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arXiv:1608.08943 · New Journal of Physics

Cavity enhanced telecom heralded single photons for spin-wave solid state quantum memories

Daniel Rieländer, Andreas Lenhard, Margherita Mazzera, Hugues de Riedmatten

Published Dec 12, 2016• 49 citations
arXivHTMLPDF

Abstract

We report on a source of heralded narrowband ( MHz) single photons compatible with solid-state spin-wave quantum memories based on praseodymium doped crystals. Widely non-degenerate narrow-band photon pairs are generated using cavity enhanced down conversion. One photon from the pair is at telecom wavelengths and serves as heralding signal, while the heralded single photon is at 606 nm, resonant with an optical transition of Pr 3+ :Y 2 SiO 5 . The source offers a heralding efficiency of 28% and a generation rate exceeding 2000 pairs mW −1 in a single-mode. The single photon nature of the heralded field is confirmed by a direct antibunching measurement, with a measured antibunching parameter down to 0.010(4). Moreover, we investigate in detail photon cross- and autocorrelation functions proving non-classical correlations between the two photons. The results presented in this paper offer prospects for the demonstration of single photon spin-wave storage in an on-demand solid state quantum memory, heralded by a telecom photon.

DOI
10.1088/1367-2630/aa4f38

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We report on a source of heralded narrowband ( MHz) single photons compatible with solid-state spin-wave quantum memories based on praseodymium doped crystals. Widely non-degenerate narrow-band photon pairs are generated using cavity enhanced down conversion. One photon from the pair is at telecom wavelengths and serves as heralding signal, while the heralded single photon is at 606 nm, resonant with an optical transition of Pr 3+ :Y 2 SiO 5 . The source offers a heralding efficiency of 28% and a generation rate exceeding 2000 pairs mW −1 in a single-mode. The single photon nature of the heralded field is confirmed by a direct antibunching measurement, with a measured antibunching parameter down to 0.010(4). Moreover, we investigate in detail photon cross- and autocorrelation functions proving non-classical correlations between the two photons. The results presented in this paper offer prospects for the demonstration of single photon spin-wave storage in an on-demand solid state quantum memory, heralded by a telecom photon.
We present a source of ultra-narrow band, widely non degenerate photon pairs source compatible with quantum repeaters architectures. One photon is compatible with a solid state Praseodymium (Pr3+) doped crystal spin wave quantum memory, and the other photon is at telecommunication wavelengths, such that it can be transmitted over large distances in optical fibers. Pr3+doped solids absorbing photons at 606 nm have shown very promising properties as QM for light. Despite this fact, so far no experiment demonstrated storage of quantum light in Pr3+doped crystals. The main challenge to realize such a source is that the bandwidth of the memory is limited to a few MHz by the excited state spacing of the ions. To achieve the required narrow linewidth we use widely non-degenerate cavity enhanced spontaneous down conversion (SPDC). We measure a correlation time of 104 ns, the longest reported to date for SPDC emitted photons, corresponding to around 2 MHz bandwidth. In addition, the number of longitudinal modes emitted by the source is strongly reduced, thanks to a clustering effect, which facilitates the filtering to reach single mode operation.
We report on experiments demonstrating the reversible mapping of heralded single photons to long-lived collective optical atomic excitations stored in a Pr3+:Y2SiO5 crystal. A cavity-enhanced spontaneous down-conversion source is employed to produce widely nondegenerate narrow-band (≈2 MHz) photon pairs. The idler photons, whose frequency is compatible with telecommunication optical fibers, are used to herald the creation of the signal photons, compatible with the Pr3+ transition. The signal photons are stored and retrieved using the atomic frequency comb protocol. We demonstrate storage times up to 4.5 μs while preserving nonclassical correlations between the heralding and the retrieved photon. This is more than 20 times longer than in previous realizations in solid state devices, and implemented in a system ideally suited for the extension to spin-wave storage.
