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Calendar of Physics Talks Vienna
| Many-body strategies for multi-qubit gates |
| Speaker: | Kareljan Schoutens |
| Abstract: | The standard method for implementing algorithms for quantum computation is through quantum circuits. Such circuits typically contain quantum gates involving more than a single or two qubits. Multi-qubit gates can be decomposed into 1- and 2-qubit gates, but this is not necessarily the most efficient strategy. We present a framework for quantum control directly at the level of multiple qubits. A key ingredient is what we call an eigengate: a simple quantum circuit that maps computational basis states to eigenstates of a many-body hamiltonian. We show how to make it all work for a Krawtchouk qubit chain, and for operators associated to a spin chain with inverse square exchange, first introduced by Polychronakos.
Based on arXiv:1707.05144, Phys Rev A97.04232, with Koen Groenland |
| Date: | Mon, 28.05.2018 |
| Time: | 09:30 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Schrödinger lecture hall |
| Contact: | secr@esi.ac.at |
| Correlation functions of the quantum sine-Gordon model in and out of equilibrium |
| Speaker: | Gabor Takacs |
| Abstract: | Recent progress in cold-atom experiments simulating QFT models led to
direct measurement of higher order correlations. I present a numerical
approach to correlation functions of the quantum sine-Gordon model,
building upon the so-called Truncated Conformal Space Approach, allowing
to construct higher order correlations in a system of finite size in
various physical states of experimental relevance, both in and out of
equilibrium. Deviations from Gaussianity due to the presence of
interaction are measured and their dependence on temperature is
analysed, exhibiting the experimentally observed crossover between
Gaussian and non-Gaussian regimes. We also studied dynamics after a
quench, observing the effects of the interaction on the time evolution
of correlation functions, their spatial dependence and their
non-Gaussianity as measured by the kurtosis. |
| Date: | Mon, 28.05.2018 |
| Time: | 10:45 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Operator Moments of Noisy Coupled Qubits and the Fredrickson--Andersen Model |
| Speaker: | Austen Lamacraft |
| Abstract: | Random noise cooks a system of coupled qubits to infinite temperature. The dynamics of noise averages of operators displays diffusive behaviour or fast relaxation, depending on whether the drive conserves one of the spin components or not. However, this tells us nothing about the dynamics of entanglement or quantum chaos, which require at least the second moment of operators. We show that these are described by the Fredrickson--Andersen model, originally introduced as a model of cooperative relaxation near the glass transition, and discuss the consequences for operator spreading and impurity decay.
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| Date: | Mon, 28.05.2018 |
| Time: | 11:30 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Probing ergodicity breaking with matrix elements |
| Speaker: | Maksym Serbyn |
| Abstract: | In many-body localized (MBL) phase strong disorder allows quantum systems to escape thermalization via emergence of extensive number of conserved quantities. Delocalization transition between MBL and ergodic phase which occurs upon decreasing disorder can provide a useful insights into workings of thermalization. In this talk I will use the matrix elements to probe the ergodicity breaking. Using statistics of matrix elements of local operators, I will show how one can locate the delocalization transition. In addition, energy structure of matrix elements will be used to reveal a wide critical region within the ergodic phase. In this region matrix elements show critical dependence on the energy difference and exhibit strong multifractality. Finally, by relating the properties of matrix elements to level statistics, I will present two-parameter level spacing distribution that governs the cr |
| Date: | Mon, 28.05.2018 |
| Time: | 14:00 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Quantum anomaly and scaling dynamics in the 2D Fermi gas |
| Speaker: | Nicolo Defenu |
| Abstract: | A scale invariant system looks similar on different length scales.
Usually this is realized only after some fine tuning, for instance
near a phase transition or a scattering resonance. Remarkably, a
classical gas in two dimensions is scale invariant for an arbitrary
strength of contact interaction. This has striking consequences for
its nonequilibrium scaling dynamics, in particular the breathing
motion in a harmonic trapping potential.
