Search results for "conductivity"
showing 10 items of 1988 documents
Charmonium properties in hot quenched lattice QCD
2012
We study the properties of charmonium states at finite temperature in quenched QCD on large and fine isotropic lattices. We perform a detailed analysis of charmonium correlation and spectral functions both below and above $T_c$. Our analysis suggests that both S wave states ($J/\psi$ and $\eta_c$) and P wave states ($\chi_{c0}$ and $\chi_{c1}$) disappear already at about $1.5 T_c$. The charm diffusion coefficient is estimated through the Kubo formula and found to be compatible with zero below $T_c$ and approximately $1/\pi T$ at $1.5 T_c\lesssim T\lesssim 3 T_c$.
On the temperature dependence of the electrical conductivity in hot quenched lattice QCD
2011
Extending our recent work, we report on a calculation of the vector current correlation function for light valence quarks in the deconfined phase of quenched QCD in the temperature range 1.16Tc<T<2.98Tc. After performing a systematic analysis of the in fluence of cut-off effects on light quark meson correlators using clover improved Wilson fermions, we discuss resulting constraints on the electrical conductivity in a quark gluon plasma.
Design of a Lambda system for population transfer in superconducting nanocircuits
2013
The implementation of a Lambda scheme in superconducting artificial atoms could allow detec- tion of stimulated Raman adiabatic passage (STIRAP) and other quantum manipulations in the microwave regime. However symmetries which on one hand protect the system against decoherence, yield selection rules which may cancel coupling to the pump external drive. The tradeoff between efficient coupling and decoherence due to broad-band colored Noise (BBCN), which is often the main source of decoherence is addressed, in the class of nanodevices based on the Cooper pair box (CPB) design. We study transfer efficiency by STIRAP, showing that substantial efficiency is achieved for off-symmetric bias only i…
GHZ state generation of three Josephson qubits in the presence of bosonic baths
2013
We analyze an entangling protocol to generate tripartite Greenberger-Horne-Zeilinger states in a system consisting of three superconducting qubits with pairwise coupling. The dynamics of the open quantum system is investigated by taking into account the interaction of each qubit with an independent bosonic bath with an ohmic spectral structure. To this end a microscopic master equation is constructed and exactly solved. We find that the protocol here discussed is stable against decoherence and dissipation due to the presence of the external baths.
Energy and temperature of superfluid turbulent vortex tangles
2007
We consider three aspects of turbulent vortex tangles in superfluids. First, we outline some contributions to the Vinen’s equation for the time evolution of the vortex line density, related to the presence of pinned vortices incorporating the effects of the walls. Afterwards, we analyze some aspects of the energy balance of the vortex tangle, related to frictional dissipation and to vortex formation and destruction. Finally, we explore the concept of an effective temperature for the vortex tangle, related to the average energy of the vortex loops and to the diffusion coefficient of vortex lines. The combination of these ideas suggests some formal similarities with other kinds of driven none…
Recovering entanglement by local operations
2012
We investigate the phenomenon of bipartite entanglement revivals under purely local operations in systems subject to local and independent classical noise sources. We explain this apparent paradox in the physical ensemble description of the system state by introducing the concept of "hidden" entanglement, which indicates the amount of entanglement that cannot be exploited due to the lack of classical information on the system. For this reason this part of entanglement can be recovered without the action of non-local operations or back-transfer process. For two noninteracting qubits under a low-frequency stochastic noise, we show that entanglement can be recovered by local pulses only. We al…
Laser induced thermal profiles in thermally and optically thin films
1988
The temperature field generated by the weak absorption of a gaussian laser beam in an optically and thermally thin film bounded by two transparent plates is discussed. An analytical solution of the problem is presented together with an algorithm for the numerical integration. The influence of the finite thermal conductivity of the plates is shown in an example.
Entanglement of distant superconducting quantum interference device rings
2005
We consider two distant mesoscopic SQUID rings, approximated with two-level systems, interacting with two-mode microwaves. The Hamiltonian of the system is used to calculate its time evolution. The cases with microwaves which at t = 0 are in separable states (classically correlated) or entangled states (quantum mechanically correlated) are studied. It is shown that the Josephson currents in the two SQUID rings are also correlated.
Incommensurate phases of a bosonic two-leg ladder under a flux
2016
A boson two--leg ladder in the presence of a synthetic magnetic flux is investigated by means of bosonization techniques and Density Matrix Renormalization Group (DMRG). We follow the quantum phase transition from the commensurate Meissner to the incommensurate vortex phase with increasing flux at different fillings. When the applied flux is $\rho \pi$ and close to it, where $\rho$ is the filling per rung, we find a second incommensuration in the vortex state that affects physical observables such as the momentum distribution, the rung-rung correlation function and the spin-spin and charge-charge static structure factors.
New state of matter: heavy-fermion systems, quantum spin liquids, quasicrystals, cold gases, and high temperature superconductors
2018
We report on a new state of matter manifested by strongly correlated Fermi systems including various heavy-fermion (HF) metals, two-dimensional quantum liquids such as $\rm ^3He$ films, certain quasicrystals, and systems behaving as quantum spin liquids. Generically, these systems can be viewed as HF systems or HF compounds, in that they exhibit typical behavior of HF metals. At zero temperature, such systems can experience a so-called fermion-condensation quantum phase transition (FCQPT). Combining analytical considerations with arguments based entirely on experimental grounds we argue and demonstrate that the class of HF systems is characterized by universal scaling behavior of their ther…