6,473 research outputs found
Persistent control of a superconducting qubit by stroboscopic measurement feedback
Making a system state follow a prescribed trajectory despite fluctuations and
errors commonly consists in monitoring an observable (temperature,
blood-glucose level...) and reacting on its controllers (heater power, insulin
amount ...). In the quantum domain, there is a change of paradigm in feedback
since measurements modify the state of the system, most dramatically when the
trajectory goes through superpositions of measurement eigenstates. Here, we
demonstrate the stabilization of an arbitrary trajectory of a superconducting
qubit by measurement based feedback. The protocol benefits from the long
coherence time (s) of the 3D transmon qubit, the high efficiency
(82%) of the phase preserving Josephson amplifier, and fast electronics
ensuring less than 500 ns delay. At discrete time intervals, the state of the
qubit is measured and corrected in case an error is detected. For Rabi
oscillations, where the discrete measurements occur when the qubit is supposed
to be in the measurement pointer states, we demonstrate an average fidelity of
85% to the targeted trajectory. For Ramsey oscillations, which does not go
through pointer states, the average fidelity reaches 75%. Incidentally, we
demonstrate a fast reset protocol allowing to cool a 3D transmon qubit down to
0.6% in the excited state.Comment: 7 pages, 3 figures and 1 table. Supplementary information available
as an ancilla fil
Probing the mechanism of electron capture and electron transfer dissociation using tags with variable electron affinity
Electron capture dissociation (ECD) and electron transfer dissociation (ETD) of doubly protonated electron affinity (EA)-tuned peptides were studied to further illuminate the mechanism of these processes. The model peptide FQpSEEQQQTEDELQDK, containing a phosphoserine residue, was converted to EA-tuned peptides via β-elimination and Michael addition of various thiol compounds. These include propanyl, benzyl, 4-cyanobenzyl, perfluorobenzyl, 3,5-dicyanobenzyl, 3-nitrobenzyl, and 3,5-dinitrobenzyl structural moieties, having a range of EA from −1.15 to +1.65 eV, excluding the propanyl group. Typical ECD or ETD backbone fragmentations are completely inhibited in peptides with substituent tags having EA over 1.00 eV, which are referred to as electron predators in this work. Nearly identical rates of electron capture by the dications substituted by the benzyl (EA = −1.15 eV) and 3-nitrobenzyl (EA = 1.00 eV) moieties are observed, which indicates the similarity of electron capture cross sections for the two derivatized peptides. This observation leads to the inference that electron capture kinetics are governed by the long-range electron−dication interaction and are not affected by side chain derivatives with positive EA. Once an electron is captured to high-n Rydberg states, however, through-space or through-bond electron transfer to the EA-tuning tags or low-n Rydberg states via potential curve crossing occurs in competition with transfer to the amide π* orbital. The energetics of these processes are evaluated using time-dependent density functional theory with a series of reduced model systems. The intramolecular electron transfer process is modulated by structure-dependent hydrogen bonds and is heavily affected by the presence and type of electron-withdrawing groups in the EA-tuning tag. The anion radicals formed by electron predators have high proton affinities (approximately 1400 kJ/mol for the 3-nitrobenzyl anion radical) in comparison to other basic sites in the model peptide dication, facilitating exothermic proton transfer from one of the two sites of protonation. This interrupts the normal sequence of events in ECD or ETD, leading to backbone fragmentation by forming a stable radical intermediate. The implications which these results have for previously proposed ECD and ETD mechanisms are discussed
Stable radiating gap solitons and their resonant interactions with dispersive waves in systems with parametric pump
We study the formation of gap solitons in the presence of parametric pump. It
is shown that parametric pump can stabilize stationary solitons continuously
emitting dispersive waves. The resonant interactions of the radiation and the
solitons are studied and it is shown that the solitons can be effectively
controlled by the radiation. In particular it is shown that the solitons can
collide or to get pinned to inhomogeneities due to the interactions mediated by
the resonant radiation
Oncogenesis- kaleidoscopic and multi-level reality
Oncogenesis is an extremely complex phenomenon. The mechanisms by which cancer is induced is only partially known. Consequently, therapeutic targets may be uncertain and results are often unsatisfactory. The purpose of this paper is to develop a trans-level and multiple transdisciplinary perspective describing the kaleidoscopic reality of oncogenesis. This manner of understanding oncogenesis as a complex process characterized by a non-linear dynamic, far from equilibrium and with unpredictable evolution, transcends the classical perspective and requires a paradigm shift. This approach is also facilitated by recent studies that focus on group phenomena, with emerging behaviors in a continuous phase transition. Biological systems, and obviously the human organism, express this type of behavior with critical self-organizing valences in the context of a genome - mesotope (environment) - phenotype interaction. For example, nature has transposed in the ecosystem, among other things, the performance pattern of its mineral history represented by the dynamic energy-matter-information unit (the principle of invariance). And multi-cell biological systems in the phylogenetic tree crown have multiple directed aerobic metabolisms in accordance with specific functions. Cancers, in turn, have a hybrid (anaerobic and aerobic) and unidirectional metabolism whose only and ultimate reason is the survival of the malignant cell. Understanding the transdisciplinary reality of oncogenesis offers novel development paths for new therapeutic strategies compared to current ones which have relatively limited efficiency