For a two-dimensional fermionic quantum gas, instead, quantum
fluctuations violate the classical scaling symmetry and give rise to
a quantum anomaly. I will discuss the consequences of this scale
anomaly and how it can be observed in the equation of state, the
pairing properties, and the nonequilibrium scaling dynamics. |
| Date: | Mon, 28.05.2018 |
| Time: | 15:40 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Damping of Josephson oscillations in strongly correlated one-dimensional atomic gases |
| Speaker: | Anna Minguzzi |
| Abstract: | We study the Josephson oscillations of two strongly correlated one-dimensional bosonic clouds separated by a localized barrier. Using a quantum-Langevin approach and the exact Tonks-Girardeau solution in the impenetrable-boson limit, we determine the dynamical evolution of the particle-number imbalance, displaying an effective damping of the Josephson oscillations which depends on barrier height, interaction strength and temperature. We show that the damping originates from the quantum and thermal fluctuations intrinsically present in the strongly correlated gas. Thanks to the density-phase duality of the model, the same results apply to particle-current oscillations in a one-dimensional ring where a weak barrier couples different angular momentum states. |
| Date: | Tue, 29.05.2018 |
| Time: | 09:30 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Quantum Lyapunov Exponents |
| Speaker: | Victor Galitski |
| Abstract: | Classical chaotic systems exhibit exponential divergence of initially infinitesimally close trajectories, which is characterized by the Lyapunov exponent. This sensitivity to initial conditions is popularly known as the “butterfly effect.” Of great recent interest has been to understand how/if the butterfly effect and Lyapunov exponents generalize to quantum mechanics, where the notion of a trajectory does not exist. In this talk, I will introduce the measure of quantum chaoticity – so called out-of-time-ordered four-point correlator (whose semiclassical limit reproduces classical Lyapunov growth), and use it to describe quantum chaotic dynamics and its eventual disappearance in the standard models of classical and quantum chaos – Bunimovich billiard and standard map or kicked rotor. I will also mention our recent results on quantum Lyapunov exponent in interacting disordered metals |
| Date: | Tue, 29.05.2018 |
| Time: | 10:45 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Large scale dynamics of an interacting 1d Bose gas: hydrodynamics, particle-hole excitations and non-equilibrium steady states |
| Speaker: | Jacopo de Nardis |
| Abstract: | I will start with a review of the generalized hydrodynamic approach to compute the non-equilibrium dynamics of
an interacting integrable system. This is a large scale hydrodynamic description of the classical motion of particle-hole excitations
thorough the system. We will then see how the single particle-hole excitations can be used also to compute exactly the
dynamical correlations at small momentum on any equilibrium state.
Finally as an application of the method, I will show how the non-equilibrium steady state that emerges at the junction between
two interacting gases at different temperatures or density is a strongly correlated state with divergent response functions
and long range correlations. |
| Date: | Tue, 29.05.2018 |
| Time: | 11:30 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Discrete Gauging and Small E8 instantons in six dimensions |
| Speaker: | Prof. Amihay Hanany (Imperial College London) |
| Abstract: | The physics of tensionless strings in six dimensions poses a long standing challenge in theoretical physics.This talk discusses such objects in a system of multiple M5 branes places at an ALE singularity of types A or D.The world volume theory on the M5 branes has (0,1) supersymmetry in 6 dimensions with massless vector, tensor and hyper multiplets.There are two branches on the moduli space of vacuum configurations where scalar fields in tensor and hyper multiplets receive VEVs, respectively.We will focus on the Higgs branch and show that each time there is a new tensionless string,there is a new Higgs branch,thus the theory has a multitude of Higgs branches depending on the types of tensionless strings in the spectrum.There are two main effects: “discrete gauging” and “small instanton transitions” and a need to efficiently describe so many Higgs branches which arise.The main tool is.... |
| Date: | Tue, 29.05.2018 |
| Time: | 13:45 |
| Duration: | 60 min |
| Location: | TU Wien, Freihaus, SEM 136, 10. Stock, Wiedner Hauptstr. 8-10, 1040 Wien |
| Contact: | S. Fredenhagen, D. Grumiller, M. Sperling |
| Order-parameter statistics out-of-equilibrium in many-body quantum systems |
| Speaker: | Mario Collura |
| Abstract: | At the base of quantum mechanics is the statistical nature of measurements:
the result of measurements is indeed described by a probability distribution function (PDF),
and measuring the same observable in identical systems will give different outcomes in accordance with this distribution.
The PDF carries very detailed information about the system, going much beyond the simple average.
I will focus on the non-equilibrium dynamics of a fully polarised antiferromagnetic state under the unitary evolution induced by the XXZ Hamiltonian.
It turns out that, depending on the quantum phase whereto the post-quench Hamiltonian belongs, the PDF of the subsystem staggered magnetisation may
retain informations about the original order, thus acquiring a shape much different from a simple Gaussian distribution.
