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SUMMARY:Criticality in noisy quantum systems
DTSTART:20260923T090000Z
DTEND:20260923T110000Z
DTSTAMP:20260917T111800Z
UID:indico-event-9444@scitalks.tifr.res.in
DESCRIPTION:Speakers: Subhayan Sahu (Perimeter Institute)\n\nIn this talk\
 , I will describe how quantum noise leads to genuinely non-equilibrium pat
 terns of quantum criticality. I study the effects of local measurements an
 d noise on the toric code ground state [1-3]\, which is topologically orde
 red\, long-range entangled\, and realises a quantum error-correcting code.
  Varying the local error probability leads to a noise-induced phase transi
 tion that coincides with the error-correction threshold. Such phase transi
 tions separate distinct mixed state phases of matter\, which are sharply d
 iagnosed via their information theoretic properties\, namely\, the conditi
 onal mutual information (CMI). The CMI defines a mixed state equivalent of
  the correlation length\, called the “Markov length”\, which diverges 
 at this noise-induced phase transition. Furthermore\, for the toric code u
 nder a particular error model\, I demonstrate the existence of an extended
  non-equilibrium critical phase. The universal properties of the phases an
 d the phase transitions can be mapped to a classical statistical mechanica
 l model of loop packing on the square lattice.Crucially\, the divergence o
 f Markov length distinguishes such noise-induced phase transitions from th
 ermal phase transitions\, where it always remains finite - a hallmark of e
 quilibrium. We uncover subtle signatures of such genuinely non-equilibrium
  criticality even in equilibrium thermal states. We study marginals of the
 rmal Gibbs states along sub dimensional manifolds\, such as their physical
  boundaries. While the bulk Markov length remains finite at thermal phase 
 transitions\, we show that the boundary Markov length generically diverges
  at bulk phase transitions [4]. Furthermore\, we relate the universal prop
 erties of the CMI to non-standard probes of the conformal field theory (CF
 T) describing these transitions\, with Ising and compact boson CFTs as our
  primary examples.[1] Negari\, SS\, Hsieh ArXiv 2307.02292 (PRB 2024)[2] N
 egari\, SS\, Behrends\, Béri\, Hsieh Arxiv 2601.10792 (PRX Quantum\, to a
 ppear)[3] Negari\, SS\, Behrends\, Béri\, Hsieh (in preparation)[4] SS\, 
 Zou\, Hsieh (in preparation)\n\nhttps://scitalks.tifr.res.in/event/9444/
LOCATION:A304 and on Zoom60
URL:https://scitalks.tifr.res.in/event/9444/
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