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arXiv:2010.06875 · Nature Communications

Room-temperature single-photon source with near-millisecond built-in memory

Karsten B. Dideriksen, Rebecca Schmieg, Michael Zugenmaier, Eugene S. Polzik

Published Jun 17, 2021• 57 citations
arXivHTMLPDF

Abstract

Abstract Non-classical photon sources are a crucial resource for distributed quantum networks. Photons generated from matter systems with memory capability are particularly promising, as they can be integrated into a network where each source is used on-demand. Among all kinds of solid state and atomic quantum memories, room-temperature atomic vapours are especially attractive due to their robustness and potential scalability. To-date room-temperature photon sources have been limited either in their memory time or the purity of the photonic state. Here we demonstrate a single-photon source based on room-temperature memory. Following heralded loading of the memory, a single photon is retrieved from it after a variable storage time. The single-photon character of the retrieved field is validated by the strong suppression of the two-photon component with antibunching as low as $${g}_{{\rm{RR| W = 1}}}^{(2)}=0.20\pm 0.07$$ g RR∣W=1 ( 2 ) = 0.20 ± 0.07 . Non-classical correlations between the heralding and the retrieved photons are maintained for up to $${\tau }_{{\rm{NC}}}^{{\mathcal{R}}}=(0.68\pm 0.08)\ {\rm{ms}}$$ τ NC R = ( 0.68 ± 0.08 ) ms , more than two orders of magnitude longer than previously demonstrated with other room-temperature systems. Correlations sufficient for violating Bell inequalities exist for up to τBI = (0.15 ± 0.03) ms.

DOI
10.1038/s41467-021-24033-8

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Abstract Non-classical photon sources are a crucial resource for distributed quantum networks. Photons generated from matter systems with memory capability are particularly promising, as they can be integrated into a network where each source is used on-demand. Among all kinds of solid state and atomic quantum memories, room-temperature atomic vapours are especially attractive due to their robustness and potential scalability. To-date room-temperature photon sources have been limited either in their memory time or the purity of the photonic state. Here we demonstrate a single-photon source based on room-temperature memory. Following heralded loading of the memory, a single photon is retrieved from it after a variable storage time. The single-photon character of the retrieved field is validated by the strong suppression of the two-photon component with antibunching as low as gRR∣W=1(2)=0.20±0.07{g}_{{\rm{RR| W = 1}}}^{(2)}=0.20\pm 0.07gRR∣W=1(2)​=0.20±0.07 g RR∣W=1 ( 2 ) = 0.20 ± 0.07 . Non-classical correlations between the heralding and the retrieved photons are maintained for up to τNCR=(0.68±0.08) ms{\tau }_{{\rm{NC}}}^{{\mathcal{R}}}=(0.68\pm 0.08)\ {\rm{ms}}τNCR​=(0.68±0.08) ms τ NC R = ( 0.68 ± 0.08 ) ms , more than two orders of magnitude longer than previously demonstrated with other room-temperature systems. Correlations sufficient for violating Bell inequalities exist for up to τBI = (0.15 ± 0.03) ms.
Interfacing light from solid-state single-photon sources with scalable and robust room-temperature quantum memories has been a long-standing challenge in photonic quantum information technologies due to inherent noise processes and time-scale mismatches between the operating conditions of solid-state and atomic systems. Here, we demonstrate on-demand storage and retrieval of single photons from a semiconductor quantum dot device in a room-temperature atomic vapor memory. A deterministically fabricated InGaAs quantum dot light source emits single photons at the wavelength of the cesium D1 line at 895\,nm which exhibit an inhomogeneously broadened linewidth of 5.1(7)\,GHz and are subsequently stored in a low-noise ladder-type cesium vapor memory. We show control over the interaction between the single photons and the atomic vapor, allowing for variable retrieval times of up to 19.8(3)\,ns at an internal efficiency of ηint=0.6(1)%η_\mathrm{int}=0.6(1)\%ηint​=0.6(1)%. Our results significantly expand the application space of both room-temperature vapor memories and semiconductor quantum dots in future quantum network architectures.
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Quantum memory capable of storage and retrieval of flying photons on demand is crucial for developing quantum information technologies. However, the devices needed for long-distance links are different from those envisioned for local processing. We present the first hybrid quantum memory-enabled network by demonstrating the interconnection and simultaneous operation of two types of quantum memory: an atomic ensemble-based memory and an all-optical Loop memory. Interfacing the quantum memories at room temperature, we observe a well-preserved quantum correlation and a violation of Cauchy-Schwarz inequality. Furthermore, we demonstrate the creation and storage of a fully-operable heralded photon chain state that can achieve memory-built-in combining, swapping, splitting, tuning, and chopping single photons in a chain temporally. Such a quantum network allows atomic excitations to be generated, stored, and converted to broadband photons, which are then transferred to the next node, stored, and faithfully retrieved, all at high speed and in a programmable fashion.
Quantum memories are a key technology for distributing entanglement in large-scale quantum networks. They allow for coherent control and temporal reordering of single photons which is a fundamental prerequisite for quantum repeaters, local synchronization and buffering of quantum information. These applications require bright and pure sources of indistinguishable single photons, as well as long-lived, efficient, and high-bandwidth quantum memories with minimal noise. The demonstration of robust, scalable, multi-mode photonic interfaces between different types of quantum memories and single-photon sources remains an open experimental challenge. This work contributes to this endeavor by investigating a heterogeneous interface between a semiconductor quantum dot single-photon source and a room-temperature atomic vapor memory. The first part of this work presents the first room-temperature, ladder-type atomic vapor memory that operates on the Cs D1 line at 895\,nm. The performance of the memory is characterized using attenuated laser pulses at the single-photon level. The memory achieves an internal efficiency of ηint=15(1) %\eta_\mathrm{int}=15(1)\,\%ηint​=15(1)% at a storage time of τs=17.4(2)\tau_\mathrm{s}=17.4(2)τs​=17.4(2)\,ns. We derive a quantitative benchmark for the memory compatibility with quantum dot single-photon sources. The memory's high signal-to-noise ratio of 830(80), and its spectral acceptance window of W=560\mathcal{W}=560W=560\,MHz promise compatibility with single photons from state-of-the-art InGaAs quantum dot devices. Furthermore, we present such a nano-integrated quantum dot device and characterize its optical properties. We measure a radiative lifetime of 1.3(1)\,ns and an inhomogeneously broadened linewidth of 5.1(1)\,GHz. The temperature tuning of the emission wavelength to the Cs D1 line allows coupling of the quantum dot to the memory in a joint experiment. The storage of single photons from a quantum dot source in a room-temperature atomic memory is demonstrated with on-demand retrieval. The variable storage time of up to τs=19.8\tau_\mathrm{s}=19.8τs​=19.8\,ns and the memory's fractional delay of Df=14(1)\mathrm{D}_\mathrm{f}=14(1)Df​=14(1) present a significant advancement in the research field. We compare our results with other types of interfaces between single-photon sources and quantum memories and discuss the performance in the context of quantum network applications. This work marks an important step towards local buffering and synchronization of quantum information in heterogeneous quantum network nodes.