Simons Collaboration on It from Qubit Annual Meeting 2019
 Organized by

Matthew Headrick, Ph.D.Brandeis University

Patrick Hayden, Ph.D.Stanford University
Invitation Only
The 2019 annual meeting of It from Qubit: Simons Collaboration on Quantum Fields, Gravity, and Information will be devoted to recent developments at the interface of fundamental physics and quantum information theory, spanning topics such as chaos and thermalization in manybody systems and their realization in quantum gravity; traversable wormholes and their informationtheoretic implications; calculable lowerdimensional models of quantum gravity; the entanglement structure of semiclassical states in quantum gravity; complexity in field theory and gravity; the blackhole information puzzle; and applications of nearterm quantum devices to problems in highenergy physics.

Agenda
Thursday, December 5
8:30 AM CHECKIN & BREAKFAST 9:30 AM Matthew Headrick  Bit Threads and Holographic Entropy Inequalities 10:30 AM BREAK 11:00 AM Don Marolf  The Universal Structure of Holographic Quantum Codes 12:00 PM LUNCH 1:00 PM Vijay Balasubramanian  Quantum Complexity of Time Evolution with Chaotic Hamiltonians 2:00 PM BREAK 2:30 PM Poster Session  IFQ Postdocs 3:30 PM BREAK 4:00 PM Christine Muschik  How to Simulate Lattice Gauge Theories on Quantum Computers 5:00 PM DAY ONE CONCLUDES Friday, December 6
8:30 AM CHECKIN & BREAKFAST 9:30 AM Alex Maloney  De Sitter Quantum Gravity in 2 and 3 Dimensions 10:30 AM BREAK 11:00 AM Stephen Shenker  Black Holes, Random Matrices, Baby Universes and Dbranes 12:00 PM LUNCH 1:00 PM Jonathan Oppenheim  A PostQuantum Theory of Classical Gravity? 2:00 PM MEETING CONCLUDES 2:30 PM Continued Discussions @ Flatiron Institute 
Public Lecture
Simons Foundation Lecture
Wednesday, December 4, 2019Leonard Susskind, Stanford University
The Quantum Origins of Gravity
Tea 4:155:00 PM
Lecture 5:006:15 PMParticipation is optional; separate registration is required.

