Physical Science Laboratory
*NTT Research Professor and University of Electro-Communications
Neutral atoms are promising candidate to realize quantum
gates. The advantage of using neutral atoms for quantum computation is as
follows. 1) We can make arbitrary amplitude distribution among internal states
with laser light. Therefore, single-qubit operations are easy and accurate.
2) Two qubits operations are possible with atom-atom interactions or indirectly
via an auxiliary quantum system. 3) Disturbance from external fields to neutral
atoms is relatively weak, and decoherence time is very long. 4) All atoms
are identical and we can expand number of qubits without taking care of the
characteristics of individual qubits. 5) We can fill qubit locations with
few defects from Bose-Einstein Condensate (BEC). However, the progress of
neutral-atom quantum computer is slow because implementation of all necessary
functions in a system is not easy.
Recent progress in laser cooling of atoms enables us to cool down atomic
samples to a temperature below one micro-Kelvin and to make 2- or 3-dimensional
array of neutral atoms. Employing high-quality micro-fabrication technology
and our experiences in laser and efficient evaporative cooling for making
BEC [1], we are trying to develop a model quantum computation system with
ultra-cold neutral atoms.
In the first project we plan to use 2-dimensional magnetic trap arrays. It
consists of micro-fabricated Z-shaped wires on a silicon surface. To realize
an array of single atoms in the ground vibrational state and to ensure atom-atom
interaction we have to reduce the distance between atoms and surface. This
short distance introduces extra potential noises and short decoherence time.
We are trying to overcome this problem with super-conducting wires on silicon
substrate (Atom Chips).
In the second project we use an optical lattice. We have proposed a scheme
to realize a scalable quantum computer with double optical lattices [2]. Employing
this scheme we can compose an universal quantum computer with complete scalability
and we hope to achieve a practical quantum computer with more than 1000 qubits
operating together. We are trying to implement the double optical lattices
scheme to a real system.
[1] T. Mukai and M. Yamashita, Physical Review A 70 (2004)
013615.
[2] F. Shimizu, Japanese Journal of Applied Physics 43 (2004)
8376.
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| Fig. 1. Sample Atom Chips |
Fig. 2. Pattern of wire |
Fig.3. Double Optical Lattice |