Chaos and complexity by design

Oct 16, 2016
77 pages
Published in:
  • JHEP 04 (2017) 121
  • Published: Apr 20, 2017
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Abstract: (Springer)
We study the relationship between quantum chaos and pseudorandomness by developing probes of unitary design. A natural probe of randomness is the “frame poten-tial,” which is minimized by unitary k-designs and measures the 2-norm distance between the Haar random unitary ensemble and another ensemble. A natural probe of quantum chaos is out-of-time-order (OTO) four-point correlation functions. We show that the norm squared of a generalization of out-of-time-order 2k-point correlators is proportional to the kth frame potential, providing a quantitative connection between chaos and pseudorandomness. Additionally, we prove that these 2k-point correlators for Pauli operators completely determine the k-fold channel of an ensemble of unitary operators. Finally, we use a counting argument to obtain a lower bound on the quantum circuit complexity in terms of the frame potential. This provides a direct link between chaos, complexity, and randomness.
Note:
  • 46+many pages, and all the figures too. v2: the director's cut -- more jokes, less typos
  • AdS-CFT Correspondence
  • Gauge-gravity correspondence
  • Random Systems
  • Holography and condensed matter physics (AdS/CMT)
  • unitarity: operator
  • chaos
  • correlation function