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Physics Colloquium: Pedram Roushan, "Spectral signatures of many-body localization of interacting photons"

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Physics Colloquium: Pedram Roushan, "Spectral signatures of many-body localization of interacting photons"
When Sep 06, 2017
from 04:00 PM to 05:00 PM
Where MR418N
Contact Name
Contact Phone 212-650-5817
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Spectral signatures of many-body localization of interacting photons
Pedram Roushan
Google Inc., Santa Barbara, California

Statistical mechanics is founded on the assumption that a system can reach therma lequilibrium, regardless of the starting state.  Interactions between particles faciitate thermalization, but, can interacting systems always equilibrate regardless of parameter values? The energy spectrum of a system can answer this question and reveal the nature of the underlying phases. However, most experimental techniques only indirectly probe the many body energy spectrum. Using a chain of nine superconducting qubits, we implement a novel technique for directly resolving the energy levels of interacting photons. We benchmark this method by capturing the intricate energy spectrum predicted for 2D electrons in a magnetic field, the Hofstadter butterfly. By increasing disorder, the spatial extent of energy eigenstates at the edge of the energy band shrink, suggesting the formation of a mobility edge.  At strong disorder, the energy levels cease to repel one another and their statistics approaches a Poisson distribution -the hallmark of transition from the thermal to the many-body localized phase.  Our work introduces a new many-body spectroscopy technique to study quantum phases of matter.


Using 9 superconducting qubits, we simulate the problem of Bloch electrons on a 2D lattice subject to a perpendicularly applied magnetic field.  We directly measure the energy spectrum of the system, which was first calculated by Hofstadter and resembles a butterfly.