Search

Distributed quantum computation in a quantum network1–3 is based on the idea that qubits can be preserved and efficiently exchanged between long-lived, stationary network nodes via photonic links4 . Although long qubit lifetimes have been observed5–10 , and non-qubit excitations have been memorized11–14 , the long-lived storage and efficient retrieval of a photonic qubit by means of a light–matter interface15–20 remains an outstanding challenge. Here, we report on a qubit memory based on a single atom coupled to a high-finesse optical resonator. By mapping the qubit between an interface basis with strong light–matter coupling and a memory basis with low decoherence, we achieve a coherence time exceeding 100 ms with a time-independent storage-and-retrieval efficiency of 22%. The former constitutes an improvement by two orders of magnitude21,22 and thus implements an efficient photonic qubit memory with a coherence time that exceeds the lower bound needed for direct qubit teleportation in a global quantum internet. A quantum memory based on a rubidium atom shows a record-long storage time of 100 ms with a readout efficiency of 22%. The photonic qubit is transferred between a basis with strong light–matter coupling and a basis with low decoherence.

We demonstrate that yttrium iron garnet microspheres support optical whispering-gallery modes similar to those in nonmagnetic dielectric materials. The direction of the ferromagnetic moment tunes both the resonant frequency via the Voigt effect as well as the degree of polarization rotation via the Faraday effect. An understanding of the magneto-optical coupling in whispering-gallery modes, where the propagation direction rotates with respect to the magnetization, is fundamental to the emerging field of cavity optomagnonics. [ABSTRACT FROM AUTHOR]

We demonstrate the long-range strong coupling of magnetostatic modes in spatially separated ferromagnets mediated by a microwave frequency cavity. Two spheres of yttrium iron garnet are embedded in the cavity and their magnetostatic modes probed using a dispersive measurement technique. We find they are strongly coupled to each other even when detuned from the cavity modes, and investigate the dependence of the magnet-magnet coupling on the cavity detuning. Dark states of the coupled magnetostatic modes of the system are observed, and ascribed to mismatches between the symmetries of the modes and the drive field. [ABSTRACT FROM AUTHOR]