Simons Collaboration on It from Qubit Annual Meeting 2020

This past year was the first full year of the renewed and reinvigorated It from Qubit (IFQ) Collaboration. While Covid-19 disrupted our schedule of in-person events, the strong collaborative network established over the previous four years proved resilient and productive. Longstanding IFQ projects continue to generate fundamental insights even as the new research projects established at renewal are off to an exciting start.

Some highlights of our research from the past year include:

• Following through on our promise to see if results established in the relatively tractable context of anti-de Sitter quantum gravity can be translated to universes more like our own, the information loss paradox as formulated by Hawking back in the 1970s has finally been laid to rest: information is preserved during the evaporation of Schwarzschild black holes in asymptotically flat spacetimes. 

• As quantum simulators based on arrays of Rydberg atoms and other technologies mature, the prospect of using these quantum many-body systems to test aspects of the emergence of quantum gravity is becoming more realistic. IFQ researchers have proposed near-term experiments using entangled quantum systems that would illustrate and generalize the traversable wormholes discovered in AdS/CFT. 

• Inspired by a conjectured relationship between information and energy flow in gravitational systems, IFQ researchers showed that there is a remarkable general constraint on energy flow that applies to any quantum system. The constraint proves a special case of the conjectured gravitational relationship and opens up new directions for exploring the relationships between energy and information. 

• New, tractable low-dimensional models of quantum gravity arising as ensemble averages over quantum systems have been established, providing alternatives to the remarkably fruitful Sachdev-Ye-Kitaev (SYK) model. As in SYK, the ability to solve both the bulk and boundary dynamics in these models provides rigorous examples of holographic duality. The increasing diversity of models makes it possible to test the broader validity of results. 

• The analog of Schrödinger’s cat in quantum gravity is a superposition of two macroscopically distinct spacetime geometries. Motivated by understanding the stability of such configurations, IFQ researchers discovered an amusing and important fact about all quantum cats: if one had the technological ability to detect the living and dead branches of a cat wave function, then one would necessarily also have the ability to bring a dead cat back to life! 


IFQ members continue to make progress on these and other problems. Inspired by the discovery of so-called ‘islands’ in evaporating black holes — regions behind the horizon that are related holographically to distant Hawking radiation — IFQ members are intensively studying the black hole interior from a quantum information viewpoint. These ideas are also being brought to bear on the stubborn problem of understanding quantum gravity in cosmological spacetimes. Quantum simulation of black holes is also a topic of intense interest; for example, it was recently discovered that a sparse version of the SYK model, which would be far easier to simulate than the full model, provides a new avenue for potentially feasible simulations of black holes. On the more mathematical side, IFQ members continue to study algebraic quantum field theory from an information-theoretic viewpoint, gaining new insights for example into global symmetries and symmetry breaking. This is just a sampling of the exciting work that continues to animate the IFQ Collaboration.

Patrick Hayden
Stanford University
Director’s Overview
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[See 2020 Collaboration Update Report above.]
 

Brian Swingle
Brandeis University
Chaos-Protected Locality
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We show that local signaling can coexist with fast scrambling and discuss possible implications for information dynamics outside black holes and for the emergence of sub-AdS scale locality.
 

Juan Maldacena
Institute for Advanced Study
The Entropy of Hawking Radiation
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When a black hole forms and evaporates, the entropy of the universe appears to rise. From quantum mechanics one would expect it to remain the same. Recently, the proper way to compute the entropy was understood. It involves a generalization of the Hawking-Bekenstein area formula that was suggested by Ryu and Takyanagi and further improved by others.

With this new method one obtains an answer which is consistent with unitarity.

Gravity and Quantum Mechanics Seen Through the Holographic Lens
Leonard Susskind, Ph.D.
Felix Bloch Professor of Theoretical Physics, Stanford University

4:45 – 5:00 PM ET Webinar waiting room opens
5:00 – 6:15 PM ET Talk + Q&A

Scientists often treat general relativity and quantum mechanics as separate subjects that don’t comfortably fit together. There is a tension, even a contradiction between them — or so one often hears. Leonard Susskind takes exception to this view. He thinks that the opposite is true. While it may be too strong to say that gravity and quantum mechanics are the same thing, the two are inseparable, and neither makes sense without the other.

In this lecture, Susskind will illustrate the quantum mechanical origins of gravitational phenomena such as the existence of wormholes, the growth of the geometry behind black hole horizons, and the most basic of all gravitational effects — the tendency for objects to fall toward massive bodies.

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