Single Atoms in an Optical Dipole Trap: Towards a Deterministic Source of Cold Atoms

Abstract

We describe a simple experimental technique which allows us to store a small and deterministic number of neutral atoms in an optical dipole trap. The desired atom number is prepared in a magneto-optical trap overlapped with a single focused Nd:YAG laser beam. Dipole trap loading efficiency of 100 % and storage times of about one minute have been achieved. We have also prepared atoms in a certain hyperfine state and demonstrated the feasibility of a state-selective detection via resonance fluorescence at the level of a few neutral atoms. A spin relaxation time of the polarized sample of 4.2 ± 0.7 s has been measured. Possible applications are briefly discussed. 32.80Pj, 42.50VkNeutral atoms can conveniently and at very low kinetic energy be stored in a magneto-optical trap (MOT) [1], not only in large quantities but also in small and exactly known numbers of up to 20 single atoms [2,3]. For several applications, for instance in cavity quantum electrodynamics [4], it is of interest to use perfectly controlled or deterministic samples of atoms for further experiments involving quantum interactions of an exactly known number of atoms. Full control of all internal and external atomic degrees of freedom is necessary in such applications, but cannot be achieved in a MOT since due to its dissipative character all degrees of freedom are intimately mixed. In order to overcome this problem one can therefore combine the operating convenience of the MOT for isolated atoms with the advantages for quantum manipulation offered by the nearly conservative potential of optical dipole traps. The interest in optical dipole traps [5] as an elegant and simple way to store laser-cooled neutral atoms has rapidly increased within the last few years [6]. Far-off-resonance optical dipole traps [7] can confine atoms in all ground states for a long time with a very small ground-state relaxation rate [8]. Cold atoms can be localized in micropotentials of a 3D periodic potential created by interfering laser beams (so-called optical lattices [9]). Such experiments always operate with at least several thousands of atoms, the atom number can not be determined exactly and is controlled only on average.In the present work we load a small and exactly known atom number into an optical dipole trap with 100% efficiency, opening up a route to a novel kind of cold atom sources free of the indeterminism intrinsic to usual sources like atom beams. We have also demonstrated the feasibility of a state-selective detection at the level of a few neutral atoms and measured a long spin relaxation time of some seconds. Together with recently demonstrated Raman sideband cooling [10] and the generation of non-classical motional states of atoms in standing-wave dipole traps [11], this system promises to be a new basis for future experiments with full control of all atomic degrees of freedom. One of the most interesting possibilities would be long-time localization of more than one atom within a mode of a high finesse cavity.The relevant part of the apparatus is shown...

Analysis of a quantum logic device based on dipole-dipole interactions of optically trapped Rydberg atoms

“…We have found in unpublished experiments that a MOT density of a few times 10 8 /cm 3 is sufficient to load single atoms as was demonstrated by several groups in recent years [31,32].…”

“…Far-offresonance optical traps (FORTs) are defined by tightly focusing laser light in a set of chosen locations. Single atoms are loaded into the optical traps after precooling in a magneto-optical trap [31,32]. Single qubit operations are performed using two-photon stimulated Raman transitions, and a two-qubit conditional phase gate is realized using dipole-dipole coupling of atoms excited to high lying Rydberg states [21].…”

Scaling the neutral-atom Rydberg gate quantum computer by collective encoding in holmium atoms

“…A number of subsequent papers have analyzed in more detail specific schemes for implementing Rydberg gates [17,18,19] with the conclusion that they present a very promising approach to quantum logic. At this time a neutral atom Rydberg gate has not been demonstrated experimentally, although many of the underlying requirements have been separately achieved including loading and manipulation of single atoms in optical traps [20,21,22], signatures of Rydberg interactions and dipole blockade at the many atom level [23], and recently coherent excitation of Rydberg states together with observation of interaction effects at the level of two atoms [24].…”

Analysis of dephasing mechanisms in a standing-wave dipole trap

“…Note that the experiments of Refs. [22,23] were only sensitive to changes of the hyperfine F -state, since the atoms were in a mixture of m F -sublevels. However, the theoretical treatment above predicts similarly long relaxation times for any particular m F -sublevel, which is consistent with our observations.…”

“…(23) shows that the shape of the Ramsey fringes is the Fourier(-Cosine)-Transform of the atomic energy distribution. Note that in the above integral we have set the upper integration limit to ∞, instead of the maximum physically reasonable value, δ 0 /2, to obtain the analytic solution…”