Andreas Weichselbaum

Brookhaven National Laboratory

Condensed Matter Physics and Materials Science Department
Bldg. 734
P.O. Box 5000
Upton, NY 11973-5000

(631) 344-3352
weichselbaum@bnl.gov

Expertise | Research | Education | Appointments | Highlights | Awards

Expertise

• Tensor network simulations for strongly-correlated quantum many-body systems
• QSpace tensor library for general abelian and non-abelian symmetries
• Symmetries and multi-channel/orbital/flavor systems in lattice models
• Quantum information and topological aspects of quantum many-body states
• Quantum impurity models with applications to dynamical mean field theory (DMFT)
• Dynamical properties of correlated systems

Research Activities

Collaborators

• Alexei Tsvelik (BNL)
• Robert Konik (BNL)
• Gabriel Kotliar (Rutgers)
• Jan von Delft (LMU, Munich, Germany)
• Oleg Yevtushenko (KIT Karlsruhe, Germany)
• Wei Li (Institute of Theoretical Physics, CAS, Beijing, China)
• Ireneusz Weymann (Poznan, Poland)

Education

• 2004 Ph.D. in theoretical condensed matter physics, at Ohio University (Athens, OH, USA).
• 1997 M.Sc. (Diploma) in experimental semiconductor physics at Johannes Kepler University (Linz, Austria).

Professional Appointments

• 2018-now  Staff scientist at Brookhaven National Lab, NY.
• 2015-2017  Heisenberg fellow at LMU, Munich (funded by DFG, WE-4819/2-1).
• 2011-2015  Independent researcher at LMU, Munich (funded by DFG WE-4819/1-1).
• 2008-2012  Venia docendi (Habilitation) at LMU, Munich
• 2008  Visiting researcher in the group of Prof. S.R. White at UC Irvine (USA).
• 2004-2008  Postdoctoral researcher at Ludwig Maximilians University (LMU, Munich, Germany).
• 1998-1999  Software Engineer at Voestalpine (Linz, Austria)

Research Highlights

Dimerization and spin decoupling in a two-leg Heisenberg ladder with frustrated trimer rungs, Andreas Weichselbaum, Weiguo Yin, and Alexei M. Tsvelik; Phys. Rev. B 103, 125120 (2021): Bringing together analytics and unbiased exact numerics with surprising results.

X-symbols for non-Abelian symmetries in tensor networks, Andreas Weichselbaum; Phys. Rev. Research 2, 023385 (2020): Tabulation of pairwise contraction in tensor network algorithms via so-called X-symbols, a versatile alternative to 6j symbols.

Exponential Thermal Tensor Network Approach for Quantum Lattice Models, Bin-Bin Chen, Lei Chen, Ziyu Chen, Wei Li, and Andreas Weichselbaum; Phys. Rev. X 8, 031082 (2018): simple elegant tensor network approach to thermal states by doubling the density matrix.

Unified phase diagram of antiferromagnetic SU(N) spin ladders, A. Weichselbaum, S. Capponi, P. Lecheminant, A. M. Tsvelik, and A. M. Läuchli; Phys. Rev. B 98, 085104 (2018): DMRG world record on keeping beyond millions of states in MPS simulations by exploiting SU(N) symmetries.

Non-abelian symmetries in tensor networks: A quantum symmetry space approach, Andreas Weichselbaum; Annals of Physics 327, 2972 (2012): general implementation of non-abelian symmetries in tensor network states: the QSpace tensor library v2.0

Sum-Rule Conserving Spectral Functions from the Numerical Renormalization Group, Andreas Weichselbaum, and Jan von Delft; Phys. Rev. Lett. 99, 076402 (2007): black-box algorithm based on complete basis sets for computing dynamical correlation functions within NRG.

Awards & Recognition

• Heisenberg fellow of the German Research Foundation (2015)
• Notable Alumni Award, Ohio University (2019)