Decoherence thermal

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. 

Abstract. We review the recent development of quantum dynamics for nonequilibrium phase transitions. To describe the detailed dynamical processes of nonequilibrium phase transitions, the Liouville-von Neumann method is applied to quenched second order phase transitions. Domain growth and topological defect formation is discussed in the second order phase transitions. Thermofield dynamics is extended to nonequilibrium phase transitions. Finally, we discuss the physical implications of nonequilibrium processes such as decoherence of order parameter and thermalization. 

Finally, we discuss the effect of nonlinear coupling on domain growth, decoherence, and thermalization. As the wave functionals l/o of Ho are easily found, Eq. (16) leads to the wave functional beyond the Hartree approximation. Putting the perturbation terms (19) into Eq. (16), we first find the wave functional of the form... 

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. 

Assume that a noninteracting nanosystem is coupled weakly to a thermal bath (in addition to the leads). The effect of the thermal bath is to break phase coherence of the electron inside the system during some time Tph, called decoherence or phase-breaking time. rph is an important time-scale in the theory, it should be compared with the so-called tunneling time - the characteristic time for the electron to go from the nanosystem to the lead, which can be estimated as an inverse level-width function / 1. So that the criteria of sequential tunneling is... 

The studies presented in this section indicate that the presence of a complex environment, which induces decoherence and dissipation, can dramatically modify the electronic response of a nanowire coupled to electrodes. Electron transport on the low-energy sector of the transmission spectrum is supported by the formation of (virtual) polaronic states. Though strongly damped, these states manifest nonetheless with a finite density of states inside the bandgap and mediate thermally activated transport. 

Decoherence theory explains that a quantum object may loose some of its particular quantum properties due to the interaction with its environment. This phenomenon is investigated along two fines. First the authors study the influence of small angle collisions exerted by a dilute thermal gas on the molecules in the interferometer. They also focus on a novel property which is unique to large objects with many internal degrees of freedom, namely the thermal emission of photons. If sufficiently many photons of sufficiently short wavelength... 

This factor 77 may be called the decoherence function since it describes the effective loss of coherence in the fullerene state. For elastic scattering with an isotropic potential and the gas initially in a thermal state it reads [Homberger 2003 (b)]... 

Figure 10. Setup for the investigation of thermal decoherence. Up to 16 laser beams are used to heat the fullerenes before they enter the Talbot-Lau interferometer.

The essence of the experiment is now to measure the variation of the interference fringe visibility. Fig. 11 clearly shows a non-trivial monotonic decrease of the interference contrast with increasing laser heating power. This is the unambiguous signature of decoherence which we attribute to the enhanced probability for the emission of thermal photons that carry which-path information. 

Thermal decoherence seems to be equally well understood and we conclude that one should be able to suppress this mechanism in future experiments with cooled particles. Internal temperatures of 77 K instead of the thousands of Kelvins in the described study appear to be reachable in future experiments. 

Diffraction experiments are carried out by thermal neutrons and with observation times of 10 13 s or more. These experiments indicate that H - H entanglement survives over an unusually long time in this particular compound. The reason for the long decoherence time was discussed in Ref. [Fillaux 1998] as a result of restricted coupling of the H - H dimers to the KII( () >, environment caused by specific fermion / boson superselection rules. 

Second, we should keep in mind that between the two extreme limits discussed above there exists a regime of intermediate behavior, where dephasing/decoherence and molecular response occur on comparable timescales. In this case the scattering process may exhibit partial coherence. Detailed description of such situations requires treatment of optical response within a formalism that explicitly includes thermal interactions between the system and its environment. In Section 18.5 we will address these issues using the Bloch-Redfield theory of Section 10.5.2. 

The majority of all neutron scattering experiments are performed with thermal neutrons (with energy about 0.03 eV) where the scattering process takes about 10 s. On this timescale, it is likely that any possible entanglement of the participating particles has already disappeared through decoherence in the solid or liquid environment. No specific quantum correlation effects are therefore expected to show up. 

The cause of this kind of decoherence is evidently thermal because of the alteration of the deBroglie wavelength of the wave packet associated with the quantum particle. Dissipation, on the other hand, arises from the exchange of energy between the system, which, in this case, comprise the tunneling particle and the environment of the electron cloud, or, for that matter, phonons that get excited because of the elastic distortion created by the particle (which are called interstitial sites). In either case, the coupling with the environment can be modeled as... 

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