arXiv subjects

Stefan Yoshi Buhmann

Publications and source records attributed to Stefan Yoshi Buhmann.

At least 19 recordsLinked to original sources

arXiv2026

Rotational Quantum Friction via Spontaneous Decay

A fascinating effect belonging to the field of vacuum forces and fluctuations is that of quantum friction. It refers to the prediction of a dissipative force acting on a moving object due to the quantum vacuum field. In this work, we investigate rotational quantum friction where a diatomic polar molecule rotates around its own center of mass in free space. We quantize the rotational motion and investigate the resulting dissipation due to spontaneous decay. We find in the Markovian regime that a friction torque $\propto Ω^3$ persists even for zero temperature, and in agreement with the classical result in the limit of large rotational quantum number $l$. Within the non-Markovian short-time regime we find a friction $\proptoΩ$.

quant-ph↗

arXiv2026

Optimally driving multi-photon transitions in the perturbative single-mode regime

The rate of $m$-photon transitions in matter, induced by an incident light field, depends on the field's $m$th order coherence function. Consequently, the coherence properties of the light field may be shaped to increase the rate of multi-photon transitions. Here, we determine the optimal state of a weak fixed-intensity, narrow-band incident light field, with a restricted maximal photon number, that optimally drives $m$-photon transitions in the case of a short-lived atomic multilevel system. We show that, in this case, no quantum properties of the light field need to be exploited, but that classical mixtures of coherent states are optimal.

quant-ph↗

arXiv2025

Time-periodic driving of a bath-coupled open quantum gas of light

We study the frequency-resolved density response of a photon Bose-Einstein condensate coupled to a bath of dye molecules by time-periodic driving. By monitoring the photon number dynamics for different drive frequencies, we obtain the spectral response of the condensate in a phase-sensitive way. We find that as the photon number increases, the response of the coupled condensate-bath system transitions from overdamped to resonant behavior, indicating a transition from closed to open system dynamics. Our spectroscopy method paves the way for studies of collective excitations in complex driven-dissipative systems.

cond-mat.quant-gas↗

arXiv2025

Spectroscopic footprints of quantum friction in nonreciprocal and chiral media

We investigate how the quantum friction experienced by a polarizable atom moving with constant velocity parallel to a planar interface is modified when the latter consists of chiral or nonreciprocal media, with special focus on topological insulators. We use macroscopic quantum electrodynamics to obtain the velocity-dependent Casimir-Polder frequency shift and decay rate. These results are a generalization to matter with time-reversal symmetry breaking. We illustrate our findings by examining the nonretarded and retarded limits for five examples: a perfectly conducting mirror, a perfectly reflecting nonreciprocal mirror, a three-dimensional topological insulator, a perfectly reflecting chiral mirror and an isotropic chiral medium. We find different asymptotic power laws for all these materials. Interestingly, we find two bridges between chirality and nonreciprocity through the frequency shift that arise as a consequence of the magnetoelectric coupling. Namely, the position-dependent Casimir-Polder frequency shift for the nonreciprocal case depend on a geometric magnetic field associated with photoionization of chiral molecules, the Casimir-Polder depending on the velocities for the chiral case have the optical rotatory strength as the atomic response while those for the nonreciprocal case depend on an analog of the optical rotatory strength.

quant-ph↗

arXiv2025

Photoelectron circular dichroism of a chiral molecule induced by resonant interatomic Coulombic decay from an antenna atom

We show that a nonchiral atom can act as an antenna to induce a photoelectron circular dichroism in a nearby chiral molecule in a three-step process: The donor atom (antenna) is initially resonantly excited by circularly polarized radiation. It then transfers its excess energy to the acceptor molecule by means of resonant interatomic Coulombic decay. The latter finally absorbs the energy and emits an electron which exhibits the aforementioned circular dichroism in its angular distribution. We study the process on the basis of the retarded dipole--dipole interaction and report an asymptotic analytic expression for the distance-dependent chiral asymmetry of the photoelectron as induced by resonant interatomic Coulombic decay for random line-of-sight and acceptor orientations. In the nonretarded limit, the predicted chiral asymmetry is reversed as compared to that of a direct photoelectron circular dichroism of the molecule.

physics.atm-clus↗

arXiv2025

Experimentally separating vacuum fluctuations from source radiation

The unique distinction between vacuum-field and source-radiation induced effects in processes such as the Lamb shift, Casimir forces or spontaneous emission, remains unresolved even at the theoretical level, and an experimental approach was never considered feasible [1-4]. In 1932, Fermi introduced the two-atom problem, which is a Gedanken-experiment that explores how two atoms interact with the surrounding electromagnetic field via vacuum and source-radiation induced processes, providing fundamental insights into the behavior of quantum fields [5-9]. Recent advancements in ultrafast optics have enabled experimental analogues of this system using two laser pulses inside a nonlinear crystal [10-12]. Here, we demonstrate the detection of vacuum and source radiation induced correlations, separated by their causal properties, between two laser pulses. In particular, we show that vacuum fluctuations and source radiation correlate different quadratures of near-infrared laser pulses, allowing them to be individually probed through phase-sensitive detection. This result provides an experimental verification of the time-domain fluctuation-dissipation theorem at the quantum level and offers a novel path to studying quantum radiation effects in time-dependent media. Beyond resolving a longstanding theoretical ambiguity, our findings open new possibilities for investigating quantum field phenomena in the context of relativistic quantum information such as entanglement harvesting from the quantum vacuum or quantum field detection in analogues of curved space-times.

