arXiv subjects

Wen-Hua Wu

Publications and source records attributed to Wen-Hua Wu.

3 recordsLinked to original sources

arXiv2026

Floquet Engineering of a Quasiequilibrium Superradiant Phase Transition in Landau Polaritons

Superradiant phase transitions (SRPTs), characterized by photon condensation and macroscopic matter polarization, are forbidden in equilibrium for homogeneous fields by no-go theorems. Here, we show that Floquet driving can circumvent this constraint in a Landau polariton system consisting of a two-dimensional electron gas coupled to a terahertz cavity in a DC magnetic field. An off-resonant AC magnetic field modulates the cyclotron frequency and light--matter coupling strength while leaving the diamagnetic term unchanged, generating an additional DC coupling contribution. This drives the system across a critical threshold into a superradiant phase, characterized by photon condensation and Landau-level polarization in the ground state of the Floquet Hamiltonian. This quasiequilibrium approach offers a route to SRPTs distinct from driven-dissipative schemes.

cond-mat.mes-hall↗

arXiv2025

Symmetry-Controlled Ultrastrong Phonon-Photon Coupling in a Terahertz Cavity

Optical cavities provide a powerful means to engineer light-matter hybrid states by coupling confined electromagnetic fields with matter excitations. Achieving in situ control of the coupling strength is essential for investigating how such hybridization evolves with the coupling strength. In this work, we use a symmetry-changing structural phase transition in lead halide perovskites to reversibly tune the phonon-photon coupling strength, leveraging the fact that their phonon frequencies and oscillator strengths are dictated by lattice symmetry. Terahertz time-domain spectroscopy of MAPbI3 embedded in nanoslot cavities reveals three polariton branches above the critical temperature Tc = 162.5 K, and the emergence of an additional branch below Tc, activated by a new phonon mode in the low-temperature phase. The full dispersion is accurately reproduced using a multimode Hopfield model, confirming that all normalized coupling strengths remain in the ultrastrong coupling regime. These results demonstrate symmetry-controlled tuning of ultrastrong coupling via phonon engineering in optical cavities.

quant-ph↗

arXiv2024

Searching for Afterglow: Light Dark Matter Boosted by Supernova Neutrinos

A novel analysis is performed, incorporating time-of-flight (TOF) information to study the interactions of dark matter (DM) with standard model particles. After supernova (SN) explosions, DM with mass $m_χ\lesssim\mathcal{O}({\rm MeV})$ in the halo can be boosted by SN neutrinos (SN$ν$) to relativistic speed. The SN$ν$ boosted DM (BDM) arrives on Earth with TOF which depends only on $m_χ$ and is independent of the cross section. These BDMs can interact with detector targets in low-background experiments and manifest as afterglow events after the arrival of SN$ν$. The characteristic TOF spectra of the BDM events can lead to large background suppression and unique determination of $m_χ$. New cross section constraints on $\sqrt{σ_{χe} σ_{χν}}$ are derived from SN1987a in the Large Magellanic Cloud with data from the Kamiokande and Super-Kamiokande experiments. Potential sensitivities for the next galactic SN with Hyper-Kamiokande are projected. This analysis extends the existing bounds on $\sqrt{σ_{χe}σ_{χν}}$ over a broad range of $r_χ=σ_{χν}/σ_{χe}$. In particular, the improvement is by 1-3 orders of magnitude for $m_χ<\mathcal{O}(100\,{\rm keV})$ for $σ_{χe}\simσ_{χν}$. Prospects of exploiting TOF information in other astrophysical systems to probe exotic physics with other DM candidates are discussed.

hep-ph↗