Quantum Initiative: Quantum Lunch

The Quantum Lunch is regularly held on Thursdays in the Theoretical Division Conference Room, TA-3, Building 123, Room 121.

The organizing committee includes Malcolm Boshier (P-21), Lukasz Cincio (T-4), Diego Dalvit (T-4), Michael Di Rosa (C-PCS), Changhyun Ryu (P-21) , Nikolai Sinitsyn (T-4), Rolando Somma (T-4), Yigit Subasi (T-4), Christopher Ticknor (T-1), and Wojciech Zurek (T-4).

For more information, or to nominate a speaker, contact Yigit Subasi.

To add your name to the Quantum Lunch email list, contact Kacy Hopwood.

Thursday February 16, 2017
12:30 PM - 2:00 PM

Speaker: Jacek Dziarmaga (Uniwersytet Jagiellonski)

Technical Host: Lukasz Cincio

TOPIC: Quantum tensor networks at finite temperature

Abstract
Progress in describing finite-temperature phase transitions in strongly correlated quantum systems is obtained by noticing that the Gibbs operator for an infinite 2D lattice system can be represented by a 3D tensor network, the third dimension being the inverse temperature \beta. Coarse-graining the network along \beta results in a 2D projected entangled-pair operator (PEPO) with a finite bond dimension D. The coarse-graining is performed by a tree tensor network of isometries. The isometries are optimized variationally — taking into account full tensor environment — to maximize the accuracy of the PEPO. I will present benchmark results in the 2D quantum compass model, the Hubbard model at high temperature, the e_g orbital model, and the Hubbard model for spin-polarized fermions on a hexagonal lattice. Our results have similar accuracy as the best results obtained by conventional methods like quantum Monte Carlo or dynamical cluster approximation but, like all tensor networks, our unbiased method is also applicable where the sing problem makes the QMC fail.