17 research outputs found
Beyond the Jaynes-Cummings model: circuit QED in the ultrastrong coupling regime
In cavity quantum electrodynamics (QED), light-matter interaction is probed
at its most fundamental level, where individual atoms are coupled to single
photons stored in three-dimensional cavities. This unique possibility to
experimentally explore the foundations of quantum physics has greatly evolved
with the advent of circuit QED, where on-chip superconducting qubits and
oscillators play the roles of two-level atoms and cavities, respectively. In
the strong coupling limit, atom and cavity can exchange a photon frequently
before coherence is lost. This important regime has been reached both in cavity
and circuit QED, but the design flexibility and engineering potential of the
latter allowed for increasing the ratio between the atom-cavity coupling rate
and the cavity transition frequency above the percent level. While these
experiments are well described by the renowned Jaynes-Cummings model, novel
physics is expected in the ultrastrong coupling limit. Here, we report on the
first experimental realization of a superconducting circuit QED system in the
ultrastrong coupling limit and present direct evidence for the breakdown of the
Jaynes-Cummings model.Comment: 5 pages, 3 figure
Equilibrium susceptibilities of superparamagnets: longitudinal & transverse, quantum & classical
The equilibrium susceptibility of uniaxial paramagnets is studied in a
unified framework which permits to connect traditional results of the theory of
quantum paramagnets, \Sm=1/2, 1, 3/2, ..., with molecular magnetic clusters,
\Sm\sim5, 10, 20, all the way up, \Sm=30, 50, 100,... to the theory of
classical superparamagnets. This is done using standard tools of quantum
statistical mechanics and linear response theory (the Kubo correlator
formalism). Several features of the temperature dependence of the
susceptibility curves (crossovers, peaks, deviations from Curie law) are
studied and their scalings with \Sm identified and characterized. Both the
longitudinal and transverse susceptibilities are discussed, as well as the
response of the ensemble with anisotropy axes oriented at random. For the
latter case a simple approximate formula is derived too, and its range of
validity assessed, so it could be used in modelization of experiments.Comment: 32 pages, 5 figures. Submitted to J.Phys.Condens.Matte
Quasi-probability representations of quantum theory with applications to quantum information science
This article comprises a review of both the quasi-probability representations
of infinite-dimensional quantum theory (including the Wigner function) and the
more recently defined quasi-probability representations of finite-dimensional
quantum theory. We focus on both the characteristics and applications of these
representations with an emphasis toward quantum information theory. We discuss
the recently proposed unification of the set of possible quasi-probability
representations via frame theory and then discuss the practical relevance of
negativity in such representations as a criteria for quantumness.Comment: v3: typos fixed, references adde
Quantum entanglement and disentanglement of multi-atom systems
We present a review of recent research on quantum entanglement, with special
emphasis on entanglement between single atoms, processing of an encoded
entanglement and its temporary evolution. Analysis based on the density matrix
formalism are described. We give a simple description of the entangling
procedure and explore the role of the environment in creation of entanglement
and in disentanglement of atomic systems. A particular process we will focus on
is spontaneous emission, usually recognized as an irreversible loss of
information and entanglement encoded in the internal states of the system. We
illustrate some certain circumstances where this irreversible process can in
fact induce entanglement between separated systems. We also show how
spontaneous emission reveals a competition between the Bell states of a two
qubit system that leads to the recently discovered "sudden" features in the
temporal evolution of entanglement. An another problem illustrated in details
is a deterministic preparation of atoms and atomic ensembles in long-lived
stationary squeezed states and entangled cluster states. We then determine how
to trigger the evolution of the stable entanglement and also address the issue
of a steered evolution of entanglement between desired pairs of qubits that can
be achieved simply by varying the parameters of a given system.Comment: Review articl