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| Date: | Tue, 29.05.2018 |
| Time: | 14:00 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Fluctuation-induced quantum Zeno effect |
| Speaker: | Alessio Chiocchetta |
| Abstract: | An isolated quantum gas with a local dissipative defect features a non-monotonic behaviour of the particle loss rate, which decreases when the strength of the dissipation exceeds a critical value.
This manifestation of this quantum-Zeno-like effect has been recently shown in experiments with cold atomic gases.
We investigate the effect of a local dissipative defect on a interacting one-dimensional fermionic system. We found that the low-energy properties are dramatically affected by the interaction: the loss rate of long-wavelength modes vanishes for an arbitrary strength of the dissipation. Remarkably, transport properties are found to be similar to the Kane-Fisher coherent impurity problem.
We substantiate these findings using both a RG-resummed perturbation theory and a low-energy Luttinger liquid description.
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| Date: | Tue, 29.05.2018 |
| Time: | 15:15 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Full counting statistics in the transverse field Ising model in and out of equilibrium |
| Speaker: | Stefan Groha |
| Abstract: | One of the basic principles of quantum mechanics is the statistical nature of measurements of observables. The
result of measurements is described by a probability distribution and measuring the same observable in identical
systems will give different outcomes in accordance with this distribution. The full probability distribution carries very
detailed information about the system and on top of expectation value encodes all fluctuations of the system. The talk will focus on full probability distributions in the transverse field Ising model in and out of equilibrium. |
| Date: | Tue, 29.05.2018 |
| Time: | 15:40 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Dipole Organization and Membrane Biophysics: A Tale of Two Studies |
| Speaker: | Amitabha Chattopadhyay (Centre for Cellular and Molecular Biology Hyderabad, India) |
| Abstract: | Biological membranes are complex assemblies of lipids and proteins that allow cellular compartmentalization and act as an interface, through which cells communicate with each other and with the external milieu. In physical terms, membranes can be treated as a complex oriented fluid which is a weakly coupled, non-covalent, and anisotropic assembly of molecules in two-dimensions, and can therefore be treated as soft matter.
In this lecture, I will focus on the application of red edge excitation shift (REES) and membrane dipole potential to explore organization and dynamics of membrane lipids and proteins. Both these phenomena are dependent on organization of membrane dipoles.
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| Date: | Tue, 29.05.2018 |
| Time: | 16:00 |
| Location: | Technische Universität Wien, Institut für Angewandte Physik, E134 yellow tower „B“, 5th floor, Sem.R. DB gelb 05 B (room number DB05L03), 1040 Wien, Wiedner Hauptstraße 8-10 |
| Contact: | Univ.Prof. Dr. Gerhard Schütz |
| Speaker: | Prof. Dieter Zeppenfeld (KIT) |
| Abstract: | The physics of vector boson scattering at hadron collliders like the LHC will be reviewed,
including QCD NLO corrections, which affect tagging jets. Deviations from SM expectations
are desrcibed by effective Lagrangians. As dimension-8 operators or higher are employed,
unitarization of the underlying vector boson scattering process becomes important
phenomenologically and has recently been implemented within the VBFNLO Monte Carlo
program.
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| Date: | Tue, 29.05.2018 |
| Time: | 16:15 |
| Duration: | 60 min |
| Location: | Fakultät für Physik, Erwin-Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock |
| Contact: | A. Hoang, M. Löschner |
| Time evolution of the bipartite entanglement in interacting integrable systems. |
| Speaker: | Maurizio Fagotti |
| Abstract: | We consider the dynamics of the entanglement entropies of bipartitions after global quantum quenches.
We review the behavior of the entropies in noninteracting models and present a revised semiclassical theory, which turns out to be fully predictive.
We discuss the generalizations to interacting systems and present new results, both in homogeneous and in inhomogeneous settings.
