Q+ Hangout: Fernando G.S.L. Brandão


Q+ Hangout

We'd like to announce the next Q+ hangout and hope to see you there!

As usual, we will reserve space in the hangout itself for those watching as a group. Comment below to reserve a seat. The talk will be livestreamed for everyone else.

Title: Exponential decay of correlations implies area law

Quantum states of many particles are fundamental to our understanding of many-body physics. Yet they are extremely daunting objects, requiring in the worst case an exponential number of parameters in the number of subsystems to be even approximately described. How then can multi-particle states be useful for giving predictions to physical observables? The intuitive explanation is that physically relevant quantum states, defined as the ones appearing in nature, are usually much simpler than generic quantum states. In this talk I will discuss a recent result that gives further justification to this intuition.

The result shows that exponential decay of correlations, a physically motivated
restriction on the set of multi-particle quantum states, implies an area law for
the entanglement entropy of systems defined on a line, and thus also an efficient
classical description for such systems. The result can be seen as a rigorous
justification to the intuition that states with exponential decay of correlations,
usually associated with non-critical phases of matter, are simple to describe.

I will outline the main ideas in the proof, that relies on several previous tools
from quantum information theory, such as the state merging protocol, and that
can also be seen as providing a limitation to the phenomenon of data hiding in
quantum states.

Based on arXiv:1206.2947, joint work with Michal Horodecki.

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