Photoionization Broadening of the 1S-2S Transition in a Beam of Atomic Hydrogen
We consider the excitation dynamics of the two-photon \sts transition in a
beam of atomic hydrogen by 243 nm laser radiation. Specifically, we study the
impact of ionization damping on the transition line shape, caused by the
possibility of ionization of the 2S level by the same laser field. Using a
Monte-Carlo simulation, we calculate the line shape of the \sts transition for
the experimental geometry used in the two latest absolute frequency
measurements (M. Niering {\it et al.}, PRL 84, 5496 (2000) and M. Fischer {\it
et al.}, PRL 92, 230802 (2004)). The calculated line shift and line width are
in excellent agreement with the experimentally observed values. From this
comparison we can verify the values of the dynamic Stark shift coefficient for
the \sts transition for the first time on a level of 15%. We show that the
ionization modifies the velocity distribution of the metastable atoms, the line
shape of the \sts transition, and has an influence on the derivation of its
absolute frequency.Comment: 10 pages, 5 figure
The Sunrise Mission
The first science flight of the balloon-borne \Sunrise telescope took place
in June 2009 from ESRANGE (near Kiruna/Sweden) to Somerset Island in northern
Canada. We describe the scientific aims and mission concept of the project and
give an overview and a description of the various hardware components: the 1-m
main telescope with its postfocus science instruments (the UV filter imager
SuFI and the imaging vector magnetograph IMaX) and support instruments (image
stabilizing and light distribution system ISLiD and correlating wavefront
sensor CWS), the optomechanical support structure and the instrument mounting
concept, the gondola structure and the power, pointing, and telemetry systems,
and the general electronics architecture. We also explain the optimization of
the structural and thermal design of the complete payload. The preparations for
the science flight are described, including AIV and ground calibration of the
instruments. The course of events during the science flight is outlined, up to
the recovery activities. Finally, the in-flight performance of the
instrumentation is briefly summarized.Comment: 35 pages, 17 figure
Large atom number dual-species magneto-optical trap for fermionic 6Li and 40K atoms
We present the design, implementation and characterization of a dual-species
magneto-optical trap (MOT) for fermionic 6Li and 40K atoms with large atom
numbers. The MOT simultaneously contains 5.2x10^9 6Li-atoms and 8.0x10^9
40K-atoms, which are continuously loaded by a Zeeman slower for 6Li and a
2D-MOT for 40K. The atom sources induce capture rates of 1.2x10^9 6Li-atoms/s
and 1.4x10^9 40K-atoms/s. Trap losses due to light-induced interspecies
collisions of ~65% were observed and could be minimized to ~10% by using low
magnetic field gradients and low light powers in the repumping light of both
atomic species. The described system represents the starting point for the
production of a large-atom number quantum degenerate Fermi-Fermi mixture
Elastic turbulence in curvilinear flows of polymer solutions
Following our first report (A. Groisman and V. Steinberg, \sl Nature , 53 (2000)) we present an extended account of experimental observations of
elasticity induced turbulence in three different systems: a swirling flow
between two plates, a Couette-Taylor (CT) flow between two cylinders, and a
flow in a curvilinear channel (Dean flow). All three set-ups had high ratio of
width of the region available for flow to radius of curvature of the
streamlines. The experiments were carried out with dilute solutions of high
molecular weight polyacrylamide in concentrated sugar syrups. High polymer
relaxation time and solution viscosity ensured prevalence of non-linear elastic
effects over inertial non-linearity, and development of purely elastic
instabilities at low Reynolds number (Re) in all three flows. Above the elastic
instability threshold, flows in all three systems exhibit features of developed
turbulence. Those include: (i)randomly fluctuating fluid motion excited in a
broad range of spatial and temporal scales; (ii) significant increase in the
rates of momentum and mass transfer (compared to those expected for a steady
flow with a smooth velocity profile). Phenomenology, driving mechanisms, and
parameter dependence of the elastic turbulence are compared with those of the
conventional high Re hydrodynamic turbulence in Newtonian fluids.Comment: 23 pages, 26 figure
Hybrid apparatus for Bose-Einstein condensation and cavity quantum electrodynamics: Single atom detection in quantum degenerate gases
We present and characterize an experimental system in which we achieve the
integration of an ultrahigh finesse optical cavity with a Bose-Einstein
condensate (BEC). The conceptually novel design of the apparatus for the
production of BECs features nested vacuum chambers and an in-vacuo magnetic
transport configuration. It grants large scale spatial access to the BEC for
samples and probes via a modular and exchangeable "science platform". We are
able to produce \87Rb condensates of five million atoms and to output couple
continuous atom lasers. The cavity is mounted on the science platform on top of
a vibration isolation system. The optical cavity works in the strong coupling
regime of cavity quantum electrodynamics and serves as a quantum optical
detector for single atoms. This system enables us to study atom optics on a
single particle level and to further develop the field of quantum atom optics.
We describe the technological modules and the operation of the combined BEC
cavity apparatus. Its performance is characterized by single atom detection
measurements for thermal and quantum degenerate atomic beams. The atom laser
provides a fast and controllable supply of atoms coupling with the cavity mode
and allows for an efficient study of atom field interactions in the strong
coupling regime. Moreover, the high detection efficiency for quantum degenerate
atoms distinguishes the cavity as a sensitive and weakly invasive probe for
cold atomic clouds
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