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DTSTART;TZID=America/New_York:20231115T103000
DTEND;TZID=America/New_York:20231115T113000
DTSTAMP:20240222T105913Z
CREATED:20240222T105852Z
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UID:10002803-1700044200-1700047800@cmsa.fas.harvard.edu
SUMMARY:A bulk gap in the presence of edge states for a truncated Haldane pseudopotential
DESCRIPTION:Topological Quantum Matter Seminar \nSpeaker: Amanda Young\, UIUC \nTitle: A bulk gap in the presence of edge states for a truncated Haldane pseudopotential \nAbstract: Haldane pseudopotentials were first introduced as Hamiltonian models for the fractional quantum Hall effect\, and it has been long expected that they should exhibit the characteristic properties of this exotic phase of matter\, including a spectral gap above the ground state energy. We will discuss recent work that verified this gap conjecture for a truncated version of the 1/3-filled Haldane pseudopotential in the cylinder geometry. Numerical evidence suggested that for open boundary conditions the gap of the truncated model closes as the cylinder radius converges to zero and that this closure is due to the presence of edge modes; in contrast\, for periodic boundary conditions\, the gap remains robustly order one in the same radius limit. The standard scheme for applying spectral gap estimating techniques to the model with periodic boundary conditions\, though\, produces a lower bound on the bulk gap that still reflects the energy of the edge modes. To obtain an estimate on the bulk gap that reflects its true behavior\, a new gap estimating strategy was developed. By customizing the spectral gap method to key invariant subspaces of the Hamiltonian\, we are able to successfully avoid the edge states and produce a more accurate lower bound on the bulk gap. In this talk\, we discuss this invariant subspace strategy for proving bulk gaps in the presence of edge states. This is based off joint work with S. Warzel. \n  \n 
URL:https://cmsa.fas.harvard.edu/event/tqms_111523/
LOCATION:Virtual
CATEGORIES:Topological Quantum Matter Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Topological-Seminar-11.15.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20231120T140000
DTEND;TZID=America/New_York:20231120T150000
DTSTAMP:20240222T105558Z
CREATED:20240222T103744Z
LAST-MODIFIED:20240222T105558Z
UID:10002800-1700488800-1700492400@cmsa.fas.harvard.edu
SUMMARY:Emergent composite-fermion Luttinger liquid at the half-filled Landau level
DESCRIPTION:Topological Quantum Matter Seminar \nSpeaker: Prashant Kumar\, University of Chicago \nTitle: Emergent composite-fermion Luttinger liquid at the half-filled Landau level \nAbstract: The half-filled Landau level is a fascinating point in the phase diagram of quantum Hall effect that has been hypothesized to be a non-Fermi liquid where composite-fermions (CFs) emerge at low energies. In this talk\, I will present our numerical calculations of the excitation spectrum of this state on infinite cylinders. By comparing our results with a quasi-1D theory of CFs\, we show compelling quantitative evidence for the emergence of a Luttinger liquid of composite-fermions at low energies\, distinct from that of electrons. I will comment on some future directions.
URL:https://cmsa.fas.harvard.edu/event/tqms_112023/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Topological Quantum Matter Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Topological-Seminar-11.20.23-1.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20231129T170000
DTEND;TZID=America/New_York:20231129T180000
DTSTAMP:20240221T100813Z
CREATED:20240221T100735Z
LAST-MODIFIED:20240221T100813Z
UID:10002773-1701277200-1701280800@cmsa.fas.harvard.edu
SUMMARY:Anomalous Landau level analog in solids: search and implications for 2d heterostructures
DESCRIPTION:Topological Quantum Matter Seminar \nSpeaker: Valentin Crepel\, Flatiron Institute \nTitle: Anomalous Landau level analog in solids: search and implications for 2d heterostructures \nAbstract: The recent experimental observation of fractional Chen insulators — the analog of fractional quantum Hall states realized in absence of any applied magnetic field — calls for more detailed theoretical investigations of the special conditions allowing their emergence. To gain some insight on this problem\, we can rely on (i) our extensive knowledge of the physical properties of Landau levels\, and (ii) the identification of their exact solid state analogs. \nIn this talk\, (i-ii) will be discussed in the case of ”anomalous Landau levels”\, which are protected by an index theorem\, and whose most famous representative are the zero-th Landau levels of graphene. In particular\, I will derive the generic form of Bloch wave functions realizing the analog of such anomalous Landau levels\, and argue that twisted transition metal dichalcogenides homobilayers (in which fractional Chern insulators were first discovered) almost realize such anomalous bands.
