Periodic Reporting for period 1 - SOUNDCONE (Scattering and Amplification of fundamental photonic-hydrodynamic excitations in Kerr non-linear media)
Reporting period: 2015-11-02 to 2017-11-01
The problem being investigated---Intense light beams propagating in nonlinear defocusing media behave identically to fluids. The governing evolution equations for small oscillations on top of the light beam are indeed the same as those for waves propagating on the surface of a fluid. This raises the fascinating perspective of studying fluid dynamics using light. These fluids made of light are referred to as `photon fluids' and have been shown to exhibit remarkable properties such as superfluidity and condensation (similar to Bose-Einstein condensation (BEC)). In this project we used photon fluids and gasses for a completely new and exciting application, namely for the creation of artificial flowing spacetime geometries otherwise thought to be the object of more complex and less (experimentally) accessible theories such as event horizons and expanding spacetimes.
The advantage of photon fluids over real fluids in this context is related to the great precision with which the fluid flow is determined by controlling the spatial phase profile of the laser beam. This allows us for example to also include angular momentum in our black holes, something that has never been done before. In essence, we study photon fluids with vorticity and look for novel effects including so-called superradiant amplification at the expense of the energy of the black hole. This effect has been predicted as a truly efficient mechanism by which energy may be extracted from a black hole yet has only very recently attracted experimental attentions.
This Project has developed these ideas and accounted for the full experimental complexity, thus paving the way for experiments that will also be carried out at the host institution.
These studies have also bridged the gap between BEC physics and photon fluid physics and in particular has focused on the presence of superfluidity within the photon fluid and novel methods for detecting related effects such as frictionless flow around obstacles.
Finally, we developed a quantised model of optical/ matter perturbations including dispersion and absorption applicable for a wide range of systems including for photon fluids, paving the way for the study of true quantum effects in these artificial fluids.
These studies have on the one the hand pushed the boundaries of general relativity applied to condensed matter systems and on the other paved the way for room-temperature superfluid physics.
The major scientific objectives were as follows:
-To understand if and under which conditions the photon fluid configurations which possess the necessary features for superradiant scattering (the analogue of an `ergo region' from gravitational terminology) are possible.
-To instigate a study of the elementary excitations on top of such a background flow, their dispersive and non-local dynamics and the possibility that `photonic sound waves' might be capable of being superradiantly scattered.
-Attain a detailed and working understanding/knowledge of the current experimental situation as pertains to the production and control of optical configurations necessary for the simulation of superradiance.
-Appropriately modify the current theoretical models for superradiance in order to describe experimentally feasible scenarios and conditions.
-Describe the optimal feasible experimental conditions required to sustain and observe other new physics predicted by the new analytic models.
-Formulate a workable quantum theory of elementary optical-matter excitations in the presence of dispersion and absorption.
All these objectives were achieved during the Project.
Importance of this work---The group of Prof. Faccio at HWU are in the process of building a world-wide centre of excellence for QFT analogues in Europe. The main challenge in this field is precisely the difficulty in bringing together state of the art QFT expertise with state of the art experiments and, most importantly, building a common knowledge base and language. This project therefore represented a unique opportunity to create a research environment that is missing in other groups worldwide and will be unique to this European group. As part of the scheduled research activities associated with this Project new technologies were required to manipulate and model optical systems in new ways and under new conditions that have not been achieved before due to their `extra-optical' underlying motivations. There is a possibility that such activities will result in patentable technologies in the future with the potential for wider implications in European society.
The advantage of photon fluids over real fluids in this context is related to the great precision with which the fluid flow is determined by controlling the spatial phase profile of the laser beam. This allows us for example to also include angular momentum in our black holes, something that has never been done before. In essence, we study photon fluids with vorticity and look for novel effects including so-called superradiant amplification at the expense of the energy of the black hole. This effect has been predicted as a truly efficient mechanism by which energy may be extracted from a black hole yet has only very recently attracted experimental attentions.
This Project has developed these ideas and accounted for the full experimental complexity, thus paving the way for experiments that will also be carried out at the host institution.
These studies have also bridged the gap between BEC physics and photon fluid physics and in particular has focused on the presence of superfluidity within the photon fluid and novel methods for detecting related effects such as frictionless flow around obstacles.
