arXiv subjects

Abdelouahed El Fatimy

Publications and source records attributed to Abdelouahed El Fatimy.

5 recordsLinked to original sources

arXiv2026

Helicity decoupling ultrastrong Rabi splitting from quantum vacuum dressing

Polaritons and quantum vacuum dressing are usually regarded as intertwined consequences of ultrastrong light-matter coupling. Here we show that they can be controlled independently through helicity. We consider cyclotron resonance coupled to a chiral cavity supporting a single circular mode. When the helicity of the cavity field matches the cyclotron motion, energy is exchanged resonantly between light and matter, producing a large Rabi splitting and conventional polaritons, while the ground state remains the bare vacuum. Reversing the magnetic field reverses the cyclotron motion without changing the cavity. The same mode then couples through anomalous processes that create and annihilate light and matter excitations in pairs: the conventional polaritonic anticrossing disappears, while the ground state acquires squeezing and virtual excitations. These two regimes show that spectral hybridization and quantum vacuum dressing are distinct manifestations of ultrastrong coupling, and that a large Rabi splitting alone does not imply a dressed quantum vacuum. Helicity therefore provides a route to controlling polariton formation and quantum correlations as distinct resources in cavity quantum materials.

quant-ph↗

arXiv2026

Tunable Electron Quantum Optics in Graphene Slit Junctions

A graphene slit junction is investigated as a compact geometry for directional electron-beam formation, coherent interference, and symmetry-controlled spin filtering. Atomistic tight-binding calculations combined with the nonequilibrium Green's function formalism show that trigonal warping in monolayer graphene produces strongly directional electron beams near E~2.7eV. Boundary reflections redirect these beams toward a common drain, where the transmission exhibits magnetic flux-dependent oscillations consistent with an h/e Aharonov-Bohm period, whose modulation is characterized by Fourier analysis and harmonic fitting. A local electrostatic gate provides additional control of the interference phase. In separate self-consistent mean-field Hubbard calculations, the pristine antiferromagnetic ground state is shown to have spin-degenerate transmission, whereas structural or electrostatic breaking of the left-right symmetry enables spin filtering. Complementary valley-resolved calculations using a four-band continuum model demonstrate analogous beam formation in bilayer graphene at E = 50meV. The results identify the slit junction as a common geometry for electron-optical and spin-dependent transport and motivate further investigation of low-energy bilayer implementations.

cond-mat.mes-hall↗

arXiv2026

Chirality routing non-polaritonic vacuum correlations in Landau polaritons

Ultrastrong coupling between matter and cavity vacuum fields can turn the electromagnetic vacuum into a structured quantum environment, thereby opening passive routes for modifying and manipulating material properties. Recent work has identified light--matter entanglement as an important ingredient in these property changes, which raises the question of where the relevant vacuum correlations actually reside. Landau polaritons provide chiral ultrastrong coupling systems in which one circular cavity polarization forms the bright polariton branches. Here, using a quantum information approach, we show that an exact chiral charge in a multimode Hopfield model routes the dominant anomalous correlations, squeezing, and cavity--matter entanglement into the opposite polarization. We find that, using parameters extracted from a multimode Landau polariton system, this hidden sector correlates the cyclotron resonance with finite momentum magnetoplasmons through Gaussian discord, while pairwise matter--matter entanglement remains absent. We further predict a polarization anisotropy of dressed vacuum electric field fluctuations as a signature of this chiral routing. These results identify chirality as a symmetry principle for organizing ultrastrong coupling vacua and show that quantum information tools provide a powerful framework for revealing the salient properties of Landau polaritons.

cond-mat.mes-hall↗

arXiv2025

Angle-dependent chiral tunneling in biased twisted bilayer graphene

In twisted bilayer graphene (TBLG), chiral tunneling can be tuned by parameters such as the twist angle, barrier height, and Fermi energy. This differs from the tunneling behavior observed in monolayer and Bernal bilayer graphene, where electrons either pass completely through or are fully blocked due to the Klein paradox. Here we investigate the effect of a perpendicular interlayer bias on electron tunneling through electrostatic barriers in TBLG. Using a dual-gated model, which controls the carrier density and interlayer potential difference independently, we compute the transmission and reflection probabilities of electrons at different angles and energies for representative twist angles of $θ= 1.8^{\circ}$, $3.89^{\circ}$, and $9.43^{\circ}$. We find that a moderate bias suppresses normal-incidence transmission by opening a band gap in the low-energy spectrum. Our results show this leads to near-total reflection at low energy, with transmission starting to increase just above the gap due to twist-dependent conducting channels. The applied bias breaks the system's effective inversion symmetry, resulting in pronounced direction-dependent and valley-specific asymmetries in the angular distribution of transmitted electrons. We show that electrons incident at different angles show notable variations in transmission under bias. Furthermore, interlayer bias modulates Fabry--Pérot--like resonances in the TBLG barrier, shifting the energies of transmission peaks and altering their intensity.

cond-mat.mes-hall↗

arXiv2025

Multisubband Plasmons in InAs/GaSb Broken Gap Quantum Well

Multi-subband plasmon (MSP) modes in heavily doped InAs/GaSb broken-gap quantum wells grown via molecular beam epitaxy (MBE) are investigated. An $8$-band $\vec{k} \cdot \vec{p}$ semiclassical model accurately predicts ellipsometric spectra, reflecting strong subband hybridization and non-parabolicity. In contrast, single-band plasmon models show qualitative discrepancies with experiment, even with adjusted effective masses. These findings highlight the potential of broken-gap wells for quantum technologies leveraging interband coupling and wavefunction hybridization.

cond-mat.mes-hall↗