Towards a manifestly SL(2,Z)-covariant action for the type IIB (p,q) super-five-branes

We determine a manifestly SL(2,Z)-covariant kappa-symmetric action for the type IIB (p,q) five-branes as a perturbative expansion in the world-volume field strengths within the framework where the brane tension is generated by a world-volume field. In this formulation the Lagrangian is expected to be polynomial; we construct the kappa-invariant action to fourth order in the world-volume field strengths.Comment: 9 pages, LaTeX2

Super-p-brane actions from interpolating dualisations

We review a recently proposed method for constructing super-p-brane world-volume actions. In this approach, starting from a democratic choice of world-volume gauge-fields guided by p-brane intersection rules, the requirements of kappa-symmetry and gauge invariance can be used to determine the corresponding action. We discuss the application of the method to some cases of interest, notably the (p,q)-5-branes of type-IIB string theory in a manifestly S-duality covariant formulation.Comment: 8 pages, LaTeX2e. Based on talks given by A.W. at QFTHEP'99, Moscow, 27 May-2 June 1999, and at the Third annual meeting of the EU TMR network `Quantum aspects of gauge theories, supersymmetry and unification', Paris, 1-7 September 199

Vacuum radiation and frequency-mixing in linear light-matter systems

Recent progress in photonics has led to a renewed interest in time-varying media that change on timescales comparable to the optical wave oscillation time. However, these studies typically overlook the role of material dispersion that will necessarily imply a delayed temporal response or, stated alternatively, a memory effect. We investigate the influence of the medium memory on a specific effect, i.e. the excitation of quantum vacuum radiation due to the temporal modulation. We construct a framework which reduces the problem to single-particle quantum mechanics, which we then use to study the quantum vacuum radiation. We find that the delayed temporal response changes the vacuum emission properties drastically: Frequencies mix, something typically associated with nonlinear processes, despite the system being completely linear. Indeed, this effect is related to the parametric resonances of the light-matter system, and to the parametric driving of the system by frequencies present locally in the drive but not in its spectrum.Comment: 16 pages + appendices, 3 figures. Accepted for publicatio

Staggered Ground States in an Optical Lattice

Non-standard Bose-Hubbard models can exhibit rich ground state phase diagrams, even when considering the one-dimensional limit. Using a self-consistent Gutzwiller diagonalisation approach, we study the mean-field ground state properties of a long-range interacting atomic gas in a one-dimensional optical lattice. We first confirm that the inclusion of long-range two-body interactions to the standard Bose-Hubbard model introduces density wave and supersolid phases. However, the introduction of pair and density-dependent tunnelling can result in new phases with two-site periodic density, single-particle transport and two-body transport order parameters. These staggered phases are potentially a mean-field signature of the known novel twisted superfluids found via a DMRG approach [PRA \textbf{94}, 011603(R) (2016)]. We also observe other unconventional phases, which are characterised by sign staggered order parameters between adjacent lattice sites.Comment: 11 pages, 7 figures, comments welcom

Synthetic Flux Attachment

Topological field theories emerge at low energy in strongly-correlated condensed matter systems and appear in the context of planar gravity. In particular, the study of Chern-Simons terms gives rise to the concept of flux attachment when the gauge field is coupled to matter, yielding flux-charge composites. Here we investigate the generation of flux attachment in a Bose-Einstein condensate in the presence of non-linear synthetic gauge potentials. In doing so, we identify the U(1) Chern-Simons gauge field as a singular density-dependent gauge potential, which in turn can be expressed as a Berry connection. We envisage a proof-of-concept scheme where the artificial gauge field is perturbatively induced by an effective light-matter detuning created by interparticle interactions. At a mean field level, we recover the action of a "charged" superfluid minimally coupled to both a background and a Chern-Simons gauge field. Remarkably, a localised density perturbation in combination with a non-linear gauge potential gives rise to an effective composite boson model of fractional quantum Hall effect, displaying anyonic vortices.Comment: 14 pages, 3 figures. Comments are welcom