quant-ph↗

arXiv2024

Strong coupling of a chiral molecule with circularly polarised modes inside a cavity

We consider the discriminatory interaction of a chiral molecule with circularly polarised modes inside a cavity. Starting from a generalised Jaynes--Cummings model that includes both electric and magnetic dipole couplings, we derive the Rabi frequency and associated Casimir--Polder potential for a cavity with a single mode of given handedness. One finds that both acquire a discriminatory component whose sign depends on the relative handedness of molecule and cavity mode. We generalise this result to a cavity that supports two modes of different handedness on the basis of superradiant collective field states.

quant-ph↗

arXiv2024

Vavilov-Cherenkov radiation for parallel motion in three-dimensional topological insulators

Our study delves into the modifications observed in Vavilov-Cherenkov radiation when its generating charged particle moves parallel to an interface formed by two generic magnetoelectric media, focusing on topological insulators. We compute the electromagnetic field through the Green's function. Applying the far-field approximation and the steepest descent method, we derive analytical expressions for the electric field, revealing contributions from spherical and lateral waves with topological origins. Subsequently, we analyze the angular distribution of the radiation, particularly focusing on parallel motions in close proximity to the interface. Our findings indicate that the radiation along the Vavilov-Cherenkov cone is inhomogeneous and asymmetric. We analyze the radiated energy at both sides of the interface. Finally, we discuss the particle's retarding force, which is notably enhanced in the ultrarelativistic regime. We illustrate these results for the topological insulator TlBiSe$_2$ and the magnetoelectric TbPO$_4$.

cond-mat.mes-hall↗

arXiv2024

Quantized Embedding Approaches for Collective Strong Coupling -- Connecting ab initio and macroscopic QED to Simple Models in Polaritonics

Collective light-matter interactions have been used to control chemistry and energy transfer, yet accessible approaches that combine ab initio methodology with large many-body quantum optical systems are missing due to the fast increase in computational cost for explicit simulations. We introduce an accessible ab initio quantum embedding concept for many-body quantum optical systems that allows to treat the collective coupling of molecular many-body systems effectively in the spirit of macroscopic QED while keeping the rigor of ab initio quantum chemistry for the molecular structure. Our approach fully includes the quantum fluctuations of the polaritonic field and yet remains much simpler and more intuitive than complex embedding approaches such as dynamical mean-field theory. We illustrate the underlying assumptions by comparison to the Tavis--Cummings model. The intuitive application of the quantized embedding approach and its transparent limitations offer a practical framework for the field of ab initio polaritonic chemistry to describe collective effects in realistic molecular ensembles.

quant-ph↗

arXiv2024

Photonic Bose-Einstein condensation in the continuum limit

We investigate the properties of the photon Bose-Einstein condensate in the limit of small mode spacing. Alongside the well-known threshold of the phase transition at large mode spacings, we find an emergence of a second threshold for sufficiently small mode spacings, defining the crossover to a fully condensed state. Furthermore, we present our findings for the mode occupations in the precondensate or supercooling region towards the continuum limit.

cond-mat.quant-gas↗

arXiv2023

Probing Vacuum Field Fluctuations and Source Radiation Separately in Space and Time

Source radiation (radiation reaction) and vacuum-field fluctuations can be seen as two inseparable contributions to processes such as spontaneous emission, the Lamb shift, or the Casimir force. Here, we propose how they can be individually probed and their space-time structure revealed in electro-optic sampling experiments. This allows to experimentally study causality at the single photon level and to reveal space- and time-like correlations in the quantum vacuum. A connection to the time-domain fluctuation-dissipation theorem is also made.

quant-ph↗

arXiv2022

Purcell-induced suppression of superradiance for molecular overlayers on noble atom surfaces

We study the impact of an environment on the electromagnetic responses of a molecule in the presence of a dielectric medium. By applying the dipole-dipole coupling between the molecule's and the environment's degrees of freedom, we can reduce the complex system into its components and predict excitation lifetimes of single and few molecules attached to a dielectric surface by knowing the entire quantum-mechanical properties of the molecules, such as transition energies and dipole moments. The derived theory allows for the description of superradiance between two molecules depending on the geometric arrangement between both concerning their separation and orientation with respect to each other. We analyse the possibility of superradiance between two molecules bound to a dielectric sphere and determine a change of the relevant length scale where the usually considered wavelength in free space is replaced with the binding distance, drastically reducing the length scales at which collective effects can take place.

quant-ph↗

arXiv2022

Macroscopic quantum electrodynamics theory of resonance energy transfer involving chiral molecules

