Decoherence collisional

Quantum-state decay to a continuum or changes in its population via coupling to a thermal bath is known as amplitude noise (AN). It characterizes decoherence processes in many quantum systems, for example, spontaneous emission of photons by excited atoms [35], vibrational and collisional relaxation of trapped ions [36] and the relaxation of current-biased Josephson junctions [37], Another source of decoherence in the same systems is proper dephasing or phase noise (PN) [38], which does not affect the populations of quantum states but randomizes their energies or phases. 

Given the significance of collisional effects in solution, we introduce the simplest of models for relaxation and concomitant decoherence. That is, the equation motion of px t) in the energy representation is given the form i... 

Finally we note that studies of control in solution [186, 187] indicate that control in the presence of collisional effects is indeed possible. For example, coherent control of the dynamics of I3 in ethanol and acetonitrile has been demonstrated. Specifically, I3 was excited with a 30-fs ultraviolet (UV) laser pulse to the first excited state, The resultant wave function was comprised of a localized wave function on the ground electronic state and a corresponding depletion of wave function density, that is, a hole, on the ground electronic state. In this instance the target of the control was the nature of the spectrum associated with the coherences associated with the symmetric stretch. By manipulating various attributes of the exciting pulse (intensity, frequency, and chirp of the excitation pulse), aspects of the spectrum were controlled, despite the decoherence associated with collision effects. 

Our previously elaborated approach, [Kofman 2000 Kofman 2001 (a)], to dynamical control of states coupled to an arbitrary zero-temperature "bath" or continuum has reaffirmed the intuitive anticipation that, in order to suppress their decay, we must modulate the system-bath coupling at a rate exceeding the spectral interval over which the coupling is significant. The spectra of baths (continua) corresponding to vibrational or collisional decay or decoherence typically allow dynamical suppression, using realistic rates of modulation, [Kofman 2000 Kofman 2001 (a)]. 

The exponential decrease of the visibility as a function of the gas pressure p is the expected experimental signature of collisional decoherence. Although similar to Beer s law for absorption, it should not be confused with it since absorption alone would lead to an exponential decrease of the mean signal at constant visibility. 

Collisional decoherence is a universal mechanism which occurs for objects of any size. In contrast to that, the following section describes a mechanism which only appears for complex quantum systems, namely decoherence,thermal due to the emission of their own heat radiation. 

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