134,312 research outputs found
Coherent State Control of Non-Interacting Quantum Entanglement
We exploit a novel approximation scheme to obtain a new and compact formula
for the parameters underlying coherent-state control of the evolution of a pair
of entangled two-level systems. It is appropriate for long times and for
relatively strong external quantum control via coherent state irradiation. We
take account of both discrete-state and continuous-variable degrees of freedom.
The formula predicts the relative heights of entanglement revivals and their
timing and duration.Comment: Published in PRA, 10 pages, 7 figure
Sudden Death of Entanglement of Two Jaynes-Cummings Atoms
We investigate entanglement dynamics of two isolated atoms, each in its own
Jaynes-Cummings cavity. We show analytically that initial entanglement has an
interesting subsequent time evolution, including the so-called sudden death
effect.Comment: 3 pages, 3 figure
Phonon decoherence of quantum entanglement: Robust and fragile states
We study the robustness and fragility of entanglement of open quantum systems
in some exactly solvable models in which the decoherence is caused by a pure
dephasing process. In particular, for the toy models presented in this paper,
we identify two different time scales, one is responsible for local dephasing,
while the other is for entanglement decay. For a class of fragile entangled
states defined in this paper, we find that the entanglement of two qubits, as
measured by concurrence, decays faster asymptotically than the quantum
dephasing of an individual qubit.Comment: 11 pages, revtex, no figure
Quantum transitions induced by the third cumulant of current fluctuations
We investigate the transitions induced by external current fluctuations on a
small probe quantum system. The rates for the transitions between the energy
states are calculated using the real-time Keldysh formalism for the density
matrix evolution. We especially detail the effects of the third cumulant of
current fluctuations inductively coupled to a quantum bit and propose a setup
for detecting the frequency-dependent third cumulant through the transitions it
induces.Comment: 4 pages, 3 figure
New powerful outburst of the unusual young star V1318 Cyg S (LkH{\alpha} 225)
Young double star V1318 Cyg, which is associated with a small isolated
star-forming region around HAeBe star BD+40o4124, has very unusual photometric
and spectral behavior. We present results of photometric and spectroscopic
observations in the optical range. We carried out BVRI CCD photometric
observations of V1318 Cyg from 2015 Sept. to 2017 July. For the same period we
acquired medium- and low-resolution spectra. Observations were performed with
the 2.6 m telescope. We analyze the historical light curve for V1318 Cyg and
demonstrate that the southern component, V1318 Cyg S, after being rather bright
in the 1970s (V14 mag) started to lower its brightness and in 1990
became practically invisible in the optical. After its reappearance in the
second half of the 1990s the star started to become very slowly brighter.
Between 2006 and 2010 V1318 Cyg S started brightening more quickly, and in 2015
had become brighter by more than five magnitudes in visible light. Since this
time V1318 Cyg S has remained at this maximum. Its spectrum shows little
variability and consists of a mixture of emission and absorption lines, which
has allowed for estimates of its spectral type as early Ae, with obvious
evidence of matter outflow. We derive its current A(V) 7.2 and L = 750
L(sun) thus confirming that V1318 Cyg S should belong to the Herbig Ae stars,
making it, along with BD+40o4124 and V1686 Cyg, the third luminous young star
in the group. It is very probable that we observe V1318 Cyg S near the pole and
that the inclination of its dense and slow ( 100 km/s) outflow is low.
The unusual variability and other features of V1318 Cyg S make it difficult to
classify this star among known types of eruptive young stars. It could be an
extreme, higher-mass example of an EXor, or an object of intermediate class
between EXors and FUors, like V1647 Ori.Comment: 9 pages, 7 figure
Chemisorption and reactions on clusters of nickel atoms
The nucleation and growth of metallic clusters on a substantially amorphous substrate are discussed with emphasis on the geometrical and electronic structure of the clusters. Several clusters of different symmetry containing five to nine nickel atoms were studied. It was found that the energy range of primary d-like states is not significantly different from the width of the d-band states in nickel metal, as long as the interatomic distance is comparable to that in the bulk metal. The approach of one or more molecules to the cluster is examined using at the hydrogenation of acetylene and the dehydrogenation of ethylene as examples
Sympathetic cooling of polyatomic molecules with S-state atoms in a magnetic trap
We present a rigorous theoretical study of low-temperature collisions of
polyatomic molecular radicals with ^1S_0 atoms in the presence of an external
magnetic field. Accurate quantum scattering calculations based on ab initio and
scaled interaction potentials show that collision-induced spin relaxation of
the prototypical organic molecule CH_2(X^3B_1) (methylene) and nine other
triatomic radicals in cold 3He gas occurs at a slow rate, demonstrating that
cryogenic buffer-gas cooling and magnetic trapping of these molecules is
feasible with current technology. Our calculations further suggest that it may
be possible to create ultracold gases of polyatomic molecules by sympathetic
cooling with alkaline-earth atoms in a magnetic trap.Comment: 5 pages, 3 figures, 1 tabl
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