08 April

A physicist introduction to quantum computing or quantum error correction as seen by a skeptic

Monday 08 April 2019, 12:00pm

ICN2 Seminar Hall, ICN2 Building, UAB

By Dr Xavier Waintal, CEA Grenoble, INAC/PHELIQS/GT

Abstract: Will quantum error correction save the quantum computer?

Quantum computers hold the promise of an exponential speed up of certain tasks with respect to classical computers. In this talk, I will review how such speed up is achieved and what it implies on the specifications that are required for the manipulation of the quantum states. I will stress that a quantum computer is inherently an analogue machine --- its internal state is described by continuous variables --- and that its computing power is not only set by its size but chiefly by its precision. Precision deteriorates with the number of operations; it is the chief resource of a quantum computer that sets the complexity of possible calculations. In the second part, I will discuss quantum error correction schemes that propose, to some extend, to trade precision with size: using several qubits, one can build a better, more precise, logical qubit. In theory, quantum error correction solves the problem of the extreme precision that is required by even the simplest realistic applications of quantum computing. In practice, quantum error correction implies massive overheads that make its applicability doubtful.

Hosted by: Prof. Stephan Roche, Theoretical and Computational Nanoscience Group Leader and Prof. Sergio Valenzuela, Physics and Engineering of Nanodevices Group Leader