119 research outputs found

    Monte Carlo study of the discontinuous quantum phase transition in the transverse-field Ising model on the pyrochlore lattice

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    The antiferromagnetic Ising model on the pyrochlore lattice exhibits a quantum phase transition in an applied transverse field from the low-field quantum spin-ice phase to the high-field polarized regime. Recent field-theoretical analysis and series expansion results indicate this to be a discontinuous, first-order transition. Here, we explore this transition using quantum Monte Carlo simulations in order to assess this scenario and study the thermodynamic properties in the vicinity of the quantum phase transition. For this purpose, we also consider several variants of extended cluster-update schemes for the transverse field Ising antiferromagnet on frustrated lattices and compare their performance to the conventional bond-based algorithm for the transverse field Ising model on the pyrochlore lattice.Comment: 13 pages, 15 figures, v2: as publishe

    Gauss Law, Minimal Coupling and Fermionic PEPS for Lattice Gauge Theories

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    In these lecture notes, we review some recent works on Hamiltonian lattice gauge theories, that involve, in particular, tensor network methods. The results reviewed here are tailored together in a slightly different way from the one used in the contexts where they were first introduced, by looking at the Gauss law from two different points of view: for the gauge field it is a differential equation, while from the matter point of view, on the other hand, it is a simple, explicit algebraic equation. We will review and discuss what these two points of view allow and do not allow us to do, in terms of unitarily gauging a pure-matter theory and eliminating the matter from a gauge theory, and relate that to the construction of PEPS (Projected Entangled Pair States) for lattice gauge theories.Comment: Fourth version: minor revision of notes (third version) for SciPost. Notes originally prepared for two lectures given in the Focus week "Tensor Networks and Entanglement" of the workshop "Entanglement in Quantum System", at the Galileo Galilei Institute for Theoretical Physics (GGI), Florence, Italy in June 201

    Fermionic Gaussian PEPS in 3+1d3+1d: Rotations and Relativistic Limits

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    Fermionic Gaussian Projected Entangled Pair States are fermionic tensor network state constructions which describe the physics of ground states of non-interacting fermionic Hamiltonians. As non-interacting states, one may study and analyze them very efficiently, in both analytical and numerical means. Recently it was shown that they may be used as the starting point - after applying so-called PEPS gauging mechanisms - for variational study of lattice gauge theories. This is done using sign-problem free variational Monte-Carlo. In this work we show how to generalize such states from two to three spatial dimensions, focusing on spin representations and requirements of lattice rotations. We present constructions which are crucial for the application of the above mentioned variational Monte-Carlo techniques for studying non-perturbative lattice gauge theory physics, with fermionic matter, in 2+12+1-d and 3+13+1-d models. Thus, the constructions presented here are crucial for the study of non-trivial lattice gauge theories with fermionic tensor network states.Comment: 13 pages, 1 figur

    Jet-ISM Interaction in the Radio Galaxy 3C293: Jet-driven Shocks Heat ISM to Power X-ray and Molecular H2 emission

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    We present a 70ks Chandra observation of the radio galaxy 3C293. This galaxy belongs to the class of molecular hydrogen emission galaxies (MOHEGs) that have very luminous emission from warm molecular hydrogen. In radio galaxies, the molecular gas appears to be heated by jet-driven shocks, but exactly how this mechanism works is still poorly understood. With Chandra, we observe X-ray emission from the jets within the host galaxy and along the 100 kpc radio jets. We model the X-ray spectra of the nucleus, the inner jets, and the X-ray features along the extended radio jets. Both the nucleus and the inner jets show evidence of 10^7 K shock-heated gas. The kinetic power of the jets is more than sufficient to heat the X-ray emitting gas within the host galaxy. The thermal X-ray and warm H2 luminosities of 3C293 are similar, indicating similar masses of X-ray hot gas and warm molecular gas. This is consistent with a picture where both derive from a multiphase, shocked interstellar medium (ISM). We find that radio-loud MOHEGs that are not brightest cluster galaxies (BCGs), like 3C293, typically have LH2/LX~1 and MH2/MX~1, whereas MOHEGs that are BCGs have LH2/LX~0.01 and MH2/MX~0.01. The more massive, virialized, hot atmosphere in BCGs overwhelms any direct X-ray emission from current jet-ISM interaction. On the other hand, LH2/LX~1 in the Spiderweb BCG at z=2, which resides in an unvirialized protocluster and hosts a powerful radio source. Over time, jet-ISM interaction may contribute to the establishment of a hot atmosphere in BCGs and other massive elliptical galaxies.Comment: Accepted by ApJ 21 pages in ApJ format, 9 figures, 8 table