Resonance energy transfer between chiral molecules can be used to discriminate between different enantiomers. The transfer rate between chiral molecules consists of a non-discriminatory and discriminatory parts. We derive these two rate contributions in the framework of macroscopic quantum electrodynamics. We show that their ratio is usually larger in the retarded regime or far-zone of large separation distances and that the degree of discrimination can be modified when considering a surrounding medium. We highlight the importance of local field effects onto the degree of discrimination and predict for general identical chiral molecules the optimum dielectric medium for discrimination. We apply our results on to 3-methylcyclopentanone and show that exotic media can even invert the discriminatory effect.

quant-ph↗

arXiv2022

Shape optimizations for body-assisted light-matter interactions

We implement a shape optimization algorithm for body-assisted light-matter interactions described by the formalism of macroscopic quantum electrodynamics. The approach uses the level-set method to represent and incrementally evolve dielectric environments. Utilizing finite-difference time-domain techniques we demonstrate the ability of the algorithm by optimizing the rate of resonance energy transfer in two dimensions. The resulting geometries enhance the transfer rate by several orders of magnitude.

quant-ph↗

arXiv2022

Quantized fields for optimal control in the strong coupling regime

We tailor the quantum statistics of a bosonic field to deterministically drive a quantum system into a target state. Experimentally accessible states of the field achieve good control of multi-level or -qubit systems, notably also at coupling strengths beyond the rotating-wave approximation. This extends optimal control theory to the realm of fully quantized, strongly coupled control and target degrees of freedom.

quant-ph↗

arXiv2022

Modification of transition radiation by three-dimensional topological insulators

We study how transition radiation is modified by the presence of a generic magnetoelectric medium with a special focus on topological insulators. To this end, we use the Green's function for the electromagnetic field in presence of a plane interface between two topological insulators with different topological parameters, permittivities and permeabilities. We employ the far-field approximation together with the steepest descent method to obtain approximate analytical expressions for the electromagnetic field. Through this method we find that the electric field is a superposition of spherical waves and lateral waves. Contributions of both kind can be attributed to a purely topological origin. After computing the angular distribution of the radiation, we find that in a region far from the interface the main contribution to the radiation comes from the spherical waves. We present typical radiation patterns for the topological insulator TlBiSe$_2$ and the magnetoelectric TbPO$_4$. In the ultra-relativistic case, the additional contributions from the magnetoelectric coupling appreciably enhance the global maximum of the angular distribution. We also present an analytic expression for the frequency distribution of the radiation for this case. We find that in the limit where the permittivities are equal there still exists transition radiation of the order of the square of the topological parameter with a pure topological origin.

cond-mat.mes-hall↗

arXiv2022

Nested Open Quantum Systems Approach to Photonic Bose$-$Einstein Condensation

The photonic Bose$-$Einstein condensate is a recently observed collective ground state of a coupled light-matter system. We describe this quantum state based on macroscopic quantum electrodynamics in dispersing and absorbing environments. To model the coupled photon$-$dye dynamics, we derive a master equation using a nested open quantum systems approach yielding all parameters essential to describe the condensation process. This approach allows us to describe photon condensates of arbitrary shapes because all geometry-dependent decay constants can be expressed in terms of the Green's tensor. In particular, we obtain the cavity mode absorption and emission rates of the dye molecules.

quant-ph↗

arXiv2021

Self-preserving ice layers on CO2 clathrate particles: implications for Enceladus, Pluto and similar ocean worlds

Under both engineering and natural conditions on Earth and in the Universe, some gas hydrates are found to be stabilised outside their window of thermodynamic stability by the formation of an ice layer-a phenomenon termed self-preservation. Low occupancy surface regions on type I CO2 clathrate structures together with the self-preserving ice layer lead to an effective buoyancy for these structures which restricts the size range of particles that float in the ocean on Enceladus, Pluto and similar oceanic worlds. Our goal here is to investigate the implications of Lifshitz forces and low occupancy surface regions on clathrate structures for their self-preservation through ice layer formation, presenting a plausible model based on multilayer interactions through dispersion forces. We predict that the growth of an ice layer between 0.01 and 0.2 $μ$m thick on CO2 clathrate surfaces depends on the presence of surface regions in the gas hydrates with low occupancy. The effective particle density is estimated delimiting a range of particles that would be buoyant in different oceans. Over geological time, deposition of floating CO2 hydrates could result in the accumulation of kilometre-thick hydrate layers above liquid water reservoirs, and below the water ice crusts of their respective ocean worlds. On Enceladus, destabilisation of near-surface hydrate deposits could lead to increased gas pressures that both drive plumes and entrain stabilised hydrates to be redeposited on the surface of Enceladus or ejected into the E-ring of Saturn. On ocean worlds such as Enceladus and particularly Pluto, the accumulation of thick CO2 hydrate deposits could insulate its ocean against freezing. In preventing the freezing of liquid water reservoirs in ocean worlds, the presence of CO2 hydrate layers could enhance the habitability of ocean worlds in our solar systems and on the exoplanets and exomoons beyond.

astro-ph.EP↗