arXiv subjects

Yanpeng Zhang

Publications and source records attributed to Yanpeng Zhang.

At least 19 recordsLinked to original sources

arXiv2026

Floquet-sideband-enhanced shortwave electrometry with Rydberg atoms

Rydberg atomic electric-field sensors, under the framework of optical excitation and readout, can overcome the size-to-wavelength constraint imposed by the Chu limit. However, their sensitivity for decametric-wavelength shortwave electric fields is substantially lower than that for microwave ones, stemming from the off-resonant nature of low-frequency signals with Rydberg transitions. Here, we demonstrate a high-sensitivity heterodyne shortwave sensor based on microwave-dressed Rydberg atoms, leveraging precisely modulated Floquet sidebands. Around local- and microwave-field-engineered Floquet sidebands, the steep response gradient, arising from the enhanced atom-shortwave interaction through additionally created coherent channels, induces pronounced amplification of the heterodyne intermediate-frequency signal. As a result, compared to the same atomic heterodyne setup without microwave modulation, such Floquet-sideband-enhanced shortwave measurement boosts the sensitivity by four orders of magnitude, yielding a sensitivity of -122.7 dBm/Hz for shortwave at 30 MHz. This work offers a potential route to high-sensitive portable shortwave receivers in radio astronomy, radar and long-distance communications.

physics.atom-ph↗

arXiv2026

Annihilation of Dirac points and its topological obstruction in a photonic Kagome lattice

Dirac points (DPs) are topological singularities that determine the extraordinary properties of two-dimensional materials. They are generally classified by discrete topological invariants, which determine the possibility of DPs' annihilation upon their collision. Here, we study the behaviors of DPs within a photonic Kagome lattice created in atomic vapor. With optically engineering the potential difference among three sites constituting the Kagome unit cell while preserving time-reversal symmetry and the stability of an isolated DP, the DPs move in reciprocal space. By employing conical diffraction to measure their position and the topological invariant (Euler number), we demonstrate an obstruction to DPs' annihilation during collision and a transition to a case where the Euler number changes and annihilation occurs. Such topological transition is induced by a non-Abelian frame rotation of the eigenstates around the Brillouin zone torus. The associated conversion of the DP quaternionic charges during their motion explains the change of Euler number.

cond-mat.mes-hall↗

arXiv2025

Nonadiabatic effect in high order harmonic generation revealed by a fully analytical method

We propose a fully analytical method for describing high-order harmonic generation (HHG). This method is based on the strong-field approximation (SFA) and electron-trajectory theory, but utilizes the perturbation expansion on the Keldysh parameter $\gamma$. This expansion allows us to clearly differentiate the nonadiabatic and adiabatic effects on HHG. We show that the nonadiabatic effect relating to high-order expansion depends on the laser wavelength and remarkably enhances the HHG yields for cases of short wavelengths, providing deeper insights into wavelength-dependent HHG yields which are important in producing attosecond pulses. Especially, our method provides the analytical and accurate descriptions of nonadiabatic exit velocity and position of the tunneling electron at the tunnel exit. These descriptions are meaningful for constructing a fully analytical and quantitative Coulomb-included HHG model, which is crucial in HHG-based attosecond measurement.

physics.optics↗

arXiv2025

Control of Photon Dynamics in Non-Euclidean Polygonal Microcavities by Joint Geometric Curvatures

Non-Euclidean geometry has recently emerged as a powerful tool, offering new insights and applications in optical microcavities supporting Whispering Gallery Modes (WGMs). In this study, we extend the concept of polygonal microcavities to non-Euclidean spaces by developing a unified model that incorporates a joint geometric parameter of curvatures. This system uncovers a range of unexplored phenomena, mechanisms, and concepts that are unique to curved spaces. Notably, we observe dissipative states characterized by hyperbolic fixed points (HFPs) that appear exclusively in non-Euclidean scenarios, leading to the formation of phase diagrams within the parametric space of curvatures. Our results reveal phase transitions across geometric boundaries, marked by abrupt changes in the cavity quality factor. These transitions are strongly influenced by the wavelike nature of photon trajectories, offering intriguing insights into quantum chaos within curved spaces. Additionally, we discover that cavities with geodesic side lines exhibit a remarkable symmetry-driven avoidance of such phase transitions, highlighting the profound connection between physical dynamics and spatial geometry. Our findings establish a promising platform for optical simulations of non-Euclidean quantum chaos and open up potential applications in on-chip photonic devices.

physics.optics↗

arXiv2025

Double-optical phase-transition in a three level Rydberg state in thermal Rubidium vapor

