arXiv subjects

Friedrich Koenig

Publications and source records attributed to Friedrich Koenig.

10 recordsLinked to original sources

arXiv2025

Backreactions from loading the stable photon sphere in Weyl conformal gravity

We investigate the accumulation of null matter at the stable photon sphere in the Mannheim-Kazanas metric, the analogue to the Schwarzschild solution in Weyl's conformal theory of gravity. In our toy problem in which we consider an infinitely-thin shell, we find that a jump in radial pressure ${T^r}_r$ is induced across the shell unless the shell has a radius of either the unstable or stable photon sphere radii. We then find that upon loading the stable photon sphere, its area remains invariant. Furthermore, at a critical threshold loading limit for this zero-width null matter shell, we are able to produce a metric containing an extremal horizon with an AdS$_2\times$S$^2$ geometry completely independent of the cosmological curvature. This hitherto unencountered and therefore unexpected result is a phenomenon unseen in standard nonconformal second-order metrics with nonzero cosmological constants.

gr-qc↗

arXiv2024

Quantum backreaction effect in optical solitons

Optical solitons classically are stationary solutions of the nonlinear Schr\"odinger equation. We perform a quantum field theoretic treatment by quantising a linearised fluctuation field around the classical soliton solution which can be seen as providing a background spacetime for the field. The linearised fluctuation modifies the soliton background, which is often neglected, reminiscent of the nondepleted-pump approximation. Going beyond this approximation and by using a number-conserving Bogoliubov approach, we find unstable modes that grow as the soliton propagates. Eventually, these unstable modes induce a considerable (backreaction) effect in the soliton. We calculate the backreaction in the classical field fully analytically in the leading second order. The result is a quadratic local decrease of the soliton photon number in propagation due to the backreaction effect of the unstable mode. Provided the initial pulse is close to the classical soliton solution, the unstable mode contributions always become dominant. We also consider practical scenarios for observing this quantum-induced soliton distortion, in the spectral domain. The backreaction, which we expect to be present in bright and dark, discrete and continuous solitons and other nonlinear pulses plays an important role in future optical analogue gravity experiments, for soliton lasers, and optical communications.

physics.optics↗

arXiv2024

Hyperboloidal Method for Quasinormal Modes of Non-Relativistic Operators

The recently reported compactified hyperboloidal method has found wide use in the numerical computation of quasinormal modes, with implications for fields as diverse as gravitational physics and optics. We extend this intrinsically relativistic method into the non-relativistic domain, demonstrating its use to calculate the quasinormal modes of the Schr\"odinger equation and solve related bound-state problems. We also describe how to further generalize this method, offering a perspective on the importance of non-relativistic quasinormal modes for the programme of black hole spectroscopy.

physics.comp-ph↗

arXiv2023

Quasinormal Modes of Optical Solitons

Quasinormal modes (QNMs) are essential for understanding the stability and resonances of open systems, with increasing prominence in black hole physics. We present here the first study of QNMs of optical potentials. We show that solitons can support QNMs, deriving a soliton perturbation equation and giving exact analytical expressions for the QNMs of fiber solitons. We discuss the boundary conditions in this intrinsically dispersive system and identify novel signatures of dispersion. From here, we discover a new analogy with black holes and describe a regime in which the soliton is a robust black hole simulator for light-ring phenomena. Our results invite a range of applications, from the description of optical pulse propagation with QNMs to the use of state-of-the-art technology from fiber optics to address questions in black hole physics, such as QNM spectral instabilities and the role of nonlinearities in ringdown.

physics.optics↗

arXiv2020

The next generation of analogue gravity experiments

This article is an introduction for a theme issue following a Scientific Discussion Meeting on \emph{The next generation of analogue gravity experiments} held at the Royal Society in December 2019. This theme issue comprises a collection of recent advances of the research programme, as well as their philosophical implications, that were presented at the meeting.

gr-qc↗

arXiv2020

Analytical description of quantum emission in optical analogues to gravity

We consider a moving refractive index perturbation in an optical medium as an optical analogue to waves under the influence of gravity. We describe the dielectric medium by the Lagrangian of the Hopfield model. We supplement the field theory in curved spacetime for this model to solve the scattering problem for all modes and frequencies analytically. Because of dispersion, the kinematic scenario of the field modes may contain optical event horizons for some frequencies. We calculate the spectra of spontaneous emission in the frame co-moving with the perturbation and in the laboratory frame. We also calculate the spectrally-resolved photon number correlations in either frame. The emitted multimode field comes in different types depending on the presence of horizons. We show that these types are robust against changes in the system parameters and thus are genuine features of optical and non-optical analogues. These methods and findings pave the way to new observations of analogue gravity in dispersive systems.

quant-ph↗

arXiv2020

The influence of spacetime curvature on quantum emission in optical analogues to gravity

Quantum fluctuations on curved spacetimes cause the emission of pairs of particles from the quantum vacuum, as in the Hawking effect from black holes. We use an optical analogue to gravity to investigate the influence of the curvature on quantum emission. Due to dispersion, the spacetime curvature varies with frequency here. We analytically calculate for all frequencies the particle flux, correlations and entanglement. We find that horizons increase the flux with a characteristic spectral shape. The photon number correlations transition from multi- to two-mode, with close to maximal entanglement. The quantum state is a diagnostic for the mode conversion in laboratory tests of quantum field theory on curved spacetimes.

gr-qc↗

arXiv2016

Pulse chirp increasing pulse compression followed by positive resonant radiation in fibers

Pulse self-compression followed by the generation of resonant radiation is a well known phenomenon in non-linear optics. Resonant radiation is important as it allows for efficient and tunable wavelength conversion. We vary the chirp of the initial pulse and find in simulations and experiments that a small positive chirp enhances the pulse compression and strongly increases the generation of resonant radiation. This result corroborates previously published simulation results indicating an improved degree of pulse compression for a small positive chirp [1]. It also demonstrates how pulse evolution can be studied without cutting back the fiber.

physics.optics↗

arXiv2015

Quantum vacuum emission from a refractive index front

A moving boundary separating two otherwise homogeneous regions of a dielectric is known to emit radiation from the quantum vacuum. An analytical framework based on the Hopfield model, describing a moving refractive index step in 1+1 dimensions for realistic dispersive media has been developed in [1]. We expand the use of this model to calculate explicitly spectra of all modes of positive and negative norm. Furthermore, for lower step heights we obtain a novel set of mode configurations. This leads to a realistic emission spectrum featuring black hole- and white hole emission for different frequencies. We also present spectra as measured in the laboratory frame that include all modes, in particular a dominant negative norm mode, which is the partner mode in any Hawking-type emission. We find that the emission spectrum is highly structured into intervals of emission with black hole-, white hole-, and no horizons. Finally we estimate the number of photons emitted as a function of the step height and find a power law of 2.5 for low step heights.

quant-ph↗

arXiv2002

Efficient generation of tunable photon pairs at 0.8 and 1.6 micrometer

We demonstrate efficient generation of collinearly propagating, highly nondegenerate photon pairs in a periodically-poled lithium niobate cw parametric downconverter with an inferred pair generation rate of 1.4*10^7/s/mW of pump power. Detection of an 800-nm signal photon triggers a thermoelectrically-cooled 20%-efficient InGaAs avalanche photodiode for the detection of the 1600-nm conjugate idler photon. Using single-mode fibers as spatial mode filters, we obtain a signal-conditioned idler-detection probability of about 3.1%.

quant-ph↗