Transmon platform for quantum computing challenged by chaotic
  fluctuations
From the perspective of many body physics, the transmon qubit architectures
currently developed for quantum computing are systems of coupled nonlinear
quantum resonators. A significant amount of intentional frequency detuning
(disorder) is required to protect individual qubit states against the
destabilizing effects of nonlinear resonator coupling. Here we investigate the
stability of this variant of a many-body localized (MBL) phase for system
parameters relevant to current quantum processors of two different types, those
using untunable qubits (IBM type) and those using tunable qubits (Delft/Google
type). Applying three independent diagnostics of localization theory -- a
Kullback-Leibler analysis of spectral statistics, statistics of many-body wave
functions (inverse participation ratios), and a Walsh transform of the
many-body spectrum -- we find that these computing platforms are dangerously
close to a phase of uncontrollable chaotic fluctuations.
Christoph Berke Evangelos Varvelis Simon Trebst Alexander Altland David P. DiVincenzo