Coherent control of light interaction with graphene

We report the experimental observation of all-optical modulation of light in a graphene film. The graphene film is scanned across a standing wave formed by two counter-propagating laser beams in a Sagnac interferometer. Through a coherent absorption process the on-axis transmission is modulated with close to 80% efficiency. Furthermore we observe modulation of the scattered energy by mapping the off-axis scattered optical signal: scattering is minimized at a node of the standing wave pattern and maximized at an antinode. The results highlight the possibility to switch and modulate any given optical interaction with deeply sub-wavelength films.Comment: 4 pages, 4 figure

Linked and knotted synthetic magnetic fields

We show that the realisation of synthetic magnetic fields via light-matter coupling in the Lambda-scheme implements a natural geometrical construction of magnetic fields, namely as the pullback of the area element of the sphere to Euclidean space via certain maps. For suitable maps, this construction generates linked and knotted magnetic fields, and the synthetic realisation amounts to the identification of the map with the ratio of two Rabi frequencies which represent the coupling of the internal energy levels of an ultracold atom. We consider examples of maps which can be physically realised in terms of Rabi frequencies and which lead to linked and knotted synthetic magnetic fields acting on the neutral atomic gas. We also show that the ground state of the Bose-Einstein condensate may inherit topological properties of the synthetic gauge field, with linked and knotted vortex lines appearing in some cases.Comment: 8 pages, 4 figures, supplementary videos attached. Comments welcom

Curved spacetime from interacting gauge theories

Phonons in a Bose–Einstein condensate can be made to behave as if they propagate in curved spacetime by controlling the condensate flow speed. Seemingly disconnected to this, artificial gauge potentials can be induced in charge neutral atomic condensates by for instance coupling two atomic levels to a laser field. In this work, we connect these two worlds and show that synthetic interacting gauge fields, i.e. density-dependent gauge potentials, induce a non-trivial spacetime structure for the phonons. Whilst the creation of effective horizons for phonons solely depends on the flow speed of the condensate, this allows for the creation of new spacetime geometries which can be easily designed by tuning the transverse laser phase. By exploiting this new degree of freedom we show that effectively charged phonons in 2+1 dimensions can be simulated, which behave as if they move under the influence of both a gravitational and an electromagnetic field

Quantum vacuum radiation in optical media

In this thesis we study quantum vacuum radiation. This is the radiation that is emitted due to changes of the electromagnetic vacuum in time. Specifically, we explore the phenomena in optical media at a macroscopic scale by introducing a time-dependent permittivity. We model this by inducing time varying changes to the medium’s resonance frequencies. To start with, we build a perturbative model, from which we learn that the physics of quantum vacuum radiation is well-described in terms of the collective light-matter excitations (polaritons) but that the retarded response of the matter degree of freedom should not be forgotten. In particular, the retarded response of the medium leads to quantum vacuum radiation that can be driven not only by frequencies supported by the spectrum of the modulation, but also local frequencies, such as the beating pattern of two waves. We then apply this model to analyse a fibre optics experiment where photon pair production was measured, and find a good agreement between the measured and predicted spectrum. Interestingly, the measured photon pair production coincide with quantum vacuum radiation driven by the beating pattern formed by a travelling polarisation wave and the spatial modulation of the fibre. Following this, we use the perturbative model to study a scenario mimicking a rapidly (∼optical timescales) expanding and contracting spacetime. In this scenario however, the probability to excite quantum vacuum radiation in naturally occurring materials is vanishingly small. Motivated partly by this, we turn to study vacuum radiation in man-made metamaterials, where large changes to the optical properties in time are possible. Specifically, we study an ε-near-zero metamaterial whose timedependent permittivity has been experimentally measured. In a model that neglects the retarded response of this metamaterial, we find that the quantum vacuum radiation becomes strongly peaked around the point where the real permittivity passes through zero. In order to extend the perturbative model to also include large changes to the optical properties in time, we finish this thesis by mapping macroscopic quantum electrodynamics to a trapped particle in a magnetic field. Using the intuition gained from this, we study a variety of non-perturbative settings including bichromatic periodic driving and return to ε-near-zero metamaterials. This confirms some of the previous analysis, as well as provides an intuitive explanation for the physics