Physical Society Colloquium

Building robust quantum computers — software approach

David Poulin

Université de Sherbrooke

Quantum computers have the potential to solve some outstanding computational problems efficiently, ranging from computing discrete logarithms (with application in code breaking) to the simulation of quantum many-body systems (with applications in condensed-matter physics, high energy physics, quantum chemistry, etc.). However, all physical implementations of quantum information processors are plagued by various sources of noise and imperfection. These cause errors in the computation that can build up to the point of completely randomizing the computer's output, making it totally useless. Some physical solutions — such as the use of topological order or other symmetry-protected operations — can be use to overcome some of these limitations. I this colloquium, I will present an alternative “software” solution to this problem that goes under the name of quantum error correction. Quantum error correction combines many noisy, imperfect systems to behave as fewer perfect systems. I will present a general introduction to this theory, emphasizing along the way some important connections to statistical physics, and give a detailed description of a particularly interesting class of quantum error-correcting codes, intimately related to topological order.