An optical conveyor belt for single neutral atoms

Abstract

Using optical dipole forces we have realized controlled transport of a single or any desired small number of neutral atoms over a distance of a centimeter with sub-micrometer precision. A standing wave dipole trap is loaded with a prescribed number of cesium atoms from a magneto-optical trap. Mutual detuning of the counterpropagating laser beams moves the interference pattern, allowing us to accelerate and stop the atoms at preselected points along the standing wave. The transportation efficiency is close to 100 %. This optical "singleatom conveyor belt" represents a versatile tool for future experiments requiring deterministic delivery of a prescribed number of atoms on demand. PACS: 32.80.Lg, 32.80.Pj, 42.50.Vk Quantum engineering of microscopic systems requires manipulation of all degrees of freedom of isolated atomic particles. The most advanced experiments are implemented with trapped chains of ions [1,2,3]. Neutral atoms are more difficult to control because of the weaker interaction of induced electric or paramagnetic dipoles with inhomogeneous electromagnetic fields. Optical dipole traps [4] could provide a level of control similar to ion traps, since they store neutral atoms in a nearly conservative potential with long coherence times [5]. The variety of different dipole traps allows for an individual design, depending on the specific experimental demands [6].Here we use a time-varying standing wave optical dipole trap to displace atoms by macroscopic distances on the order of a centimeter with sub-micrometer precision [7]. A similar technique of moving optical lattices has been applied for the acceleration of large ensembles of atoms in [8,9]. Time-dependent magnetic fields can also be used for controlled transport of clouds of neutral atoms as has been demonstrated with a micro-fabricated device [10]. Recently, techniques have been developed to load a dipole trap with single atoms only [11,12]. In our case, we have combined controlled manipulation of the trapping potential with deterministic loading of a dipole trap with a prescribed small number of atoms [7]. These atoms are then transported with high efficiency over macroscopic distances and observed by positionsensitive fluorescence detection in the dipole trap. Here we describe the transportation technique in detail. We also analyze the dependency of the measured transportation efficiency on both the transportation distance and the acceleration. This is followed by a brief discussion of possible applications and alternative approaches. The standing-wave dipole trapOur dipole trap ( Fig.1) consists of two counter-propagating Gaussian laser beams with equal intensities and optical frequencies ν 1 and ν 2 producing a position-and time-dependent dipole potentialThe optical wavelength is λ = 2π/k, wis the beam radius with waist w 0 and the Rayleigh length z 0 = πw 2 0 /λ, and ∆ν = ν 1 −ν 2 ≪ ν 1 , ν 2 is the mutual detuning of the laser beams. The laser beams have parallel linear polarization and thus produce a standing wave interference pa...

Analysis of dephasing mechanisms in a standing-wave dipole trap

“…where ∆ eff = −1.2×10 7 Γ is an effective detuning, taking into account the weighted contributions of the D 1 and D 2 lines [10]. ω hfs = 2.0×10 3 Γ is the ground state hyperfine splitting.…”

Fast atomic transport without vibrational heating

“…The magnetic traps can be translated by moving the coils mechanically [5], by timevarying currents in a lithographic conductor pattern [17], or on a conveyor belt with a chain of permanent magnets [18]. Optical traps can be used as optical tweezers whose focal point is translated by moving mechanically lenses [4,19], or by traveling lattices (conveyor belts) made with two counterpropagating beams slightly detuned one respect to each other [15,16,20]. There are also mixed magneto-optical approaches [6].…”

Adiabatic quantum state manipulation of single trapped atoms

“…For larger 1/τ -values, the experimental data falls off faster than predicted by theory. This is most probably due to the increasing excitation of axial oscillations of the atoms inside the potential wells caused by the abrupt changes in acceleration, which further reduce adiabaticity [10]. For 1/τ < 0.05 ms −1 the experimental data also falls below the theoretical curve.…”

“…They interfere and produce a chain of potential wells of typically 1 mK depth. Further details can be found in previous publications [10,13].As qubit states we employ the outermost Zeeman sublevels |F = 4, m F = 4 (|0 ) and |F = 3, m F = 3 (|1 ) of the two 6S 1/2 hyperfine ground states with a transition frequency ω at /2π near 9.2 GHz. In order to spectroscopically distinguish atoms at different positions along the dipole trap axis we apply a magnetic field gradient of 13 G/cm along this axis.…”

“…We now examine the possibility of inducing adiabatic spin flips with a fixed microwave frequency by transporting the atoms across the position of resonance with our optical conveyor belt technique [9,10]. This option is particularly interesting for quantum information processing schemes in neutral atom cavity QED, see e. g. [17].…”