    A Christmas Story about Quantum Teleportation

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    Quantum teleportation is a concept that fascinates and confuses many people, in particular, given that it combines quantum physics and the concept of teleportation. With quantum teleportation likely to play a key role in several communication technologies and the quantum internet in the future, it is imperative to create learning tools and approaches that can accurately and effectively communicate the concept. Recent research has indicated the importance of teachers enthusing students about the topic of quantum physics. Therefore, educators at both high school and early university level need to find engaging and perhaps unorthodox ways of teaching complex, yet interesting topics such as quantum teleportation. In this paper, we present a paradigm to teach the concept of quantum teleportation using the Christmas gift-bringer Santa Claus. Using the example of Santa Claus, we use an unusual context to explore the key aspects of quantum teleportation, and all without being overly abstract. In addition, we outline a worksheet designed for use in the classroom setting which is based on common naive conceptions from quantum physics. This worksheet will be evaluated as a classroom resource to teach quantum teleportation in a subsequent study.Comment: 11 + 8 pages, 3 figures, v2: as publishe

    A variational Monte Carlo algorithm for lattice gauge theories with continuous gauge groups: a study of (2+1)-dimensional compact QED with dynamical fermions at finite density

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    Lattice gauge theories coupled to fermionic matter account for many interesting phenomena in both high energy physics and condensed matter physics. Certain regimes, e.g. at finite fermion density, are difficult to simulate with traditional Monte Carlo algorithms due to the so-called sign-problem. We present a variational, sign-problem-free Monte Carlo method for lattice gauge theories with continuous gauge groups and apply it to (2+1)-dimensional compact QED with dynamical fermions at finite density. The variational ansatz is formulated in the full gauge field basis, i.e. without having to resort to truncation schemes for the U(1)U(1) gauge field Hilbert space. The ansatz consists of two parts: first, a pure gauge part based on Jastrow-type ansatz states (which can be connected to certain neural-network ansatz states) and secondly, on a fermionic part based on gauge-field dependent fermionic Gaussian states. These are designed in such a way that the gauge field integral over all fermionic Gaussian states is gauge-invariant and at the same time still efficiently tractable. To ensure the validity of the method we benchmark the pure gauge part of the ansatz against another variational method and the full ansatz against an existing Monte Carlo simulation where the sign-problem is absent. Moreover, in limiting cases where the exact ground state is known we show that our ansatz is able to capture this behavior. Finally, we study a sign-problem affected regime by probing density-induced phase transitions.Comment: 14+6 pages, 9+1 figure

    Real-time dynamics in 2+1d compact QED using complex periodic Gaussian states

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    We introduce a class of variational states to study ground state properties and real-time dynamics in (2+1)-dimensional compact QED. These are based on complex Gaussian states which are made periodic in order to account for the compact nature of the U(1)U(1) gauge field. Since the evaluation of expectation values involves infinite sums, we present an approximation scheme for the whole variational manifold. We calculate the ground state energy density for lattice sizes up to 20×2020 \times 20 and extrapolate to the thermodynamic limit for the whole coupling region. Additionally, we study the string tension both by fitting the potential between two static charges and by fitting the exponential decay of spatial Wilson loops. As the ansatz does not require a truncation in the local Hilbert spaces, we analyze truncation effects which are present in other approaches. The variational states are benchmarked against exact solutions known for the one plaquette case and exact diagonalization results for a Z3\mathbb{Z}_3 lattice gauge theory. Using the time-dependent variational principle, we study real-time dynamics after various global quenches, e.g. the time evolution of a strongly confined electric field between two charges after a quench to the weak-coupling regime. Up to the points where finite size effects start to play a role, we observe equilibrating behavior.Comment: 20 pages, 16 figures, v2: as publishe

    Variational Monte Carlo simulation with tensor networks of a pure Z3\mathbb{Z}_3 gauge theory in (2+1)d

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    Variational minimization of tensor network states enables the exploration of low energy states of lattice gauge theories. However, the exact numerical evaluation of high-dimensional tensor network states remains challenging. By combining gauged Gaussian projected entangled pair states with a variational Monte Carlo procedure, we are able to efficiently compute ground state energies. We demonstrate the method for a pure gauge Kogut-Susskind Hamiltonian with a Z3\mathbb{Z}_3 gauge field in two spatial dimensions. The method provides an inherent way to increase the number of variational parameters and can be readily extended to systems with physical fermions.Comment: 13 pages, 7 figure

    A reversible posterior leucoencephalopathy syndrome including blindness caused by preeclampsia.

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    Complications of (pre)eclampsia may involve multiple systems and organs. Neurological symptoms may occur. Visual symptoms concern up to 25% the of patients with severe preeclampsia and 50% of the patients with eclampsia. An uncommon effect of severe preeclampsia is sudden blindness. Blindness may be part of a clinical and radiological presentation named Posterior Reversible Encephalopathy Syndrome (PRES). PRES may lead to permanent neurological deficit, recurrences or death. We report the case of a 24-year-old Caucasian patient, gravida 5 para 2 who developed preeclampsia and PRES complicated with blindness at 32 weeks of gestation. Optimal care allowed visual symptoms to resolve within 24 hours and a favourable maternal outcome and no long- term sequelae. We describe different causes and manifestations of PRES and highlight the need for immediate care in order to optimize the chance of symptoms reversibility
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