Quantum decoherence

A quantum state loses quantum coherence (decoheres) when Sqd wave functions are peaked along classical trajectories. And it decoheres when each trajectory loses quantum coherence with its neighbors. Quantum decoherence is realized when the diagonal term density matrix dominates over the off-diagonal term (fts-... 

On the other hand, after the phase transition, in the weak coupling limit (A [Pg.288]

Therefore, we conclude that the long wavelength mode neither decoheres nor is classically correlated before the phase transition. However, after the phase transitions, the unstable long wavelength mode becomes classical, gaining both quantum decoherence and classical correlation. Thus an order parameter appears from long wavelength modes (S.P. Kim et.al., 2000 2002 2001). 

For the weak coupling case with Eq. (32), our master equation reduces to the well-known quantum master equation, obtained through the approximation, widely used in quantum optics. This equation describes, among other things, quantum decoherence due to Brownian motion. Hence, we have derived an exact quantum master equation for the transformed density operator p that describes exact decoherence. Furthermore, our master equation cannot keep the purity of the transformed density matrix. Indeed, one can show that if p(t) is factorized into a product of transformed wave functions at t = 0, it will not be factorized into their product for t > 0. This is consistent the nondistributivity of the nonunitary transformation (18). 

In conclusion, we present herein a rather compelling model for the short-time dynamics of the excited states in DNA chains that incorporates both charge-transfer and excitonic transfer. It is certainly not a complete model and parametric refinements are warranted before quantitative predictions can be established. For certain, there are various potentially important contributions we have left out disorder in the system, the fluctuations and vibrations of the lattice, polarization of the media, dissipation, quantum decoherence. We hope that this work serves as a starting point for including these physical interactions into a more comprehensive description of this system. 

E. R. Bittner and P. J. Rossky. Quantum decoherence in mixed quantum-classical systems Nonadiabatic processes. J. Chem. Phys., 103(18) 8130-8143, 1995. 

O. Prezhdo B. Schwartz, E. Bittner, and P. Rossky (1996) Quantum decoherence and the isotope effect in condensed phase nonadiabatic molecular dynamics simulations. J. Chem. Phys. 104, p. 5942... 

It seems intuitively clear that such an achievement is due to the control of quantum dissipative dynamics through the application of a suitably tailored, time-modulated driving field. Indeed, some interesting examples of suppression of quantum decoherence by the modulation of system parameters have been considered in [Viola 1998 Vitali 1999], An improvement of sub-Poissonian statistics of an anharmonic oscillator by the application of amplitude-modulated pump field have been demonstrated in [Kryuchkyan 2002 Kryuch-kyan 2003],... 

Analysis of this state is interesting from the point of view of the quantum measurement problem, an issue that has been debated since the inception of quantum theory by Einstein, Bohr, and others, and continues today [31]. One practical approach toward resolving this controversy is the introduction of quantum decoherence, or the environmentally induced reduction of quantum superpoations into clasacal statistical mbrtures [32], Decoherence provides a way to quantify the elusive boundary between classical and quantum worlds, and almost always precludes the existence of macroscopic Schrodinger-cat states, except for extremely short times. On the othm hand, the creation of mesoscopic Schrddinger-cat states like that of q. (10) may allow controlled studies of quantum decoherence and the quantum-classical boundary. This problem is directly relevant to quantum computation, as we discuss below. 

Finally, a number of observations had been published of energy splittings between symmetric and antisymmetric superposition states [14—17] that were reported to be larger than the expected rate of quantum decoherence and hence taken as a signature of quantum coherence in these systems. However, the direct observation of quantum coherence in MNMs was possible only with the help of pulse EPR measurements... 

Quantum Decoherence at the Femtosecond Level in Liquids and Solids Observed by Neutron Compton Scattering... 

The concept of quantum decoherence is often at the forefront of discussions on quantum communication and quantum information since it presents a serious obstacle to the extended use of many of the suggested future techniques. At the same time, this concept is a basic ingredient in our understanding of the quantum measurement problem and for the transition from a quantum to a classical description of the physical world. 

