5,111 research outputs found
On a conjecture regarding Fisher information
Fisher's information measure plays a very important role in diverse areas of
theoretical physics. The associated measures as functionals of quantum
probability distributions defined in, respectively, coordinate and momentum
spaces, are the protagonists of our present considerations. The product of them
has been conjectured to exhibit a non trivial lower bound in [Phys. Rev. A
(2000) 62 012107]. We show here that such is not the case. This is illustrated,
in particular, for pure states that are solutions to the free-particle
Schr\"odinger equation. In fact, we construct a family of counterexamples to
the conjecture, corresponding to time-dependent solutions of the free-particle
Schr\"odinger equation. We also give a new conjecture regarding any
normalizable time-dependent solution of this equation.Comment: 4 pages; revised equations, results unchange
Comment on "Quantum discord through the generalized entropy in bipartite quantum states"
In [X.-W. Hou, Z.-P. Huang, S. Chen, Eur. Phys. J. D 68, 1 (2014)], Hou et
al. present, using Tsallis' entropy, possible generalizations of the quantum
discord measure, finding original results. As for the mutual informations and
discord, we show here that these two types of quantifiers can take negative
values. In the two qubits instance we further determine in which regions they
are non-negative. Additionally, we study alternative generalizations on the
basis of R\'enyi entropies.Comment: 5 pages, 4 figure
Quantum synchronization as a local signature of super- and subradiance
We study the relationship between the collective phenomena of super and
subradiance and spontaneous synchronization of quantum systems. To this aim we
revisit the case of two detuned qubits interacting through a pure dissipative
bosonic environment, which contains the minimal ingredients for our analysis.
By using the Liouville formalism, we are able to find analytically the ultimate
connection between these phenomena. We find that dynamical synchronization is
due to the presence of long standing coherence between the ground state of the
system and the subradiant state. We finally show that, under pure dissipation,
the emergence of spontaneous synchronization and of subradiant emission occur
on the same time scale. This reciprocity is broken in the presence of dephasing
noise.Comment: 12 pages, 6 figure
Dynamics of Entanglement and Bell-nonlocality for Two Stochastic Qubits with Dipole-Dipole Interaction
We have studied the analytical dynamics of Bell nonlocality as measured by
CHSH inequality and entanglement as measured by concurrence for two noisy
qubits that have dipole-dipole interaction. The nonlocal entanglement created
by the dipole-dipole interaction is found to be protected from sudden death for
certain initial states
Urinalysis and pre-renal acute kidney injury: time to move on.
Urinary indices are classically believed to allow differentiation of transient (or pre-renal) acute kidney injury (AKI) from persistent (or acute tubular necrosis) AKI. However, the data validating urinalysis in critically ill patients are weak. In the previous issue of Critical Care, Pons and colleagues demonstrate in a multicenter observational study that sodium and urea excretion fractions as well as urinary over plasma ratios performed poorly as diagnostic tests to separate such entities. This study confirms the limited diagnostic and prognostic ability of urine testing. Together with other studies, this study raises more fundamental questions about the value, meaning and pathophysiologic validity of the pre-renal AKI paradigm and suggests that AKI (like all other forms of organ injury) is a continuum of injury that cannot be neatly divided into functional (pre-renal or transient) or structural (acute tubular necrosis or persistent)
Dispersion of Klauder's temporally stable coherent states for the hydrogen atom
We study the dispersion of the "temporally stable" coherent states for the
hydrogen atom introduced by Klauder. These are states which under temporal
evolution by the hydrogen atom Hamiltonian retain their coherence properties.
We show that in the hydrogen atom such wave packets do not move
quasi-classically; i.e., they do not follow with no or little dispersion the
Keplerian orbits of the classical electron. The poor quantum-classical
correspondence does not improve in the semiclassical limit.Comment: 6 pages, 2 figure
Entanglement degradation in the solid state: interplay of adiabatic and quantum noise
We study entanglement degradation of two non-interacting qubits subject to
independent baths with broadband spectra typical of solid state nanodevices. We
obtain the analytic form of the concurrence in the presence of adiabatic noise
for classes of entangled initial states presently achievable in experiments. We
find that adiabatic (low frequency) noise affects entanglement reduction
analogously to pure dephasing noise. Due to quantum (high frequency) noise,
entanglement is totally lost in a state-dependent finite time. The possibility
to implement on-chip both local and entangling operations is briefly discussed.Comment: Replaced with published version. Minor change
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