Please read these instructions before posting any event on Fermilab Indico

Indico search will be reestablished in the next version upgrade of the software:


This search is only for public events. Restricted events are not available.


IMPORTANT! Indico has been upgraded. Please let us know as soon as possible if you find any issues and email

22-28 July 2018
Kellogg Hotel and Conference Center
EST timezone

Phase Unwrapping and One-Dimensional Sign Problems

Jul 27, 2018, 2:20 PM
Centennial (Kellogg Hotel and Conference Center)


Kellogg Hotel and Conference Center

219 S Harrison Rd, East Lansing, MI 48824
Nonzero Temperature and Density Nonzero Temperature and Density


Mr Gurtej Kanwar (MIT)


Lattice QCD estimates of correlation functions with non-zero U(1) baryon number suffer from a well known signal-to-noise problem at large time separations. Previous work has shown that this can be attributed to a widening phase distribution over a circular domain, where standard estimators perform exponentially poorly as the distribution approaches uniform. We present a new approach to this problem: we apply phase unwrapping from the MRI and radar domains to translate the phase circular distribution to an "unwrapped phase" distribution over the reals. Applied to the simple harmonic oscillator as a toy model, unwrapping demonstrates no exponential signal-to-noise growth in time at leading order in a convergent cumulant expansion. We explore choices of unwrapping schemes and demonstrate precise ground-state energy estimates with a good scheme choice. Truncation error in the cumulant expansion is found to be highly sensitive to the choice of unwrapping scheme, indicating that more a robust family of schemes or choice of expansion is needed to apply this technique to non-trivial models. Arguments based on topological defects suggest that multidimensional unwrapping schemes should be more robust to regions of undersampling, motivating future work with spatially-resolved correlators in higher dimensions.

Primary authors

Presentation Materials