14 Dec 2017 Garching - Scientists of the Quantum Dynamics Division led by Professor Gerhard Rempe at the Max Planck Institute of Quantum Optics have now achieved a major breakthrough: they demonstrated the long-lived storage of a photonic qubit on a single atom trapped in an optical resonator. The coherence time of the stored quantum bit outlasts 100 milliseconds and therefore matches the requirement for the creation of a global quantum network in which qubits are directly teleported between end nodes.
The research was reported in Nature Photonics, 11 December 2017.
"The major problem for storing quantum bits is the phenomenon of dephasing", explained Stefan Langenfeld,on the institute's website. "Characteristic of a quantum bit is the relative phase of the wave functions of the atomic states that are coherently superimposed. Unfortunately, in real-world experiments, this phase relation is lost over time mostly due to interaction with fluctuating ambient magnetic fields."
In their experiment, the scientists take new measures to counteract the impact of those fluctuations. Once the information is transferred from the photon to the atom, the population of one atomic state is coherently transferred to another state. This is done by using a pair of laser beams to induce a Raman transition. In this new configuration, the stored qubit is 500 times less sensitive to magnetic field fluctuations.
The new technique allows the researchers to preserve the quantum nature of the stored bit for more than 100 milliseconds.