A collisional quantum phase gate on an atom chip
Microwave near-fields are a key ingredient for quantum information processing with individual atoms on atom chips. A long-term goal of our experiment is to realize a quantum gate with the following features: The qubit is encoded in two hyperfine states of 87Rb which are both magnetically trappable and allow for very long coherence lifetimes (see our experiments on coherence near chip surfaces). Microwave near-fields guided on the atom chip are used to drive single qubit rotations and provide state-selectivity to the magnetic trapping potential. The quantum phase gate is implemented by state-selective collisions of two qubit atoms in this potential. Optimal control of the trapping potential is used to improve gate performance in realistic potentials.
In a detailed theoretical investigation (P. Treutlein et al., Phys. Rev. A 74, 022311 (2006), see our list of publications), we have shown that for a realistic atom chip geometry the gate operation time is 1 ms, three orders of magnitude shorter than the experimentally demonstrated coherence lifetime of the qubit. Taking a large number of error sources into account, such as loss and decoherence effects due to the proximity of the surface, we find an overall infidelity of the order of a few 10-3, compatible with requirements for fault-tolerant quantum computation.
Experimentally, this gate can be realized by combining the state selective microwave potentials demonstrated in our experiments with the on-chip fiber cavities for single atom detection and preparation developed by our collaborators from Prof. Jakob Reichel's group at ENS Paris.