We observe multiple stable states of nuclear polarization and nuclear self-tuning over a large range of fields in a double quantum dot under conditions of electron spin resonance. The observations can be understood within an elaborated theoretical rate equation model for the polarization in each of the dots, in the limit of strong driving. This model also captures unusual features of the data, such as fast switching and a "wrong" sign of polarization. The results reported enable applications of this polarization effect, including accurate manipulation and control of nuclear fields.

Syntheses of protein molecules in a cell are carried out by ribosomes. A ribosome can be regarded as a molecular motor which utilizes the input chemical energy to move on a messenger RNA (mRNA) track that also serves as a template for the polymerization of the corresponding protein. The forward movement, however, is characterized by an alternating sequence of translocation and pause.

Accurate multideterminant ground-state energies of circular quantum dots containing N≤13 electrons as a function of interaction strength have been evaluated by the diffusion quantum Monte Carlo method. Two unique features are found for these confined two-dimensional systems: (1) as the electron density decreases, the quantum dots favor states with zero orbital angular momentum (L=0); and (2) for some values of N, the ground state cannot be fully spin-polarized because of a symmetry constraint. © 2009 The American Physical Society.

We present a series of theoretical studies of the boundary between a superfluid and a normal region in a partially polarized gas of strongly interacting fermions. We present mean-field estimates of the surface energy in this boundary as a function of temperature and scattering length. We discuss the structure of the domain wall, and use a previously introduced phenomonological model to study its influence on experimental observables.

We present a theoretical study of vortices within a harmonically trapped Bose-Einstein condensate in a rotating optical lattice. Due to the competition between vortex-vortex interactions and pinning to the optical lattice, we find a very complicated energy landscape, which leads to hysteretic evolution. The qualitative structure of the vortex configurations depends on the commensurability between the vortex density and the site density-with regular lattices when these are commensurate and the appearance of ringlike structures when they are not.

Two aspects of quantum Monte Carlo are discussed. First, we review a procedure for obtaining trial wavefunctions for use in quantum Monte Carlo simulations that have both smaller statistical errors and improved expectation values than commonly used functions. Second, we present a correlated sampling approach for calculating energy differences in variational Monte Carlo much more accurately than the values of the energies. This method is used to calculate the potential energy surfaces of H2 and BH.

We propose ways to create and detect fractionally charged excitations in integer quantum Hall edge states. The charge fractionalization occurs due to the Coulomb interaction between electrons propagating on different edge channels. The fractional charge of the solitonlike collective excitations can be observed in time-resolved or frequency-dependent shot noise measurements. © 2009 The American Physical Society.

High-stress silicon nitride microresonators exhibit a remarkable room temperature Q factor that even exceeds that of single crystal silicon. A study of the temperature dependent variation of the Q of a 255μm×255μ m×30nm thick high-stress Si3N4 membrane reveals that the dissipation Q-1 decreases with lower temperatures and is □ 3 orders of magnitude smaller than the universal behavior. Stress-relieved cantilevers fabricated from the same material show a Q that is more consistent with typical disordered materials.