4,768 research outputs found
Quantum Hysteresis in Coupled Light-Matter Systems
We investigate the non-equilibrium quantum dynamics of a canonical
light-matter system, namely the Dicke model, when the light-matter interaction
is ramped up and down through a cycle across the quantum phase transition. Our
calculations reveal a rich set of dynamical behaviors determined by the cycle
times, ranging from the slow, near adiabatic regime through to the fast, sudden
quench regime. As the cycle time decreases, we uncover a crossover from an
oscillatory exchange of quantum information between light and matter that
approaches a reversible adiabatic process, to a dispersive regime that
generates large values of light-matter entanglement. The phenomena uncovered in
this work have implications in quantum control, quantum interferometry, as well
as in quantum information theory.Comment: 9 pages and 4 figure
Quantum Phase Transitions detected by a local probe using Time Correlations and Violations of Leggett-Garg Inequalities
In the present paper we introduce a way of identifying quantum phase
transitions of many-body systems by means of local time correlations and
Leggett-Garg inequalities. This procedure allows to experimentally determine
the quantum critical points not only of finite-order transitions but also those
of infinite order, as the Kosterlitz-Thouless transition that is not always
easy to detect with current methods. By means of simple analytical arguments
for a general spin- Hamiltonian, and matrix product simulations of
one-dimensional and anisotropic models, we argue that
finite-order quantum phase transitions can be determined by singularities of
the time correlations or their derivatives at criticality. The same features
are exhibited by corresponding Leggett-Garg functions, which noticeably
indicate violation of the Leggett-Garg inequalities for early times and all the
Hamiltonian parameters considered. In addition, we find that the infinite-order
transition of the model at the isotropic point can be revealed by the
maximal violation of the Leggett-Garg inequalities. We thus show that quantum
phase transitions can be identified by purely local measurements, and that
many-body systems constitute important candidates to observe experimentally the
violation of Leggett-Garg inequalities.Comment: Minor changes, 11 pages, 11 figures. Final version published in Phys.
Rev.
Dynamics of Entanglement and the Schmidt Gap in a Driven Light-Matter System
The ability to modify light-matter coupling in time (e.g. using external
pulses) opens up the exciting possibility of generating and probing new aspects
of quantum correlations in many-body light-matter systems. Here we study the
impact of such a pulsed coupling on the light-matter entanglement in the Dicke
model as well as the respective subsystem quantum dynamics. Our dynamical
many-body analysis exploits the natural partition between the radiation and
matter degrees of freedom, allowing us to explore time-dependent
intra-subsystem quantum correlations by means of squeezing parameters, and the
inter-subsystem Schmidt gap for different pulse duration (i.e. ramping
velocity) regimes -- from the near adiabatic to the sudden quench limits. Our
results reveal that both types of quantities indicate the emergence of the
superradiant phase when crossing the quantum critical point. In addition, at
the end of the pulse light and matter remain entangled even though they become
uncoupled, which could be exploited to generate entangled states in
non-interacting systems.Comment: 15 pages, 4 figures, Accepted for publication in Journal of Physics
B, special issue Correlations in light-matter interaction
AID Induces Double-Strand Breaks at Immunoglobulin Switch Regions and c-MYC Causing Chromosomal Translocations in Yeast THO Mutants
Transcription of the switch (S) regions of immunoglobulin genes in B cells generates stable R-loops that are targeted by Activation Induced Cytidine Deaminase (AID), triggering class switch recombination (CSR), as well as translocations with c-MYC responsible for Burkitt's lymphomas. In Saccharomyces cerevisiae, stable R-loops are formed co-transcriptionally in mutants of THO, a conserved nuclear complex involved in mRNP biogenesis. Such R-loops trigger genome instability and facilitate deamination by human AID. To understand the mechanisms that generate genome instability mediated by mRNP biogenesis impairment and by AID, we devised a yeast chromosomal system based on different segments of mammalian S regions and c-MYC for the analysis of chromosomal rearrangements in both wild-type and THO mutants. We demonstrate that AID acts in yeast at heterologous S and c-MYC transcribed sequences leading to double-strand breaks (DSBs) which in turn cause chromosomal translocations via Non-Homologous End Joining (NHEJ). AID–induced translocations were strongly enhanced in yeast THO null mutants, consistent with the idea that AID–mediated DSBs depend on R-loop formation. Our study not only provides new clues to understand the role of mRNP biogenesis in preventing genome rearrangements and the mechanism of AID-mediated genome instability, but also shows that, once uracil residues are produced by AID–mediated deamination, these are processed into DSBs and chromosomal rearrangements by the general and conserved DNA repair functions present from yeast to human cells
Arthropod pests and their management, natural enemies and flora visitors associated with castor (Ricinus communis), a biofuel plant: a review.
