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November 20 - November 26
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  • 20
    November 20, 2022
    No events
  • 21
    November 21, 2022
    No events
  • 22
    November 22, 2022

    CMSA Quantum Matter in Mathematics and Physics: 3d gravity and gravitational entanglement entropy

    9:30 AM-11:00 AM
    November 22, 2022
    Recent progress in AdS/CFT has provided a good understanding of how the bulk spacetime is encoded in the entanglement structure of the boundary CFT. However, little is known about how spacetime emerges directly from the bulk quantum theory. We address this question in an effective 3d quantum theory of pure gravity, which describes the high temperature regime of a holographic CFT.  This theory can be viewed as a $q$-deformation and dimensional uplift of JT gravity.  Using this model, we show that the Bekenstein-Hawking entropy of a two-sided black hole equals the bulk entanglement entropy of gravitational edge modes.  These edge modes transform under a quantum group, which defines the data associated to an extended topological quantum field theory  Our calculation suggests an effective description of bulk microstates in terms of collective, anyonic degrees of freedom whose entanglement leads to the emergence of the bulk spacetime.  Finally, we give a proposal for obtaining the Ryu Takayanagi formula using the same quantum group edge modes.

    For information on how to join, please see: https://cmsa.fas.harvard.edu/event_category/quantum-matter-seminar/

  • 23
    November 23, 2022

    CMSA Topological Quantum Matter: Continuum field theory of graphene bilayer system

    9:00 AM-10:00 AM
    November 23, 2022
    CMSA, 20 Garden St, G10
    20 Garden Street, Cambridge, MA 02138

    The Bistritzer-MacDonald (BM) model predicted the existence of the narrow bands in the magic-angle twisted bilayer graphene (MATBG), and nowadays is a starting point for most theoretical works. In this talk, I will briefly review the BM model and then present a continuum field theory [1] for graphene bilayer system allowing any smooth lattice deformation including the small twist angle. With the gradient expansion to the second order, the continuum theory for MATBG [2] produces the spectrum that almost perfectly matches the spectrum of the microscopic model, suggesting the validity of this theory. In the presence of the lattice deformation, the inclusion of the pseudo-vector potential does not destroy but shift the flat band chiral limit to a smaller twist angle. Furthermore, the continuum theory contains another important interlayer tunneling term that was overlooked in all previous works. This term non-negligibly breaks the particle-hole symmetry of the narrow bands and may be related with the experimentally observed particle-hole asymmetry.

    1. O. Vafek and JK, arXiv: 2208.05933.
    2. JK and O. Vafek, arXiv: 2208.05953.

     

    For more information on how to join, please see: https://cmsa.fas.harvard.edu/event_category/topological-quantum-matter-seminar/

  • 24
    November 24, 2022
    No events
  • 25
    November 25, 2022
    No events
  • 26
    November 26, 2022
    No events