We investigate experimentally the energy distribution of a single rubidium atom trapped in a strongly focused dipole trap under various cooling regimes. Using two different methods to measure the mean energy of the atom, we show that the energy distribution of the radiatively cooled atom is close to thermal. We then demonstrate how to reduce the energy of the single atom, first by adiabatic cooling, and then by truncating the Boltzmann distribution of the single atom. This provides a non-deterministic way to prepare atoms at low microKelvin temperatures, close to the ground state of the trapping potential.Comment: 9 pages, 6 figures, published in PR

Quantum computers have the capability of out-performing their classical counterparts for certain computational problems 1 . Several scalable quantum-computing architectures have been proposed. An attractive architecture is a large set of physically independent qubits arranged in three spatial regions where (1) the initialized qubits are stored in a register, (2) two qubits are brought together to realize a gate and (3) the readout of the qubits is carried out 2,3 . For a neutral-atom-based architecture, a natural way to connect these regions is to use optical tweezers to move qubits within the system. In this letter we demonstrate the coherent transport of a qubit, encoded on an atom trapped in a submicrometre tweezer, over a distance typical of the separation between atoms in an array of optical traps 4-6 . Furthermore, we transfer a qubit between two tweezers, and show that this manipulation also preserves the coherence of the qubit.In the quest for an implementation of a quantum computer, scalability is a major concern. In the trapped-ion approach (see for example ref. 7), a lot of effort is being devoted to building arrays of small ion traps 8 , and to moving ion qubits whilst avoiding heating and decoherence 9 . Neutral atoms also offer promising properties for the realization of large quantum registers. For example, one-or two-dimensional addressable arrays of dipole traps have been demonstrated using holographic techniques 4 , micro-fabricated elements 5 , or active rearrangement of single atoms 6,10 . An alternative approach is to use the Mott insulator transition to initialize a three-dimensional register by loading a Bose-Einstein condensate into an optical lattice 11 . Recent progress has shown subwavelength addressability in such a system 12 . To carry out quantum computations, however, an additional key feature is the ability to realize the gate between two arbitrary qubits of the register.Here we demonstrate a scheme where a neutral-atom qubit is transferred between two moving tweezers ('register' to 'moving head'), and then transported towards an interaction zone where the two-qubit gate should be implemented [13][14][15][16] . We show that these manipulations of the external degrees of freedom preserve the coherence of the qubit, and do not induce any heating. This transport in a moving tweezer is a promising alternative to the recently demonstrated transport of qubits in 'optical conveyor belts' 6,17 , or in state-dependent moving optical lattices 18 . Altogether, these results could pave the way towards a scalable neutral-atom quantum-computing architecture.