5,359 research outputs found

    Coherent Feedback Networks for Distributed Generation of Continuous-Variable Entanglement

    Full text link
    Research interest in quantum information processing is spurred by non-classical phenomena such as entanglement. This thesis focuses on Einstein-Podolsky-Rosen (EPR)-like entanglement between a pair of Gaussian continuous-mode fields, which can be produced by a nondegenerate optical parametric amplifier (NOPA). The thesis aims to exploit coherent feedback networks in the form of the feedback interconnection of multiple NOPAs to generate entanglement in a distributed and power efficient manner. Firstly, we show how EPR entanglement can be generated by a dual-NOPA coherent feedback system connecting two NOPAs over two transmission channels. We analyse stability and EPR entanglement in a lossless scenario and under the effect of transmission losses, amplification losses, time delays and phase shifts in the transmission channels. It is shown that in an ideal scenario without losses and delays, and when only transmission losses are present, the feedback connection can yield an increase in the quality of the entanglement while consuming less power, compared to a single NOPA and a two cascaded NOPA system. The thesis is then concerned with linear quantum networks of multiple NOPAs. The NOPAs are interconnected in a coherent feedback chain, connecting two communicating parties over two transmission channels. We analyse stability and EPR entanglement between two outgoing fields of interest under the effect of losses and time delays, and bipartite entanglement of two-mode Gaussian states of internal cavity modes of the multiple-NOPA networks in the lossless case. It is numerically shown that the network with more NOPAs is more power efficient for EPR entanglement generation. Finally, we study optimization of EPR entanglement of linear quantum systems consisting of two NOPAs and a static linear passive network of optical devices. The passive network has six inputs and six outputs. By employing a steepest descent method, we find an optimized static passive network made of beamsplitters. Subsequently, we look at a special case of the above configuration, where the passive network has two inputs and two outputs, and the system is considered in the idealized infinite bandwidth limit. We show that the dual-NOPA coherent feedback system has a local optimality property for generation of EPR entanglement

    Quantum teleportation between light and matter

    Full text link
    Quantum teleportation is an important ingredient in distributed quantum networks, and can also serve as an elementary operation in quantum computers. Teleportation was first demonstrated as a transfer of a quantum state of light onto another light beam; later developments used optical relays and demonstrated entanglement swapping for continuous variables. The teleportation of a quantum state between two single material particles (trapped ions) has now also been achieved. Here we demonstrate teleportation between objects of a different nature - light and matter, which respectively represent 'flying' and 'stationary' media. A quantum state encoded in a light pulse is teleported onto a macroscopic object (an atomic ensemble containing 10^12 caesium atoms). Deterministic teleportation is achieved for sets of coherent states with mean photon number (n) up to a few hundred. The fidelities are 0.58+-0.02 for n=20 and 0.60+-0.02 for n=5 - higher than any classical state transfer can possibly achieve. Besides being of fundamental interest, teleportation using a macroscopic atomic ensemble is relevant for the practical implementation of a quantum repeater. An important factor for the implementation of quantum networks is the teleportation distance between transmitter and receiver; this is 0.5 metres in the present experiment. As our experiment uses propagating light to achieve the entanglement of light and atoms required for teleportation, the present approach should be scalable to longer distances.Comment: 23 pages, 8 figures, incl. supplementary informatio

    Superconducting quantum node for entanglement and storage of microwave radiation

    Full text link
    Superconducting circuits and microwave signals are good candidates to realize quantum networks, which are the backbone of quantum computers. We have realized a quantum node based on a 3D microwave superconducting cavity parametrically coupled to a transmission line by a Josephson ring modulator. We first demonstrate the time-controlled capture, storage and retrieval of an optimally shaped propagating microwave field, with an efficiency as high as 80%. We then demonstrate a second essential ability, which is the timed-controlled generation of an entangled state distributed between the node and a microwave channel.Comment: 6 pages, 4 figures. Supplementary information can be downloaded as the ancillary file her
    • …
    corecore