We report on the observation of electromagnetically induced transparency (EIT) with intrinsic phase transitions in a three-level ladder system within rubidium atomic vapor. The observed abrupt transitions between low and high Rydberg occupancy states manifest in the probe beam transmission, depending on the principal quantum number, the Rabi frequency of the coupling field, atomic density, and probe beam detuning. Our study elucidates the underlying interaction mechanisms governing the EIT phase transition and enriches the existing experiments of multi-parameter regulation phase transitions. These findings establish a robust platform for investigating nonequilibrium phase transitions in atomic ensembles, bridging the gap between classical mean-field theories and microscopic quantum dynamics.

physics.optics↗

arXiv2025

Spin-to-orbital angular momentum conversion in non-Hermitian photonic graphene

Optical beams with orbital angular momentum (OAM) have numerous potential applications, but the means used for their generation often lack crucial on-demand control. In this work, we present a mechanism of converting spin angular momentum (SAM) to OAM in a non-structured beam. The conversion occurs through spin-orbit coupling in a reconfigurable photonic honeycomb lattice with staggering implemented by electromagnetically-induced transparency in an atomic vapor cell. The spin-orbit coupling allows to outcouple the OAM signal from a particular band in a given valley determined by the chirality of light or the lattice staggering, providing a non-zero Berry curvature for generating OAM. The dependence of the output OAM on the chirality of the input beam is the first control knob. The staggering works as a second control knob, flipping the sign of OAM for the fixed chirality. The demonstrated conversion between SAM and OAM is important for optical communications. Our results can be extended to other implementations of paraxial photonic graphene.

cond-mat.mes-hall↗

arXiv2025

Dual phase transitions in a 1D lattice with PT-symmetric Floquet defect

Systems with non-Hermitian potential or Floquet modulation often result in phase transition related phenomena. In this paper, we study the dual phase transitions in a one-dimensional lattice by introducing a defect containing both Floquet modulation and PT-symmetric potential. In such a configuration, we demonstrate how the gain-loss from PT-symmetry and the control parameters in Floquet modulation adjust the wave dynamic behaviors. When these parameters change, the system will undergo dual phase transitions from an energy-delocalized phase to a localized phase where energy oscillates with time, and then to a PT-symmetry broken phase with energy boost. In particular, we find that the energy oscillations in the second phase is resulted from the beating of two energy oscillations: one is introduced by the PT-symmetric potential and the other is introduced by the Floquet modulation, rather than the field interference of the defect modes. Furthermore, we find that the first phase transition can be non-exist and the second phase transition is affected by the Floquet parameters. Our results reveal the underlying physics of dual phase transitions that occur in simple lattice systems with PT-symmetric Floquet defect, which extends the study of non-Hermitian Floquet systems.

physics.optics↗

arXiv2025

Vectorial Symmetry Decoding with Single-Particle Precision via Room-Temperature Lanthanide Luminescence Polarimetry

Determining the local symmetry of luminescent centers in crystals is critical for understanding and controlling their optical transitions, yet current methods are limited by stringent experimental requirements and ambiguous symmetry assignments. Here, we develop a robust computational electromagnetics framework that directly connect the local symmetry and chirality of rare-earth-doped single crystals to the polarization states of their emitted light. This framework is experimentally validated through the precise determination of point and space group symmetries using high-resolution, polarization-resolved micro-photoluminescence ({\mu}-PL) spectra. Unlike conventional approaches that usually rely on analyzing multiple transitions at cryogenic temperatures, our technique operates at room temperature, requires only a single optical transition, and enables accurate orientation of symmetry axes. This enables deterministic polarization control of nano-emitters by tailoring symmetry groups and selecting appropriate transition dipoles, eliminating the need for bulky or complex photonic structures. Additionally, we demonstrate the function of bio-sensing, via determining single particle orientations in complex cellular environments using minimal polarization measurements. These results pave the way for advances in energy transfer systems, ultra-bright rare-earth nanocrystals, nanophotonic materials, and real-time single-particle tracking in biological contexts.

physics.optics↗

arXiv2024

Observation of nonreciprocal transverse localization of light

Magnetic-free nonreciprocal optical devices that can prevent backscattering of signals are essential for integrated optical information processing. The achieved nonreciprocal behaviors mostly rely on various dispersive effects in optical media, which give rise to dispersive modulations of the transverse beam profile, such as spatial broadening and discretization, of the incident signals. Such deformation inevitably reduces the matching with subsequent components for information processing. Here we experimentally demonstrate the nonreciprocal transverse localization of light in a moir\'e photonic lattice induced in atomic vapors. When the probe field is set to co- or counter-propagate with the coupling field formed by superposing two identical honeycomb beams in a certain rotation angle, the output pattern can exhibit localized or dispersive behavior. The localization in the forward case is derived from the moir\'e structure, and the nonreciprocal behaviors (in both beam size and transmitted intensity) are introduced by the thermal motion of atoms. The thermal-motion-induced Doppler effect can destroy the coherent condition for electromagnetically induced transparency in the backward case, because of which the probe beam becomes immune to the modulation of the coupling field. The current work provides an approach to control the transverse beam profile in one-way transmission.

