Quantum-state transfer from an ion to a photon

Abstract

One model for quantum networks1,2 is based on the probabilistic measurement of two photons, each entangled with a distant node, e.g., an atom or atomic ensemble3–7. A second, deterministic model transfers information directly from an atom onto a cavity photon, which carries it to a second node8, as recently demonstrated with neutral atoms9. In both cases, the challenge is to transfer information efficiently while preserving coherence. Here, following the second scheme, we map the quantum state of an ion onto a photon within an optical cavity. Using an ion enables deterministic state initialization10,11, while the cavity provides coherent coupling to a well-defined output mode12–15. Although it is often assumed that a cavity-based quantum interface requires the strong-coupling regime, we show transfer fidelities of 92% in the presence of non-negligible decoherence and characterize the interplay between fidelity and efficiency. Our time-independent mapping process offers a promising route toward ion-based quantum networks.

Non-classical correlations between single photons and phonons from a mechanical oscillator

“…Shown is the cross-correlation (green bars) between the mechanical (read pulse) and optical state (write pulse) for δt = 100 ns, as well as the classical (Cauchy-Schwarz) bound obtained from the autocorrelations at ∆n = 0 (grey horizontal line, shading indicates a 68% confidence interval; see text). For photon-phonon pairs that emerge from different pulse sequences (∆n = 0) the Cauchy-Schwarz inequality is fulfilled, g (2) om (∆n = 0, 100 ns) = 1.04 ± 0.04, consistent with statistical independence. For pulses from the same pair, the cross-correlation g (2) om(0, 100 ns) clearly exceeds the classical bound.…”

“…For photon-phonon pairs that emerge from different pulse sequences (∆n = 0) the Cauchy-Schwarz inequality is fulfilled, g (2) om (∆n = 0, 100 ns) = 1.04 ± 0.04, consistent with statistical independence. For pulses from the same pair, the cross-correlation g (2) om(0, 100 ns) clearly exceeds the classical bound. g (2) om can be interpreted as the ratio of heralded phonons n h to unheralded (thermal) phonons n th at the time of the read pulse.…”

“…P (W ∩R) is the probability for a joint detection of both a Stokes (W , 'write') and an anti-Stokes (R, 'read') photon from these pulses, and P (W ) and P (R) are the unconditional probabilities to detect either of the two photons. For all pair correlations of classical origin, the value of g (2) om is bounded by a Cauchy-Schwarz inequality of the form [3] g (2) om (0, δt) ≤ g (2) oo,δt (0)g (2) mm,δt (0)…”

“…oo,δt (0) and g (2) mm,δt (0) are the autocorrelation functions for the optical and mechanical mode, respectively (see Methods). A violation of this inequality [3,31,32] is an unambiguous measure for the non-classicality of the generated photon-phonon state.…”

“…For pulses from the same pair, the cross-correlation g (2) om(0, 100 ns) clearly exceeds the classical bound. g (2) om can be interpreted as the ratio of heralded phonons n h to unheralded (thermal) phonons n th at the time of the read pulse. c, Storage of non-classical correlations.…”