One-way quantum computing in optical lattices with many atom measurements.

Tim Friesen, David L. Feder

One of the fundamental conditions for one-way quantum computation (1WQC) is the ability to make sequential measurements on isolated qubits that comprise the highly entangled resource for 1WQC, the cluster state. This has been a significant impediment in the implementation of 1WQC with ultracold atoms confined in optical lattices, because the width of the measuring lasers is generally much greater than the atomic (qubit) spacing. We demonstrate that deterministic 1WQC is nevertheless possible, with a polynomial increase in the number of operations, as long as the center of the beams can be positioned with high accuracy and the beam width is reproducible. Extending the number of cluster atoms, the scheme is also able to compensate for accidental measurements of an arbitrary number of nearby qubits.

Hans J. Briegel

Alastair Kay, Jiannis K. Pachos, Charles S. Adams

We present a way to manipulate ultracold atoms where four atomic levels are trapped by appropriately tuned optical lattices. When employed to perform quantum computation via global control, this unique structure dramatically reduces the number of steps involved in the control procedures, either for the standard, network, model, or for one-way quantum computation. The use of a far-blue-detuned lattice and a magnetically insensitive computational basis makes the scheme robust against decoherence. The present scheme is a promising candidate for experimental implementation of quantum computation and for graph-state preparation in one, two, or three spatial dimensions.

David S. Weiss

Shi Yu, Peng Xu, Min Liu +3 more

We demonstrate the transfer of a single atom in a ring optical lattice with the aid of an auxiliary moving tweezer and investigate the influences on fidelity of the qubit encoded in the atom. When the tweezer has deeper trap depth and moves across the lattice, it is observed that an atom in one site follows the movement. The transfer efficiency of one atom to the destination site reaches up to 95%. This scheme is suitable for scalable quantum registers because of no influence on the other sites. We obtain atomic qubit fidelity during the transfer process by using quantum state tomography. Extracted fidelity indicates that the eigenstate is well preserved, while the superposition state is influenced. In combination with spin-echo measurement, dephasing mechanisms in this process are analyzed and discussed in detail. Loss of qubit fidelity is found to result from heating effects induced by this process and pointing instabilities of the trap laser. Our results pave the way for quantum computation with single atoms trapped in a scalable optical lattice.

Karl D. Nelson