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Technologies

Single Atoms Preparation Using Light-Assisted Collisions

Y. H. Fung, Pimonpan Sompet, Mikkel F. Andersen

Published Jan 27, 2016• 14 citations
Publisher

Abstract

The detailed control achieved over single optically trapped neutral atoms makes them candidates for applications in quantum metrology and quantum information processing. The last few decades have seen different methods developed to optimize the preparation efficiency of single atoms in optical traps. Here we review the near-deterministic preparation of single atoms based on light-assisted collisions and describe how this method can be implemented in different trap regimes. The simplicity and versatility of the method makes it feasible to be employed in future quantum technologies such as a quantum logic device.

DOI
10.3390/technologies4010004

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The detailed control achieved over single optically trapped neutral atoms makes them candidates for applications in quantum metrology and quantum information processing. The last few decades have seen different methods developed to optimize the preparation efficiency of single atoms in optical traps. Here we review the near-deterministic preparation of single atoms based on light-assisted collisions and describe how this method can be implemented in different trap regimes. The simplicity and versatility of the method makes it feasible to be employed in future quantum technologies such as a quantum logic device.
The fact that a single neutral atom stored in an optical micro-trap is very well isolated from the environment makes it attractive for application in a quantum logic device. Scaling such a device requires a consistent and efficient method of loading a single atom into the micro-trap. By inducing light-assisted collisions between trapped pairs of atoms we observe the outcome of individual collision events. This allowed us to devise a method that enables a loading efficiency of 83% of a single atom into a micro-trap. Furthermore, we are able to accurately count the small number of atoms using fluorescence imaging at high densities while minimizing loss through light assisted collisions.
In this thesis, we present our methods and results towards the development of deterministic preparation of single neutral atoms with a known quantum state in a single trap potential. Firstly, we experimentally study the dynamics of two atoms that undergo light-assisted collisions, where we can quantify different two-atom loss channels. We find that a combination of repulsive light-assisted collisions and in-trap laser cooling can result in only one of the two colliding atoms escaping the trap with near unity probability. This forms the essential basis in our single atom preparation method. With optimized repulsive light-assisted collisions and laser cooling parameters, we can prepare single neutral atoms with a preparation efficiency of 91%. When similar methods are applied in collisional blockade loading of single atoms in a tight trap, the preparation efficiency can be enhanced from the previously observed limit of around 50% to 80%. In a separate experiment, we also demonstrate an in-trap fluorescence detection method to count the number of atoms in a high density trap from 1 to more than 100 atoms with sub-Poissonian precision. Finally, we perform Raman sideband cooling on the prepared single atom with a single pair of Raman transition beams that couples both of the radial vibrational dimensions of the trapped atom. We show that the atom occupies the vibrational ground state in the two radial dimensions with a probability of 84%. This gives a 69% fidelity for the preparation of a pure atomic quantum state for a 2-D system.
The fact that a single neutral atom stored in an optical micro-trap is very well isolated from the environment makes it attractive for application in a quantum logic device. Scaling such a device requires a consistent and efficient method of loading a single atom into the micro-trap. By inducing light-assisted collisions between trapped pairs of atoms we observe the outcome of individual collision events. This allowed us to devise a method that enables a loading efficiency of 83% of a single atom into a micro-trap. Furthermore, we are able to accurately count the small number of atoms using fluorescence imaging at high densities while minimizing loss through light assisted collisions.
We review light assisted collisions in a high-density far-off resonant optical trap (FORT). By tuning the parameters of the light that induces the collisions, the effects of the collisions can be controlled. Trap loss can be suppressed even at high atomic densities, allowing us to count the atoms using fluorescence detection. When only two atoms are trapped, individual loss events reveal new information about the process, and the simplicity of the system allows for a numerical simulation of the dynamics. By optimizing the experimental parameters, we implement an efficient method to prepare single atoms in the FORT. Our methods can be extended to load quantum registers for quantum information processing.