December 2014

Abstracts of the QSIT Lunch Seminar, Thursday December 4, 2014

Witnessing genuine multipartite optical-path entanglement

Valentina Caprara Vivoli, GAP Quantique, Université de Genève

Optical path entanglement is a promising resource for large scale quantum networks, like quantum repeaters, as well as for more complex, 2-D, network structures. However, the challenge is to detect and verify the entanglement in a distributed scenario, i.e. using only local measurement. Here, we propose an entanglement witness specifically developed as a trustworthy means of detecting path entanglement. It requires no post-selection, uses only local measurements and can be scaled for genuine n-partite entangled states. A measurement scheme that combines weak optical displacement operations and single photon counting techniques is also developed. We finally experimentally demonstrate the entanglement witness for bipartite and tripartite entangled states, highlighting the scalability and robustness of the witness.

Direct characterization of a squeezed oscillator state and squeezed cat state production with trapped ions

Hsiang-yu Lo, Trapped Ion Quatnum Infomartion - Jonathan Home's Lab, ETH Zurich

In this seminar, I will present the creation of novel quantum states of a single ion, in which two distinct displaced-squeezed oscillator states are entangled with a microscopic spin. These states are generated by applying spin-dependent forces to an ion which has been initialized in a squeezed motional state by reservoir engineering. This method allows us two complementary methods for characterizing the initial squeezed state. The spin-motion entanglement allows us to deduce the shape of the initial wavepacket, while the Fock state distributions of the displaced-squeezed states of motion show clear differences for displacements applied along the two principal axes of the squeezed state. We also illustrate the coherence of the spin-motion entangled superposition states for displacements applied along the squeezed quadrature, observing revivals in coherence for phase-space separations of alpha > 16, which is 48 times the width of the wavepacket in phase space.

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