Thursday, February 26, 2009

Tripartite entanglement versus tripartite nonlocality in 3 qubit GHZ-class states
by Shohini Ghose et. al.

We analyze the relationship between tripartite entanglement and genuine tripartite nonlocality for 3-qubit pure states in the GHZ class. We consider a family of states known as the generalized GHZ states and derive an analytical expression relating the 3-tangle, which quantifies tripartite entanglement, to the Svetlichny inequality, which is a Bell-type inequality that is violated only when all three qubits are nonlocally correlated. We show that states with 3-tangle less than 1/2 do not violate the Svetlichny inequality. On the other hand, a set of states known as the maximal slice states always violate the Svetlichny inequality, and exactly analogous to the two-qubit case, the amount of violation is directly related to the degree of tripartite entanglement. We discuss further interesting properties of the generalized GHZ and maximal slice states.

**Groupmeeting by Rene Stock**

Wednesday, February 18, 2009

Coherent excitation of a strongly coupled quantum dot - cavity system
by Dirk Englund, ....., Jelena Vuckovic

Photonic nanocavities coupled to semiconductor quantum dots are becoming well developed systems for studying cavity quantum electrodynamics and constructing the basic architecture for quantum information science. One of the key challenges is to coherently control the state of the quantum dot/cavity system for quantum memory and gates that exploit the non-linearity of such a system. Recently, coherent control of quantum dots has been studied in bulk semiconductor. Here we investigate the coherent excitation of a strongly coupled InAs quantum dot - photonic crystal cavity system. When the quantum dot and cavity are on resonance, we observe time-domain Rabi oscillation in the transmission of a laser pulse. This coherent excitation promises to enable an all-optical method to observe and manipulate the state a single quantum dot in a cavity. When the detuned dot is resonantly excited, we show that the resonantly driven quantum dot efficiently emits through the cavity mode, an effect that is explained in part by an incoherent dephasing mechanism similar to recent theoretical models. When the detuned quantum dot is resonantly excited, the cavity signal represents a spectrally separated read-out channel for high resolution single quantum dot spectroscopy. In this case, we observe antibunching of the cavity mode. Such a single photon source could allow photon indistinguishability that approaches unity as could lift the limi-itation due to dephasing and timing jitter. The single photon emission is controlled by the cavity resonance, which relaxes the demands for spectrally matching quantum dots for two-photon interference and may therefore be of use in linear optics quantum computation and quantum communication.

**Groupmeeting by Jason McKeever**