594 research outputs found
Collective spontaneous emission in a q-deformed Dicke model
The q-deformation of a single quantized radiation mode interacting with a
collection of two level atoms is introduced, analysing its effects on the
cooperative behavior of the system.Comment: 11 pages, RevTeX file, 2 figures available from authors, accepted for
publication in Mod. Phys. Lett.
Targeting qubit states using open-loop control
We present an open-loop (bang-bang) scheme which drives an open two-level
quantum system to any target state, while maintaining quantum coherence
throughout the process. The control is illustrated by a realistic simulation
for both adiabatic and thermal decoherence. In the thermal decoherence regime,
the control achieved by the proposed scheme is qualitatively similar, at the
ensemble level, to the control realized by the quantum feedback scheme of Wang,
Wiseman, and Milburn [Phys. Rev. A 64, #063810 (2001)] for the spontaneous
emission of a two-level atom. The performance of the open-loop scheme compares
favorably against the quantum feedback scheme with respect to robustness,
target fidelity and transition times.Comment: 27 pages, 7 figure
Quantum State Reconstruction of a Bose-Einstein Condensate
We propose a tomographic scheme to reconstruct the quantum state of a
Bose-Einstein condensate, exploiting the radiation field as a probe and
considering the atomic internal degrees of freedom. The density matrix in the
number state basis can be directly retrieved from the atom counting
probabilities.Comment: 11 pages, LaTeX file, no figures, to appear in Europhysics Letter
Discovery of ultra-fast outflows in a sample of Broad Line Radio Galaxies observed with Suzaku
We present the results of a uniform and systematic search for blue-shifted Fe
K absorption lines in the X-ray spectra of five bright Broad-Line Radio
Galaxies (BLRGs) observed with Suzaku. We detect, for the first time at X-rays
in radio-loud AGN, several absorption lines at energies greater than 7 keV in
three out of five sources, namely 3C 111, 3C 120 and 3C 390.3. The lines are
detected with high significance according to both the F-test and extensive
Monte Carlo simulations. Their likely interpretation as blue-shifted Fe XXV and
Fe XXVI K-shell resonance lines implies an origin from highly ionized gas
outflowing with mildly relativistic velocities, in the range 0.04-0.15c. A fit
with specific photo-ionization models gives ionization parameters in the range
log_xi~4-5.6 and column densities of N_H~10^22-10^23 cm^-2. These
characteristics are very similar to those of the Ultra-Fast Outflows (UFOs)
previously observed in radio-quiet AGN. Their estimated location within
~0.01-0.3pc from the central super-massive black hole suggests a likely origin
related with accretion disk winds/outflows. Depending on the absorber covering
fraction, the mass outflow rate of these UFOs can be comparable to the
accretion rate and their kinetic power can correspond to a significant fraction
of the bolometric luminosity and is comparable to their typical jet power.
Therefore, these UFOs can play a significant role in the expected feedback from
the AGN on the surrounding environment and can give us further clues on the
relation between the accretion disk and the formation of winds/jets in both
radio-quiet and radio-loud AGN.Comment: Accepted for publication in The Astrophysical Journal; corrected
reference
Generating continuous variable quantum codewords in the near-field atomic lithography
Recently, D. Gottesman et al. [Phys. Rev. A 64, 012310 (2001)] showed how to
encode a qubit into a continuous variable quantum system. This encoding was
realized by using non-normalizable quantum codewords, which therefore can only
be approximated in any real physical setup. Here we show how a neutral atom,
falling through an optical cavity and interacting with a single mode of the
intracavity electromagnetic field, can be used to safely encode a qubit into
its external degrees of freedom. In fact, the localization induced by a
homodyne detection of the cavity field is able to project the near-field atomic
motional state into an approximate quantum codeword. The performance of this
encoding process is then analyzed by evaluating the intrinsic errors induced in
the recovery process by the approximated form of the generated codeword.Comment: 9 pages, 5 figure
Interference effects in f-deformed fields
We show how the introduction of an algeabric field deformation affects the
interference phenomena. We also give a physical interpretation of the developed
theory.Comment: 6 pages, Latex file, no figures, accepted by Physica Script
Pulse Control of Decoherence with Population Decay
The pulse control of decoherence in a qubit interacting with a quantum
environment is studied with focus on a general case where decoherence is
induced by both pure dephasing and population decay. To observe how the
decoherence is suppressed by periodic pi pulses, we present a simple method to
calculate the time evolution of a qubit under arbitrary pulse sequences
consisting of bit-flips and/or phase-flips. We examine the effectiveness of the
two typical sequences: bb sequence consisting of only bit-flips, and bp
sequence consisting of both bit- and phase-flips. It is shown that the
effectiveness of the pulse sequences depends on a relative strength of the two
decoherence processes especially when a pulse interval is slightly shorter than
qubit-environment correlation times. In the short-interval limit, however, the
bp sequence is always more effective than, or at least as effective as, the bb
sequence.Comment: 11 pages, 7 figure
Electrochemical Characterization of Charge Storage at Anodes for Sodium-Ion Batteries Based on Corncob Waste-Derived Hard Carbon and Binder
Sodium-ion batteries (SIBs) represent a potential alternative to lithium-ion batteries in large-scale energy storage applications. To improve the sustainability of SIBs, the utilization of anode carbonaceous materials produced from biomass and the selection of a bio-based binder allowing an aqueous electrode processing are fundamental. Herein, corncobs are used as raw material for the preparation of hard carbon and it is also used as cellulose sources for the synthesis of carboxymethyl cellulose (CMC) binder. The corncob-derived electrodes deliver a high discharge capacity of around 264 mAhg(-1) at 1 C (300 mAg(-1)), with promising capacity retention (84 % after 100 cycles) and good rate capability. Additionally, this work expands the fundamental insight of the sodium storage behavior of Hard Carbons through an electrochemical approach, suggesting that the reaction mechanism is controlled by capacitive process in the sloping voltage region, while the diffusion-controlled intercalation is the predominant process in the low-voltage plateau
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