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- Coherence in logical quantum channels

In quantum error correcting codes, there is a distinction

between coherent and incoherent noise. Coherent noise can cause the

average infidelity to accumulate quadratically when a fixed channel is

applied many times in succession, rather than linearly as in the case

of incoherent noise. I will present a proof that unitary single qubit

noise in the 2D toric code with minimum weight decoding is mapped to

less coherent logical noise, and as the code size grows, the coherence

of the logical noise channel is suppressed. In the process, I will

describe how to characterize the coherence of noise using either the

growth of infidelity or the relation between the diamond distance from

identity and the average infidelity. I will explain how coherence in

the noise on physical qubits is transformed by error correction in

stabilizer codes. Then, I will sketch the proof that coherence is

suppressed for the 2D toric code. The result holds even when the

single qubit unitary rotation are allowed to have arbitrary directions

and angles, so long as the angles are below a threshold, and even when

the rotations are correlated. Joint work with John Preskill.

Collection/Series:

Event Type:

Seminar

Speaker(s):

Event Date:

Wednesday, August 28, 2019 - 16:00 to 17:30

Location:

Bob Room

Room #:

405

©2012 Perimeter Institute for Theoretical Physics