Talks

Entanglement Renormalization for Interacting Field Theories

We firstly introduce the Multiscale Entanglement Renormalization Ansatz (cMERA). Then, a general method for interacting QFTs is presented. We improve upon the well-known Gaussian formalism used in free theories through a class of variational non-Gaussian wavefunctionals for which expectation values of local operators can be efficiently calculated analytically and in a closed form. The method consists of a series of scale-dependent nonlinear canonical transformations on the fields of the theory under consideration. We will discuss the λϕ^4 and the sine-Gordon scalar theories to illustrate how non-perturbative effects far beyond the Gaussian approximation are obtained. [Based on: 1904.07241]

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IMPRS Seminar: Constructing a Single Molecule-Machinery?

C. Joachim, Nanoscience Group Pico-Lab, CEMES-CNRS, Toulouse (France) WPI MANA-NIMS, Tsukuba (Japan) After the Blaise Pascal's calculating clock, the vacuum lamps calculators, the computers lithographed on the surface of a silicon crystal, what about embedding all or parts of an electronic calculator on a single molecule and more practically atom by atom at the surface of a large electronic gap semi-conductor? Even mechanical machinery like a train of gears, a motor or a car may be one day fully miniaturized down to the end of the material world on a single molecule? We will show how the idea of for example molecular electronics explored for over 30 years and boosted in 1987 by the 1981 invention of the scanning tunneling microscope had introduced a plethora of questions (The same a bit latter for single molecule mechanics starting in 1998): Are there enough quantum resources in a single molecule 1 nm in size to make a machine or the elementary parts of a nanoscale machine? Can quantum physics provides enough technological paths for exchanging energy and information with one and always the same molecule deposited on a surface? Does synthetic Chemistry allows for enlarging enough the molecule chemical structure so that it becomes a calculator or a motor by itself without reaching the size up of a protein by elementary function?

IMPRS Seminar: Current-Induced Rotation and Modelling of Molecular-Scale Gears

Current-Induced Rotation and Modelling of Molecular-Scale Gears The possibility of creating nanoscale molecular gears able to transfer motion has opened novel routes to implement true molecule-based mechanical analogs[1]. In the first part, we investigate, within model Hamiltonian approach, the rotational dynamics of a molecular gear. For this, we combine Langevin dynamics and non-equilibrium Green’s functions to computed a current-induced torque, which allows to study the influence of the electronic system on the rotational dynamics. Our model provides the rotational analog of the Anderson-Holstein Hamiltonian. In the second part, we focus on rotation transfer among many gears. In particular, we use molecular dynamics (MD) simulation and also analytic approach to investigate the dynamics of coupled gears for two gears and many gears problem; Then we demonstrate the solution analytically and numerically. [1] Chao Li, Zhongping Wang, Yan Lu, Xiaoqing Liu & Li Wang, Nature Nanotechnology 12, 1071–1076 (2017)

Colloquium: New Phases of Quantum Magnets in and out of Equilibrium

In quantum magnets spins form well-defined lattices and serve as model systems to study many-body quantum phases such as interacting quantum-dimer qubits, spin Luttinger-liquids, Bose glasses, or magnon Bose-Einstein condensates. Neutron, muon and photon sources are unique tools for high-precision studies of such phases, and of their correlations and excitations in as well as out of equilibrium. An overview of current frontiers in the field will be presented with special focus on recent developments in computational physics and exciting new opportunities that free electron lasers like SwissFEL and European XFEL will offer to study the time-dependence and out-of-equilibrium quantum mechanics of such systems.

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