Trapping Atoms with a Superconducting Atom Chip
Tetsuya Mukai1, Alexander Kasper1 and Fujio Shimizu2
1Physical Science Laboratory
2University of Electro-Communications/NTT Research Professor
Neutral atoms have specific features suitable for realizing quantum computers/gates, e.g. quantized internal states, indistinguishability, controllability of the atom-atom and atom-photon interactions, and very small influence from the environment. A promising approach is using a pair of internal states of the atom as a unit of quantum computation (qubit). To realize this "internal-state-qubit", making confinement of single atoms in 2- or 3-dimensional arrays will be a key technique. In the world of atom optics experiments, making single atom traps is a challenging job because of the influence from a surface and current noise.
We are trying to achieve the atomic arrays with two different approaches: using lasers to form an optical lattice (3D) and employing magnetic micro traps formed by wires, i.e. atom chip (2D). With the optical lattice approach, we have two original schemes: (i) double optical lattices , which is using two different atomic species trapped in independent optical lattices with the same lattice constant, and (ii) an all optically controlled "lattice-in-cavity", which uses a cavity mode as a bus for all qubits. With these methods we will be able to achieve a universal set of gates with more than 1,000 qubits.
The atom chip approach is using our fine processing technique for making a 2-dimensional array of atoms. An advantage of the atom chip, which is not possible with optical lattices, is that we can control and address specific lattice sites, which is essential for future applications. Our approach in addition allows us to overcome for example current noise problem by using superconducting materials. We have constructed an apparatus combining two functions: a flux cryostat to cool a superconducting atom chip (Fig.1) and a laser/magnetic trap system to pre cool and trap atoms. With this apparatus we have for the first time demonstrated the trapping of atoms with magnetic potential generated by a superconducting current. Figure 2 represents the absorption images of atoms (a) before and (b) after trapping with a magnetic potential (the brighter represents the higher atomic density). With this superconducting atom chip technique we are going to make single atom traps in the vicinity of a surface as a resource for quantum computations.
 F. Shimizu, Jpn. J. Appl. Phys. 43 (2004) 8376.
Fig.1. MgB2 atom chip.
Fig.2. Images (a) before and (b) after loading atoms on chip.
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