QUROPE Quantum Information Processing and Communication in Europe

Due to their low mass, high quality factor, and good optical properties, silicon nitride (SiN) micromembrane resonators are widely used in force and mass sensing applications, particularly in optomechanics. The metallization of such membranes would enable an electronic integration with the prospect for exciting new devices, such as optoelectromechanical transducers.

For a certain class of isolated quantum systems, we report the existence of irreversible processes in which the energy is not dissipated. After a closed cycle in which the initial energy distribution is fully recovered, the expectation value of a symmetry-breaking observable changes from a value differing from zero in the initial state to zero in the final state. This entails the unavoidable loss of a certain amount of information and constitutes a source of irreversibility.

We present a comprehensive and up to date review on the concept of quantum non-Markovianity, a central theme in the theory of open quantum systems. We introduce the concept of quantum Markovian process as a generalization of the classical definition of Markovianity via the so-called divisibility property and relate this notion to the intuitive idea that links non-Markovianity with the persistence of memory effects. A detailed comparison with other definitions presented in the literature is provided.

The ability to measure weak signals such as pressure, force, electric field, and temperature with nanoscale devices and high spatial resolution offers a wide range of applications in fundamental and applied sciences. Here we present a proposal for a hybrid device composed of thin film layers of diamond with color centers implanted and piezo-active elements for the transduction and measurement of a wide variety of physical signals.

We propose an all-optical scheme to prolong the quantum coherence of a negatively charged nitrogen-vacancy (NV) center in diamond. Optical control of the NV spin suppresses energy fluctuations of the 3A2 ground states and forms an energy gap protected subspace. By optical control, the spectral linewidth of magnetic resonance is much narrower and the measurement of the frequencies of magnetic field sources has higher resolution.

Interferometry with massive particles may have the potential to explore the limitations of standard quantum mechanics in particular where it concerns its boundary with general relativity and the yet to be developed theory of quantum gravity. This development is hindered considerably by the lack of experimental evidence and testable predictions.

Presented material: 

poster.pdf

Quantum metrology gives bounds on achievable precision in measurements of parameters like phase delays, frequencies etc. However it is not known if those bounds are saturable and what is the optimal state, i.e. what quantum resources like entanglement should be used to get it. It is known that asymptotically optimal states should be tensor products of some states with lower particle number, thus they would not be highly entangled.

Veldhoven (Netherlands), 23 January 2013
Immanuel Bloch (MPQ) “Probing Quantum Matter under Extreme Conditions”

Stockholm (Sweden), 6-8 February 2013
Immanuel Bloch (MPQ) “New Frontiers with Ultracold Quantum Gases in Optical Lattices”

Queenstown (New Zealand), 17-20 February 2013
Immanuel Bloch (MPQ) “Probing Non-Equilibrium Dynamics Using Ultracold Quantum Gases”