Geometric phases in open systems: an exact model to study how they are corrected by decoherence

We calculate the geometric phase for an open system (spin-boson model) which interacts with an environment (ohmic or nonohmic) at arbitrary temperature. However there have been many assumptions about the time scale at which the geometric phase can be measured, there has been no reported observation yet for mixed states under nonunitary evolution. We study not only how they are corrected by the presence of the different type of environments but also estimate the corresponding times at which decoherence becomes effective. These estimations should be taken into account when planning experimental setups to study the geometric phase in the nonunitary regime, particularly important for the application of fault-tolerant quantum computation.Comment: Revtex 4, 5 pages, one eps figure. Version Publishe

Generation of Kerr non-Gaussian motional states of trapped ions

Non-Gaussian states represent a powerful resource for quantum information protocols in the continuous variables regime. Cat states, in particular, have been produced in the motional degree of freedom of trapped ions by controlled displacements dependent on the ionic internal state. An alternative method harnesses the Kerr nonlinearity naturally existent in this kind of system. We present detailed calculations confirming its feasibility for typical experimental conditions. Additionally, this method permits the generation of complex non-Gaussian states with negative Wigner functions. Especially, superpositions of many coherent states are achieved at a fraction of the time necessary to produce the cat state.Comment: 6 pages, 5 figure

Generation of Bright Two-Color Continuous Variable Entanglement

We present the first measurement of squeezed-state entanglement between the twin beams produced in an Optical Parametric Oscillator (OPO) operating above threshold. Besides the usual squeezing in the intensity difference between the twin beams, we have measured squeezing in the sum of phase quadratures. Our scheme enables us to measure such phase anti-correlations between fields of different frequencies. In the present measurements, wavelengths differ by ~1 nm. Entanglement is demonstrated according to the Duan et al. criterion [Phys. Rev. Lett. 84, 2722 (2000)] $\Delta^2\hat{p}_- +\Delta^2\hat{q}_+=1.47(2)<2$. This experiment opens the way for new potential applications such as the transfer of quantum information between different parts of the electromagnetic spectrum.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let

Light yield determination in large sodium iodide detectors applied in the search for dark matter

Application of NaI(Tl) detectors in the search for galactic dark matter particles through their elastic scattering off the target nuclei is well motivated because of the long standing DAMA/LIBRA highly significant positive result on annual modulation, still requiring confirmation. For such a goal, it is mandatory to reach very low threshold in energy (at or below the keV level), very low radioactive background (at a few counts/keV/kg/day), and high detection mass (at or above the 100 kg scale). One of the most relevant technical issues is the optimization of the crystal intrinsic scintillation light yield and the efficiency of the light collecting system for large mass crystals. In the frame of the ANAIS (Annual modulation with NaI Scintillators) dark matter search project large NaI(Tl) crystals from different providers coupled to two photomultiplier tubes (PMTs) have been tested at the Canfranc Underground Laboratory. In this paper we present the estimates of the NaI(Tl) scintillation light collected using full-absorption peaks at very low energy from external and internal sources emitting gammas/electrons, and single-photoelectron events populations selected by using very low energy pulses tails. Outstanding scintillation light collection at the level of 15~photoelectrons/keV can be reported for the final design and provider chosen for ANAIS detectors. Taking into account the Quantum Efficiency of the PMT units used, the intrinsic scintillation light yield in these NaI(Tl) crystals is above 40~photoelectrons/keV for energy depositions in the range from 3 up to 25~keV. This very high light output of ANAIS crystals allows triggering below 1~keV, which is very important in order to increase the sensitivity in the direct detection of dark matter

Background model of NaI(Tl) detectors for the ANAIS Dark Matter Project

A thorough understanding of the background sources is mandatory in any experiment searching for rare events. The ANAIS (Annual Modulation with NaI(Tl) Scintillators) experiment aims at the confirmation of the DAMA/LIBRA signal at the Canfranc Underground Laboratory (LSC). Two NaI(Tl) crystals of 12.5 kg each produced by Alpha Spectra have been taking data since December 2012. The complete background model of these detectors and more precisely in the region of interest will be described. Preliminary background analysis of a new 12.5 kg crystal received at Canfranc in March 2015 will be presented too. Finally, the power of anticoincidence rejection in the region of interest has been analyzed in a 4x 5 12.5 kg detector matrix.Comment: Contributed to the 11th Patras Workshop on Axions, WIMPs and WISPs, Zaragoza, June 22 to 26, 201