Biomedical subjects

Doron Cohen

Publications and source records attributed to Doron Cohen.

6 recordsLinked to original sources

PubMed2004

Quantum dissipation due to the interaction with chaos.

We discuss the possibility of having "quantum dissipation" due to the interaction with chaotic degrees of freedom. We define the conditions that should be satisfied in order to have a dissipative effect similar to the one due to an interaction with a (many body) bath. We also compare with the case where the environment is modeled by a random matrix model. In the case of interaction with "chaos" we observe a regime where the relaxation process is nonuniversal and reflects the underlaying semiclassical dynamics. As an example we consider a two level system (spin) that interacts with a two-dimensional anharmonic oscillator.

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PubMed2004

Quantum reversibility: is there an echo?

We study the possibility to undo the quantum mechanical evolution in a time reversal experiment. The naive expectation, as reflected in the common terminology ("Loschmidt echo"), is that maximum compensation results if the reversed dynamics extends to the same time as the forward evolution. We challenge this belief and demonstrate that the time t(r) for maximum return probability is in general shorter. We find that t(r) depends on lambda=epsilon(evol)/epsilon(prep), being the ratio of the error in setting the parameters (fields) for the time-reversed evolution to the perturbation which is involved in the preparation process. Our results should be observable in spin-echo experiments where the dynamical irreversibility of quantum phases is measured.

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PubMed2003

Stadium billiard with moving walls.

We study the evolution of the energy distribution for a stadium with moving walls. We consider a one period driving cycle, which is characterized by an amplitude A and a wall velocity V. This evolving energy distribution has both "parametric" and "stochastic" components. The latter are important for the theory of quantum irreversibility and dissipation in driven mesoscopic devices. For an extremely slow wall velocity V, the spreading mechanism is dominated by transitions between neighboring levels, while for larger (nonadiabatic) velocities, the spreading mechanism has both perturbative and nonperturbative features. We present a numerical study which is aimed at identifying the latter features. A procedure is developed for the determination of the various V regimes. The possible implications of linear response theory are discussed.

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PubMed2003

Two-step enantio-selective optical switch.

We present an optical "enantio-selective switch" that, in two steps, turns a ("racemic") mixture of left-handed and right-handed chiral molecules into the enantiomerically pure state of interest. The optical switch is composed of an "enantio-discriminator" and an "enantio-converter" acting in tandem. The method is robust, insensitive to decay processes, and does not require molecular preorientation. We demonstrate the method on the purification of a racemate of (transiently chiral) D2S2 molecules, performed on the nanosecond time scale.

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PubMed2002

Quantum irreversibility, perturbation independent decay, and the parametric theory of the local density of states.

The idea of perturbation independent decay (PID) has appeared in the context of survival-probability studies, and lately has emerged in the context of quantum irreversibility studies. In both cases the PID reflects the Lyapunov instability of the underlying semiclassical dynamics, and it can be distinguished from the Wigner-type decay that holds in the perturbative regime. The theory of the survival probability is manifestly related to the parametric theory of the local density of states (LDOS). In contrast to that the physics of quantum irreversibility requires subtle cross correlations, which are not captured by the LDOS alone, to be taken into account.

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PubMed2002

Dephasing due to the interaction with chaotic degrees of freedom.

We consider the motion of a particle, taking into account its interaction with environmental degrees of freedom. The dephasing time is determined by the nature of the environment and depends on the particle velocity. Our interest is in the case where the environment consists of few chaotic degrees of freedom. We obtain results for the dephasing time and compare them with those of the effective-bath approach. The latter approach is based on the conjecture that the environment can be modeled as a collection of infinitely many harmonic oscillators. The work is related to studies of driven systems, quantum irreversibility, and fidelity. The specific model that we consider requires the solution of the problem of a particle in a box with a moving wall, whose one-dimensional version is related to the Fermi acceleration problem.

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