130 research outputs found
Noise-induced transition in a quantum system
We examine the noise-induced transition in a fluctuating bistable potential
of a driven quantum system in thermal equilibrium. Making use of a Wigner
canonical thermal distribution for description of the statistical properties of
the thermal bath, we explore the generic effects of quantization like vacuum
field fluctuation and tunneling in the characteristic stationary probability
distribution functions undergoing transition from unimodal to bimodal nature
and in signal-to-noise ratio characterizing the co-operative effect among the
noise processes and the weak periodic signal.Comment: To appear on Physics Letters
Numerical simulation of transmission coefficient using c-number Langevin equation
We numerically implement the reactive flux formalism on the basis of a
recently proposed c-number Langevin equation [Barik \textit{et al}, J. Chem.
Phys. {\bf 119}, 680 (2003); Banerjee \textit{et al}, Phys. Rev. E {\bf 65},
021109 (2002)] to calculate transmission coefficient. The Kramers' turnover,
the enhancement of the rate at low temperatures and other related
features of temporal behaviour of the transmission coefficient over a range of
temperature down to absolute zero, noise correlation and friction are examined
for a double well potential and compared with other known results. This simple
method is based on canonical quantization and Wigner quasiclassical phase space
function and takes care of quantum effects due to the system order by order
Noise-induced quantum transport
We analyze the problem of directed quantum transport induced by external
exponentially correlated telegraphic noise. In addition to quantum nature of
the heat bath, nonlinearity of the periodic system potential brings in quantum
contribution. We observe that quantization, in general, enhances classical
current at low temperature, while the differences become insignificant at
higher temperature. Interplay of quantum diffusion and quantum correction to
system potential is analyzed for various ranges of temperature, correlation
time and strength of external noise and asymmetry parameters. A possible
experimental realization of the observed quantum effects in a superionic
conductor placed in a random asymmetric dichotomous electric field has been
suggested.Comment: 23 pages and 5 figures. To be published in Physical Review
Anharmonic quantum contribution to vibrational dephasing
Based on a quantum Langevin equation and its corresponding Hamiltonian within
a c-number formalism we calculate the vibrational dephasing rate of a cubic
oscillator. It is shown that leading order quantum correction due to
anharmonicity of the potential makes a significant contribution to the rate and
the frequency shift. We compare our theoretical estimates with those obtained
from experiments for small diatomics , and .Comment: 21 pages, 1 figure and 1 tabl
Quantum escape kinetics over a fluctuating barrier
The escape rate of a particle over a fluctuating barrier in a double well
potential exhibits resonance at an optimum value of correlation time of
fluctuation. This has been shown to be important in several variants of kinetic
model of chemical reactions . We extend the analysis of this phenomenon of
resonant activation to quantum domain to show how quantization significantly
enhances resonant activation at low temperature due to tunneling
Quantum phase-space function formulation of reactive flux theory
On the basis of a coherent-state representation of the quantum noise operator and an ensemble averaging procedure a scheme for quantum Brownian motion has been proposed recently [Banerjee et al., Phys. Rev. E 65, 021109 (2002); 66, 051105 (2002)]. We extend this approach to formulate reactive flux theory in terms of quantum phase space distribution functions and to derive a time-dependent quantum transmission coefficient-a quantum analog of the classical Kramers-Grote-Hynes coefficient in the spirit of Kohen and Tannor's classical formulation. The theory is valid for arbitrary noise correlation and temperature. The specific forms of this coefficient in the Markovian as well as in the non-Markovian limits have been worked out in detail for the intermediate to strong damping regimes with an analysis of quantum effects. While the classical transmission coefficient is independent of temperature, its quantum counterpart has significant temperature dependence particularly in the low-temperature regime
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