Department of Physics, National University of Singapore
Condensed Matter Seminar Series
To receive email notifications of this seminar series, please send an email to zouliujun@gmail.com to request.
Condensed Matter Seminar Series
To receive email notifications of this seminar series, please send an email to zouliujun@gmail.com to request.
Upcoming Seminars
(Both online and in-person seminars will be broadcast via Zoom.)
(Click the upper right corner of this page to see the previous seminars and their recordings.)
Time: 9am, October 2 2026, GMT+8
Location: Online
Zoom: https://nus-sg.zoom.us/j/88911975409?pwd=ixb7zXPuROkgclFcXZ2Wzh5vx6fmz4.1
Password: 835700
Speaker: Lei Gioia
Title: Disetangling the toric code
Abstract: Commuting-projector Hamiltonians with integer spectrum such as the 1+1d Ising ferromagnet and the 2+1d toric code may be regarded as the generators of non-on-site U(1) symmetries. In this talk we will answer whether these symmetries can be made “on-site”, i.e., disentangled, in the presence of finite and infinite-dimensional ancillae. In the finite-dimensional case, we will prove that the fractionalized excitations, such as domain walls and anyons, make it impossible to on-site these Hamiltonians. On the other hand, we will show that when infinite dimensional ancillae (e.g., rotors) are allowed, both the 1+1d Ising ferromagnet and the 2+1d toric code can be disentangled, yielding on-site symmetries. This is not in contradiction with the non-trivial ground state order of these Hamiltonians, since the ancilla Hamiltonians are no longer bounded from below and therefore do not have a well-defined ground state manifold. We will also construct exact short-range entangled eigenstates of the toric code Hamiltonian. Our results indicate agreement between lattice and quantum field theory anomalies in the presence of infinite-dimensional ancillae, while with finite-dimensional ancillae the obstruction to on-siteability may even be non-invertible.
[1] Lei Gioia, Salvatore D. Pace, Ruben Verresen, Shu-Heng Shao, Ryan Thorngren, arXiv:2609.XXXX (to appear Monday)
There is no seminar on October 9 because it is the NUS Well-Being Day.
Time: 9am, October 16 2026, GMT+8
Location: Online
Zoom: https://nus-sg.zoom.us/j/88911975409?pwd=ixb7zXPuROkgclFcXZ2Wzh5vx6fmz4.1
Password: 835700
Speaker: Rahul Sahay
Title: TBD
Abstract: TBD
Time: 9am, October 23 2026, GMT+8
Location: Online
Zoom: https://nus-sg.zoom.us/j/88911975409?pwd=ixb7zXPuROkgclFcXZ2Wzh5vx6fmz4.1
Password: 835700
Speaker: Ruizhi Liu
Title: TBD
Abstract: TBD
Time: 9am, October 30 2026, GMT+8
Location: Online
Zoom: https://nus-sg.zoom.us/j/88911975409?pwd=ixb7zXPuROkgclFcXZ2Wzh5vx6fmz4.1
Password: 835700
Speaker: Jacob Zavatone-Veth
Title: TBD
Abstract: TBD
Time: 9am, November 6 2026, GMT+8
Location: Online
Zoom: https://nus-sg.zoom.us/j/88911975409?pwd=ixb7zXPuROkgclFcXZ2Wzh5vx6fmz4.1
Password: 835700
Speaker: Gautam Greddy
Title: TBD
Abstract: TBD
Time: 9am, November 13 2026, GMT+8
Location: Online
Zoom: https://nus-sg.zoom.us/j/88911975409?pwd=ixb7zXPuROkgclFcXZ2Wzh5vx6fmz4.1
Password: 835700
Speaker: Linhao Li
Title: TBD
Abstract: TBD
The seminar series in the fall semester of 2026 is over, and the next seminar will take place in the spring semester of 2027.