155 research outputs found
Autoresonant excitation of Bose-Einstein condensates
Controlling the state of a Bose-Einstein condensate driven by a chirped
frequency perturbation in a one-dimensional anharmonic trapping potential is
discussed. By identifying four characteristic time scales in this
chirped-driven problem, three dimensionless parameters are defined
describing the driving strength, the anharmonicity of the trapping potential,
and the strength of the particles interaction, respectively. As the driving
frequency passes the linear resonance in the problem, and depending on the
location in the parameter space, the system may exhibit two very
different evolutions, i.e. the quantum energy ladder climbing (LC) and the
classical autoresonance (AR). These regimes are analysed both in theory and
simulations with the emphasis on the effect of the interaction parameter
. In particular, the transition thresholds on the driving parameter
and their width in in both the AR and LC regimes are discussed.
Different driving protocols are also illustrated, showing efficient control of
excitation and de-excitation of the condensate
Assignment of the NV0 575 nm zero-phonon line in diamond to a 2E-2A2 transition
The time-averaged emission spectrum of single nitrogen-vacancy defects in
diamond gives zero-phonon lines of both the negative charge state at 637 nm
(1.945 eV) and the neutral charge state at 575 nm (2.156 eV). This occurs
through photo-conversion between the two charge states. Due to strain in the
diamond the zero-phonon lines are split and it is found that the splitting and
polarization of the two zero-phonon lines are the same. From this observation
and consideration of the electronic structure of the nitrogen-vacancy center it
is concluded that the excited state of the neutral center has A2 orbital
symmetry. The assignment of the 575 nm transition to a 2E - 2A2 transition has
not been established previously.Comment: 5 pages, 5 figure
Anomalous autoresonance threshold for chirped-driven Korteweg-de-Vries waves
Large amplitude traveling waves of the Korteweg-de-Vries (KdV) equation can be excited and controlled by a chirped frequency driving perturbation. The process involves capturing the wave into autoresonance (a continuous nonlinear synchronization) with the drive by passage through the linear resonance in the problem. The transition to autoresonance has a sharp threshold on the driving amplitude. In all previously studied autoresonant problems the threshold was found via a weakly nonlinear theory and scaled as α3/4,α being the driving frequency chirp rate. It is shown that this scaling is violated in a long wavelength KdV limit because of the increased role of the nonlinearity in the problem. A fully nonlinear theory describing the phenomenon and applicable to all wavelengths is developed. © 2015 American Physical Society
Low temperature studies of the excited-state structure of Nitrogen-Vacancy color centers in diamond
We report a study of the 3E excited-state structure of single
nitrogen-vacancy (NV) defects in diamond, combining resonant excitation at
cryogenic temperatures and optically detected magnetic resonance. A theoretical
model of the excited-state structure is developed and shows excellent agreement
with experimental observations. Besides, we show that the two orbital branches
associated with the 3E excited-state are averaged when operating at room
temperature. This study leads to an improved physical understanding of the NV
defect electronic structure, which is invaluable for the development of
diamond-based quantum information processing.Comment: 4 pages, 4 figure
Excited-state spectroscopy of single NV defects in diamond using optically detected magnetic resonance
Using pulsed optically detected magnetic resonance techniques, we directly
probe electron-spin resonance transitions in the excited-state of single
Nitrogen-Vacancy color centers in diamond. Unambiguous assignment of excited
state fine structure is made, based on changes of NV defect photoluminescence
lifetime. This study provides significant insight into the structure of the
emitting 3E excited state, which is invaluable for the development of
diamond-based quantum information processing.Comment: 10 pages, 4 figure
Demonstration of entanglement-by-measurement of solid state qubits
Projective measurements are a powerful tool for manipulating quantum states.
In particular, a set of qubits can be entangled by measurement of a joint
property such as qubit parity. These joint measurements do not require a direct
interaction between qubits and therefore provide a unique resource for quantum
information processing with well-isolated qubits. Numerous schemes for
entanglement-by-measurement of solid-state qubits have been proposed, but the
demanding experimental requirements have so far hindered implementations. Here
we realize a two-qubit parity measurement on nuclear spins in diamond by
exploiting the electron spin of a nitrogen-vacancy center as readout ancilla.
The measurement enables us to project the initially uncorrelated nuclear spins
into maximally entangled states. By combining this entanglement with
high-fidelity single-shot readout we demonstrate the first violation of Bells
inequality with solid-state spins. These results open the door to a new class
of experiments in which projective measurements are used to create, protect and
manipulate entanglement between solid-state qubits.Comment: 6 pages, 4 figure
Ultrasound diagnosis of congestion in the pulmonary and systemic circulations in patients with atrial fibrillation and chronic heart failure
High throughput mutagenesis for identification of residues regulating human prostacyclin (hIP) receptor
The human prostacyclin receptor (hIP receptor) is a seven-transmembrane G protein-coupled receptor (GPCR) that plays a critical role in vascular smooth muscle relaxation and platelet aggregation. hIP receptor dysfunction has been implicated in numerous cardiovascular abnormalities, including myocardial infarction, hypertension, thrombosis and atherosclerosis. Genomic sequencing has discovered several genetic variations in the PTGIR gene coding for hIP receptor, however, its structure-function relationship has not been sufficiently explored. Here we set out to investigate the applicability of high throughput random mutagenesis to study the structure-function relationship of hIP receptor. While chemical mutagenesis was not suitable to generate a mutagenesis library with sufficient coverage, our data demonstrate error-prone PCR (epPCR) mediated mutagenesis as a valuable method for the unbiased screening of residues regulating hIP receptor function and expression. Here we describe the generation and functional characterization of an epPCR derived mutagenesis library compromising >4000 mutants of the hIP receptor. We introduce next generation sequencing as a useful tool to validate the quality of mutagenesis libraries by providing information about the coverage, mutation rate and mutational bias. We identified 18 mutants of the hIP receptor that were expressed at the cell surface, but demonstrated impaired receptor function. A total of 38 non-synonymous mutations were identified within the coding region of the hIP receptor, mapping to 36 distinct residues, including several mutations previously reported to affect the signaling of the hIP receptor. Thus, our data demonstrates epPCR mediated random mutagenesis as a valuable and practical method to study the structurefunction relationship of GPCRs. © 2014 Bill et al
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