QUROPE Quantum Information Processing and Communication in Europe

A. Stute, B. Casabone, B, Brandstätter, K. Friebe, T. E. Northup and R. Blatt
Nature Photonics 7, 219-222 (2013)

One model for a quantum network is based on the measurement of two photons, each entangled with a
distant node, such as an atom or atomic ensemble. An inherent drawback of this method is that the network is
only established if measurement produces a certain outcome, thus it is an inherently probabilistic method of
creating a quantum network.. A second, deterministic model transfers information directly, from an atom
onto a cavity photon, which carries it to a second node, a method which has recently been demonstrated with
neutral atoms. In both cases, the key challenge is to transfer quantum information efficiently while
preserving fragile quantum coherence.

In their work, Stute and colleagues advance the second scheme, by demonstrating that the quantum state of
an ion can be mapped onto a photon which is stored within an optical cavity. The advantage of using an ion
is that it enables deterministic initialization of the state, while the advantage of the cavity is that it provides
coherent coupling to a well-defined output mode. One seeming drawback of this approach is that it is often
assumed that a cavity-based quantum interface requires the strong coupling regime. In their work however
Stute and colleagues show high transfer fidelities (of 92%) even in the presence of non-negligible
decoherence noise. Their work thus offers a promising route towards ion-based quantum networks.