IAS Workshop on Qubits and Spacetime
Separate registration is required. Please click the link below for additional information:
https://www.sns.ias.edu/quantuminformationworkshop2019 
Abstracts
Matthew Headrick
Brandeis UniversityBit Threads and Holographic Entropy Inequalities
Entanglement entropies in holographic theories as computed by the RyuTakayanagi formula are known to obey many inequalities beyond those required of general quantum states. Headrick will explain how these special properties can be understood in the language of bit threads and what they might imply for the entanglement structure of the underlying states.
Don Marolf
University of California, Santa BarbaraThe Universal Structure of Holographic Quantum Codes
Don Marolf argues that the structure of holographic quantum codes is related to a simple splitting into two parts of the bulk gravitational path integrals. In particular, treating the bulk as an effective field theory means that we are given an effective Lagrangian \(L_\Lambda\) associated with a cutoff energy scale \(\Lambda\). We show that aspects of the code are then determined by classical computations involving \(L_\Lambda\), while the path integral over fluctuations below the scale \(\Lambda\) determines the states to be encoded. As a result, in each superselection sector, all such codes turn out to have flat entanglement spectrum up to corrections of order \(G\) (i.e., up to corrections of order \(G^2\) times the leading term, which is itself of order \(1/G\)). This statement holds for any \(L_\Lambda\), no matter what higher derivative terms it may contain. Marolf also comments on other applications of fixedarea states or more generally of states with fixed geometric entropy.
Vijay Balasubramanian
University of PennsylvaniaQuantum Complexity of Time Evolution with Chaotic Hamiltonians
Balasubramanian studies the quantum complexity of time evolution in largeN chaotic systems, with the SYK model as our main example. This complexity is expected to increase linearly for exponential time prior to saturating at its maximum value and is related to the length of minimal geodesics on the manifold of unitary operators that act on Hilbert space. Using the EulerArnold formalism, Balasubramanian demonstrates that there is always a geodesic between the identity and the time evolution operator e−iHt, whose length grows linearly with time. This geodesic is minimal until there is an obstruction to its minimality, after which it can fail to be a minimum either locally or globally. Balasubramanian identifies a criterion — the Eigenstate Complexity Hypothesis (ECH) — which bounds the overlap between offdiagonal energy eigenstate projectors and the klocal operators of the theory — and uses it to show that the linear geodesic will at least be a local minimum for exponential time. He shows numerically that the largeN SYK model (which is chaotic) satisfies ECH and thus has no local obstructions to linear growth of complexity for exponential time, as expected from holographic duality. In contrast, he also studies the case with N=2 fermions (which is integrable) and finds shorttime linear complexity growth followed by oscillations. His analysis relates complexity to familiar properties of physical theories, like their spectra and the structure of energy eigenstates, and has implications for the hypothesized computational complexity class.
Christine Muschik
University of WaterlooHow to Simulate Lattice Gauge Theories on Quantum Computers
Gauge theories are fundamental to our understanding of interactions between the elementary constituents of matter as mediated by gauge bosons. Muschik will talk about proposals for quantum simulations of gauge theories and their recent implementation on a trapped ion quantum computer. Considering onedimensional quantum electrodynamics, Muschik and collaborators addressed the realtime evolution of particleantiparticle pair production in a digital quantum simulation [Nature 534, 516519 (2016)] as well as hybrid classicalquantum algorithms [Nature 569, 355 (2019)] to simulate equilibrium problems. Muschik will also discuss recent results on extending this work beyond one spatial dimension.
Alex Maloney
McGill UniversityDe Sitter Quantum Gravity in 2 and 3 Dimensions
Maloney will discuss aspects of JT gravity in twodimensional nearly de Sitter (dS) spacetime and pure de Sitter quantum gravity in three dimensions. Both are essentially topological theories of gravity where it is possible to study precisely the wave function of the universe following the HartleHawking construction. The wave function can be computed by analytic continuation to Euclidean AdS, rather than the sphere; this allows us to compute all of the perturbative and (in two dimensions) nonperturbative corrections to the wave function and to formulate the theory as a Matrix integral and provides a connection with the quantization of the moduli space of Riemann surfaces.
Stephen Shenker
Stanford UniversityBlack Holes, Random Matrices, Baby Universes and Dbranes
The energy spectrum of generic large AdS black holes is discrete because their entropy is finite. The explanation for this is clear from the boundary field theory point of view in AdS/CFT — it is just the discrete spectrum of a bound quantum system. But the explanation for this discreteness from the bulk gravitational point of view remains a mystery. We will discuss some progress on a simpler related problem: the gravitational origin of the statistical properties of this discrete spectrum in an ensemble of quantum systems. Because black holes are quantum chaotic systems, we expect these statistics to be described by random matrix ensembles. Shenker’s analysis will focus on the simple model black hole described by the SachdevYeKitaev (SYK) model and, in particular, on its lowenergy limit, JackiwTeitelboim (JT) gravity. We will be led to consider an asymptotic expansion described by spacetime manifolds with an arbitrary number of handles and its completion by an analog of Dbranes. We will close by discussing some of the questions this analysis raises — based on joint work with Phil Saad and Douglas Stanford.
Jonathan Oppenheim
University College LondonA PostQuantum Theory of Classical Gravity?
Oppenheim presents a consistent theory of classical gravity coupled to quantum field theory. The dynamics are linear in the density matrix, completely positive and trace preserving, and reduce to Einstein’s equations in the classical limit. The constraints of general relativity are imposed as a symmetry on the equations of motion. The assumption that gravity is classical necessarily modifies the dynamical laws of quantum mechanics; the theory must be fundamentally stochastic involving finitesized and probabilistic jumps in spacetime and in the quantum field. Nonetheless, the quantum state of the system can remain pure, conditioned on the classical degrees of freedom. The measurement postulate of quantum mechanics is not needed since the interaction of the quantum degrees of freedom with classical spacetime necessarily causes collapse of the wave function. More generally, Oppenheim derives a form of classicalquantum dynamics using a noncommuting divergence, which has as its limit deterministic classical Hamiltonian evolution and which doesn’t suffer from the pathologies of the semiclassical theory. The theory can be regarded as fundamental or as an effective theory of QFT in curved space where backreaction is consistently accounted for.

Travel
Air and Train
Groups A & B
The foundation will arrange and pay for all air and train travel to the conference for those in Groups A and B. Please provide your travel specifications by clicking the registration link above. If you are unsure of your group, please refer to your invitation sent via email.Group C
Individuals in Group C will not receive financial support. Please register at the link above so we can capture your dietary requirements. If you are unsure of your group, please refer to your invitation sent via email.Personal Car
For participants in Groups A & B driving to Manhattan, the Roger Hotel offers valet parking. Please note there are no inandout privileges when using the hotel’s garage, therefore it is encouraged that participants walk or take public transportation to the Simons Foundation. 
Hotel
Participants in Groups A & B who require accommodations are hosted by the foundation for a maximum of three nights at The Roger hotel. Any additional nights are at the attendee’s own expense.
The Roger New York
131 Madison Avenue
New York, NY 10016
(between 30^{th} and 31^{st} Streets)To arrange accommodations, please register at the link above.
For driving directions to The Roger, please click here.

Contacts
Travel and Hotel Assistance
Belmys Hidalgo
Meetings Coordinator, Protravel
simons.foundation@protravelinc.com
Direct: 7862062734
Toll free: 8002847070 ext 2734
Afterhours number: 8008586319 ID Code A9J0General Meeting Assistance
Meghan Fazzi
Senior Executive Assistant, Simons Foundation
mfazzi@simonsfoundation.org
(212) 5246080