Finally, we developed a quantised model of optical/ matter perturbations including dispersion and absorption applicable for a wide range of systems including for photon fluids, paving the way for the study of true quantum effects in these artificial fluids.
These studies have on the one the hand pushed the boundaries of general relativity applied to condensed matter systems and on the other paved the way for room-temperature superfluid physics.
The major scientific objectives were as follows:
-To understand if and under which conditions the photon fluid configurations which possess the necessary features for superradiant scattering (the analogue of an `ergo region' from gravitational terminology) are possible.
-To instigate a study of the elementary excitations on top of such a background flow, their dispersive and non-local dynamics and the possibility that `photonic sound waves' might be capable of being superradiantly scattered.
-Attain a detailed and working understanding/knowledge of the current experimental situation as pertains to the production and control of optical configurations necessary for the simulation of superradiance.
-Appropriately modify the current theoretical models for superradiance in order to describe experimentally feasible scenarios and conditions.
-Describe the optimal feasible experimental conditions required to sustain and observe other new physics predicted by the new analytic models.
-Formulate a workable quantum theory of elementary optical-matter excitations in the presence of dispersion and absorption.
All these objectives were achieved during the Project.
Importance of this work---The group of Prof. Faccio at HWU are in the process of building a world-wide centre of excellence for QFT analogues in Europe. The main challenge in this field is precisely the difficulty in bringing together state of the art QFT expertise with state of the art experiments and, most importantly, building a common knowledge base and language. This project therefore represented a unique opportunity to create a research environment that is missing in other groups worldwide and will be unique to this European group. As part of the scheduled research activities associated with this Project new technologies were required to manipulate and model optical systems in new ways and under new conditions that have not been achieved before due to their `extra-optical' underlying motivations. There is a possibility that such activities will result in patentable technologies in the future with the potential for wider implications in European society.
During this project theoretical models for the study of the excitations in photon fluids have been developed. Previously only a very superficial theoretical framework was outlined. In contrast the models developed here take into account more complex aspects of the physics, aspects which are necessary to correctly model to match the results with any experimental work, for example, absorption, modified dispersion and the non-locality of optical beams. Indeed, the low level phenomenological models which exist in the current optics literature are tailored to the experimental conditions and therefore the accurate modelling of experimental complexities is necessary even to make contact with this existing literature. The new microscopic theory developed in this project is therefore a bridge between the traditional analogue gravity approach, which neglects all the inessential complexity for the sake of building the first interdisciplinary bridge, and the traditional non-linear optics approach which glosses over the precise nature of the wave interactions and equations of motion for the sake of remaining in the vicinity of what is immediate;y doable in practice in an experiment.
Specific models which have been developed in this project:
-Precise derivation of the full and exact perturbative equations of motion for fundamental photonic excitations in a non-linear medium for the `propagating geometry' type of photon fluid.
-Developed the theoretical tools necessary to study wave scattering of the particular (non-standard from a theory perspective) kind which exists in current experiments.
-A quantum theory of matter-photon interaction which is a hybrid between the fundamental`macroscopic QED' type approach familiar to high energy physicists and the `optical metric' type approach familiar to analogue gravity community.
Specific models which have been developed in this project:
-Precise derivation of the full and exact perturbative equations of motion for fundamental photonic excitations in a non-linear medium for the `propagating geometry' type of photon fluid.
-Developed the theoretical tools necessary to study wave scattering of the particular (non-standard from a theory perspective) kind which exists in current experiments.
-A quantum theory of matter-photon interaction which is a hybrid between the fundamental`macroscopic QED' type approach familiar to high energy physicists and the `optical metric' type approach familiar to analogue gravity community.
This project has gone beyond the previous state-of-the-art by providing a unique hybrid theoretical and numerical base which bridges between idealised theory and rough and complex experimental conditions. This kind of hybrid is rare if not non-existent in the literature where authors normally focus on a phenomenological approach describing experimental data or a purely theoretical approach, which is simplified to the extent in which an exact or highly digestible result can be obtained. Of course both of these approaches are necessary components in the experimental / theoretical discourse. However, during this project several interesting and new connections between superradiance and other topics have been uncovered precisely due to the desire to push the theory towards the experimental conditions. On top of this, a new theoretical development of the problem has needed to be formulated in order accurately model a real experiment. Thus this hybrid approach has led also to new purely theoretical developments themselves.