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arXiv:2210.16157

A Quantum Repeater Platform based on Single SiV$^-$ Centers in Diamond with Cavity-Assisted, All-Optical Spin Access and Fast Coherent Driving

Gregor W. Bayer, Robert Berghaus, Selene Sachero, Andrea B. Filipovski, Lukas Antoniuk, Niklas Lettner, Richard Waltrich, Marco Klotz, Patrick J. Maier, V. Agafonov, Alexander Kubanek

Published Oct 28, 2022• 5 citations
arXivHTMLPDF

Abstract

Quantum key distribution enables secure communication based on the principles of quantum mechanics. The distance in fiber-based quantum communication is limited to about a hundred kilometers due to signal attenuation. Thus, quantum repeaters are required to establish large-scale quantum networks. Ideal quantum repeater nodes possess a quantum memory which is efficiently connected to photons, the carrier of quantum information. Color centers in diamond and, in particular, the negatively-charged silicon-vacancy centers are promising candidates to establish such nodes. The major obstacle is an inefficient connection between the color centers spin to the Gaussian optics of fiber networks. Here, we present an efficient spin-photon interface. Individual silicon-vacancy centers coupled to the mode of a hemispherical Fabry-Pérot microcavity show Purcell-factors larger than 1 when operated in a bath of liquid Helium. We demonstrate coherent optical driving with a Rabi frequency of $290\,\mathrm{MHz}$ and all-optical access to the electron spin in strong magnetic fields of up to $3.2\,\mathrm{T}$. Spin initialization within $67\,\mathrm{ns}$ with a fidelity of $80\,\%$ and a lifetime of $350\,\mathrm{ns}$ are reached inside the cavity. The spin-photon interface is passively stable, enabled by placing a color center containing nanodiamond in the hemispherical Fabry-Pérot mirror structure and by choosing short cavity lengths. Therefore, our demonstration opens the way to realize quantum repeater applications.

