Significance Quantum phase transitions are characterized by a dramatic change of the ground-state behavior; famous examples include the appearance of magnetic order or superconductivity as a function ...of doping in cuprates. In this work, we explore how a system dynamically crosses such a transition and in particular, investigate in detail how coherence emerges when an initially incoherent Mott insulating system enters the superfluid regime. We present results from an experimental study using ultracold atoms in an optical lattice as well as numerical simulations and find a rich behavior beyond the scope of any existing theory. This quantum simulation of a complex many-body system is an important stepping stone for a deeper understanding of the intricate dynamics of quantum phase transitions.
The dynamics of quantum phase transitions pose one of the most challenging problems in modern many-body physics. Here, we study a prototypical example in a clean and well-controlled ultracold atom setup by observing the emergence of coherence when crossing the Mott insulator to superfluid quantum phase transition. In the 1D Bose–Hubbard model, we find perfect agreement between experimental observations and numerical simulations for the resulting coherence length. We, thereby, perform a largely certified analog quantum simulation of this strongly correlated system reaching beyond the regime of free quasiparticles. Experimentally, we additionally explore the emergence of coherence in higher dimensions, where no classical simulations are available, as well as for negative temperatures. For intermediate quench velocities, we observe a power-law behavior of the coherence length, reminiscent of the Kibble–Zurek mechanism. However, we find nonuniversal exponents that cannot be captured by this mechanism or any other known model.
A nontrivial interplay between quantum coherence and dissipative environment-driven dynamics is becoming increasingly recognized as the key for efficient energy transport in photosynthetic ...pigment–protein complexes, and converting these biologically inspired insights into a set of design principles that can be implemented in artificial light-harvesting systems has become an active research field. Here we identify a specific design principle, the phonon antenna, by which interpigment coherence is able to modify and optimize the way that excitations spectrally sample their local environmental fluctuations. We provide numerical simulations that suggest that the Fenna–Matthews–Olson complex of green sulfur bacteria has an excitonic structure that is close to such an optimal operating point, and place the phonon antenna concept into a broader context that leads us to conjecture that this general design principle might well be exploited in other biomolecular systems.
In this work we develop a formalism for describing localised quanta for a real-valued Klein–Gordon field in a one-dimensional box 0,R. We quantise the field using non-stationary local modes which, at ...some arbitrarily chosen initial time, are completely localised within the left or the right side of the box. In this concrete set-up we directly face the problems inherent to a notion of local field excitations, usually thought of as elementary particles. Specifically, by computing the Bogoliubov coefficients relating local and standard (global) quantisations, we show that the local quantisation yields a Fock representation of the Canonical Commutation Relations (CCR) which is unitarily inequivalent to the standard one. In spite of this, we find that the local creators and annihilators remain well defined in the global Fock space FG, and so do the local number operators associated to the left and right partitions of the box. We end up with a useful mathematical toolbox to analyse and characterise local features of quantum states in FG. Specifically, an analysis of the global vacuum state |0G〉∈FG in terms of local number operators shows, as expected, the existence of entanglement between the left and right regions of the box. The local vacuum |0L〉∈FL, on the contrary, has a very different character. It is neither cyclic (with respect to any local algebra of operators) nor separating and displays no entanglement between left and right partitions. Further analysis shows that the global vacuum also exhibits a distribution of local excitations reminiscent, in some respects, of a thermal bath. We discuss how the mathematical tools developed herein may open new ways for the analysis of fundamental problems in local quantum field theory.
La calidad e inocuidad del agua de bebida de los animales de abasto es esencial para garantizar la salud y bienestar animal. El objetivo de esta investigación fue determinar la calidad e inocuidad ...del agua de consumo de animales de abasto para identificación de condiciones sanitarias de predios en los municipios de El Dorado y Granada (Meta, Colombia). Se seleccionaron 60 sistemas de producción animal donde se tomaron muestras de agua desde puntos de extracción y abastecimiento tanto para animales como para humanos. Se analizaron sus características fisicoquímicas (pH, Amoniaco-amonio, nitratos y nitritos) y microbiológicas (recuento de organismos mesófilos aerobios y facultativos, así como determinación de coliformes totales y fecales). El pH del agua de los sistemas de producción varió entre 6,0-7,2 en Granada y 7,2-7,6 en El Dorado. Respecto a nitratos y nitritos, todos los valores fueron considerados normales. Los valores de amoniaco-amonio variaron entre 0-1 ppm en los sistemas de producción de Granada y entre 0-0,5 en los sistemas de producción de El Dorado. En relación con la presencia de bacterias coliformes totales y fecales, se encontró en el 100 % de las muestras. El 58 % de los predios del municipio de El Dorado presentaron valores ≥ 48.000 ufc/100 mL de microorganismos mesófilos aerobios, mientras que en el municipio de Granada el porcentaje más alto de microorganismos mesófilos aerobios se encontró entre 100-1.000 ufc/100 mL. Todos los sistemas de producción animal presentaron en su agua de bebida contaminación por coliformes fecales, siendo un riesgo para la salud humana y animal al ser fuente de enfermedades trasmitidas por el agua.
It is well known that the vacuum state of a quantum field is spatially entangled. This is true both in free and confined spaces, for example in an optical cavity. The obvious consequence of this, ...however, is surprising and intuitively challenging; namely, that in a mathematical sense half of an empty cavity is not empty. Formally this is clear, but what does this physically mean in terms of, say, measurements that can actually be made? In this paper we utilize the tools of Gaussian quantum mechanics to easily characterize the reduced state of a subregion in a cavity and expose the spatial profile of its entanglement with the opposite region. We then go on to discuss a thought experiment in which a mirror is introduced between the regions. In so doing we expose a simple and physically concrete answer to the above question: the vacuum excitations resulting from entanglement are mathematically equivalent to the real excitations generated by suddenly introducing a mirror. Performing such an experiment in the laboratory may be an excellent method of verifying vacuum entanglement, and we conclude by discussing different possibilities of achieving this aim.
In this work we develop a formalism for describing localised quanta for a real-valued Klein-Gordon field in a one-dimensional box \(0, R\). We quantise the field using non-stationary local modes ...which, at some arbitrarily chosen initial time, are completely localised within the left or the right side of the box. In this concrete set-up we directly face the problems inherent to a notion of local field excitations, usually thought of as elementary particles. Specifically, by computing the Bogoliubov coefficients relating local and standard (global) quantizations, we show that the local quantisation yields a Fock space \(\mathfrak F^L\) which is unitarily inequivalent to the standard one \(\mathfrak F^G\). In spite of this, we find that the local creators and annihilators remain well defined in the global Fock space \(\mathfrak F^G\), and so do the local number operators associated to the left and right partitions of the box. We end up with a useful mathematical toolbox to analyse and characterise local features of quantum states in \(\mathfrak F^G\). Specifically, an analysis of the global vacuum state \(|0_G\rangle\in\mathfrak F^G\) in terms of local number operators shows, as expected, the existence of entanglement between the left and right regions of the box. The local vacuum \(|0_L\rangle\in\mathfrak F^L\), on the contrary, has a very different character. It is neither cyclic nor separating and displays no entanglement. Further analysis shows that the global vacuum also exhibits a distribution of local excitations reminiscent, in some respects, of a thermal bath. We discuss how the mathematical tools developed herein may open new ways for the analysis of fundamental problems in local quantum field theory.
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