Optimising fibre-tip microcavities with Gaussian-shaped mirrors for quantum networks

In many quantum information applications quantum bits (qubits) are stored in single trapped atoms or ions. In particular, single ions held in radio frequency electromagnetic traps are preferred because of their long achievable decoherence time and record-breaking quantum gate fidelity [1]. However, for scalable quantum information processing many such stationary qubits need to be connected. A preferred way of doing this would be via optical fibres, i.e., by transferring quantum information between stationary qubits with the help of “flying” single-photon qubits. Efficient operation of the quantum network thus requires (i) high-fidelity transfer of an ion qubit onto a single photon, (ii) low-loss coupling of the photon into a single-mode optical fibre, and (iii) achieving conditions (i) and (ii) without disturbing the ion trap