arXiv subjects

Daniel Rieländer

Publications and source records attributed to Daniel Rieländer.

7 recordsLinked to original sources

arXiv2023

Towards metropolitan free-space quantum networks

Quantum communication has seen rapid progress towards practical large-scale networks, with quantum key distribution (QKD) spearheading this development. While fibre based systems have been shown to be well suited for metropolitan scales, suitable fibre infrastructure may not always be in place. Here, we make the case for an entanglement-based free-space quantum network as a practical and efficient alternative for metropolitan applications. We developed a deployable free space QKD system and demonstrated its use in realistic scenarios. For a representative 1.7-km free-space link, we showcase its ad hoc deployability and achieve secure key rates of up to 5.7 kbps, with 2.5 kbps in direct noon sunlight. By extrapolating experimental data, we show that kbps key rates are achievable even for 10-km distances and multi-user scenarios. We anticipate that our work will establish free space networks as a viable solution for metropolitan applications and an indispensable complementary building block in the future global quantum internet.

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arXiv2022

Clock synchronization with correlated photons

Event synchronisation is a ubiquitous task, with applications ranging from 5G technology to industrial automation and smart power grids. The emergence of quantum communication networks will further increase the demand for precise synchronization in the optical and electronic domains, which implies significant resource overhead, such as the requirement for ultrastable clocks or additional synchronization lasers. Here we show how temporal correlations of energy-time entangled photons may be harnessed for synchronisation in quantum networks. We achieve stable synchronisation jitter <68 ps with as few as 44 correlated detection events per 100-ms data package and demonstrate feasibility in realistic emulated high-loss link scenarios, including atmospheric turbulence. In contrast to previous work, this is accomplished without any external timing reference and only simple crystal oscillators. Our approach replaces the optical and electronic transmission of timing signals with classical communication and computer-aided postprocessing. It can be easily integrated into a wide range of quantum communication networks and could pave the way to future applications in entanglement-based secure time transmission.

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arXiv2021

Topical White Paper: A Case for Quantum Memories in Space

It has recently been theoretically shown that Quantum Memories (QM) could enable truly global quantum networking when deployed in space thereby surpassing the limited range of land-based quantum repeaters. Furthermore, QM in space could enable novel protocols and long-range entanglement and teleportation applications suitable for Deep-Space links and extended scenarios for fundamental physics tests. In this white paper we will make the case for the importance of deploying QMs to space, and also discuss the major technical milestones and development stages that will need to be considered.

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arXiv2017

Quantum correlations between single telecom photons and a multimode on-demand solid state quantum memory

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 on-demand 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 (SPDC) 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.

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arXiv2017

Frequency-Bin Entanglement of Ultra-Narrow Band Non-Degenerate Photon Pairs

We demonstrate frequency-bin entanglement between ultra-narrowband photons generated by cavity enhanced spontaneous parametric down conversion. Our source generates photon pairs in widely non-degenerate discrete frequency modes, with one photon resonant with a quantum memory material based on praseodymium doped crystals and the other photon at telecom wavelengths. Correlations between the frequency modes are analyzed using phase modulators and narrowband filters before detection. We show high-visibility two photon interference between the frequency modes, allowing us to infer a coherent superposition of the modes. We develop a model describing the state that we create and use it to estimate optimal measurements to achieve a violation of the Clauser-Horne (CH) Bell inequality under realistic assumptions. With these settings we perform a Bell test and show a significant violation of the CH inequality, thus proving the entanglement of the photons. Finally we demonstrate the compatibility with a quantum memory material by using a spectral hole in the praseodymium (Pr) doped crystal as spectral filter for measuring high-visibility two-photon interference. This demonstrates the feasibility of combining frequency-bin entangled photon pairs with Pr-based solid state quantum memories.

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arXiv2016

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

We report on a source of heralded narrowband (3MHz) 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 606nm, resonant with an optical transition in Pr:YSO. The source offers a heralding efficiency of 28% and a generation rate exceeding 2000 pairs/mW 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 represent significant improvement over the state of the art and offer prospects for the demonstration of single photon spin-wave storage in an on-demand solid state quantum memory, heralded by a telecom photon.

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arXiv2014

Quantum Storage of Heralded Single Photons in a Praseodymium Doped Crystal

We report on experiments demonstrating the reversible mapping of heralded single photons to long lived collective optical atomic excitations stored in a Pr$^{3+}$:Y$_2$SiO$_5$ crystal. A cavity-enhanced spontaneous down-conversion source is employed to produce widely non-degenerate narrow-band ($\approx 2\,\mathrm{MHz}$) 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 Pr$^{3+}$ transition. The signal photons are stored and retrieved using the atomic frequency comb protocol. We demonstrate storage times up to $4.5\,\mathrm{μs}$ while preserving non-classical 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.

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