Quantum Diamonds

by Kathryn Zurek (Caltech)

Wednesday 7 Oct 2026, 14:00 → 15:00 Europe/Zurich

4/3-006 - TH Conference Room (CERN)

We consider the quantization of gravity at finite-sized causal horizons—causal diamonds--in 4-d Minkowski space.  Utilizing the covariant phase space, we identify the degrees-of-freedom that, upon canonical quantization, determine the commutators—one proportional to the area of the horizon and a second depending on a time shift operator.  We show that the area and time shift operators directly map to the soft graviton and Goldstone arising from the breaking of supertranslation symmetry.  We construct a density matrix describing the quantum state of the diamond in terms of these degrees-of-freedom, and show how the geometry fluctuates.  Lastly, since finite causal diamonds are measurable in experiments, we comment on how infrared effects might enter into observables in quantum gravity.