arXiv subjects

Sascha Lang

Publications and source records attributed to Sascha Lang.

4 recordsLinked to original sources

arXiv2022

Ginzburg effect in a dielectric medium with dispersion and dissipation

As a quantum analog of Cherenkov radiation, an inertial photon detector moving through a medium with constant refractive index $n$ may perceive the electromagnetic quantum fluctuations as real photons if its velocity $v$ exceeds the medium speed of light $c/n$. For dispersive Hopfield type media, we find this Ginzburg effect to extend to much lower $v$ because the phase velocity of light is very small near the medium resonance. In this regime, however, dissipation effects become important. Via an extended Hopfield model, we present a consistent treatment of quantum fluctuations in dispersive and dissipative media and derive the Ginzburg effect in such systems. Finally, we propose an experimental test.

quant-ph↗

arXiv2021

Optical absorption and carrier multiplication at graphene edges in a magnetic field

We study optical absorption at graphene edges in a transversal magnetic field. The magnetic field bends the trajectories of particle- and hole excitations into antipodal direction which generates a directed current. We find a rather strong amplification of the edge current by impact ionization processes. More concretely, the primary absorption and the subsequent carrier multiplication is analyzed for a graphene fold and a zigzag edge. We identify exact and approximate selection rules and discuss the dependence of the decay rates on the initial state.

cond-mat.mes-hall↗

arXiv2020

Quantum radiation in dielectric media with dispersion and dissipation

By a generalization of the Hopfield model, we construct a microscopic Lagrangian describing a dielectric medium with dispersion and dissipation. This facilitates a well-defined and unambiguous $\textit{ab initio}$ treatment of quantum electrodynamics in such media, even in time-dependent backgrounds. As an example, we calculate the number of photons created by switching on and off dissipation in dependence on the temporal switching function. This effect may be stronger than quantum radiation produced by variations of the refractive index $Δn(t)$ since the latter are typically very small and yield photon numbers of order $(Δn)^2$. As another difference, we find that the partner particles of the created medium photons are not other medium photons but excitations of the environment field causing the dissipation (which is switched on and off).

quant-ph↗

arXiv2019

Analog of cosmological particle creation in electromagnetic waveguides

We consider an electromagnetic waveguide with a time-dependent propagation speed $v(t)$ as an analog for cosmological particle creation. In contrast to most previous studies which focus on the number of particles produced, we calculate the corresponding two-point correlation function. For a small step-like variation $δv(t)$, this correlator displays characteristic signatures of particle pair creation. As another potential advantage, this observable is of first order in the perturbation $δv(t)$, whereas the particle number is second order in $δv(t)$ and thus stronger suppressed for small $δv(t)$.

quant-ph↗