Numerical solution of thermo-solutal mixed convective slip flow from a radiative plate with convective boundary condition
A mathematical model for mixed convective slip flow with heat and mass transfer in the presence of thermal radiation is presented. A convective boundary condition is included and slip is simulated via the hydrodynamic slip parameter. Heat generation or absorption effects are also incorporated. The Rosseland diffusion flux model is employed. The governing partial differential conservation equations are reduced to a system of coupled, ordinary differential equations via Lie group theory methods. The resulting coupled equations are solved using shooting method. The influences of the emerging parameters on dimensionless velocity, temperature and concentration distributions are investigated. Increasing radiative-conductive parameter accelerates the boundary layer flow and increase temperatures whereas it depresses concentration. An elevation in convection-conduction parameter also accelerates the flow and temperatures whereas it reduces concentrations. Velocity near the wall is considerably boosted with increasing momentum slip parameter although both temperature and concentration boundary layer thicknesses are decreased. The presence of a heat source is found to increase momentum and thermal boundary layer thicknesses but reduces concentration boundary layer thickness. Excellent correlation of the numerical solutions with previous non-slip studies is demonstrated. The current study has applications in bio-reactor diffusion flows and high-temperature chemical materials processing systems
Modifying effect of dual antiplatelet therapy on incidence of stent thrombosis according to implanted drug-eluting stent type
Aim To investigate the putative modifying effect of dual antiplatelet therapy (DAPT) use on the incidence of stent thrombosis at 3 years in patients randomized to Endeavor zotarolimus-eluting stent (E-ZES) or Cypher sirolimus-eluting stent (C-SES). Methods and results Of 8709 patients in PROTECT, 4357 were randomized to E-ZES and 4352 to C-SES. Aspirin was to be given indefinitely, and clopidogrel/ticlopidine for ≥3 months or up to 12 months after implantation. Main outcome measures were definite or probable stent thrombosis at 3 years. Multivariable Cox regression analysis was applied, with stent type, DAPT, and their interaction as the main outcome determinants. Dual antiplatelet therapy adherence remained the same in the E-ZES and C-SES groups (79.6% at 1 year, 32.8% at 2 years, and 21.6% at 3 years). We observed a statistically significant (P = 0.0052) heterogeneity in treatment effect of stent type in relation to DAPT. In the absence of DAPT, stent thrombosis was lower with E-ZES vs. C-SES (adjusted hazard ratio 0.38, 95% confidence interval 0.19, 0.75; P = 0.0056). In the presence of DAPT, no difference was found (1.18; 0.79, 1.77; P = 0.43). Conclusion A strong interaction was observed between drug-eluting stent type and DAPT use, most likely prompted by the vascular healing response induced by the implanted DES system. These results suggest that the incidence of stent thrombosis in DES trials should not be evaluated independently of DAPT use, and the optimal duration of DAPT will likely depend upon stent type (Clinicaltrials.gov number NCT00476957
Perturbation and numerical study of double-diffusive dissipative reactive convective flow in an open vertical duct containing a non-darcy porous medium with robin boundary conditions
A mathematical model for thermosolutal convection flow in an open two-dimensional vertical channel containing a porous medium saturated with reactive Newtonian fluid is developed and studied. Robin boundary conditions are prescribed, and a first-order homogenous chemical reaction is considered. The Darcy–Forchheimer model is used to simulate both the first- and second-order porous mediums’ drag effects. For the general non-Darcy-case, a numerical solution is presented using the Runge–Kutta quadrature and a shooting method. The influences of thermal (0≤λ1≤15) and solute Grashof numbers (0≤λ2≤20) , Biot numbers (1≤Bi1≤10,Bi2=10) , Brinkman number (0≤Br≤0.5) , first-order chemical reaction parameter (2≤α≤8) , porous medium parameter (2≤σ≤8) and Forchheimer (inertial drag) parameter (0≤I≤12) on the evolutions of velocity, temperature and concentration (species) distributions are visualized graphically. Nusselt number and skin friction at the walls are also computed for specific values of selected parameters. The study is relevant to the analysis of geothermal energy systems with chemical reaction