cond-mat.mes-hall↗

arXiv2024

Beam dynamics induced by the quantum metric of exceptional rings

Topological physics has broadened its scope from the study of topological insulating phases to include nodal phases containing band structure singularities. The geometry of the corresponding quantum states is described by the quantum metric which provides a theoretical framework for explaining phenomena that conventional approaches fail to address. The field has become even broader by encompassing non-Hermitian singularities: in addition to Dirac, Weyl nodes, or nodal lines, it is now common to encounter exceptional points, exceptional or Weyl rings, and even Weyl spheres. They give access to fascinating effects that cannot be reached within the Hermitian picture. However, the quantum geometry of non-Hermitian singularities is not a straightforward extension of the Hermitian one, remaining far less understood. Here, we study experimentally and theoretically the dynamics of wave packets at exceptional rings stemming from Dirac points in a photonic honeycomb lattice. First, we demonstrate a transition between conical diffraction and non-Hermitian broadening in real space. Next, we predict and demonstrate a new non-Hermitian effect in the reciprocal space, induced by the non-orthogonality of the eigenstates. We call it transverse non-Hermitian drift, and its description requires biorthogonal quantum metric. The non-Hermitian drift can be used for applications in beam steering.

cond-mat.mes-hall↗

arXiv2024

Nonreciprocal spontaneous parametric process

Mediated by the interaction with quantum vacuum fields, a laser field propagating in a nonlinear optical medium can generate new light fields via spontaneous parametric process. Such process is inherent independent of the propagation direction of light and reciprocal thus far, due to the direction-independent field-vacuum interaction. In this work, we experimentally demonstrate a nonreciprocal spontaneous parametric four-wave mixing process in sodium atomic vapors with dispersive nonlinearity and further broadband optical isolation by unidirectionally coupling the probe field to an auxiliary quantum vacuum field in another four-wave mixing process. Thanks to the broad bandwidth of the spontaneous parametric process, in combination with the Doppler and power-induced broadening of atomic energy levels, we achieve optical isolation with a bandwidth larger than 100 GHz for isolation ratio >25 dB. Considering that both spontaneous parametric processes and wave mixing in nonlinear medium have been realized in diverse on-chip photonic platforms, our work paves the way for integrated broadband optical isolations and thus can boost scalability and function of photonic chips.

physics.optics↗

arXiv2024

Tailoring chaotic motion of microcavity photons in ray and wave dynamics by tuning the curvature of space

Microcavity photon dynamics in curved space is an emerging interesting area at the crossing point of nanophotonics, chaotic science and non-Euclidean geometry. We report the sharp difference between the regular and chaotic motions of cavity photons subjected to the varying space curvature. While the island modes of regular motion rise in the phase diagram in the curved space, the chaotic modes show special mechanisms to adapt to the space curvature, including the fast diffusion of ray dynamics, and the localization and hybridization of the Husimi wavepackets among different periodic orbits. These obser-vations are unique effects enabled by the combination of the chaotic trajectory, the wave nature of light and the non-Euclidean orbital motion, and therefore make the system a versatile optical simulator for chaotic science under quan-tum mechanics in curved space-time.

physics.optics↗

arXiv2023

Non-Hermitian delocalization in a 2D photonic quasicrystal

Quasicrystals show long-range order, but lack translational symmetry. So far, theoretical and experimental studies suggest that both Hermitian and non-Hermitian quasicrystals show localized eigenstates. This localization is due to the fractal structure of the spectrum in the Hermitian case and to the transition to diffusive bands via exceptional points in the non-Hermitian case. Here, we present an experimental study of a dodecagonal (12-fold) photonic quasicrystal based on electromagnetically-induced transparency in a Rb vapor cell. The transition to a quasicrystal is obtained by superposing two honeycomb lattices at 30$^\circ$ with a continuous tuning of their amplitudes. Non-Hermiticity is controlled independently. We study the spatial expansion of a probe wavepacket. In the Hermitian case, the wavepacket expansion is suppressed when the amplitude of the second lattice is increased (quasicrystal localization). We find a new regime, where increasing the non-Hermitian potential in the quasicrystal enhances spatial expansion, with the $C_{12}$ symmetry becoming visible in the wavepacket structure. This real-space expansion is due to a k-space localization on specific quasicrystal modes. Our results show that the non-Hermitian quasicrystal behavior is richer than previously thought. The localization properties of the quasicrystals can be used for beam tailoring in photonics, but are also important in other fields.

