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"Quantum communication with resonant qubit-photon interactions"

Dr. J. Zsolt Bernad
Technische Universität Darmstadt


The realization of a quantum repeater capable of creating entanglement between qubits over large distances still represents a major quantum technological challenge. In this context the proposal of a hybrid quantum repeater in which continuous variables of the electromagnetic field exchange quantum information with spatially separated material qubits offers interesting perspectives for preparing highly entangled material qubit pairs over large distances. In this talk I present a hybrid quantum repeater based on resonant coupling of material qubits to a quantized mode of the radiation field. In general quantum repeaters consist of many intermediate nodes and have three sequentially applied building blocks: an entanglement is generated between qubits in the neighbouring nodes; entanglement purification is carried out over the ensemble of low-fidelity entangled pairs; the entanglement swapping procedure transforms the entangled states on the neighbouring stations into entangled states on the second neighbouring stations, thus increasing the distance of shared entanglement. First, I demonstrate that resonant matter-field interactions result in high fidelity Bell-states between two spatially well-separated neighbouring nodes. A model for the optical fiber, i.e, the quantum channel connecting the distant nodes, and effects originating from the centre-of-mass motion of the trapped qubits in the Lamb-Dicke limit are briefly discussed. I will continue my talk with a cavity QED based entanglement purification scheme. I present the theoretical possibilities of realizing a high-fidelity two-qubit quantum operation necessary for the purification protocol with the help of a postselective balanced homodyne photodetection. Bell measurements are core elements in entanglement-assisted quantum teleportation and entanglement swapping. Therefore, in the last part of this seminar a theoretical proposal for an unambiguous Bell measurement of material qubits is discussed.

Thursday, September 8, 2016
IQSE 578, 12:30 Noon
Mitchell Physics Building

Institute for Quantum Science and Engineering
Texas A&M University

(Pizza, salad, and soda to be served at 12:00 noon)

Host: Dr. Marlan Scully