Quantum/Gravity Seminar Series
Unless otherwise noted, seminars take place at 11:15 am on Thursdays in Abelson 333.
Spring 2026 Seminars
January 15, 2026
Title:
"Filtering" CFTs at large N: Euclidean Wormholes, Closed Universes, and Black Hole Interiors
Abstract:
Despite its successes, the large-N holographic dictionary remains incomplete. Key features of gravitational path integrals--most notably Euclidean wormholes and the associated failure of factorization--lack a clear interpretation in the standard large-N framework. A related challenge is the possibility of erratic N-dependence in CFT observables, behavior with no evident semiclassical gravitational counterpart.
We argue that these puzzles point to a missing ingredient in the dictionary: a large-N filter. This filter projects out the erratic N-dependence of CFT quantities when mapping them to semiclassical bulk physics, providing an intrinsic boundary definition of gravitational "averages." It also offers a boundary explanation of wormhole contributions and a boundary prediction of their amplitudes, thereby giving a natural resolution of the factorization puzzle. In addition, we derive an infinite tower of inequalities constraining wormhole amplitudes and argue that internal wormholes do not induce random couplings in the low-energy effective theory.
Beyond resolving factorization, the large-N filter supplies a generalized framework from which richer Lorentzian spacetime structures can emerge, including closed universes and black hole interiors. We argue that, as a consequence of erratic large-N behavior, both closed universes and black hole interiors are quantum volatile, and that an AdS spacetime entangled with a baby universe is likewise quantum volatile. This volatility may allow an observer in AdS to infer the existence of the baby universe, whereas for an infalling observer, the ability to make measurements near a black hole horizon may become fundamentally limited--even if they may not live long enough to notice.
January 29, 2026
Title: Comments on the Hartle--Hawking state and quantum mechanics for de Sitter observers
Abstract: It has been argued that, for any fixed holographic theory, there exists only a single closed universe state in the fundamental description. We explore the consequences of this one-state statement in different contexts and point out the difference between AdS closed universe and de Sitter spacetime. We also make general comments on how quantum mechanics can be recovered for an observer living in de Sitter space. Time permitting, we’ll discuss calculations from a simple toy model.
February 5, 2026
Title: Haar random codes attain the quantum Hamming bound, approximately
Abstract: We study the error correcting properties of Haar random codes, in which a K-dimensional code space ⊆ ℂ^N is chosen at random from the Haar distribution. Our main result is that Haar random codes can approximately correct errors up to the quantum Hamming bound, meaning that a set of m Pauli errors can be approximately corrected so long as mK ≪ N. This is the strongest bound known for any family of quantum error correcting codes (QECs), and continues a line of work showing that approximate QECs can significantly outperform exact QECs.
Joint work with Fermi Ma and John Wright: https://arxiv.org/abs/2510.07158 [arxiv.org]
February 12, 2026
Title: Universal randomness in many-body dynamics
Abstract: I will talk about a recent series of works where we discover a universal form of randomness manifest by the simplest kind of quantum many-body dynamics: evolution under a time-independent Hamiltonian. Motivated by initial experimental observations, we find that under a very general set of conditions including evolution under local, physical Hamiltonians, the trajectory of a quantum state traces out a probability distribution over Hilbert space equal to the Haar ensemble deformed to satisfy energy conservation. This is known as the Scrooge ensemble, a family of probability distributions that reveal as little information as possible. This universal behavior allows for quantum information protocols to be adapted to analog quantum dynamics, including fidelity estimation and noise learning. If time permits, I will remark on ongoing work that studies the effect of symmetries on this universality.
Based on PRX 14, 041051 (2024), PRX 15, 031001 (2025), and upcoming work.
February 26, 2026
Title: Information-theoretic principle of emergent 1-form symmetries
Abstract: Higher-form symmetries act on sub-dimensional spatial manifolds of a quantum system. They can emerge as an exact symmetry at low energies even when they are explicitly broken at the microscopic level, making them difficult to characterize. In this work, we propose that the emergence of 1-form symmetries is information-theoretic in nature, precisely characterized by the preservation of information about how quantum states transform under the symmetry. As a consequence, the loss of the emergent 1-form symmetry is an information-theoretic transition which we argue to be revealed from the long-range entanglement in the ensemble of post-measurement states. We analytically determine the regimes in which a 1-form symmetry emerges in product states on one- and two-dimensional lattices. In analytically intractable regimes, we demonstrate how to efficiently detect 1-form symmetries with a global quantum error correction (QEC) decoder and numerically examine the information-theoretic transition of the 1-form symmetry, including systems with Z2 topological order. As a practical application of our framework, we show that once the 1-form symmetry is detected to exist, a topological quantum phase transition characterized by the spontaneous breaking of the 1-form symmetry can be accurately determined by a disorder parameter. We further argue that our proposed theory for emergent 1-form symmetries offers new perspectives on particle condensation and suggests sharp information-theoretic phase boundaries between Higgs and confining regimes in the Z2 lattice gauge theory.
March 19, 2026
March 26, 2026
April 16, 2026
April 23, 2026
April 30, 2026