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| Date: | Wed, 30.05.2018 |
| Time: | 09:30 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Solution of a minimal model for many-body quantum chaos |
| Speaker: | Andrea de Luca |
| Abstract: | I will present a minimal model for quantum chaos in a spatially extended
many-body system. It consists of a chain of sites with nearest-neighbour
coupling under Floquet time evolution. Quantum states at each site span a
q-dimensional Hilbert space and the time evolution is specified as a random
circuit, which is random in space but periodic in time (Floquet). Each site
is coupled via a random matrix to its neighbour on one side during the
first half of the evolution period, and to its neighbour on the other side
during the second half of the period. I will introduce a diagrammatic
formalism useful to average the many-body dynamics over realisations of the
random matrices. This approach leads to exact expressions in the large-q
limit and sheds light on the universality of random matrices in many-body
quantum systems and the ubiquitous entanglement growth |
| Date: | Wed, 30.05.2018 |
| Time: | 10:45 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Quasiparticle Excitations with Tensor Network States |
| Speaker: | Laurens Vanderstraeten |
| Abstract: | In the last decade tensor networks have become one of the main variational methods for studying strongly-correlated quantum lattice systems in low dimensions. In particular, they provide an efficient parametrization for the ground state of these systems directly in the thermodynamic limit. We show that the tensor-network language can be extended to describe the quasiparticle excitations on top of these ground states as well. This method has proven to work extremely well for one-dimensional systems, and we show that it can be generalized to two dimensions as well. As such, our results provide the first simulation of dynamical properties using projected entangled-pair states. |
| Date: | Wed, 30.05.2018 |
| Time: | 11:30 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Out-equilibrium dynamics of quantum integrable models : what can we compute exactly ? |
| Speaker: | Eric Vernier |
| Abstract: | While quantum integrability has proved extremely successful as a tool to study the properties of many-body quantum systems, its application out of equlibrium has remained very challenging. In this talk I will discuss to which extent quantum integrability can be used to compute exactly the out-of-equilbrium dynamics of physical observables after a quantum quench. I will present the "boundary quantum transfer matrix" construction (developed in collaboration with Lorenzo Piroli and Balázs Pozgay), and its application to computing the dynamics of the Loschmidt echo and of local observables. This construction calls for a classification of "integrable initial states", which I will also discuss.
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| Date: | Wed, 30.05.2018 |
| Time: | 14:00 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Entanglement and diagonal entropies after a quench with no pair structure |
| Speaker: | Elena Tartaglia |
| Abstract: | In the study of quantum quenches, one generally considers initial states that produce a distribution of quasiparticle excitations with an opposite-momentum-pair structure. In this talk, we discuss the dynamical and stationary properties of the entanglement entropy after a quench from initial states which do not have such structure: instead of pairs of excitations, they generate $\nu$-plets of correlated excitations with $\nu > 2$. Looking at a system of non-interacting fermions on the lattice, we show that the standard semiclassical formula does not apply when prepared in such an initial state. We then propose a generalised picture which correctly describes the entanglement entropy evolution and perfectly matches the numerical data. |
| Date: | Wed, 30.05.2018 |
| Time: | 14:25 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Quantum many-body Kapitza phases of periodically driven spin systems |
| Speaker: | Alessio Lerose |
| Abstract: | As realised by Kapitza long ago, a rigid pendulum can be stabilised upside down by periodically driving its suspension point with tuned amplitude and frequency. While this dynamical stabilisation is feasible in a variety of instances in systems with few degrees of freedom, it is natural to search for generalizations to multi-particle systems. In particular, a fundamental question is whether, by periodically driving a single parameter in a many-body system, one can stabilise an otherwise unstable phase of matter against all possible fluctuations of its microscopic degrees of freedom. In this work we show that such stabilisation occurs in experimentally realisable quantum many-body systems: a periodic modulation of a transverse magnetic field can make ferromagnetic spin systems with long-range interactions stably trapped around unstable paramagnetic configurations |
| Date: | Wed, 30.05.2018 |
| Time: | 15:20 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Long-range topological insulators and weakened bulk-boundary correspondence |
| Speaker: | Luca Lepori |
| Abstract: | I describe the appearance of new types of insulators and
superconductors, not included in the famous ”ten-fold way classification”,
in fermionic quantum systems with long-range couplings. This study is
relevant for the physics of
some set-ups realized by trapped ions, superconductors with impurities
on the edges, ultracold lattices. |
| Date: | Wed, 30.05.2018 |
| Time: | 15:45 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
| Integrability for dynamics, topology and disorder. |
| Speaker: | Vladimir Gritsev |
| Abstract: | I will make an overview of our recent results in the field of integrable models:
I will discuss integrable Floquet systems, integrable interacting disordered model and
novel class of integrable 1D and Richardson-Gaudin systems. |
| Date: | Fri, 01.06.2018 |
| Time: | 11:00 |
| Location: | Erwin Schrödinger International Institute, Boltzmanngasse 9, 1090 Wien, Boltzmann lecture hall |
| Contact: | secr@esi.ac.at |
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