# Seminars

## IQI: Institute for Quantum Information Weekly Seminars

We invite experts to our weekly IQI Seminar Series to tell us about their recent research advances. We also hold more informal group meetings and sponsor IQI Workshops from time to time. Below is a calendar of these and other events of interest to the IQI community.

**TBD **

Lior Eldar, MIT

Tuesday,March 17, 2015 3:00 p.m. 107 Annenberg

TBD

**Information Causality, Szemeredi-Trotter, and algebraic variants
of CHSH **

Mohammad Bavarian, MIT

Tuesday, November 18, 2014, 3:00 p.m. 107 Annenberg

In this work, we consider the following family of two prover one-round games. In the CHSH_q game, two parties are given x,y in F_q uniformly at random, and each must produce an output a,b in F_q without communicating with the other. The players' objective is to maximize the probability that their outputs satisfy a+b=xy in F_q. This game was introduced by Buhrman and Massar (PRA 2005) as a large alphabet generalization of the celebrated CHSH game---which is one of the most well-studied two-prover games in quantum information theory, and which has a large number of applications to quantum cryptography and quantum complexity. Our main contributions in this paper are the first asymptotic and explicit bounds on the entangled and classical values of CHSH_q, and the realization of a rather surprising connection between CHSH_q and geometric incidence theory. On the way to these results, we also resolve a problem of Pawlowski and Winter about pairwise independent Information Causality, which, beside being interesting on its own, gives as an application a short proof of our upper bound for the entangled value of CHSH_q.

Joint work with Peter W. Shor.

**Entanglement in one-dimensional quantum systems **

Yichen Huang, UC Berkeley

Tuesday, October 14, 2014, 3:00 p.m. 107 Annenberg

Quantum entanglement, a concept from quantum information theory, has been widely used in condensed matter physics to characterize quantum correlations that are difficult to study using conventional methods. It provides unique insights into the physics of critical states and topological order. It is also quantitatively related to the difficulty of describing ground states using matrix-product-state representations in numerical approximations. In this talk, I will discuss some recent examples in these directions in the context of 1D quantum systems. I will focus on conceptual messages rather than technical perspectives.

Area law: Starting with a review of known rigorous results on the relation between gapped states, correlation decay, area law, and efficient matrix-product-state representations, I will discuss area law for Renyi entropy and possible generalizations in the presence of ground-state degeneracy.

Entanglement and topological order: It is argued that topological order is essentially a pattern of long-range entanglement. I will discuss a quantitative characterization of long-range entanglement using local quantum circuits. In particular, I will show that to generate a topologically ordered state from a product state a local quantum circuit of linear (in system size) depth is necessary and (up to small errors) sufficient.

Entanglement in critical disordered systems: Many-body localization studies how disorder leads to localized states in strongly correlated systems. It is a property associated with all eigenstates (not just the ground state) of disordered systems. I will show how to use entanglement for probing the singularities of all eigenstates.

References:

http://arxiv.org/abs/1403.0327

http://arxiv.org/abs/1401.3820

http://arxiv.org/abs/1405.1817

For a complete listing of IQI seminars from 2001 through April 2012, see the archived IQI web page

[IQI Seminar Schedule for 2013-14]

[IQI Seminar Schedule for 2012]

[IQI Archive - includes IQI Seminars from 2001 through September 2012]