Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2410.08962 · Physical Review Applied

Gain-momentum locking in chiral-gain media

Anonymous, Nader Engheta, Mário G. Silveirinha

Published Jul 14, 2026• 2 citations
arXivHTMLPDF

Abstract

Conventional optical materials are characterized by either a dissipative response, which results in polarization-independent absorption, or by a gain response that leads to wave amplification. In this work, we study a peculiar class of materials with chiral-gain properties, where gain selectively amplifies waves of one polarization handedness, while dissipation suppresses the opposite handedness. We uncover a novel phenomenon, gain-momentum locking, at the boundary of chiral-gain media, where surface plasmons are amplified or attenuated based on their direction of propagation. This effect, driven by the interplay between spin-momentum locking and polarization-sensitive non-Hermitian responses, enables precise control over unidirectional wave propagation. Our findings open the door to photonic devices with unprecedented capabilities, such as lossless unidirectional edge-wave propagation and the generation of light with intrinsic orbital angular momentum.

DOI
10.1103/8qmb-p6nk

Related papers

Chiral gain-induced time-reversal symmetry breaking in quantum systems

Mário G. Silveirinha, Daigo Oue

Structured light offers a powerful approach to tailor light--matter interactions in quantum systems with chiral properties. While chirality has been extensively studied in passive platforms, the role of optical gain in controlling chiral quantum dynamics remains largely unexplored. In this work, we develop a general theoretical framework to describe the dynamics of an atomic system interacting with structured gain environments, where amplification depends on the light's polarization or momentum. By quantizing the electromagnetic field in linear bianisotropic media with gain and extending the Lindblad formalism to these settings, we derive a master equation governing the atom's irreversible evolution. We show that chiral gain can break time-reversal symmetry and drive the system toward a symmetry-broken steady state with nonreciprocal properties. This effect is illustrated in detail for moving plasmonic substrates, which exhibit inherently chiral gain that selectively amplifies transitions of a given handedness. Our results establish chiral gain as a novel mechanism for engineering nonreciprocal quantum steady states.

arXiv:2505.02718•Physical Review A•Sep 12, 2025•0 citations

Chiral quantum optics

Arno Rauschenbeutel

Summary form only given. Controlling the interaction of light and matter is the basis for diverse applications ranging from light technology to quantum information processing. Nowadays, many of these applications are based on nanophotonic structures. It turns out that the confinement of light in such nanostructures imposes an inherent link between its local polarization and its propagation direction, also referred to as spin-momentum locking of light [1]. Remarkably, this leads to chiral, i.e., propagation direction-dependent effects in the emission and absorption of light, and elementary processes of light-matter interaction are fundamentally altered. For example, when coupling plasmonic particles or atoms to evanescent fields, the intrinsic mirror symmetry of the particles' emission can be broken. In our group, we observed this effect in the interaction between single rubidium atoms and the evanescent part of a light field that is confined by continuous total internal reflection in a whispering-gallery-mode microresonator [2]. In the following, this allowed us to realize chiral nanophotonic interfaces in which the emission direction of light into the structure is controlled by the polarization of the excitation light [3] or by the internal quantum state of the emitter [4], respectively. Moreover, we employed this chiral interaction to demonstrate an integrated optical isolator [5] as well as an integrated optical circulator [6] which operate at the single-photon level and which exhibit low loss. The latter are the first two examples of a new class of nonreciprocal nanophotonic devices which exploit the chiral interaction between single quantum emitters and transversally confined photons.

Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)•Jun 1, 2017•0 citations

A photonic interface of chiral cavity quantum electrodynamics

Zhang, Fan, Lingxiao Shan, Juanjuan Ren +5 more

Cavity quantum electrodynamics studies light-matter interactions at single quanta level. Chiral photon-emitter coupling in photonic structures is characterized as unidirectional propagation locked by the local polarization of light. However, to realize the strong interaction of photon-emitter with direction-locked propagation, which will bring novel applications in nonreciprocal quantum devices, has not been reported yet. Here, we propose the coupled photonic crystal and metallic nanoparticle structure, where through strong local field with high helicity, the rate of circularly polarized photons emitting into photonic crystal waveguide is one order larger than that without the nanoparticle and the linewidth of Rabi splitting spectra is about one-tenth of that with only the nanoparticle, both with $\sim$ 95$\%$ photons propagating unidirectionally, which can be utilized in directional quantum light sources.

arXiv:1808.07210•Aug 22, 2018•0 citations

Interaction of light with generic active media

Malin Premaratne, Govind Prasad Agrawal

The study of optical effects in active media is rich with unexpected consequences. For instance, one may imagine that absorption and amplification in a dielectric medium will exhibit some sort of symmetry because both are related to the same imaginary part of the dielectric constant, except for a sign change. It turns out that such a symmetry does not exist [1]. This issue has also been investigated in detail for random or disordered gain media, with varying viewpoints [2]. Traditionally, much of the research on amplifying media has considered the interaction of light within the entire volume of such a medium. Recent interest in metamaterials and other esoteric structures in which plasmons are used to manipulate optical signals has brought attention to the role of surface waves in active dielectrics [3, 4]. From a fundamental perspective, the main difference between active and passive media is that spontaneous emission cannot be avoided in gain media. As a result, a rigorous analysis of gain media demands a quantum-mechanical treatment. Spontaneous emission in a gain medium depends not only on the material properties of that medium but also on the optical modes supported by the structure containing that material [5]. By a clever design of this structure (e.g., photonic crystals or microdisk resonators with a metallic cladding), it is possible to control the local density of optical modes and the spontaneous emission process itself. In Chapter 4, we discuss how to model a gain medium under such conditions by deploying optical Bloch equations.

Cambridge University Press eBooks•Feb 3, 2011•0 citations

Exact Helicity-Orbital Coupled Dynamics in Chiral Media: An Optical Dirac Framework for Photonic Rabi Oscillations

Xuhui Cheng, Longlong Feng

We demonstrate that light propagation in reciprocal chiral photonic media admits a unified description in terms of an emergent Dirac structure in helicity space. Starting from Maxwell's equations, we reformulate the electromagnetic field as a four-component spinor governed by an effective non-Hermitian optical Dirac equation. In this representation, the magnetoelectric response of the chiral medium appears as a helicity-dependent background that modifies the spectrum and eigenmodes, while the breaking of the spin-degenerate condition generates the intrinsic spin-orbit coupling between helicity and orbital degrees of freedom. After projection onto the positive-frequency sector, the theory reduces to an exact two-level helicity-orbital model. This model is found to have an analytical solution and describes coherent Rabi-like oscillations between spin-orbit-coupled vector modes. Chirality controls the helicity splitting and detuning, whereas the electromagnetic mismatch of the medium determines the coupling strength responsible for oscillatory spin-orbit conversion. The resulting dynamics is constrained by exact conservation of the total angular momentum, leading to reversible conversion between spin and orbital angular momentum with well-defined selection rules. Our work establishes an optical Dirac framework for structured light in chiral media, and provides experimentally accessible predictions for chirality-controlled oscillations, polarization dynamics, and orbital angular momentum conversion in structured optical fields.

physics.opticsCross-listedarXiv:2606.30295•Jun 30, 2026

Optical activity and excitation of surface plasmon polaritons with electromagnetically induced chiral media

