טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentKlecner Michael
SubjectQuantum Decoherence in Gaseous Environment
DepartmentDepartment of Physics
Supervisor Professor Emeritus Amiram Ron


Abstract

We study the effect of the environment on the process of measurement of a state of a microscopic spin-half system. The measuring apparatus is a heavy particle, whose center-of-mass coordinates can be considered at the end of the measurement as approximately classical, and thus can be used as a pointer. The state of the pointer, which is the result of its interaction with the spin, is transformed into a mixed state by the coupling of the pointer to the environment. The environment is considered to be a gas reservoir, whose particles interact with the pointer. This results in a Fokker-Planck equation for the reduced density matrix of the pointer. The solution of the equation shows that the quantum coherences, which are characteristic of the entangled state between the probability amplitudes to find the pointer in one of two positions, decay exponentially in time. We calculate the exponential decay function of this decoherence effect, and express it in terms of the parameters of the model. Next we consider a possible scheme for experimentally observing gas induced decoherence. For this purpose the Stern-Gerlach interferometer is studied in the presence of an ambient gas. By varying the density of the residual gas in the chamber, the decoherence induced by the gas particles on the interference can be controlled. Finally we consider some aspects of the transfer of decoherence between two separate particles in a simple interferometer. We find that the transfer of decoherence "information'' from the pointer's center-of-mass to the spin state of the atom, occurs only when the interferometric paths are recombined locally.