Bringing order through disorder: Localisation of errors in topological quantum memories

speaker: Jiannis Pachos (University of Leeds)

abstract: The ability to reliably store quantum states is an essential element for any task in quantum information. Topological systems promise to protect quantum information by topological and energetic considerations. If undesired anyonic excitations are propagated at large distances, either through coherent or probabilistic processes, they can cause logical errors in the topologically encoded information. Here we show that Anderson localisation induced by disorder in the system can successfully protect topological quantum memories from the coherent propagation of anyons. For concreteness we employ the toric code model at zero temperature. It is known that in the absence of a magnetic field it can tolerate a finite initial density of anyonic errors. In the presence of a spurious magnetic field anyonic quantum walks are induced and the tolerable density becomes zero. We demonstrate that disorder in the couplings of the model can successfully localise anyons. This allows the topological quantum memory to tolerate a finite initial density of anyonic errors for arbitrarily long times. We anticipate that disorder inherent in any physical realisation of topological systems will help to strengthen the fault-tolerance of quantum memories.

timetable:
Mon 16 May, 17:00 - 18:00, Aula Dini
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