Common trends in non-Hermitian Physics: Black Holes and Quantum Optics

24 Mar 2025, 09:00 → 26 Mar 2025, 17:45 Europe/London

etc.venues Chancery Lane

Lionel London, Sarben Sarkar (Department of Physics)

This three-day physics workshop aims to explore the shared concepts and structures that emerge in non-Hermitian physics, with a particular focus on black hole perturbation theory and quantum optics. Through a carefully curated mix of research talks and collaborative brainstorming sessions, participants will have the opportunity to engage in cross-disciplinary discussions and identify new directions for inquiry.

The workshop is supported by the EPSRC (UK) through a grant ''PT symmetric field theory'' (with PI Sarben Sarkar).

Items of note:

• Dinner: Monday March 24th @ Masala Zone Covent Garden 
• See timetable for day-to-day schedule.
• Breakfast 8am to 9am.
• Contribute brainstorming topics/ideas here.

Monday, 24 March

09:20 → 09:35 Workshop Introduction

Workshop overview

This workshop is funded by the EPSRC (UK) through a grant ''PT symmetric field theory'' held in the Physics Department of King's College London (with Sarben Sarkar as PI). Its role is to relate the study of non-Hermiticity in two areas, black hole physics and quantum optics

Speakers: Lionel London, Sarben Sarkar (Department of Physics)

09:35 → 11:00 Input output formalism and other methods in quantum optics of much interest to the black hole community

Speaker: Dr Almut Beige

alm.pdf

11:00 → 11:30 Coffee break

11:35 → 12:20 Non-Hermitian Black Hole Physics I

Speaker: Lionel London

lionel-non-hermitian-review.pdf

12:25 → 13:10 Non-Hermitian Black Hole Physics II

Speaker: Dr Rodrigo Panosso Macedo

Hyperboloidal.pdf

13:15 → 14:15 Catered lunch

14:20 → 15:25 General working break

15:30 → 15:55 Non-hermitian quantum electrodynamics and photon localisation

Speaker: Dr Almut Beige

alm2.pdf

16:00 → 16:30 Coffee break

16:35 → 17:55 Brainstorming session

Review and questions and potential connections from the day's talks

19:30 → 21:50 Workshop dinner

Tuesday, 25 March

09:35 → 10:55 The Input output formalism & developments involving nonMarkovian effects I

Speaker: Sarben Sarkar (Department of Physics)

11:00 → 11:30 Coffee break

11:35 → 12:40 Loss of coherence and coherence protection from a graviton bath

Speaker: Sougato Bose (UCL)

12:45 → 13:10 General break

13:15 → 14:15 Catered lunch

14:20 → 15:20 On the Green's-function approach to deriving balance laws in perturbation theory

Speaker: Dr Adam Pound

15:25 → 15:55 Rotating black holes in the lab: ringdown and superradiance

Wave phenomena around spinning black holes can be simulated using rotating draining fluid flows. These are inherently leaky systems due to the presence of a central sink, through which fluid and waves escape. Over the past decade, these simulators have been used to study black hole ringdown and superradiance in the gravity laboratory at the University of Nottingham. In this talk, I will summarise these experiments and the subsequent theoretical investigations they sparked.

Speaker: Dr Sam Patrick

Rotating blak holes in the lab.pdf

16:00 → 16:30 Coffee break

16:35 → 17:55 Brainstorming

Wednesday, 26 March

09:30 → 10:25 The Input output formalism & developments involving nonMarkovian effects II

Speaker: Sarben Sarkar (Department of Physics)

10:30 → 10:55 Quasi-normal mode expansions of black hole perturbations: a hyperboloidal Keldysh's approach

We study asymptotic quasinormal mode expansions of linear fields propagating on a black hole background by adopting a Keldysh scheme for the spectral construction of the resonant expansions. This scheme requires to cast quasinormal modes in terms of a non-selfadjoint problem, something achieved by adopting a hyperboloidal scheme for black hole perturbations. The method provides a spectral version of Lax-Phillips resonant expansions, adapted to the hyperboloidal framework, and extends and generalises Ansorg & Macedo black hole quasinormal mode expansions beyond one-dimensional problems. We clarify the role of scalar product structures in the Keldysh construction that prove non-necessary to construct the resonant expansion, in particular providing a unique quasinormal mode time-series at null infinity, but are required to define constant coefficients in the bulk resonant expansion by introducing a notion of 'size' (norm). By (numerical) comparison with the time-domain signal for test-bed initial data, we demonstrate the efficiency and accuracy of the Keldysh spectral approach. Indeed, we are able to recover Schwarzschild black hole tails, something that goes beyond the a priori limits of validity of the method and constitutes one of the main results. We also demonstrate the critical role of highly-damped quasinormal mode overtones to accurately account for the early time behaviour. As a by-product of the analysis, Sobolev H^p pseudospectra are constructed and the convergence issues of the black hole quasinormal mode pseudospectra are clarified in agreement with Warnick’s theorem.

Speaker: Jerem Besson

presentation.pdf

11:00 → 11:30 Coffee break

11:35 → 13:10 Biorthogonality in quantum mechanics

Speaker: Dorje Brody

London_26_March_2025.pdf

13:15 → 14:15 Catered lunch

14:20 → 14:50 Merger-ringdown in the self-force approach

Speaker: Adam Pound

KCL2025.pdf

14:55 → 15:25 A new approach in classical Klein-Gordon cosmology

Speaker: Eleni Kontou (KCL)

Eleni Kontou.pdf

15:30 → 16:00 Coffee break

16:00 → 17:00 Brainstorming

17:05 → 17:25 Closing Remarks

Speakers: Lionel London, Sarben Sarkar (Department of Physics)