust the field in the center of the trap to B 0
doi:10.1103/physrevlett.92.203005 pmid:15169350 fatcat:5al2vryq55bdtcf4odd7qesptm