1,572 research outputs found
Quantum MERA Channels
Tensor networks representations of many-body quantum systems can be described
in terms of quantum channels. We focus on channels associated with the
Multi-scale Entanglement Renormalization Ansatz (MERA) tensor network that has
been recently introduced to efficiently describe critical systems. Our approach
allows us to compute the MERA correspondent to the thermodynamic limit of a
critical system introducing a transfer matrix formalism, and to relate the
system critical exponents to the convergence rates of the associated channels.Comment: 4 pages, 2 figure
Signatures of the super fluid-insulator phase transition in laser driven dissipative nonlinear cavity arrays
We analyze the non-equilibrium dynamics of a gas of interacting photons in an
array of coupled dissipative nonlinear cavities driven by a pulsed external
coherent field. Using a mean-field approach, we show that the system exhibits a
phase transition from a Mott-insulator-like to a superfluid regime. For a given
single-photon nonlinearity, the critical value of the photon tunneling rate at
which the phase transition occurs increases with the increasing photon loss
rate. We checked the robustness of the transition by showing its insensitivity
to the initial state prepared by the the pulsed excitation. We find that the
second-order coherence of cavity emission can be used to determine the phase
diagram of an optical many-body system without the need for thermalization.Comment: 4 pages, 4 figure
Optimal estimation of quantum observables
We consider the problem of estimating the ensemble average of an observable
on an ensemble of equally prepared identical quantum systems. We show that,
among all kinds of measurements performed jointly on the copies, the optimal
unbiased estimation is achieved by the usual procedure that consists in
performing independent measurements of the observable on each system and
averaging the measurement outcomes.Comment: Submitted to J. Math Phy
Quantum Illumination with Gaussian States
An optical transmitter irradiates a target region containing a bright
thermal-noise bath in which a low-reflectivity object might be embedded. The
light received from this region is used to decide whether the object is present
or absent. The performance achieved using a coherent-state transmitter is
compared with that of a quantum illumination transmitter, i.e., one that
employs the signal beam obtained from spontaneous parametric downconversion
(SPDC). By making the optimum joint measurement on the light received from the
target region together with the retained SPDC idler beam, the quantum
illumination system realizes a 6 dB advantage in error probability exponent
over the optimum reception coherent-state system. This advantage accrues
despite there being no entanglement between the light collected from the target
region and the retained idler beam.Comment: 4 pages, 1 figur
Geometrical bounds on irreversibility in open quantum systems
Clausius inequality has deep implications for reversibility and the arrow of
time. Quantum theory is able to extend this result for closed systems by
inspecting the trajectory of the density matrix on its manifold. Here we show
that this approach can provide an upper and lower bound to the irreversible
entropy production for open quantum systems as well. These provide insights on
the thermodynamics of the information erasure. Limits of the applicability of
our bounds are discussed, and demonstrated in a quantum photonic simulator
Decoherence induced by interacting quantum spin baths
We study decoherence induced on a two-level system coupled to a
one-dimensional quantum spin chain. We consider the cases where the dynamics of
the chain is determined by the Ising, XY, or Heisenberg exchange Hamiltonian.
