Classical and quantum fluid interfaces as simulators for gravity and the early Universe

Barroso Silveira, Vitor (2023) Classical and quantum fluid interfaces as simulators for gravity and the early Universe. PhD thesis, University of Nottingham.

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For the past few decades, gravity and early Universe analogue simulators have been used to experimentally replicate elusive processes and predictions of Quantum Field Theory (QFT) occurring on classical backgrounds of General Relativity using accessible physical systems, such as ultracold atoms, optical devices, and fluid surfaces. The analogies are typically devised by mapping the dynamics of small excitations on the analogue systems to the linear evolution of quantum fields on curved spacetimes. However, the territory of more intricate, interacting QFT problems remains largely unexplored by analogue simulations. This thesis extends the premises of gravity simulators on classical and quantum fluid interfaces to include non-linear processes and discusses suitable measurement schemes required for their development and experimental implementation.

We derive an effective field-theoretical description of the interfacial dynamics between two classical or quantum fluids. Our formalism can be used to systematically include non-linear terms in an effective Lagrangian for the interfacial height disturbances. This approach allows us to devise simulations for gravitational scenarios where scattering and decays are relevant, such as in the early Universe, and for fundamental phenomena of QFT in curved spacetimes (QFTCS). We then present a proof-of-principle non-linear Effective Field Theory (EFT) simulator in a classical liquid-liquid interface built to investigate the dynamical features of post-inflationary preheating. In this system, we show that suitable experimental control and repetition with a precise and accurate interfacial reconstruction enables the characterisation of the EFT through statistical measures, as previously realised in quantum simulators using Bose gases.

In our gravity simulators, the core physical observable is the interfacial height and measuring it is the utmost requirement for conducting experiments. Accordingly, we detail existing detection schemes and introduce a novel method based on Digital Holography. The latter is designed to reconstruct changes in the spatial profile of the interfacial height with unprecedented resolution and potential for applications at both room and low-temperature setups. Expanding on these measurement schemes, we generalise the particle detector concept in QFTCS to an analogue simulator. We specialise in a localised laser probe and consider its effective interaction with the analogue height field in thin films of superfluid helium-4. With this setup, we propose an experiment to extract the observer dependence in the response of a detector probing a thermal analogue field, in line with the circular-motion, finite-temperature Unruh effect.

Our experimental results show that liquid-liquid and liquid-gas interfaces, classical or not, hold great promise for analogue simulations tackling non-equilibrium gravitational scenarios and emulating fundamental aspects of QFTCS. Our work builds on the solid foundation laid by previous analogue black-hole and early Universe simulators to offer the stepping stones for a new generation of experiments using classical and quantum fluids that we anticipate will dive deeper into fundamental physics questions.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Weinfurtner, Silke
Keywords: mathematical physics, quantum field theory, curved spacetimes, fluid interfaces
Subjects: Q Science > QC Physics > QC170 Atomic physics. Constitution and properties of matter
Faculties/Schools: UK Campuses > Faculty of Science > School of Mathematical Sciences
Item ID: 76644
Depositing User: Barroso Silveira, Vitor
Date Deposited: 13 Dec 2023 15:39
Last Modified: 13 Dec 2023 15:39

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