Inelastic-neutron-scattering study of methyl tunneling and the quantum sine-Gordon breather in isotopic mixtures of 4-methyl-pyridine at low temperature

Fillaux, F.; Carlile, C.J.

doi:10.1103/physrevb.42.5990

Cited by 82 publications

(46 citation statements)

References 32 publications

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“…In the framework of the RRDM [25,[31][32][33][34][35][36][88][89][90][91][92][93][94], it is assumed that the only effect of the structural disorder on methyl group dynamics is to introduce a distribution of rotational barriers g(V 3 ), originated from the different local environments felt by the individual methyl groups. A non-trivial assumption is that the distribution of distances between neighbouring methyl groups does not introduce significant coupling forces for the smallest distances, which, in particular, would modify the single-particle Hamiltonian (9) leading to a more complex energy level scheme [95][96][97][98][99][100].…”

Section: Methyl Group Dynamics In Polymer Systems a Rotation Ratmentioning

confidence: 99%

Neutron scattering investigations on methyl group dynamics in polymers

Colmenero

Moreno

Alegría

2005

Progress in Polymer Science

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Among the different dynamical processes that take place in polymers, methyl group rotation is perhaps the simplest one, since all the relevant interactions on the methyl group can be condensed in an effective mean-field one-dimensional potential. Recent experimental neutron scattering results have stimulated a new revival of the interest on methyl group dynamics in glasses and polymer systems. The existence of quantum rotational tunnelling of methyl groups in polymers was expected for a long time but only very recently (1998), these processes have been directly observed by high-resolution neutron scattering techniques. This paper revises and summarizes the work done on this topic over last ten years by means of neutron scattering. It is shown that the results obtained in many chemically and structurally different polymers can be consistently described in the whole temperature range -from the quantum tunnelling limit to the classical hopping regime -as well as in the librational spectrum, in terms of the Rotation Rate Distribution Model (RRDM), which was first proposed in 1994. This model introduces a distribution of potential barriers for methyl group rotation, which is associated to the disorder present in any structural glass. The molecular and structural origin of the barrier distribution in polymers is discussed on the basis of a huge collection of investigations reported in the literature, including recent fully atomistic molecular dynamics simulations.

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Section: Methyl Group Dynamics In Polymer Systems a Rotation Ratmentioning

confidence: 99%

Neutron scattering investigations on methyl group dynamics in polymers

Colmenero

Moreno

Alegría

2005

Progress in Polymer Science

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“…In these cases, if the anharmonicity (interaction strength) is strong enough, there is an extended Bloch state with two or more particles in a strongly correlated state. There exist various theoretical [18,19,20] and numerical [21] results as well as experimental observations of these states in different quantum systems [22,23,24].…”

Section: Introductionmentioning

confidence: 99%

Aharonov-Bohm effect for an exciton in a finite-width nanoring

et al. 2005

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We study the Aharonov-Bohm effect for an exciton on a nano-ring using a 2D attractive fermionic Hubbard model. We extend previous results obtained for a 1D ring in which only azimuthal motion is considered, to a more general case of 2D annular lattices. In general, we show that the existence of the localization effect, increased by the nonlinearity, makes the phenomenon in the 2D system similar to the 1D case. However, the introduction of radial motion introduces extra frequencies, different from the original isolated frequency corresponding to the excitonic AharonovBohm oscillations. If the circumference of the system becomes large enough, the Aharonov-Bohm effect is suppressed.

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“…So far the direct observation of this kind of excitations evolving in time has not been reported. Up to date evidences of QB excitations were obtained spectroscopically in molecules and solids [14,15,16,17,18,19,20,21,22,23].…”

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confidence: 99%

Quantum localized modes in capacitively coupled Josephson junctions

Pinto

Flach

2007

Europhys. Lett.

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We consider the quantum dynamics of excitations in a system of two capacitively coupled Josephson junctions. Quantum breather states are found in the middle of the energy spectrum of the confined nonescaping states of the system. They are characterized by a strong excitation of one junction. These states perform slow tunneling motion from one junction to the other, while keeping their coherent nature. The tunneling time sensitively depends on the initial excitation energy. By using an external bias as a control parameter, the tunneling time can be varied with respect to the escape time and the experimentally limited coherence time. Thus one can control the flow of quantum excitations between the two junctions.PACS numbers: 63.20. Pw, 74.50.+r, 63.20.Ry Josephson junctions are the subject of extensive studies in quantum information experiments because they possess two attractive properties: they are nonlinear devices, and also show macroscopic quantum behavior [1,2,3]. The dynamics of a biased Josephson junction (JJ) is analogous to the dynamics of a particle with a mass proportional to the junction capacitance C J , moving on a tilted washboard potentialwhich is sketched in Fig.1-b. Here ϕ is the phase difference between the macroscopic wave functions in both superconducting electrodes of the junction, I c is the critical current of the junction, and Φ 0 = h/2e the flux quantum. When the energy of the particle is large enough to overcome the barrier ∆U (that depends on the bias current I b ) it escapes and moves down the potential, switching the junction into a resistive state with a nonzero voltage proportional toφ. Quantization of the system leads to discrete energy levels inside the wells in the potential, which are nonequidistant because of the anharmonicity. Note that even if there is not enough energy to classically overcome the barrier, the particle may perform a quantum escape and tunnel outside the well, thus switching the junction into the resistive state [1]. Thus each state inside the well is characterized by a bias and a statedependent inverse lifetime, or escape rate. Progress on manipulation of quantum JJs includes spectroscopic analysis, better isolation schemes, and simultaneous measurement techniques [2,3,4,5,6,7], and paves the way for using them as JJ qubits in arrays for experiments on processing quantum information. Typically the first two or three quantum levels of one junction are used as quantum bits. Since the levels are nonequidistant, they can be separately excited by applying microwave pulses.So far, the studies on JJ qubits focused on low energy excitations involving the first few energy levels of the junctions. Larger energies in the quantum dynamics of JJs give rise to new phenomena that can be observed by using the already developed techniques for quantum information experiments. For instance, it was suggested that Josephson junctions operating at higher energies may be used for experiments on quantum chaos [8,9,10]. Another phenomenon is the excitation of quantum breathers (Q...

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Inelastic-neutron-scattering study of methyl tunneling and the quantum sine-Gordon breather in isotopic mixtures of 4-methyl-pyridine at low temperature

Cited by 82 publications

References 32 publications

Neutron scattering investigations on methyl group dynamics in polymers

Neutron scattering investigations on methyl group dynamics in polymers

Aharonov-Bohm effect for an exciton in a finite-width nanoring

Quantum localized modes in capacitively coupled Josephson junctions

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