Scott Aaronson

Massachusetts Institute of Technology, USA

Scott Aaronson (left) with Renato Renner
Scott Aaronson (left) with Renato Renner

Date

27 May 2009

Host

Renato Renner

Title

How Much Information is in a Quantum State?

Abstract

People often talk about the quantum state of n entangled particles as if it contained an amount of information exponential in n. Sometimes, they draw the conclusion from this that quantum mechanics must be an "extravagant" theory valid only for simple systems or small numbers of particles, or that largescale quantum computing must be impossible in principle. In this talk, I'll survey how in the senses relevant for computation, prediction, and learning, quantum states actually don't behave as if they contain exponential amounts of information. Specifically, I'll discuss the limitations of "quantum advice states," the approximate "learnability" of quantum states from random measurement results, and a recently-discovered simulation of arbitrary quantum state preparation tasks by the preparation of ground states of local Hamiltonians. Some of the talk represents joint work with Andrew Drucker and Eyal Dechter.

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