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Scalable photonic network architecture based on motional averaging in room temperature gas

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      Abstract

      Quantum interfaces between photons and ensembles of atoms have emerged as powerful tools for quantum technologies. A major objective for such interfaces is high fidelity storage and retrieval of a photon in a collective quantum state of many atoms. This requires long-lived collective superposition states, which is typically achieved with immobilized atoms. Thermal atomic vapors, which present a simple and scalable resource, have, so far, only been used for continuous variable processing or for discrete variable processing on short time scales where atomic motion is negligible. We develop a theory based on the concept of motional averaging to enable room temperature discrete variable quantum memories and coherent single photon sources. We show that by choosing the interaction time so that atoms kept under spin protecting conditions can cross the light beam several times during the interaction combined with suitable spectral filtering, we erase the "which atom" information and obtain an efficient and homogenous coupling between all atoms and the light. Heralded single excitations can thus be created and stored as collective spinwaves, which can later be read out to produce coherent single photons in a scalable fashion. We demonstrate the feasibility of this approach to scalable quantum memories with a proof-of-principle experiment with room temperature atoms contained in microcells with spin protecting coating, placed inside an optical cavity. The experiment is performed at conditions corresponding to a few photons per pulse and clearly demonstrates a long coherence time of the forward scattered photons, which is the essential feature of the motional averaging.

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      Most cited references 16

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      The Quantum Internet

       H. Kimble (2008)
      Quantum networks offer a unifying set of opportunities and challenges across exciting intellectual and technical frontiers, including for quantum computation, communication, and metrology. The realization of quantum networks composed of many nodes and channels requires new scientific capabilities for the generation and characterization of quantum coherence and entanglement. Fundamental to this endeavor are quantum interconnects that convert quantum states from one physical system to those of another in a reversible fashion. Such quantum connectivity for networks can be achieved by optical interactions of single photons and atoms, thereby enabling entanglement distribution and quantum teleportation between nodes.
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        Long-distance quantum communication with atomic ensembles and linear optics

         ,  ,   (2001)
        Quantum communication holds a promise for absolutely secure transmission of secret messages and faithful transfer of unknown quantum states. Photonic channels appear to be very attractive for physical implementation of quantum communication. However, due to losses and decoherence in the channel, the communication fidelity decreases exponentially with the channel length. We describe a scheme that allows to implement robust quantum communication over long lossy channels. The scheme involves laser manipulation of atomic ensembles, beam splitters, and single-photon detectors with moderate efficiencies, and therefore well fits the status of the current experimental technology. We show that the communication efficiency scale polynomially with the channel length thereby facilitating scalability to very long distances.
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          Experimental long-lived entanglement of two macroscopic objects

           ,  ,   (2001)
          Entanglement is considered to be one of the most profound features of quantum mechanics. An entangled state of a system consisting of two subsystems cannot be described as a product of the quantum states of the two subsystems. In this sense the entangled system is considered inseparable and nonlocal. It is generally believed that entanglement manifests itself mostly in systems consisting of a small number of microscopic particles. Here we demonstrate experimentally the entanglement of two objects, each consisting of about 10^12 atoms. Entanglement is generated via interaction of the two objects - more precisely, two gas samples of cesium atoms - with a pulse of light, which performs a non-local Bell measurement on collective spins of the samples. The entangled spin state can be maintained for 0.5 millisecond. Besides being of fundamental interest, the robust, long-lived entanglement of material objects demonstrated here is expected to be useful in quantum information processing, including teleportation of quantum states of matter and quantum memory.
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            Author and article information

            Journal
            1501.03916
            10.1038/ncomms11356

            Quantum physics & Field theory

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