We have for the first time generated multi-particle entanglement on an atom chip by controlling elastic collisional interactions with a state-dependent potential. We employ this technique to generate spin-squeezed states of a two-component Bose-Einstein condensate that are a useful resource for quantum metrology. The observed reduction in spin noise combined with the spin coherence imply four-partite entanglement between the condensate atoms and could be used to improve an interferometric measurement by about a factor of 2 over the standard quantum limit. [more]

We have demonstrated coherent manipulation of Bose-condensed atoms in a state-selective potential, generated in a novel way with microwave near-fields on our atom chip. We reversibly entangle atomic internal and motional states, realizing a trapped-atom interferometer with internal-state labeling. Our system provides control over collisions in mesoscopic condensates, paving the way for on-chip generation of many-particle entanglement and quantum-enhanced metrology with spin-squeezed states. [more]

Microwave near-fields are a key ingredient for quantum information processing on atom chips. A long-term goal of our experiment is to realize collisional quantum phase gates between individual atoms. In a detailed theoretical investigation we have shown that for a realistic atom chip geometry the gate operation time is 1 ms. Taking a large number of error sources into account, we find an overall infidelity of the order of a few 10^-3, compatible with requirements for fault-tolerant quantum computation. [more]