Abstract
Entangling quantum systems with different characteristics through the exchange of photons is a prerequisite for building future quantum networks. Proving the presence of entanglement between quantum memories for light working at different wavelengths furthers this goal. Here, we report on a series of experiments with a thulium-doped crystal, serving as a quantum memory for 794 nm photons, an erbium-doped fibre, serving as a quantum memory for telecommunication-wavelength photons at 1535 nm, and a source of photon pairs created via spontaneous parametric down-conversion. Characterizing the photons after re-emission from the two memories, we find non-classical correlations with a cross-correlation coefficient of $g^{(2)}_{12} = 53\pm8$; entanglement preserving storage with input-output fidelity of $\mathcal{F}_{IO}\approx93\pm2\%$; and non-locality featuring a violation of the Clauser-Horne-Shimony-Holt Bell-inequality with $S= 2.6\pm0.2$. Our proof-of-principle experiment shows that entanglement persists while propagating through different solid-state quantum memories operating at different wavelengths.
Highlights
Entanglement is central to applications of quantum mechanics [1]
Our proof-of-principle experiment shows that entanglement persists while propagating through different solid-state quantum memories operating at different wavelengths
This result demonstrates that nonclassical correlations between the members of photon pairs were preserved during storage
Summary
Entanglement is central to applications of quantum mechanics [1]. In particular, photon-mediated distribution of entanglement over different and widely spaced quantum systems underpins the creation of a future quantum network [2]. It appears likely that they will operate within different wavelength regions, ranging from visible [6,7] via near-infrared [8,9,10,11,12,13], to telecommunication wavelengths [14,15] This will allow leveraging the best properties of each device, and thereby offer heightened capabilities compared to a network consisting of identical quantum systems. The development of such networks creates a need, immediately and in the future, for hybridization experiments to bridge existing frequency and bandwidth mismatches.
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