Interest in bioenergetic crops, such as the castor oil plant Ricinus communis (Euphorbiaceae), for production of biodiesel has increased in recent years. In this paper, phytophagous arthropods, their natural enemies and floral visitors associated with this plant in the world are reviewed. Despite its insecticidal properties, arthropods have been reported feeding on R. communis plants. The arthropod pests of R. communis damage all parts of the plant, including the seeds, where some toxic compounds are even more concentrated. In the scientific databases, we found reports of 193 arthropods associated to R. communis in different parts of the world. This information obtained in the scientific databases was concentrated in a database and analyzed according to the coevolutive hypothesis, which allows us to predict that the greatest wealth and abundance of phytogenic arthropods is found in the center of origin by R. communis. According to this review, Achaea janata, Spodoptera litura, Edwardsiana flavescens, Liriomyza trifolii, L. sativae, Spilosoma obliqua, Cogenethes punctiferalis, Oxyrhachis taranda, and Helicoverpa armigera are the most devastating pests in Asia. In Africa, Agrotis ipsilon, S. exigua, Nezara viridula, Trialeurodes ricini, and Tetranychus urticae were mentioned as the most important. In Central and South-America, Phyllophaga sp., Agrietes sp., Erinnyis ello, N. viridula, Corythucha gossypii, Falconia antioquiana, and S. marima are reported as pests of economic importance. The most commonly reported natural enemies of some of these arthropod pests were species of Bacillus thuringiensis, B. cereus, B. popilliae, Trichogramma achaeae, T. chilonis, T. minutum, T. australicum, T. dendrolimi, T. pretiosum, T. evanescens, Microplitis rufiventris, M. maculipennis, M. ophiusae, Telenomus remus, T. proditor, Stethorus siphonulus and S. histrio. Apis mellifera is recorded as the main insect pollinator of R. communis. Pest management methods used against the arthropod pests of R. communis include biological, ethological, mechanical, cultural, genetic, and chemical control
Long-range ferromagnetism of Mn12 acetate single-molecule magnets under a transverse magnetic field
We use neutron diffraction to probe the magnetization components of a crystal
of Mn12 single-molecule magnets. Each of these molecules behaves, at low
temperatures, as a nanomagnet with spin S = 10 and strong anisotropy along the
crystallographic c axis. Application of a magnetic field perpendicular to c
induces quantum tunneling between opposite spin orientations, enabling the
spins to attain thermal equilibrium. Below approximately 0.9 K, intermolecular
interactions turn this equilibrium state into a ferromagnetically ordered
phase. However, long range ferromagnetic correlations nearly disappear for
fields larger 5.5 T, possibly suggesting the existence of a quantum critical
point.Comment: 4 pages, 4 figure
Efectos de la temporalidad sobre la formación recibida durante el empleo
En un mercado de trabajo como el español donde existe una gran temporalidad, puede surgir un conflicto sobre el nivel socialmente óptimo de formación específica que sería necesario que recibieran los trabajadores y el que de hecho obtienen, en un mercado laboral con esas características. En este estudio se pretende verificar esta posible relación negativa entre capital humano específico y grado de flexibilidad externa del mercado laboral en España. Concretamente, se analiza la influencia del tipo de contrato sobre la decisión, que toman conjuntamente trabajadores y empleadores, de financiar y adquirir formación útil para el empleo, usando esta última variable como una proxy del capital humano específico. Para lograr este objetivo se estiman modelos de elección discreta, utilizando la información estadística proveniente del Panel de Hogares de la Unión Europea para España (PHOGUE) elaborado por el INE. La estructura de panel de dichos datos nos permite considerar en las estimaciones la posible existencia de heterogeneidad individual inobservada, mediante la especificación de un modelo probit con efectos aleatorios
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