The Experts below are selected from a list of 32130 Experts worldwide ranked by ideXlab platform

Charlesedouard Pfister - One of the best experts on this subject based on the ideXlab platform.

A.v. Smilga - One of the best experts on this subject based on the ideXlab platform.

  • Supersymmetric Proof of the Hirzebruch-Riemann-Roch Theorem for Non-Kähler Manifolds
    Symmetry Integrability and Geometry : Methods and Applications, 2012
    Co-Authors: A.v. Smilga
    Abstract:

    We present the proof of the HRR theorem for a generic complex compact manifold by evaluating the functional integral for the Witten index of the appropriate supersymmetric Quantum Mechanical System.

  • Abelian matrix models in two loops
    Nuclear Physics B, 2003
    Co-Authors: A.v. Smilga
    Abstract:

    We perform a two-loop calculation of the effective Lagrangian for the low--energy modes of the Quantum Mechanical System obtained by dimensional reduction from 4D, N = 1 supersymmetric QED. The bosonic part of the Lagrangian describes the motion over moduli space of vector potentials A_i endowed with a nontrivial conformally flat metric. We determined the coefficient of the two-loop correction to the metric, which is proportional to 1/A^6. For the matrix model obtained from Abelian 4D, N = 2 theory, this correction vanishes, as it should.

  • On the relation between effective supersymmetric actions in different dimensions
    Physics of Atomic Nuclei (Yadernaya fizika), 2003
    Co-Authors: E. T. Akhmedov, A.v. Smilga
    Abstract:

    We make two remarks: (i) Renormalization of the effective charge in a 4--dimensional (supersymmetric) gauge theory is determined by the same graphs and is rigidly connected to the renormalization of the metric on the moduli space of the classical vacua of the corresponding reduced Quantum Mechanical System. Supersymmetry provides constraints for possible modifications of the metric, and this gives us a simple proof of nonrenormalization theorems for the original 4-dimensional theory. (ii) We establish a nontrivial relationship between the effective (0+1)-dimensional and (1+1)-dimensional Lagrangia (the latter represent conventional Kahlerian sigma models).

Stephanie Wehner - One of the best experts on this subject based on the ideXlab platform.

  • Dependence of a Quantum-Mechanical System on its own initial state and the initial state of the environment it interacts with
    Physical Review A, 2013
    Co-Authors: Adrian Hutter, Stephanie Wehner
    Abstract:

    We present a unifying framework to the understanding of when and how Quantum-Mechanical Systems become independent of their initial conditions and adapt macroscopic properties (like temperature) of the environment. By viewing this problem from a Quantum information theory perspective, we are able to simplify it in a very natural and easy way. We first show that for any interaction between the System and the environment, and almost all initial states of the System, the question of how long the System retains memory of its initial conditions can be answered by studying the temporal evolution of just one special initial state. This special state thereby depends only on our knowledge of macroscopic parameters of the System. We provide a simple entropic inequality for this state that can be used to determine whether most states of the System have or have not become independent of their initial conditions after time $t$. We discuss applications of our entropic criterion to thermalization times in Systems with an effective light cone and to Quantum memories suffering depolarizing noise. We make a similar statement for almost all initial states of the environment and finally provide a sufficient condition for which a System never thermalizes but remains close to its initial state for all times.

  • when does a Quantum Mechanical System depend on the initial conditions of the System or the environment
    2011
    Co-Authors: Adrian Hutter, Stephanie Wehner
    Abstract:

    any interaction between the System and the environment, and almost all initial states of the System, the question of how long such memory lasts can be answered by studying the temporal evolution of just one special initial state. This special state thereby depends only on our knowledge of macroscopic parameters of the System. We provide a simple entropic inequality for this state that can be used to determine whether mosts states of the System have, or have not become independent of their initial conditions after time t. Analyzing the rate of entropy change over time for a particular kind of interaction then allows us to place rigorous bounds on such time scales. We make a similar statement for almost all initial states of the environment, and nally provide a sucient condition for which a System never thermalizes, but remains close to its initial state for all times.

  • lower bound on the dimension of a Quantum System given measured data
    Physical Review A, 2008
    Co-Authors: Stephanie Wehner, Matthias Christandl, Andrew C Doherty
    Abstract:

    We imagine an experiment on an unknown Quantum Mechanical System in which the System is prepared in various ways and a range of measurements are performed. For each measurement M and preparation rho the experimenter can determine, given enough time, the probability of a given outcome a: p(a|M,rho). How large does the Hilbert space of the Quantum System have to be in order to allow us to find density matrices and measurement operators that will reproduce the given probability distribution? In this paper, we prove a simple lower bound for the dimension of the Hilbert space. The main insight is to relate this problem to the construction of Quantum random access codes, for which interesting bounds on the Hilbert space dimension already exist. We discuss several applications of our result to hidden-variable or ontological models, to Bell inequalities, and to properties of the smooth min-entropy.

Baptiste Schubnel - One of the best experts on this subject based on the ideXlab platform.

  • Scattering Theory for Lindblad Master Equations
    Communications in Mathematical Physics, 2017
    Co-Authors: Marco Falconi, Jürg Fröhlich, Jérémy Faupin, Baptiste Schubnel
    Abstract:

    We study scattering theory for a Quantum-Mechanical System consisting of a particle scattered off a dynamical target that occupies a compact region in position space. After taking a trace over the degrees of freedom of the target, the dynamics of the particle is generated by a Lindbladian acting on the space of trace-class operators. We study scattering theory for a general class of Lindbladians with bounded interaction terms. First, we consider models where a particle approaching the target is always re-emitted by the target. Then we study models where the particle may be captured by the target. An important ingredient of our analysis is a scattering theory for dissipative operators on Hilbert space.

Alain Joye - One of the best experts on this subject based on the ideXlab platform.