# Difference between revisions of "Afternoon Session: Quantum Monte Carlo"

From ALPS

Line 12: | Line 12: | ||

** Anatoly Kuklov: ''Flowgram Method in QM'' | ** Anatoly Kuklov: ''Flowgram Method in QM'' | ||

** Matthias Troyer: ''The Sign Problem'' | ** 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 | ** Boris Svistunov |

## Revision as of 04:02, 4 May 2009

- 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

- Why large load imbalance for parallel tempering?
- 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

- More than one variable? Possible, but no examples where it helps significantly
- 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

- Where does it appear?
- Boris Svistunov

- Synge Todo: