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Colloquium

Topic:

Soft X-ray Spectroscopy of Quantum Materials

Date:

15.11.22

Time:

14:15

Place:

H6

Guest:

Prof. Kai Rossnagel

Universität Kiel

Abstract:

Contact person:

A. Hütten

Colloquium Mathematical Physics

Topic:

tba

Date:

04.11.22

Time:

16:15

Place:

D5-153

Guest:

Lisa Hartung

Universität Mainz

Abstract:

Contact person:

G. Akemann

Seminar High Energy Physics

Topic:

Mitigating the Hubbard Sign Problem. A Novel Application of Machine Learning

Date:

07.11.22

Time:

16:15

Place:

D6-135

Guest:

Marcel Rodekamp

FZ Jülich

Abstract:

Many fascinating systems suffer from a severe (complex action) sign problem preventing us from simulating them with Markov Chain Monte Carlo. One promising method to alleviate the sign problem is the transformation towards Lefschetz Thimbles. Unfortunately, this suffers from poor scaling originating in numerically integrating of flow equations and evaluation of an induced Jacobian. In this talk we present a Neural Network architecture based on complex-valued affine coupling layers. This network performs such a transformation efficiently, ultimately allowing simulation of systems with a severe sign problem. We test this method within the Hubbard Model at finite chemical potential, modelling strongly correlated electrons on a spatial lattice of ions.

Contact person:

O. Kaczmarek

Seminar Condensed Matter

Topic:

Assigning Temperatures to Eigenstates

Date:

04.11.22

Time:

14:15

Place:

D5-153

Guest:

Masudul Haque

TU Dresden

Abstract:

In formulating the statistical mechanics of isolated quantum systems, an inescapable issue is the definition of temperature, which is not a priori defined within closed-system quantum mechanics. We examine and compare different possible ways of assigning temperatures to energies, or equivalently, to eigenstates. The commonly used assignment of temperature is based on the canonical energy-temperature relationship, which depends only on energy eigenvalues and not on the structure of eigenstates. For eigenstates, we consider defining temperature by minimizing the distance between (full or reduced) eigenstate density matrices and canonical density matrices. We show that for full eigenstates, the minimizing temperature depends on the distance measure chosen, and matches the canonical temperature for the trace distance; however the two matrices are not close. With reduced density matrices, the minimizing temperature has fluctuations that scale with subsystem and system size but is apparently independent of distance measure, and in particular limits the two matrices become equivalent.

Contact person:

FOR2692/Jürgen Schnack

Seminar Mathematical Physics

Topic:

tba

Date:

01.12.22

Time:

16:00

Place:

D5-153

Guest:

José Gracia Bondia

University of Zaragoza, Spain

Abstract:

Contact person:

Gernot Akemann

Seminar AG Zufallsmatrizen

Topic:

Unitary matrix integrals, spectral form factors, and long range random walk models

Date:

05.10.22

Time:

09:00

Place:

ZOOM / Konferenzschaltung

Guest:

Ward Vleeshouwers

University of Amsterdam

Abstract:

Unitary matrix integrals over symmetric functions have a wide variety of applications, including quantum chaos, random processes, enumerative combinatorics, and number theory. In this talk, we derive various novel identities on such integrals, demonstrating universality of the spectral form factor for a broad class of matrix models. We then extend these results and apply them to correlation functions of long-range random walk models, leading to various surprising relations and dualities between them, as well convenient methods for their computation.

Contact person:

Leslie Molag



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  • | Letzte Änderung: 23.11.2011
  •  Olaf Kaczmarek
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