DOI
10.48550/arxiv.2210.16157

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A Quantum Repeater Platform based on Single SiV−^-− Centers in Diamond with Cavity-Assisted, All-Optical Spin Access and Fast Coherent Driving
Quantum key distribution enables secure communication based on the principles of quantum mechanics. The distance in fiber-based quantum communication is limited to about a hundred kilometers due to signal attenuation. Thus, quantum repeaters are required to establish large-scale quantum networks. Ideal quantum repeater nodes possess a quantum memory which is efficiently connected to photons, the carrier of quantum information. Color centers in diamond and, in particular, the negatively-charged silicon-vacancy centers are promising candidates to establish such nodes. The major obstacle is an inefficient connection between the color centers spin to the Gaussian optics of fiber networks. Here, we present an efficient spin-photon interface. Individual silicon-vacancy centers coupled to the mode of a hemispherical Fabry-Pérot microcavity show Purcell-factors larger than 1 when operated in a bath of liquid Helium. We demonstrate coherent optical driving with a Rabi frequency of 290 MHz290\,\mathrm{MHz}290MHz and all-optical access to the electron spin in strong magnetic fields of up to 3.2 T3.2\,\mathrm{T}3.2T. Spin initialization within 67 ns67\,\mathrm{ns}67ns with a fidelity of 80 %80\,\%80% and a lifetime of 350 ns350\,\mathrm{ns}350ns are reached inside the cavity. The spin-photon interface is passively stable, enabled by placing a color center containing nanodiamond in the hemispherical Fabry-Pérot mirror structure and by choosing short cavity lengths. Therefore, our demonstration opens the way to realize quantum repeater applications.
Abstract Large-scale quantum communication networks require quantum repeaters due to the signal attenuation in optical fibers. Ideal quantum repeater nodes efficiently link a quantum memory with photons serving as flying qubits. Color centers in diamond, particularly the negatively charged silicon vacancy center, are promising candidates to establish such nodes. Inefficient connection between the color center’s spin to the optical fiber networks is a major obstacle, that could be resolved by utilizing optical resonators. Here, we couple individual silicon vacancy centers incorporated in a nanodiamond to a hemispherical, stable Fabry-Perot microcavity, achieving Purcell-factors larger than 1. We demonstrate coherent optical driving between ground and excited state with a Rabi-frequency of 330 MHz, all-optical initialization and readout of the electron spin in magnetic fields of up to 3.2 T. Spin initialization within 67 ns with a 80 % fidelity and a lifetime of 350 ns are reached. Our demonstration opens the way to realize quantum repeater applications.
Building a long distance quantum network is one of the big challenges in the field of quantum communication, which requires the development of a quantum repeater. A crucial component of this is an efficient, coherent spin photon interface, and coupling single NV centers to a microcavity is a promising approach therefor. In our experiment, we integrate a diamond membrane to an open access fiber-based Fabry-Perot microcavity to increase the weak ZPL emission of NV centers. Simulations predict the feasibility of a strong enhancement of the ZPL emission efficiency, reaching values of up to 80%. We present a spatially resolved characterization of a coupled cavity-membrane device and report on the current status of the experiment.
Quantum networks require functional nodes consisting of stationary registers with the capability of high-fidelity quantum processing and storage, which efficiently interface with photons propagating in an optical fiber. We report a significant step towards realization of such nodes using a diamond nanocavity with an embedded silicon-vacancy (SiV) color center and a proximal nuclear spin. Specifically, we show that efficient SiV-cavity coupling (with cooperativity C>30) provides a nearly deterministic interface between photons and the electron spin memory, featuring coherence times exceeding 1 ms. Employing coherent microwave control, we demonstrate heralded single photon storage in the long-lived spin memory as well as a universal control over a cavity-coupled two-qubit register consisting of a SiV and a proximal ^{13}C nuclear spin with nearly second-long coherence time, laying the groundwork for implementing quantum repeaters.
Quantum networks hold the potential to enable quantum-secured communication, distributed quantum computing, and non-local quantum sensing. To realize these applications, a versatile quantum network infrastructure must support entanglement between network nodes capable of storing, processing, and distributing quantum information, alongside high-fidelity photonic qubits that efficiently interface with these nodes. The silicon-vacancy (SiV) center in diamond, coupled to nanophotonic cavities, has recently emerged as a promising platform to meet these requirements. This system provides access to an electron spin as an optically active communication qubit and a 29Si nuclear spin as a memory qubit, capable of storing quantum information for extended periods. We first demonstrate that the SiV center's electron spin can efficiently generate single photons with complex spatiotemporal waveforms, facilitated by a novel asymmetric nanophotonic cavity design. We then establish a two-node quantum network between two SiV centers housed in separate laboratories and connected via optical fiber. To do so, we use photonic qubits to mediate entanglement between two spatially separated electron spins, as well as between two spatially separated nuclear spins. Finally, using bidirectional quantum frequency conversion, we convert the photonic qubits to telecommunication frequencies, enabling entanglement generation between the two nuclear spins via a 35 km fiber deployed in the Boston metropolitan area. These advancements mark progress toward large-scale, deployable quantum networks using SiV centers coupled to nanophotonic cavities.
Developing technologies for distributing entanglement over long distances, and employing this technology to create quantum communication networks, has been a standing goal of the quantum optics community for almost two decades. Such networks could be used for secure communication enabled by quantum key distribution (QKD), enhancement of quantum sensors, and even the creation of networked quantum computers. We present a platform, based on the negatively charged Silicon Vacancy (SiV) in diamond, capable of correcting for the photon loss that currently limits the size of such networks. Furthermore, we lay the groundwork for its use for scalable implementation of the full quantum repeater protocol, the missing ingredient for the deployment of large quantum networks. First, we demonstrate improved diamond nanofabrication techniques that enable the creation of an integrated, cooperativity 100 spin-photon interface. We further discuss the techniques used to integrate this platform with microwave coplanar waveguides (CPWs) that enable coherent control of the SiV spin state. Next, we demonstrate the integration of diamond nanophotonic technology with nanomechanical strain control, enabling the reduction of variations between, and fluctuations of, diamond color center optical and spin properties. These techniques are used to enable quantum interference between two initially distinguishable quantum emitters. To further demonstrate the utility of this platform, we employ coherent spin control and our platform's high cooperativity spin-photon interface to create an integrated quantum network node capable of high fidelity, coherent photon storage and the formation of multiqubit quantum registers. We discuss the engineering and physics principles relevant to the implementation of such a system, and provide a framework for future improvements to the underlying technology. Finally, we employ the developed techniques to perform Bell state measurements between asynchronously arriving photons. By utilizing this technique we demonstrate enhancement of the quantum communication rate between two parties, thus implementing the key functionality of a single quantum repeater node. This demonstration, combined with the other technical advances presented here, positions the diamond photonics-SiV platform as a leading candidate for the implementation quantum networking technology and provides a path towards large scale deployment of such systems.