Highlights for Q-ESSENCE

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Format: 2017-04-24
Format: 2017-04-24
Format: 2017-04-24


Nov 4, 2013

We study the nonequilibrium dynamics of correlations in quantum lattice models in the presence of long-range interactions decaying asymptotically as a power law. For exponents larger than the lattice dimensionality, a Lieb-Robinson-type bound effectively restricts the spreading of correlations to a causal region, but allows supersonic propagation. We show that this decay is not only sufficient but also necessary.


Mar 30, 2012

Current attempts to probe general relativistic effects in quantum mechanics focus on precision measurements of phase shifts in matterwave interferometry. Yet, phase shifts can always be explained as arising because of an AharonovBohm effect, where a particle in a flat spacetime is subject to an effective potential. Here we propose a quantum effect that cannot be explained without the general relativistic notion of proper time.


Mar 30, 2012

Quantum states and measurements exhibit wave-like - continuous, or particle-like - discrete, character. Hybrid discrete-continuous quantum optical systems are key to investigating fundamental quantum phenomena such as the violation of local realism by Einstein-Podolsky-Rosen states, measuring non-classical correlations of radiation fields and superpositions of macroscopic states, and form essential resources for quantum-enhanced applications and high- efficient optical telecommunications.


Mar 30, 2012

We show that the process of three-wave mixing in a non-linear crystal (such as employed in down conversion processes) can be used for versatile weak measurements. That is the crystal field interaction Hamiltonian enables weak measurements of pairs of complementary variables. To obtain the weak value of variable $A$ one has to perform weak measurements twice. This seems to be drawback, but as a compensation we get for free the weak value of a complementary variable $B$.


Mar 30, 2012

Studying mechanical resonators via radiation pressure offers a rich avenue for the exploration of quantum mechanical behavior in a macroscopic regime. However, quantum state preparation and especially quantum state reconstruction of mechanical oscillators remains a significant challenge. Here we propose a scheme to realize quantum state tomography, squeezing, and state purification of a mechanical resonator using short optical pulses.


Mar 30, 2012

In this paper, we report on the performance of the SwissQuantum quantum key distribution (QKD) network. The network was installed in the Geneva metropolitan area and ran for more than one-and-a-half years, from the end of March 2009 to the beginning of January 2011. The main goal of this experiment was to test the reliability of the quantum layer over a long period of time in a production environment. A key management layer has been developed to manage the key between the three nodes of the network.


Mar 30, 2012

We demonstrate the in-plane emission of highly-polarized single photons from an InAs quantum dot embedded into a photonic crystal waveguide. The spontaneous emission rates are Purcell-enhanced by the coupling of the quantum dot to a slow-light mode of the waveguide. Photon-correlation measurements confirm the sub-Poissonian statistics of the in-plane emission. Under optical pulse excitation, single photon emission rates of up to 19 MHz into the guided mode are demonstrated, which corresponds to a device efficiency of 24%.


Mar 30, 2012

The monolithic integration of single-photon sources, passive optical circuits and single-photon detectors enables complex and scalable quantum photonic integrated circuits, for application in linear-optics quantum computing and quantum communications. Here we demonstrate a key component of such a circuit, a waveguide single-photon detector.


Mar 30, 2012

Room-temperature, easy-to-operate quantum memories are essential building blocks for future long distance quantum information networks operating on an intercontinental scale, because devices like quantum repeaters, based on quantum memories, will have to be deployed in potentially remote, inaccessible locations. Here we demonstrate controllable, broadband and efficient storage and retrieval of weak coherent light pulses at the single-photon level in warm atomic cesium vapor using the robust far off-resonant Raman memory scheme.


Mar 30, 2012

Engineering and controlling well defined states of light for quantum information applications is of increasing importance as the complexity of quantum systems grows. For example, in quantum networks high multi-photon interference visibility requires properly devised single mode sources. In this paper we propose a spontaneous parametric down conversion source based on an integrated cavity-waveguide, where single narrow-band, possibly distinct, spectral modes for the idler and the signal fields can be generated.

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