Afternoon Session: Quantum Monte Carlo

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  • Chair: Boris Svistunov and Synge Todo
  • Speakers
    • Synge Todo: Parallel Monte Carlo
      • Why large load imbalance for parallel tempering?
        • Dependence of CPU time on temperature requires fine-tuning
      • Multi-canonical ensemble
        • Weight depends on global properties of the system
    • Simon Trebst: Extended statistical ensembles
      • More than one variable? Possible, but no examples where it helps significantly
        • Energy/temperature are good choices for thermal phase transitions
        • Ising: energy allone suffices, cannot get better than N^2 behaviour
    • Anatoly Kuklov: Flowgram Method in QM
    • Matthias Troyer: The Sign Problem
      • Where does it appear?
        • Bosonic systems: no
        • Fermions: exchanging fermions leads to sign problems
        • Bosons in a gauge field: phases
        • Frustrated magnets: exchange leads to sign problem
      • Can it be solved?
        • Basis-dependent!
        • In general: NP-hard & QMA-hard
        • Scaling with system size
      • Where does it come from?
        • Sampling with absolute value of the weights is equivalent to sampling bosons to learn about fermions
    • Boris Svistunov