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Baby Universes from Thermal Pure States in the Sachdev-Ye-Kitaev Model
Martin Sasieta1, Brian Swingle2, Alejandro Vilar López3
1University of California, Leinweber Institute for Theoretical Physics, Berkeley, California 94720, USA.
Physical Review Letters
|August 10, 2026
Summary
We created a holographic model of a "baby" universe using two Sachdev-Ye-Kitaev (SYK) models. This model demonstrates a phase transition, revealing insights into black hole interiors and quantum gravity.
Area of Science:
- Theoretical physics
- Quantum gravity
- Holographic principle
Background:
- Jackiw-Teitelboim gravity describes a specific type of black hole spacetime.
- Sachdev-Ye-Kitaev (SYK) models are quantum mechanical models with applications in black hole physics and condensed matter systems.
- Holography suggests a connection between gravitational theories in higher dimensions and quantum field theories in lower dimensions.
Purpose of the Study:
- To construct a simple two-dimensional holographic model of a closed "baby" universe.
- To explore the holographic description of a black hole interior in Jackiw-Teitelboim gravity.
- To investigate the role of thermal phase transitions in holographic models.
Main Methods:
- Constructing a low-temperature thermal pure state from two coupled Sachdev-Ye-Kitaev (SYK) models.
- Utilizing a heavy matter operator to support the baby universe.
- Employing a Maldacena-Qi phase transition between black hole and anti-de Sitter phases.
Main Results:
- The holographic description of the baby universe is a thermal pure state of two SYK models.
- A first-order thermal phase transition occurs between a black hole phase and an empty anti-de Sitter phase.
- Bulk entanglement remains significant below the transition due to light bulk fields.
Conclusions:
- The model provides a novel holographic realization of a baby universe originating from a black hole interior.
- The study highlights the utility of SYK models and phase transitions in understanding quantum gravity and holography.
- Entanglement in this holographic context can be defined via coarse-graining over SYK couplings.
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