Towards an efficient nanophotonic platform integrating quantum memories and single qubits based on rare-earth ions

Abstract

The integration of rare-earth ions in an on-chip photonic platform would enable quantum repeaters and scalable quantum networks. While ensemble-based quantum memories have been routinely realized, implementing single rare-earth ion qubit remains an outstanding challenge due to its weak photoluminescence. Here we demonstrate a nanophotonic platform consisting of yttrium vanadate (YVO) photonic crystal nanobeam resonators coupled to a spectrally dilute ensemble of Nd ions. The cavity acts as a memory when prepared with spectral hole burning, meanwhile it permits addressing of single ions when high-resolution spectroscopy is employed. For quantum memory, atomic frequency comb (AFC) protocol was implemented in a 50 ppm Nd:YVO nanocavity cooled to 480 mk. The high-fidelity quantum storage of time-bin qubits is demonstrated with a 80% efficient WSi superconducting nanowire single photon detector (SNSPD). The small mode volume of the cavity results in a peak atomic spectral density of <10 ions per homogeneous linewidth, suitable for probing single ions when detuned from the center of the inhomogeneous distribution. The high-cooperativity coupling of a single ion yields a strong signature (20%) in the cavity reection spectrum, which could be detected by our efficient SNSPD. We estimate a signal-to-noise ratio exceeding 10 for addressing a single Nd ion with its 879.7nm transition. This, combines with the AFC memory, constitutes a promising platform for preparation, storage and detection of rare-earth qubits on the same ship.