314 research outputs found
Strongly Correlated States of Ultracold Rotating Dipolar Fermi Gases
We study strongly correlated ground and excited states of rotating quasi-2D
Fermi gases constituted of a small number of dipole-dipole interacting
particles with dipole moments polarized perpendicular to the plane of motion.
As the number of atoms grows, the system enters {\it an intermediate regime},
where ground states are subject to a competition between distinct bulk-edge
configurations. This effect obscures their description in terms of composite
fermions and leads to the appearance of novel composite fermion quasi-hole
states. In the presence of dipolar interactions, the principal Laughlin state
at filling exhibits a substantial energy gap for neutral (total
angular momentum conserving) excitations, and is well-described as an
incompressible Fermi liquid. Instead, at lower fillings, the ground state
structure favors crystalline order.Comment: 5 pages, 5 figures, paper presented at DPG Meeting 2006, as well as
Fritz Haber Institute Colloquiu
Water mobility and microstructure evolution in the germinating Medicago truncatula seed studied by NMR relaxometry. A revisited interpretation of multicomponent relaxation
The water status of Medicago truncatula Gaertn. seed was followed by low-field NMR relaxometry during germination with and without oryzalin or fusicoccin used as growth modulators. T1 and T2 relaxation times and proportions P1 and P2 were determined on fresh, frozen, and freeze-thawed samples to characterize changes in water dynamics and compartmentation and in the nonfreezing water fraction. The results demonstrate that low-field NMR relaxometry allowed differentiating germination phases and events occurring during them as well as perturbations related to the presence of growth modulators. The results provide clear evidence that the classical multicomponent relaxation interpretation cannot directly relate T2 components and morphological compartments in biological tissue
Ultracold Dipolar Gases in Optical Lattices
This tutorial is a theoretical work, in which we study the physics of
ultra-cold dipolar bosonic gases in optical lattices. Such gases consist of
bosonic atoms or molecules that interact via dipolar forces, and that are
cooled below the quantum degeneracy temperature, typically in the nK range.
When such a degenerate quantum gas is loaded into an optical lattice produced
by standing waves of laser light, new kinds of physical phenomena occur. These
systems realize then extended Hubbard-type models, and can be brought to a
strongly correlated regime. The physical properties of such gases, dominated by
the long-range, anisotropic dipole-dipole interactions, are discussed using the
mean-field approximations, and exact Quantum Monte Carlo techniques (the Worm
algorithm).Comment: 56 pages, 26 figure
Entangling interactions between artificial atoms mediated by a multimode left-handed superconducting ring resonator
Superconducting metamaterial transmission lines implemented with lumped
circuit elements can exhibit left-handed dispersion, where the group and phase
velocity have opposite sign, in a frequency range relevant for superconducting
artificial atoms. Forming such a metamaterial transmission line into a ring and
coupling it to qubits at different points around the ring results in a
multimode bus resonator with a compact footprint. Using flux-tunable qubits, we
characterize and theoretically model the variation in the coupling strength
between the two qubits and each of the ring resonator modes. Although the
qubits have negligible direct coupling between them, their interactions with
the multimode ring resonator result in both a transverse exchange coupling and
a higher order interaction between the qubits. As we vary the detuning
between the qubits and their frequency relative to the ring resonator modes, we
observe significant variations in both of these inter-qubit interactions,
including zero crossings and changes of sign. The ability to modulate
interaction terms such as the scale between zero and large values for
small changes in qubit frequency provides a promising pathway for implementing
entangling gates in a system capable of hosting many qubits.Comment: 8 + 11 pages, 5 + 5 figures, 0 + 3 table
Dynamical electron transport through a nanoelectromechanical wire in a magnetic field
We investigate dynamical transport properties of interacting electrons moving
in a vibrating nanoelectromechanical wire in a magnetic field. We have built an
exactly solvable model in which electric current and mechanical oscillation are
treated fully quantum mechanically on an equal footing. Quantum mechanically
fluctuating Aharonov-Bohm phases obtained by the electrons cause nontrivial
contribution to mechanical vibration and electrical conduction of the wire. We
demonstrate our theory by calculating the admittance of the wire which are
influenced by the multiple interplay between the mechanical and the electrical
energy scales, magnetic field strength, and the electron-electron interaction
Ultrasensitive force and displacement detection using trapped ions
The ability to detect extremely small forces is vital for a variety of
disciplines including precision spin-resonance imaging, microscopy, and tests
of fundamental physical phenomena. Current force-detection sensitivity limits
have surpassed 1 (atto ) through coupling of micro or
nanofabricated mechanical resonators to a variety of physical systems including
single-electron transistors, superconducting microwave cavities, and individual
spins. These experiments have allowed for probing studies of a variety of
phenomena, but sensitivity requirements are ever-increasing as new regimes of
physical interactions are considered. Here we show that trapped atomic ions are
exquisitely sensitive force detectors, with a measured sensitivity more than
three orders of magnitude better than existing reports. We demonstrate
detection of forces as small as 174 (yocto ), with a
sensitivity 390 using crystals of Be
ions in a Penning trap. Our technique is based on the excitation of normal
motional modes in an ion trap by externally applied electric fields, detection
via and phase-coherent Doppler velocimetry, which allows for the discrimination
of ion motion with amplitudes on the scale of nanometers. These experimental
results and extracted force-detection sensitivities in the single-ion limit
validate proposals suggesting that trapped atomic ions are capable of detecting
of forces with sensitivity approaching 1 . We anticipate that
this demonstration will be strongly motivational for the development of a new
class of deployable trapped-ion-based sensors, and will permit scientists to
access new regimes in materials science.Comment: Expanded introduction and analysis. Methods section added. Subject to
press embarg
DNA damage signalling prevents deleterious telomere addition at DNA breaks
The response to DNA damage involves regulation of multiple essential processes to maximize the accuracy of DNA damage repair and cell survival 1. Telomerase has the potential to interfere with repair by inappropriately adding telomeres to DNA breaks. It was unknown whether cells modulate telomerase in response to DNA damage, to increase the accuracy of repair. Here we report that telomerase action is regulated as a part of the cellular response to a DNA double-strand break (DSB). Using yeast, we show that the major ATR/Mec1 DNA damage signalling pathway regulates telomerase action at DSBs. Upon DNA damage, MEC1-RAD53-DUN1-dependent phosphorylation of the telomerase inhibitor Pif1 occurs. Utilizing a separation of function PIF1 mutation, we show that this phosphorylation is required for the Pif1-mediated telomerase inhibition that takes place specifically at DNA breaks, but not telomeres. Hence DNA damage signalling down-modulates telomerase action at a DNA break via Pif1 phosphorylation, thus preventing aberrant healing of broken DNA ends by telomerase. These findings uncover a novel regulatory mechanism that coordinates competing DNA end-processing activities and thereby promotes DNA repair accuracy and genome integrity
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