URL:https://cmsa.fas.harvard.edu/event/tqms_112923/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Topological Quantum Matter Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Topological-Seminar-11.29.23.docx-1_Page_1.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20231201T163000
DTEND;TZID=America/New_York:20231201T173000
DTSTAMP:20240222T103010Z
CREATED:20240222T101228Z
LAST-MODIFIED:20240222T103010Z
UID:10002799-1701448200-1701451800@cmsa.fas.harvard.edu
SUMMARY:Quantum information: the interplay of mathematics and physics
DESCRIPTION:Topological Quantum Matter Seminar \nSpeaker: Kaifeng Bu (Harvard University) \nTitle: Quantum information: the interplay of mathematics and physics \nAbstract: I will provide an introduction to quantum information\, which points to a new connection with experiment on the one hand\, and a potential new area of mathematical analysis on the other. I will introduce two recent results about the application of this new area in quantum information: (1) a novel Quantum Central Limit Theorem (QCLT)\, and (2) a physically realizable protocol for testing and measuring quantum advantage. This talk is based on a collaboration with Arthur Jaffe\, and Weichen Gu (PNAS120(25)2023\, arXiv: 2302.08423\, arXiv:2306.09292). \n 
URL:https://cmsa.fas.harvard.edu/event/tqms_12123/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Topological Quantum Matter Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Topological-Seminar-12.01.23.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20231204T140000
DTEND;TZID=America/New_York:20231204T150000
DTSTAMP:20240226T112046Z
CREATED:20240226T112024Z
LAST-MODIFIED:20240226T112046Z
UID:10002869-1701698400-1701702000@cmsa.fas.harvard.edu
SUMMARY:The Fractional Quantum Hall Effect at ν=5/2: Past\, Recent\, and Future
DESCRIPTION:Topological Quantum Matter Seminar \nSpeaker:  Ken K. W. Ma (Northeastern University) \nTitle: The Fractional Quantum Hall Effect at ν=5/2: Past\, Recent\, and Future \nAbstract: The discovery of fractional quantum Hall (FQH) states started a new chapter in modern physics. Nowadays\, more than 70 FQH states at different filling factors have been observed. Among them\, the FQH state at the filling factor ν=5/2 in GaAs (or the 5/2 state) remains one of the most special and attractive states. Since its discovery in 1987\, different possible topological orders have been proposed to describe the 5/2 state. Some of them can host an exotic type of particles\, known as non-Abelian anyons. Recent experiments have provided more insights into the understanding of the 5/2 state\, but its underlying nature is still under debate. \nIn this talk\, I will review the basics of the 5/2 state [1] and a more unified theoretical description of different possible topological orders of the 5/2 state that we have recently proposed [2]. I will also review the groundbreaking thermal Hall conductance experiment [3] and the follow-up quantum Hall interface experiments by the Weizmann Institute group [4\, 5]\, and discuss what possible lessons that we can learn from the experimental results. Lastly\, I will talk about some possible directions and related topics for future investigations. \nReferences: \n[1] K. K. W. Ma\, M. R. Peterson\, V. W. Scarola\, and K. Yang\, “Fractional quantum Hall effect at the filling factor ν = 5/2” in Encyclopedia of Condensed Matter Physics (Second Edition)\, edited by T. Chakraborty\, Academic Press (2024).\n[2] K. K. W. Ma and D. E. Feldman\, “The sixteenfold way and the quantum Hall effect at half-integer filling factors”\, Phys. Rev. B 100\, 035302 (2019).\n[3] M. Banerjee\, M. Heiblum\, V. Umansky\, D. E. Feldman\, Y. Oreg\, and A. Stern\, “Observation of half-integer thermal Hall conductance”\, Nature (London) 559\, 205 (2018).\n[4] B. Dutta\, W. Yang\, R. Melcer\, H. K. Kundu\, M. Heiblum\, V. Umansky\, Y. Oreg\, A. Stern\, D. Mross\, “Distinguishing between non-Abelian topological orders in a quantum Hall system”\, Science 375\, 193 (2021).\n[5] B. Dutta\, V. Umansky\, M. Banerjee\, and M. Heiblum\, “Isolated ballistic non-Abelian interface channel”\, Science 377\, 1198 (2022). \n 
URL:https://cmsa.fas.harvard.edu/event/tqms_12423/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Topological Quantum Matter Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Topological-Seminar-12.04.23.png
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