Rare-earth Ensemble Research Articles

Storage of photonic time-bin qubits for up to 20\u2009ms in a rare-earth doped crystal

Long-duration quantum memories for photonic qubits are essential components for achieving long-distance quantum networks and repeaters. The mapping of optical states onto coherent spin-waves in rare earth ensembles is a particularly promising approach to quantum storage. However, it remains challenging to achieve long-duration storage at the quantum level due to read-out noise caused by the required spin-wave manipulation. In this work, we apply dynamical decoupling techniques and a small magnetic field to achieve the storage of six temporal modes for 20, 50, and 100 ms in a 151Eu3+:Y2SiO5 crystal, based on an atomic frequency comb memory, where each temporal mode contains around one photon on average. The quantum coherence of the memory is verified by storing two time-bin qubits for 20 ms, with an average memory output fidelity of F = (85 ± 2)% for an average number of photons per qubit of μin = 0.92 ± 0.04. The qubit analysis is done at the read-out of the memory, using a type of composite adiabatic read-out pulse we developed.

Interfacing broadband photonic qubits to on-chip cavity-protected rare-earth ensembles

Ensembles of solid-state optical emitters enable broadband quantum storage and transduction of photonic qubits, with applications in high-rate quantum networks for secure communications and interconnecting future quantum computers. To transfer quantum states using ensembles, rephasing techniques are used to mitigate fast decoherence resulting from inhomogeneous broadening, but these techniques generally limit the bandwidth, efficiency and active times of the quantum interface. Here, we use a dense ensemble of neodymium rare-earth ions strongly coupled to a nanophotonic resonator to demonstrate a significant cavity protection effect at the single-photon level—a technique to suppress ensemble decoherence due to inhomogeneous broadening. The protected Rabi oscillations between the cavity field and the atomic super-radiant state enable ultra-fast transfer of photonic frequency qubits to the ions (∼50 GHz bandwidth) followed by retrieval with 98.7% fidelity. With the prospect of coupling to other long-lived rare-earth spin states, this technique opens the possibilities for broadband, always-ready quantum memories and fast optical-to-microwave transducers.

An atomistic view of structural and electronic properties of rare earth ensembles on Si(0 0 1) substrates

Synergistic experimental and theoretical studies of low coverage adsorption geometries of rare earth adatoms on Si(0 0 1) were performed. Density functional calculations showed charge transfer from adatoms to Si(0 0 1) and explained observed bias dependence in scanning tunneling microscopy images. Comparison of STM simulations with empty states STM data revealed a direct correlation between coverage and surface reconstructions; the (4 × 8) reconstruction is a low coverage precursor to (2 × 4) reconstruction. Charge transfer from adatom to substrate was also confirmed by Kelvin probe force microscopy; contact potential difference measurements of Dy/Si(0 0 1) reveal a 0.28 eV higher surface potential than that of (2 × 1) reconstructed Si.