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arXiv:1310.8261 · Physical Review Letters

Quantum Storage of Heralded Single Photons in a Praseodymium-Doped Crystal

Daniel Rieländer, Kutlu Kutluer, Patrick M. Ledingham, Mustafa Gündoğan, J. Fekete, Margherita Mazzera, Hugues de Riedmatten

Published Jan 31, 2014• 92 citations
arXivHTMLPDF

Abstract

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.

DOI
10.1103/physrevlett.112.040504

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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.
We report on the quantum storage of a heralded frequency-multiplexed single photon in an integrated laser-written rare-earth doped waveguide. The single photon contains 15 discrete frequency modes separated by 261 MHz and spanning across 4 GHz. It is obtained from a nondegenerate photon pair created via cavity-enhanced spontaneous down-conversion, where the heralding photon is at telecom wavelength and the heralded photon is at 606 nm. The frequency-multimode photon is stored in a praseodymium-doped waveguide using the atomic frequency comb (AFC) scheme, by creating multiple combs within the inhomogeneous broadening of the crystal. Thanks to the intrinsic temporal multimodality of the AFC scheme, each spectral bin includes 9 temporal modes, such that the total number of stored modes is about 130. We demonstrate that the storage preserves the nonclassical properties of the single photon, and its normalized frequency spectrum.
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.
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.
Atomic ensembles in the form of rare-earth-doped crystals offer significant potential for implementing a quantum memory due to their long coherence lifetimes, enhanced light-matter interaction, and the potential for integration. We use a double Lambda configuration based on hyperfine levels in praseodymium doped yttrium orthosilicate. In this scheme, a probabilistically generated collective excitation of the internal atomic states in the form of a spin-wave is signaled by emission of a Stokes-shifted herald photon via spontaneous Raman scattering. After a storage delay, a read field addresses the appropriate transition, mapping the spin wave back to a photon, resulting in the emission of an anti-Stokes shifted retrieved photon. Momentum conservation, as dictated by phase-matching conditions, ensure that the herald and retrieved photons are emitted in a well-defined spatial modes relative to the co-propagating write and read optical fields. Inhomogeneous broadening of the absorption profile precludes straightforward implementation of the above scheme, and we resort to spectral hole-burning techniques to prepare a sub-ensemble of atoms with a narrow range of optical transition energy in the ground state. Using a second identical crystal, we also implement an optical spectral filter that suppresses the powerful write and read beams, and spontaneous-emission noise, while transmitting the herald and retrieved photons. We report on the second-order optical correlations between the herald and retrieved photons that are the signature of generation and retrieval of a stored spin-wave excitation. Demonstration of such a quantum memory is an enabling step towards distributing entanglement for a quantum repeater scheme.
Multiplexing is essential for improving entanglement distribution rates in quantum communication. Frequency multiplexing provides a promising and scalable path toward large-capacity quantum networks. Further progress requires increasing the number of frequency modes and developing broadband photon-pair sources and quantum memories that are spectrally compatible. Here, we report the integration of a cavity-enhanced spontaneous parametric down-conversion source in the telecom C-band with a frequency-multiplexed atomic frequency comb memory. The bow-tie cavity source was simultaneously resonant at 606 nm and 1550 nm, generating non-degenerate photon pairs exhibiting a clustered frequency-comb spectrum. The atomic frequency comb memory, implemented in Praseodymium-doped Yttrium Orthosilicate crystals, provided up to 83 frequency modes with 123 MHz spacing and enabled broadband storage of 606 nm signal photons. By filtering the main cluster, we obtained 32.7±4.832.7 \pm 4.832.7±4.8 effective modes, as confirmed from coincidence measurements. Importantly, we observed strong nonclassical correlations after storage, with cross-correlation values of gs,i(2)=8.1±0.7g_{s,i}^{(2)} = 8.1\pm0.7gs,i(2)​=8.1±0.7. Our experimental results demonstrate the feasibility of integrating cavity-enhanced photon-pair sources with rare-earth-ion-doped solid-state memories. The integration reveals a high frequency multiplicity that is essential for scalable quantum networks.