Search results for "QUANTUM MECHANICS"
showing 10 items of 2468 documents
Note on the slope parameter of the baryonic Λb→Λc Isgur–Wise function
2005
Abstract Using the framework of the Heavy Quark Effective Theory we have re-analyzed the Isgur–Wise function describing semileptonic Λ b → Λ c decays in the QCD sum rule approach. The slope parameter of the Isgur–Wise function is found to be ρ 2 = 1.35 ± 0.13 , which is consistent with an experimental measurement and a lattice calculation. To O ( 1 / m b , 1 / m c ) of the heavy quark expansion the integrated Λ b decay width is used to extract the CKM matrix element V c b for which we obtain a value of | V c b | = 0.041 ± 0.004 ± 0.001 in excellent agreement with the value of | V c b | determined from semileptonic B → D ∗ decays.
Determination of the chiral couplingsL10andC87from semileptonicτdecays
2008
Using recent precise hadronic {tau}-decay data on the V-A spectral function, and general properties of QCD such as analyticity, the operator product expansion, and chiral perturbation theory, we get accurate values for the QCD chiral order parameters L{sub 10}{sup r}(M{sub {rho}}) and C{sub 87}{sup r}(M{sub {rho}}). These two low-energy constants appear at order p{sup 4} and p{sup 6}, respectively, in the chiral perturbation theory expansion of the V-A correlator. At order p{sup 4} we obtain L{sub 10}{sup r}(M{sub {rho}})=-(5.22{+-}0.06)x10{sup -3}. Including in the analysis the two-loop (order p{sup 6}) contributions, we get L{sub 10}{sup r}(M{sub {rho}})=-(4.06{+-}0.39)x10{sup -3} and C{s…
Coupled-cluster methods including noniterative corrections for quadruple excitations
2005
A new method is presented for treating the effects of quadruple excitations in coupled-cluster theory. In the approach, quadruple excitation contributions are computed from a formula based on a non-Hermitian perturbation theory analogous to that used previously to justify the usual noniterative triples correction used in the coupled cluster singles and doubles method with a perturbative treatment of the triple excitations (CCSD(T)). The method discussed in this paper plays a parallel role in improving energies obtained with the full coupled-cluster singles, doubles, and triples method (CCSDT) by adding a perturbative treatment of the quadruple excitations (CCSDT(Q)). The method is tested fo…
(Un)conditioned open dynamics in quantum optics
2021
The study of the dynamics of open quantum systems sheds light on dissipative processes in quantum mechanics. Any system under continuous measurement is open and the act of measuring induces abrupt changes of the system’s state (collapses). The evolution conditioned to measurement records generates the so-called quantum trajectories. A continuous (unconditioned) evolution of the system is recovered by averaging over a large number of trajectories. Historically this kind of evolution has been the main focus of theoretical investigations. In this dissertation we consider both conditional and unconditional dynamics of quantum optical systems. Unconditioned dynamics is studied through the collis…
The Emergence of Chaos in Quantum Mechanics
2020
Nonlinearity in Quantum Mechanics may have extrinsic or intrinsic origins and is a liable route to a chaotic behaviour that can be of difficult observations. In this paper, we propose two forms of nonlinear Hamiltonian, which explicitly depend upon the phase of the wave function and produce chaotic behaviour. To speed up the slow manifestation of chaotic effects, a resonant laser field assisting the time evolution of the systems causes cumulative effects that might be revealed, at least in principle. The nonlinear Schrö
Population trapping due to cavity losses
2008
In population trapping the occupation of a decaying quantum level keeps a constant non-zero value. We show that an atom-cavity system interacting with an environment characterized by a non-flat spectrum, in the non-Markovian limit, exhibits such a behavior, effectively realizing the preservation of nonclassical states against dissipation. Our results allow to understand the role of cavity losses in hybrid solid state systems and pave the way to the proper description of leakage in the recently developed cavity quantum electrodynamic systems.
Entanglement trapping in structured environments
2008
The entanglement dynamics of two independent qubits each embedded in a structured environment under conditions of inhibition of spontaneous emission is analyzed, showing entanglement trapping. We demonstrate that entanglement trapping can be used efficiently to prevent entanglement sudden death. For the case of realistic photonic band-gap materials, we show that high values of entanglement trapping can be achieved. This result is of both fundamental and applicative interest since it provides a physical situation where the entanglement can be preserved and manipulated, e.g. by Stark-shifting the qubit transition frequency outside and inside the gap.
Two-qubit entanglement generation through non-Hermitian Hamiltonians induced by repeated measurements on an ancilla
2020
In contrast to classical systems, actual implementation of non-Hermitian Hamiltonian dynamics for quantum systems is a challenge because the processes of energy gain and dissipation are based on the underlying Hermitian system&ndash
Multi-State Quantum Dissipative Dynamics in Sub-Ohmic Environment: The Strong Coupling Regime
2015
We study the dissipative quantum dynamics and the asymptotic behavior of a particle in a bistable potential interacting with a sub-Ohmic broadband environment. The reduced dynamics, in the intermediate to strong dissipation regime, is obtained beyond the two-level system approximation by using a real-time path integral approach. We find a crossover dynamic regime with damped intra-well oscillations and incoherent tunneling and a completely incoherent regime at strong damping. Moreover, a nonmonotonic behavior of the left/right well population difference is found as a function of the damping strength.
Incoherent Dispersive Shocks and Spectral Collapse
2014
We predict the existence of incoherent dispersive shock waves and collapse-like singularities that occur in the spectral evolution of incoherent optical waves propagating in a noninstantaneous nonlinear medium.