cond-mat.mes-hall↗

arXiv2023

Diverse Entanglement Mechanisms in Multimode Nonlinear Continuous Variables

Non-Gaussian entangled states play a crucial role in harnessing quantum advantage in continuous-variable quantum information. However, how to fully characterize N-partite (N > 3) non-Gaussian entanglement without quantum state tomography remains elusive, leading to a very limited understanding of the underlying entanglement mechanism. Here, we propose several necessary and sufficient conditions for the positive-partial-transposition separability of multimode nonlinear quantum states resulting from high-order Hamiltonians and successive beam splitting operations. When applied to the initial state, the beam-splitter operations induce the emergence of different types of entanglement mechanisms, including pairwise high-order entanglement, collective high-order entanglement and the crossover between the two. We show numerically that for the four-mode scenario, the threshold for the existence of entanglement for any bipartition does not exceed the entanglement of the original state at fixed high-order moments. These results provide a new perspective for understanding multipartite nonlinear entanglement and will promote their application in quantum information processing.

quant-ph↗

arXiv2023

Direct Manipulation of quantum entanglement from the non-Hermitian nature of light-matter interaction

Biphoton process is an essential benchmark for quantum information science and technologies, while great efforts have been made to improve the coherence of the system for better quantum correlations. Nevertheless, we find that the non-Hermitian features induced by the atomic quantum interference could be well employed for the direct control of entanglement. We report the demonstration of exceptional point (EP) in biphotons by measuring the light-atom interaction as a natural non-Hermitian system, in which the electromagnetically induced transparency regime provides a powerful mechanism to precisely tune the non-Hermitian coupling strength. Such biphoton correlation is tuned within an unprecedented large range from Rabi oscillation to antibunching-exponential-decay, also indicating high-dimensional entanglement within the strong and weak light-matter coupling regimes. The EP at the transition point between the two regimes is clearly observed with the biphoton quantum correlation measurements, exhibiting a single exponential decay and manifesting the coalesced single eigenstate. Our results provide a unique method to realize the controllability of natural non-Hermitian processes without the assistance of artificial photonic structures, and paves the way for quantum control by manipulating the non-Hermitian features of the light-matter interaction.

quant-ph↗

arXiv2023

Effective potential engineering by emergent anisotropy in a tunable open-access microcavity

Photonic spin-orbit (SO) coupling is an important physical mechanism leading to numerous interesting phenomena in the systems of microcavity photons and exciton-polaritons. We report the effect of SO coupling in a tunable open-access microcavity embedded with anisotropic active media. The SO coupling associated with the TE-TM splitting results in an emergent anisotropy, which further leads to fine energy splittings allowing clear observation of the full set of eigenstates, in sharp contrast with the isotropic situation which leads to the isotropic eigenstates of spin vortices. We show that the photonic potential can be engineered by playing with the relation between the emergent anisotropy and the cavity ellipticity. All the experimental results are well reproduced by the degenerate perturbation theory. Our results constitute a significant extension to the research field of microcavity spinoptronics, with potential applications in polarization control and optical property measurement of photonic devices and materials.

physics.optics↗

arXiv2023

Direct generation of time-energy-entangled W triphotons in atomic vapor

Sources of entangled multiphotons are not only essential for fundamental tests of quantum foundations, but are also the cornerstone of a variety of optical quantum technologies today. Over past three decades, tremendous efforts have been devoted to creating multiphoton entanglement by multiplexing existing biphoton sources with linear optics and postselections. Different from all previous protocols, here we report, for the first time, the observation of continuous-mode time-energy-entangled W-class triphotons with an unprecedented generation rate directly through the process of spontaneous six-wave mixing (SSWM) in a four-level triple-Lambda atomic vapor cell. Facilitated by electromagnetically induced transparency and coherence control, our SSWM scheme enables versatile narrowband triphoton generation with many intriguing properties including long temporal coherence and controllable waveforms, ideal for implementing long-distance quantum communications, networking, and information processing by interfacing photons and atoms. Most importantly, our work paves a way for the development of a reliable and efficient genuine triphoton source, thus making the research on multiphoton entanglement within easy reach.

quant-ph↗

arXiv2023

Loss-difference-induced localization in a non-Hermitian honeycomb photonic lattice

Non-Hermitian systems with complex-valued energy spectra provide an extraordinary platform for manipulating unconventional dynamics of light. Here, we demonstrate the localization of light in an instantaneously reconfigurable non-Hermitian honeycomb photonic lattice that is established in a coherently-prepared atomic system. One set of the sublattices is optically modulated to introduce the absorptive difference between neighboring lattice sites, where the Dirac points in reciprocal space are extended into dispersionless local flat bands. When these local flat bands are broad enough due to larger loss difference, the incident beam is effectively localized at one set of the lattices with weaker absorption, namely, the commonly seen power exchange between adjacent channels in photonic lattices is effectively prohibited. The current work unlocks a new capability from non-Hermitian two-dimensional photonic lattices and provides an alternative route for engineering tunable local flat bands in photonic structures.

physics.optics↗