Phonon engineering with superlattices: generalized nanomechanical potentials

Earlier implementations to simulate coherent wave propagation in one-dimensional potentials using acoustic phonons with gigahertz-terahertz frequencies were based on coupled nanoacoustic resonators. Here, we generalize the concept of adiabatic tuning of periodic superlattices for the implementation of effective one-dimensional potentials giving access to cases that cannot be realized by previously reported phonon engineering approaches, in particular the acoustic simulation of electrons and holes in a quantum well or a double well potential. In addition, the resulting structures are much more compact and hence experimentally feasible. We demonstrate that potential landscapes can be tailored with great versatility in these multilayered devices, apply this general method to the cases of parabolic, Morse and double-well potentials and study the resulting stationary phonon modes. The phonon cavities and potentials presented in this work could be probed by all-optical techniques like pump-probe coherent phonon generation and Brillouin scattering

Fractional photon-assisted tunneling of ultra-cold atoms in periodically shaken double-well lattices

Fractional photon-assisted tunneling is investigated both numerically and analytically in a double-well lattice. While integer photon-assisted tunneling is a single-particle effect, fractional photon-assisted tunneling is an interaction-induced many-body effect. Double-well lattices with few particles in each double well are ideal to study this effect far from the mean-field effects. It is predicted that the 1/4-resonance is observable in such systems. Fractional photon-assisted tunneling provides a physically relevant model, for which N-th order time-dependent perturbation theory can be large although all previous orders are small. All predicted effects will be observable with an existing experimental setup [1]

Water penetration profile at the protein-lipid interface in Na,K-ATPase membranes.

The affinity of ionized fatty acids for the Na,K-ATPase is used to determine the transmembrane profile of water penetration at the protein-lipid interface. The standardized intensity of the electron spin echo envelope modulation (ESEEM) from 2H-hyperfine interaction with D2O is determined for stearic acid, n-SASL, spin-labeled systematically at the C-n atoms throughout the chain. In both native Na,K-ATPase membranes from shark salt gland and bilayers of the extracted membrane lipids, the D2O-ESEEM intensities of fully charged n-SASL decrease progressively with position down the fatty acid chain toward the terminal methyl group. Whereas the D2O intensities decrease sharply at the n = 9 position in the lipid bilayers, a much broader transition region in the range n = 6 to 10 is found with Na,K-ATPase membranes. Correction for the bilayer population in the membranes yields the intrinsic D2O-intensity profile at the protein-lipid interface. For positions at either end of the chains, the D2O concentrations at the protein interface are greater than in the lipid bilayer, and the positional profile is much broader. This reveals the higher polarity, and consequently higher intramembrane water concentration, at the protein-lipid interface. In particular, there is a significant water concentration adjacent to the protein at the membrane midplane, unlike the situation in the bilayer regions of this cholesterol-rich membrane. Experiments with protonated fatty acid and phosphatidylcholine spin labels, both of which have a considerably lower affinity for the Na,K-ATPase, confirm these results

Fractional photon-assisted tunneling in an optical superlattice: large contribution to particle transfer

Fractional photon-assisted tunneling is investigated both analytically and numerically for few interacting ultra-cold atoms in the double-wells of an optical superlattice. This can be realized experimentally by adding periodic shaking to an existing experimental setup [Phys. Rev. Lett. 101, 090404 (2008)]. Photon-assisted tunneling is visible in the particle transfer between the wells of the individual double wells. In order to understand the physics of the photon-assisted tunneling, an effective model based on the rotating wave approximation is introduced. The validity of this effective approach is tested for wide parameter ranges which are accessible to experiments in double-well lattices. The effective model goes well beyond previous perturbation theory approaches and is useful to investigate in particular the fractional photon-assisted tunneling resonances. Analytic results on the level of the experimentally realizable two-particle quantum dynamics show very good agreement with the numerical solution of the time-dependent Schr\"odinger equation. Far from being a small effect, both the one-half-photon and the one-third-photon resonance are shown to have large effects on the particle transfer.Comment: 9 pages, 11 png-figure

Topological acoustics in coupled nanocavity arrays

The Su-Schrieffer-Heeger (SSH) model is likely the simplest one-dimensional concept to study non-trivial topological phases and topological excitations. Originally developed to explain the electric conductivity of polyacetylene, it has become a platform for the study of topological effects in electronics, photonics and ultra-cold atomic systems. Here, we propose an experimentally feasible implementation of the SSH model based on coupled one-dimensional acoustic nanoresonators working in the GHz-THz range. In this simulator it is possible to implement different signs in the nearest neighbor interaction terms, showing full tunability of all parameters in the SSH model. Based on this concept we construct topological transition points generating nanophononic edge and interface states and propose an easy scheme to experimentally probe their spatial complex amplitude distribution directly by well-established optical pump-probe techniques.Comment: 10 pages, 4 figure

Tunneling of polarized fermions in 3D double wells

We study the tunneling of a spin polarized Fermi gas in a three-dimensional double well potential, focusing on the time dynamics starting from an initial state in which there is an imbalance in the number of particles in the two wells. Although fermions in different doublets of the double well tunnel with different frequencies, we point out that (incoherent) oscillations of a large number of particles can arise, as a consequence of the presence of transverse degrees of freedom. Estimates of the doublet structure and of the occupation of transverse eigenstates for a realistic experimental setup are provided.Comment: 10 pages, Typos corrected and figures changed - published in Laser Physics, issue on the LPHYS'11 conference (Sarajevo, 2011