Quantum entanglement in the motion of macroscopic solid bodies has implications both for quantum technologies and foundational studies of the boundary between the quantum and classical worlds. Entanglement is usually fragile in room-temperature solids, owing to strong interactions both internally and with the noisy environment. We generated motional entanglement between vibrational states of two spatially separated, millimeter-sized diamonds at room temperature. By measuring strong nonclassical correlations between Raman-scattered photons, we showed that the quantum state of the diamonds has positive concurrence with 98% probability. Our results show that entanglement can persist in the classical context of moving macroscopic solids in ambient conditions.

READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.Access and use of this website and the material on it are subject to the Terms and Conditions set forth at http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en Towards high-speed optical quantum memories K. F. Reim 1 , J. Nunn 1 ,V .O .L o r en z 1,2 ,B.J .Su s sm a n 1,3 ,K .C .L ee 1 ,N .K.La n gfo r d 1 ,D .Ja ks ch 1 and I. A. Walmsley 1 * Quantum memories, capable of controllably storing and releasing a photon, are a crucial component for quantum computers 1 and quantum communications 2 . To date, quantum memories 3-6 have operated with bandwidths that limit data rates to megahertz. Here we report the coherent storage and retrieval of sub-nanosecond low-intensity light pulses with spectral bandwidths exceeding 1 GHz in caesium vapour. The novel memory interaction takes place through a far off-resonant two-photon transition in which the memory bandwidth is dynamically generated by a strong control field 7,8 . This should allow data rates more than 100 times greater than those of existing quantum memories. The memory works with a total efficiency of 15%, and its coherence is demonstrated through direct interference of the stored and retrieved pulses. Coherence times in hot atomic vapours are on the order of microseconds 9 , the expected storage time limit for this memory.Photons are ideal carriers of quantum information. They have a very large potential information capacity, and do not interact with one another, making encoded information robust. Recent developments in sources, detectors, gates and protocols have laid the basis for the construction of large-scale photonic quantum computers with unique capabilities 1,10 , as well as inter-continental quantum networks that are immune to undetected eavesdropping 11 . However, the effects of photon loss and the inherently probabilistic character of some of these components make photon storage desirable. The difficulty that many photonic networks successfully produce a result only rarely is overcome if photons can be stored, because this allows complex protocols to be orchestrated by holding the output of successful operations until all have been correctly executed 1 . Quantum memories are therefore an active area of research, with much interest being focused on reversibly mapping photons into collective atomic excitations 5,12 .The key characteristics for quantum memories are long storage time, high memory efficiency, the ability to store multiple modes (multiple distinct photons) 11,13 and high bandwidth. High bandwidth allows the storage of temporally short photons, enabling quantum information to be processed at a higher 'clock rate'. This can be difficult to achieve with atomic memories, because photons must be stored in long-lived atomic states with narrow linewidths. Here we demonstrate the storage of signal pulses with a bandwidth 300 times larger than the natural width of the caesium D2 line that mediates the interaction.Previously implemented memory protocols include ele...

We describe a general analytical framework of a nanoplasmonic cavity-emitter system interacting with a dielectric photonic waveguide. Taking into account emitter quenching and dephasing, our model directly reveals the single photon extraction efficiency, η, as well as the indistinguishability, I, of photons coupled into the waveguide mode. Rather than minimizing the cavity modal volume, our analysis predicts an optimum modal volume to maximize η that balances waveguide coupling and spontaneous emission rate enhancement. Surprisingly, our model predicts that near-unity indis-tinguishability is possible, but this requires a much smaller modal volume, implying a fundamental performance trade-off between high η and I at room temperature. Finally, we show that maximizing ηI requires that the system has to be driven in the weak coupling regime because quenching effects and decreased waveguide coupling drastically reduce η in the strong coupling regime. INTRODUCTION Atomic and photonic quantum systems are central in many areas of quantum information processing, including quantum computing, communication, and precision sensing. [1-3] A central remaining challenge is to improve the naturally weak interaction between single pho-tons and single emitters. [4] To this end, a plethora of approaches using dielectric (Ref. [5-12]) as well as plas-monic (Ref.[4, 13-18, 20]) cavities and waveguides has been suggested. While several theoretical studies analyzed the interaction between quantum emitters and dielectric (Ref. [4, 21-24]) or plasmonic (Ref. [13-15]) waveguides, it has been a remaining issue to develop a comprehensive physical model of a nanoplas-monic cavity interacting with a single quantum emit-ter and evanescently coupled to a dielectric waveguide. [25, 26] In particular, there is a need for a comprehensive theoretical model to analyze the single photon extraction efficiency and indistinguishability of such integrated nanoplasmonic systems. In this paper we present for the first time a general theory framework of an integrated nanoplasmonic quantum interface which incorporates the impact of quenching and dephasing on the single photon extraction efficiency η and indistinguishability I. Our analysis yields optimal operating conditions to maximize η and I and gives clear physical intuition in the fundamental performance trade-offs. We reveal that η is maximized for an optimum cavity modal volume V opt η which is inversely proportional to the cavity Q−factor. On the other hand, I can only be maximized for much smaller V c V opt η at room temperature , imposing a fundamental limit on the ηI product. Finally, it is shown that the maximum ηI product is obtained for weak coupling because quenching effects and reduced waveguide coupling induce a huge decrease of η in the strong coupling regime. MODEL The quantum photonic platform under investigation is shown in Fig. 1. It consists of a dielectric nanopho-tonic waveguide that evanescently interacts with a cavity-emitter system. The cavity has a resonance frequency ω c and an...

The ability to store multiple optical modes in a quantum memory allows for increased efficiency of quantum communication and computation. Here we compute the multimode capacity of a variety of quantum memory protocols based on light storage in ensembles of atoms. We find that adding a controlled inhomogeneous broadening improves this capacity significantly.

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