This model of quantum baths can be of fundamental importance for the
understanding of decoherence in open quantum systems, since it can be
experimentally engineered by using atoms in optical lattices. As an example,
here we show how to implement a pure dephasing model for a qubit system coupled
to an interacting spin bath. We provide results that go beyond the case of a
central spin coupled uniformly to all the spins of the bath, in particular
showing what happens when the bath enters different phases, or becomes
critical; we also study the dependence of the coherence loss on the number of
bath spins to which the system is coupled and we describe a
coupling-independent regime in which decoherence exhibits universal features,
irrespective of the system-environment coupling strength. Finally, we establish
a relation between decoherence and entanglement inside the bath. For the Ising
and the XY models we are able to give an exact expression for the decay of
coherences, while for the Heisenberg bath we resort to the numerical
time-dependent Density Matrix Renormalization Group.Comment: 18 pages, 20 figure
Theoretical prediction of multiferroicity in double perovskite YNiMnO
We put forward double perovskites of the RNiMnO family (with a
rare-earth atom) as a new class of multiferroics on the basis of {\it ab
initio} density functional calculations. We show that changing from La to Y
drives the ground-state from ferromagnetic to antiferromagnetic with
spin patterns. This E-type ordering
breaks inversion symmetry and generates a ferroelectric polarization of few
. By analyzing a model Hamiltonian we understand the microscopic
origin of this transition and show that an external electric field can be used
to tune the transition, thus allowing electrical control of the magnetization.Comment: 4 pages, 3 figure
Bridging thermodynamics and metrology in non-equilibrium Quantum Thermometry
Single-qubit thermometry presents the simplest tool to measure the
temperature of thermal baths with reduced invasivity. At thermal equilibrium,
the temperature uncertainty is linked to the heat capacity of the qubit,
however the best precision is achieved outside equilibrium condition. Here, we
discuss a way to generalize this relation in a non-equilibrium regime, taking
into account purely quantum effects such as coherence. We support our findings
with an experimental photonic simulation.Comment: 7 pages, 4 figure
Novel electronic states close to Mott transition in low-dimensional and frustrated systems
Recent studies demonstrated that there may appear different novel states in
correlated systems close to localized-itinerant crossover. Especially
favourable conditions for that are met in low-dimensional and in frustrated
systems. In this paper I discuss on concrete examples some of such novel
states. In particular, for some spinels and triangular systems there appears a
"partial Mott transition", in which first some finite clusters (dimers, trimes,
tetramers, heptamers) go over to the itinerant regime, and the real bulk Mott
transition occurs only later. Also some other specific possibilities in this
crossover regime are shortly discussed, such as spin-Peierls-Peierls transition
in TiOCl, spontaneous charge disproportionation in some cases, etc.Comment: To be published in Journal of Physics - Condensed Matter, conference
serie
Synergistic cytotoxicity and pharmacogenetics of gemcitabine and pemetrexed combination in pancreatic cancer cell lines
PURPOSE:
Gemcitabine is an inhibitor of ribonucleotide reductase (RR) and DNA synthesis and is an effective agent in the treatment of pancreas cancer. The present study investigates whether the multitargeted antifolate pemetrexed would be synergistic with gemcitabine against MIA PaCa-2, PANC-1, and Capan-1 pancreatic cancer cell lines.
EXPERIMENTAL DESIGN:
Cells were treated with gemcitabine and pemetrexed, and the type of drug interaction was assessed using the combination index. Cytotoxicity of gemcitabine was examined with inhibitors of (a) deoxycytidine kinase (dCK), which activates gemcitabine by phosphorylation, and (b) 5'-nucleotidase (drug dephosphorylation) and cytidine deaminase (drug deamination), the main inactivating enzymes. The effects of gemcitabine and pemetrexed on cell cycle were analyzed by flow cytometry, and apoptosis was examined by fluorescence microscopy. Finally, quantitative, real-time PCR was used to study the pharmacogenetics of the drug combination.
RESULTS:
Synergistic cytotoxicity and enhancement of apoptosis was demonstrated, mostly with the sequence pemetrexed-->gemcitabine. Pemetrexed increased cells in S phase, the most sensitive to gemcitabine, and a positive correlation was found between the expression ratio of dCK:RR and gemcitabine sensitivity. Indeed, pemetrexed significantly enhanced dCK gene expression (+227.9, +86.0, and +135.5% in MIA PaCa-2, PANC-1, and Capan-1 cells, respectively), and the crucial role of this enzyme was confirmed by impairment of gemcitabine cytotoxicity after dCK saturation with 2'-deoxycytidine.
CONCLUSIONS:
These data demonstrate that the gemcitabine and pemetrexed combination displays schedule-dependent synergistic cytotoxic activity, favorably modulates cell cycle, induces apoptosis, and enhances dCK expression in pancreatic cancer cells
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