QUROPE Quantum Information Processing and Communication in Europe

We advocate a Bayesian approach to optimal quantum frequency estimation—an important issue for future quantum enhanced atomic clock operation. The approach provides a clear insight into the interplay between decoherence and the extent of prior knowledge in determining the optimal interrogation times and optimal estimation strategies.

The conductance of a quantum point contact is quantized in units of 1/h, with h being Planck's constant, which is the universal upper bound to transport set by Heisenberg's and Pauli's principles. Can interactions cause a breakdown of this quantization? Here we answer this question using a cold atom quantum simulation. Our simulation yields the spin and particle conductance of a Fermi gas flowing through a single mode quantum point contact as a function of the strength of attractive interactions.

Point contacts provide simple connections between macroscopic particle reservoirs. In electric circuits, strong links between metals, semiconductors, or superconductors have applications for fundamental condensed-matter physics as well as quantum information processing. However, for complex, strongly correlated materials, links have been largely restricted to weak tunnel junctions. We studied resonantly interacting Fermi gases connected by a tunable, ballistic quantum point contact, finding a nonlinear current-bias relation.

We study the emergence of a fragmented state in a strongly interacting Fermi gas subject to a tunable
disorder. We investigate its properties using a combination of high-resolution in situ imaging and
conductance measurements. The fragmented state exhibits saturated density modulations, a strongly
reduced density percolation threshold, lower than the average density, and a resistance equal to that of a
noninteracting Fermi gas in the same potential landscape. The transport measurements further indicate that

Annual gathering of all the groups involved in the Project SIQS

See attachment for the workshop schedule

Quantized integrable systems can be made to perform universal quantum computation by the application of a global time-varying control. The action-angle variables of the integrable system function as qubits or qudits, which can be coupled selectively by the global control to induce universal quantum logic gates. By contrast, chaotic quantum systems, even if controllable, do not generically allow quantum computation under global control.

The Kibble-Zurek (KZ) hypothesis identifies the relevant time scales in out-of-equilibrium dynamics of critical systems employing concepts valid at equilibrium: It predicts the scaling of the defect formation immediately after quenches across classical and quantum phase transitions as a function of the quench speed. Here we study the crossover between the scaling dictated by a slow quench, which is ruled by the critical properties of the quantum phase transition, and the excitations due to a faster quench, where the dynamics is often well described by the classical model.