In a similar way, chemically induced dimmer configuration prepared on the silicon Si(l 0 0) surface is essentially untitled and differs, both electronically and structurally, from the dynamically tilting dimers normally found on this surface [71]. The dimer units that compose the bare Si(l 0 0) surface tilt back and forth in a low-frequency ( 5 THz) seesaw mode. In contrast, dimers that have reacted with H2 have their Si—Si dimer bonds elongated and locked in the horizontal plane of the surface. They are more reactive than normal dimers. For molecular hydrogen (H2) adsorption, the enhancement is even 10 at room temperature. In a similar way, boundaries between crystaUites and amorphous regions seem to be active sites of chain adsorption on CB surface. CB nanoparticles can be understood as open quantum systems, and the uncompensated forces can be analyzed in terms of quantum decoherence effects [70]. The dynamic approach to reinforcement proposed in this chapter becomes an additional support in epistemology of it, and with data from sub-nanolevel. 

Dugic, M., Rakovic, D., and Plavsic, M., The polymer conformational stability and transitions a quantum decoherence theory approach, in Finely Dispersed Particles Micro-, Nano- and Atto-Engineering, Spasic, A.M., Hsu, J.P., Eds., Marcel Dekker/CRC Press/Taylor Francis, Chap. 9. 

In this chapter, we describe the problem of polymer conformational stability and transitions in the framework of the so-called quantum decoherence theory. We propose a rather qualitative scenario yet bearing generality in the context of the quantum decoherence theory, enabling us to reproduce both, existence and stability of the polymers conformations, and the short time scales for the quantum-mechanical processes resulting effectively in the conformational transitions. The... 

Introduces the quantum decoherence theory approach to polymer conformational stability and transitions... 

Part II continues with a section on various approaches and transitions. Chapter 6 covers polymer networks and transitions from nano- to macroscale by Plavsic. The following chapter is on the atomic scale imaging of oscillation and chemical waves at catalytic surface reactions by Elokhin and Gorodetskii. Then next chapter relates the characterization of catalysts by means of an oscillatory reaction written by Kolar-Anic, Anic, and Cupic. Then Dugic, Rakovic, and Plavsic address polymer conformational stability and transitions based on a quantum decoherence theory approach. Chapter 10 of this section, by Jaric and Kuzmanovic, presents a perspective of the physics of interfaces from a standpoint of continuum physics. 

J.D. Frueh, J.R. Tohnan, G. Bodenhausen, Triple quantum decoherence under multiple refocusing slow correlated chemical shift modulations of C and N nnclei in proteins, J. Biomol. NMR 28 (2004) 263—272. 

The following three sections describe the Bohmian quantum-classical approach [22,23] that uniquely solves the quantum back-reaction branching problem, the stochastic mean-field approximation [20] (SMF) that both resolves the back-reaction problem and incorporates the quantum decoherence and Franck-Condon overlap effects into NA-MD, and the quantized mean-field method [21] (QMF) that takes into account ZPE. The Bohmian and QMF approaches are illustrated by a model designed to capture some features of the O2 dissociation on a Pt surface. The concluding section summarizes the features of the methods and discusses further avenues for development and consideration. 

Decoherence in condensed phase typically slows down chemical reactions as has been exemplified by the non-radiative relaxation of solvated electrons [3,18,67]. In the case of an electron in water the difference in the rates of quantum decoherence induced in the electron subsystem by water and deuterated water explains the absence of a solvent isotope effect on the relaxation rate [18,67]. In rare instances, decoherence can enhance chemical reactivity. The SMF approach has been used to provide evidence for acceleration of a chemical reaction in a condensed phase due to the quantum anti-Zeno effect [55]. The mechanism indicates that the anti-Zeno effect involves both delocalization of the quantum dynamics and a feedback loop by coupling to the solvent. Believed to be the first example of the quantum anti-Zeno effect in chemistry, the observed phenomenon suggests the possibility of quantum control of chemical reactivity by choice of solvent. 

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