Long-lived storage of single photons under the form of atomic excitations is at the foundation of long-distance entanglement distribution in quantum networks. To mitigate decoherence effects induced by the environment, rephasing of the hyperfine coherences using microwave pulses have been implemented in a variety of single-emitter and ensemble-based solid-state systems. However, the demonstration of storage of single photons in an absorptive quantum memory including such spin rephasing mechanism remains elusive. In this work, we show non-classical storage of telecom-heralded single photons in a Pr3+^{3+}3+:Y2_22​SiO5_55​ rare-earth ion doped crystal quantum memory using the atomic frequency comb (AFC) spin-wave protocol combined with a XY4 spin rephasing sequence. Long-lived AFC photon echoes are first observed in the classical regime for storage times of up to approximately 3 ms. We then demonstrate non-classical correlations between heralding photons and stored signal photons generated by a cavity-enhanced parametric photon-pair source for storage times of up to 180 μμμs and with measured cross-correlation values as high as 4.6(4). Together with the capacity of Pr3+^{3+}3+:Y2_22​SiO5_55​ QMs to support highly efficient and multiplexed storage, this result represents a significant step towards scalable long-distance quantum repeater links.
We report on quantum frequency conversion of memory-compatible narrow-bandwidth photons at 606 nm to the telecom C-band at 1552 \,nm. The 200 \,ns long photons, compatible with Praseodymium-based solid-state quantum memories are frequency converted using a single-step difference frequency generation process in a periodically poled Lithium Niobate waveguide. We characterize the noise processes involved in the conversion and by applying strong spectral filtering of the noise, we demonstrate high signal-to-noise ratio conversion at the single photon level (SNR$\,>\,100forameaninputphotonnumberperpulseof1).Wefinallyobservethatamemorycompatibleheraldedsinglephotonwithabandwidthof1.8100 for a mean input photon number per pulse of 1). We finally observe that a memory compatible heralded single photon with a bandwidth of 1.8100forameaninputphotonnumberperpulseof1).Wefinallyobservethatamemorycompatibleheraldedsinglephotonwithabandwidthof1.8\,$MHz, obtained from a spontaneous parametric down conversion pair source, still shows a strong non-classical behavior after conversion. We first demonstrate that correlations between heralding and converted heralded photons stay in the non-classical regime. Moreover, we measured the heralded autocorrelation function of the heralded photon using the converter device as a frequency-domain beam splitter, yielding a value of 0.19±0.070.19\pm0.070.19±0.07. The presented work represents a step towards the connection of several quantum memory systems emitting narrow-band visible photons to the telecommunication wavelengths.
We report on the realization of an efficient solid-state spin-wave quantum memory, with on-demand readout, using the full atomic frequency comb (AFC) scheme in a Pr^{3+}:Y_{2}SiO_{5} crystal embedded in an impedance-matched cavity. We demonstrate operation at the single-photon level by storing weak coherent states with an efficiency up to (40±2)% and a signal-to-noise ratio of 14 for an input photon number of 0.42 photons per pulse. We also investigated the enhancement of the incoherent noise due to the impedance-matched cavity and characterized the quantum memory performance, showing a two-way transfer from excited to spin states and back of up to 83%. Finally, we confirmed the quantum nature of our memory by storing nonclassical states of light, i.e., a heralded single photon from a nondegenerate spontaneous parametric down-conversion source, and achieved nonclassical correlations between the heralding and the stored-and-retrieved photon. These results demonstrate that impedance-matched AFC spin-wave quantum memories with on-demand readout can be used for experiments involving the storage of photonic quantum states. They also open the door to solid-state on-demand quantum memories with very high efficiencies, serving as a key resource for quantum networks and quantum repeaters.
Quantum correlations between long-lived quantum memories and telecom photons that can propagate with low loss in optical fibers are an essential resource for the realization of large-scale quantum information networks. Significant progress has been realized in this direction with atomic and solid-state systems. Here, we demonstrate quantum correlations between a telecom photon and a multimode ondemand solid state quantum memory. This is achieved by mapping a correlated single photon onto a spin collective excitation in a Pr 3+ :Y 2 SiO 5 crystal for a controllable time. The stored single photons are generated by cavity-enhanced spontaneous parametric down-conversion and heralded by their partner photons at telecom wavelength. These results represent the first demonstration of a multimode on-demand solid state quantum memory for external quantum states of light. They provide an important resource for quantum repeaters and pave the way for the implementation of quantum information networks with distant solid state quantum nodes.