2,802 research outputs found
Self-Aligned Ballistic Molecular Transistors and Electrically Parallel Nanotube Arrays
Carbon nanotube field-effect transistors with structures and properties near
the scaling limit with short (down to 50 nm) channels, self aligned geometries,
palladium electrodes with low contact resistance and high-k dielectric gate
insulators are realized. Electrical transport in these miniature transistors is
near ballistic up to high biases at both room and low temperatures. Atomic
layer deposited (ALD) high-k films interact with nanotube sidewalls via van der
Waals interactions without causing weak localization at 4 K. New fundamental
understanding of ballistic transport, optical phonon scattering and potential
interfacial scattering mechanisms in nanotubes are obtained.Comment: Nano Letters, in pres
A Quantum Tweezer for Atoms
We propose a quantum tweezer for extracting a desired number of neutral atoms
from a reservoir. A trapped Bose-Einstein condensate (BEC) is used as the
reservoir, taking advantage of its coherent nature, which can guarantee a
constant outcome. The tweezer is an attractive quantum dot, which may be
generated by red-detuned laser light. By moving with certain speeds, the dot
can extract a desired number of atoms from the BEC through Landau-Zener
tunneling. The feasibility of our quantum tweezer is demonstrated through
realistic and extensive model calculations.Comment: 4 pages, 6 figures Revised versio
Transition to Instability in a Kicked Bose-Einstein Condensate
A periodically kicked ring of a Bose-Einstein condensate is considered as a
nonlinear generalization of the quantum kicked rotor. For weak interactions
between atoms, periodic motion (anti-resonance) becomes quasiperiodic (quantum
beating) but remains stable. There exists a critical strength of interactions
beyond which quasiperiodic motion becomes chaotic, resulting in an instability
of the condensate manifested by exponential growth in the number of
noncondensed atoms. Similar behavior is observed for dynamically localized
states (essentially quasiperiodic motions), where stability remains for weak
interactions but is destroyed by strong interactions.Comment: 4 pages, 6 figs. A new affiliation is added. Accepted by Phys. Rev.
Let
Quantum Chaos of Bogoliubov Waves for a Bose-Einstein Condensate in Stadium Billiards
We investigate the possibility of quantum (or wave) chaos for the Bogoliubov
excitations of a Bose-Einstein condensate in billiards. Because of the mean
field interaction in the condensate, the Bogoliubov excitations are very
different from the single particle excitations in a non-interacting system.
Nevertheless, we predict that the statistical distribution of level spacings is
unchanged by mapping the non-Hermitian Bogoliubov operator to a real symmetric
matrix. We numerically test our prediction by using a phase shift method for
calculating the excitation energies.Comment: minor change, 4 pages, 4 figures, to appear in Phys. Rev. Let
Ultra-high fidelity qubits for quantum computing
We analyze a system of fermionic Li atoms in an optical trap, and show
that an atom "on demand" can be prepared with ultra-high fidelity, exceeding
0.99998. This process can be scaled to many sites in parallel, providing a
realistic method to initialize N qubits at ultra-high fidelity for quantum
computing. We also show how efficient quantum gate operation can be implemented
in this system, and how spatially resolved single-atom detection can be
performed
Calculation of Atomic Number States: a Bethe Ansatz Approach
We analyze the conditions for producing atomic number states in a
one-dimensional optical box using the Bethe ansatz method. This approach
provides a general framework, enabling the study of number state production
over a wide range of realistic experimental parameters
Recovery of dilute (bio-based) volatile fatty acids by adsorption with magnetic hyperthermal swing desorption
Circular Permutation in the Ω-Loop of TEM-1 β-Lactamase Results in Improved Activity and Altered Substrate Specificity
Generating diverse protein libraries that contain improved variants at a sufficiently high frequency is critical for improving the properties of proteins using directed evolution. Many studies have illustrated how random mutagenesis, cassette mutagenesis, DNA shuffling and similar approaches are effective diversity generating methods for directed evolution. Very few studies have explored random circular permutation, the intramolecular relocation of the N- and C-termini of a protein, as a diversity-generating step for directed evolution. We subjected a library of random circular permutations of TEM-1 β-lactamase to selections on increasing concentrations of a variety of β-lactam antibiotics including cefotaxime. We identified two circularly permuted variants that conferred elevated resistance to cefotaxime but decreased resistance to other antibiotics. These variants were circularly permuted in the Ω-loop proximal to the active site. Remarkably, one variant was circularly permuted such that the key catalytic residue Glu166 was located at the N-terminus of the mature protein
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