Tue November 4, 2025 4:00 pm
CUA Seminar: Sarang Gopalakrishnan – Surprises in the weak-noise limit
Location:Harvard Ory Forum (301 A/B) in the Goel Building (60 Oxford)
Sarang Gopalakrishnan,
Princeton University
Ten Minute Talk:"TBD" by
David Spierings,
MIT
The coherent quantum dynamics of large systems is exponentially hard to simulate on a classical computer. However, noisy dynamics is asymptotically easy. Many physically relevant quantities (such as diffusion constants in generic systems) behave smoothly in the zero-noise limit, so the noiseless value can be efficiently computed by extrapolation: a strongly interacting many-body system “acts as its own bath,” so it is relatively insensitive to coupling to an outside environment. I will show that this extrapolation can fail even in classical hydrodynamics: under widely applicable assumptions, the diffusion constant changes discontinuously between zero noise and any finite noise. I will also introduce a family of simple correlation functions whose asymptotic behavior senses quantum coherence at arbitrary temperatures: they decay exponentially in the presence of noise and subexponentially in isolated systems, due to a mechanism we call diffusion-limited dephasing.