Polytechnic University of Turin

About: Polytechnic University of Turin is a education organization based out in Turin, Piemonte, Italy. It is known for research contribution in the topics: Finite element method & Nonlinear system. The organization has 11553 authors who have published 41395 publications receiving 789320 citations. The organization is also known as: POLITO & Politecnico di Torino.

Ultrastable optical clock with two cold-atom ensembles

Abstract: Optical clocks with a record low zero-dead-time instability of 6 × 10–17 at 1 second are demonstrated in two cold-ytterbium systems. The two systems are interrogated by a shared optical local oscillator to nearly eliminate the Dick effect. Atomic clocks based on optical transitions are the most stable, and therefore precise, timekeepers available. These clocks operate by alternating intervals of atomic interrogation with the ‘dead’ time required for quantum state preparation and readout. This non-continuous interrogation of the atom system results in the Dick effect, an aliasing of frequency noise from the laser interrogating the atomic transition1,2. Despite recent advances in optical clock stability that have been achieved by improving laser coherence, the Dick effect has continually limited the performance of optical clocks. Here we implement a robust solution to overcome this limitation: a zero-dead-time optical clock that is based on the interleaved interrogation of two cold-atom ensembles3. This clock exhibits vanishingly small Dick noise, thereby achieving an unprecedented fractional frequency instability assessed to be for an averaging time τ in seconds. We also consider alternate dual-atom-ensemble schemes to extend laser coherence and reduce the standard quantum limit of clock stability, achieving a spectroscopy line quality factor of Q > 4 × 1015.

XAFS, IR, and UV−Vis Study of the CuI Environment in CuI-ZSM-5

Abstract: XAFS, IR, and UV−vis (diffuse reflectance and photoluminescence) spectroscopies have been employed to investigate the local environment of CuI in CuI-ZSM-5 prepared by gas phase reaction of H-ZSM-5 (SiO2/Al2O3 = 90−50) with CuCl The measurements confirm that the absolutely predominant copper species formed with this procedure are CuI:Cu species in other oxidation states are less than 1% Direct proof of the absence of both unreacted CuCl microaggregates and of copper clusters in the zeolite channels is also given CuI-ZSM-5 prepared in this way represents a model solid for investigating the structure of isolated CuI sites in zeolites EXAFS analysis reveal that, in vacuum conditions, Cu+ cations are surrounded by 25 ± 03 oxygens at 200 ± 002 A The combined use of EXAFS, IR, and photoluminescence UV−vis spectroscopies and computer graphic simulations allows to infer that Cu+ ions in CuI-ZSM-5 are located in two families of sites, indicated as I and II, (site II having the highest coordinative unsatur

Entangling power of quantum evolutions

Abstract: We analyze the entangling capabilities of unitary transformations U acting on a bipartite ${(d}_{1}\ifmmode\times\else\texttimes\fi{}{d}_{2})$-dimensional quantum system. To this aim we introduce an entangling power measure $e(U)$ given by the mean linear entropy produced acting with U on a given distribution of pure product states. This measure admits a natural interpretation in terms of quantum operations. For a uniform distribution explicit analytical results are obtained using group-theoretic arguments. The behavior of the features of $e(U)$ as the subsystem dimensions ${d}_{1}$ and ${d}_{2}$ are varied is studied both analytically and numerically. The two-qubit case ${d}_{1}{=d}_{2}=2$ is argued to be peculiar.