Decoherence mechanisms

Thus in the zero dephasing case, 8s reduces to the Breit-Wigner phase of the intermediate state resonance, elaborated on in the previous sections. In the dissipative environment, it is sensitive also to decay and decoherence mechanisms, as illustrated later. 

We presented our most recent NCS results of short lived protonic quantum entanglement in different materials. Quantum entanglement manifests itself by a strong shortfall of the protonic SCS density. The emphasis of the present work is on the different electronic environments the protons are coupled to. As pointed out in the introduction, within the framework of modern quantum theory, the environment may be responsible both for the creation and destruction of QE. The present experimental results on II O / D2O, LiH and LaH-2 and Lai 1-2 indicate that the electronic environment surrounding the hydrogen atom in the material is responsible for the different features of the cross section anomalies of the proton and thus for different decoherence mechanisms. 

Kashida 1990] and proton disorder could be an alternative decoherence mechanism. Crystal structures determined at various temperatures show that above 150 K protons are distributed over two sites located at 0.3 A off-center of the hydrogen bond (see below Sec. 3). The occupation ratio for the two sites increases from 4 96 at 200 K to 18 82 at 300 K. 

They confirm that any decoherence mechanism is largely cancelled. There is no evidence for significant incoherent scattering, as anticipated for fully entangled protons. 

In conclusion we present various experimental schemes for overcoming dephasing, in order to study the intrinsic decoherence of BEC. Using some of these methods, we quantify nontrivial decoherence mechanisms both for weak excitations in BEC and in strongly excited condensates. We calculate the effects of a stronger inter-atomic interaction, namely, the appearance of a peak in the static structure factor of the system. Matter wave interference spectra are shown to be a highly sensitive probe of condensate response, with the sensitivity of this method approaching the few excitation limit. 

Use of a surfactant allows solubilization of the polyoxometalate cluster K6[Vi5As6042(H20)] 8H20 (V15) in the organic solvent chloroform. Spin echo measurements revealed a phase memory time of Tm = 340 ns, which was attributed to resonances in the 5 = 3/2 excited state of the cluster [166]. No quantum coherence was detected in the pair of 5 = 1/2 ground states [151]. By measurement of the z-magnetization after a nutation pulse, and a delay to ensure decay of all coherences, Rabi oscillations were observed. From the analysis of the different possible decoherence mechanisms, it was concluded that decoherence is almost entirely caused by hyperfine coupling to the nuclear spins. 

Whereas coherence can persist up to the nanosecond range for atomic and molecular systems exposed to dilute gaseous environments, the situation is radically different in liquids and solids. Interactions with neighbouring atoms, with phonons in crystalline materials and with conduction electrons in metals, shift the coherence times down by several orders of magnitude, and local quantum superpositions are usually not observable. Intermediate cases are the electronic states used as qubits in the form of superconducting islands introduced by Y. Nakamura et al. [4]. The latest reports [5] show coherence times up to 10 s for these objects, which would allow time for operations of a quantum computer. The decoherence mechanisms in such circuits have been discussed theoretically by Burkhard et al. [6],... 

In this unique book, many questions that arise beyond the standard streamlined presentation of quantum theory are addressed. The reader finds insightful essays on the emergence of classical physics from quantum physics and the decoherence mechanism, the measurement problem and the collapse of the wave function, and many other related subjects. 

At these special values of the fleld relaxation from one spin state to another is enhanced. However at intermediate values of the fleld relaxation occurs presumably by coupling with the environment through a quantum decoherence mechanism as observed above for redox isomers (Figs. 2.5 and 2.6). 

Before reviewing existing examples, a very brief explanation on the mechanisms of decoherence for molecular spin qubits is necessary more details are available elsewhere [67]. Broadly speaking, the three decoherence sources for these systems are spin bath decoherence, oscillator bath decoherence and pairwise dipolar decoherence, and can be regulated by a combination of temperature, magnetic field and chemical design of the system [70]. The spin bath mainly consists of nuclear spins, but in general it also includes any localized excitations that can couple to the... 

Section 4 is entitled Ideas (for mechanisms and models). It deals with how we can interpret/calculate the behavior of molecular transport junctions utilizing particular model approaches and chemical mechanisms. It also discusses time parameters, and coherence/decoherence as well as pathways and structure/function relationships. 

The results presented Irom vibrational relaxation calculations show that the method is numerically very feasible and that the short time approximatiorrs are welljustified as long as the energy difference between the initial and final quantum states is not too small. It is also found that the crossover from the early time quantiun regime to the rate constant regime can be due to either phase decoherence or due to the loss of correlation in the coupling between the states, or to a combination of these factors. The methodology described in Section n.C has been formulated to account for both of these mechanisms. 

It is advantageous to consider the frequency domain as it gives more insight into the mechanisms of decoherence. For this purpose, we define the finite-time Fourier transform of the modulation function ... 

The realization of SPODS via PL, that is, impulsive excitation and discrete temporal phase variations, benefits from high peak intensities inherent to short laser pulses. In view of multistate excitation scenarios, this enables highly efficient population transfer to the target states (see Section 6.3.3). Furthermore, PL can be implemented on very short timescales, which is desirable in order to outperform rapid intramolecular energy redistribution or decoherence processes. On the other hand, since PL is an impulsive scenario, it is sensitive to pulse parameters such as detuning and intensity [44]. A robust realization of SPODS is achieved by the use of adiabatic techniques. The underlying physical mechanism will be discussed next. 

Feshbach shape resonance in the exchange-like off-diagonal interband pairing term, as predicted since 1993, appears to be the mechanism for evading temperature decoherence effects and enhancing the critical temperature. 

The object of the workshop was the quantum mechanism that allows the macroscopic quantum coherence of a superconducting condensate to resist to the attacks of high temperature. Solution to this problem of fundamental physics is needed for the design of room temperature superconductors, for controlling the decoherence effects in the quantum computers and for the understanding of a possible role of quantum coherence in living matter that is debated today in quantum biophysics. 

The finite decoherence time is due to some inelastic scattering mechanism inside the system, but typically this time is shorter than the energy relaxation time re, and the distribution function of electrons inside the system can be nonequilibrium (if the finite voltage is applied), this transport regime is well known in semiconductor superlattices and quantum-cascade structures. 

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