Rafi Ud Din, Shaoliang Zhang, Manzoor Ikram +2 more

Chiral materials possess some unusual properties for which they have attracted tremendous interest in recent research. In this paper, we discuss the interaction of electromagnetic fields with an initially isotropic material, making it anisotropic chiral by inducing magnetoelectric cross coupling. We consider a four-level double Λ -type configuration of an atomic ensemble, which is simultaneously sensitive to relative phase of the applied fields due to its closed-loop nature, providing an extra degree of freedom for controlling the birefringent nature of the medium. We show that the material splits a linearly polarized probe field into left- (LCP) and right-circularly polarized (RCP) components, and their angular divergence can be related to the optical activity of the medium. This leads to efficient modulation of the probe field, which may be helpful in accurate position detection of the transmitted beams and images. Next, we demonstrate that such a medium can be used to couple incident light with surface plasmons (SPs) in two ways: (1) as a prism-like coupler, in either Otto- or Kretschmann-type geometry, where excitation of SPs can be achieved beyond a certain incident angle of the interacting pulse in a plasmonic waveguide placed closed to it; and (2) direct excitation of SPs by a LCP or RCP beam from the chiral medium in a particular slit-type plasmonic waveguide. We find that the coupled modes in the latter case are unidirectional and highly tunable. Further, we show that the birefringent nature of the medium as well as the plasmonic field intensities can be efficiently manipulated with a number of controlling parameters. Our results may find applications in image coding, plasmonic sensors, and bio-photonics.

Journal of the Optical Society of America B•Aug 17, 2020•0 citations
Conventional optical materials are characterized by either a dissipative response, which results in polarization-independent absorption, or by a gain response that leads to wave amplification. In this work, we study a peculiar class of materials with chiral-gain properties, where gain selectively amplifies waves of one polarization handedness, while dissipation suppresses the opposite handedness. We uncover a novel phenomenon, gain-momentum locking, at the boundary of chiral-gain media, where surface plasmons are amplified or attenuated based on their direction of propagation. This effect, driven by the interplay between spin-momentum locking and polarization-sensitive non-Hermitian responses, enables precise control over unidirectional wave propagation. Our findings open the door to photonic devices with unprecedented capabilities, such as lossless unidirectional edge-wave propagation and the generation of light with intrinsic orbital angular momentum.
Structured light offers a powerful approach to tailor light--matter interactions in quantum systems with chiral properties. While chirality has been extensively studied in passive platforms, the role of optical gain in controlling chiral quantum dynamics remains largely unexplored. In this work, we develop a general theoretical framework to describe the dynamics of an atomic system interacting with structured gain environments, where amplification depends on the light's polarization or momentum. By quantizing the electromagnetic field in linear bianisotropic media with gain and extending the Lindblad formalism to these settings, we derive a master equation governing the atom's irreversible evolution. We show that chiral gain can break time-reversal symmetry and drive the system toward a symmetry-broken steady state with nonreciprocal properties. This effect is illustrated in detail for moving plasmonic substrates, which exhibit inherently chiral gain that selectively amplifies transitions of a given handedness. Our results establish chiral gain as a novel mechanism for engineering nonreciprocal quantum steady states.
Summary form only given. Controlling the interaction of light and matter is the basis for diverse applications ranging from light technology to quantum information processing. Nowadays, many of these applications are based on nanophotonic structures. It turns out that the confinement of light in such nanostructures imposes an inherent link between its local polarization and its propagation direction, also referred to as spin-momentum locking of light [1]. Remarkably, this leads to chiral, i.e., propagation direction-dependent effects in the emission and absorption of light, and elementary processes of light-matter interaction are fundamentally altered. For example, when coupling plasmonic particles or atoms to evanescent fields, the intrinsic mirror symmetry of the particles' emission can be broken. In our group, we observed this effect in the interaction between single rubidium atoms and the evanescent part of a light field that is confined by continuous total internal reflection in a whispering-gallery-mode microresonator [2]. In the following, this allowed us to realize chiral nanophotonic interfaces in which the emission direction of light into the structure is controlled by the polarization of the excitation light [3] or by the internal quantum state of the emitter [4], respectively. Moreover, we employed this chiral interaction to demonstrate an integrated optical isolator [5] as well as an integrated optical circulator [6] which operate at the single-photon level and which exhibit low loss. The latter are the first two examples of a new class of nonreciprocal nanophotonic devices which exploit the chiral interaction between single quantum emitters and transversally confined photons.
Cavity quantum electrodynamics studies light-matter interactions at single quanta level. Chiral photon-emitter coupling in photonic structures is characterized as unidirectional propagation locked by the local polarization of light. However, to realize the strong interaction of photon-emitter with direction-locked propagation, which will bring novel applications in nonreciprocal quantum devices, has not been reported yet. Here, we propose the coupled photonic crystal and metallic nanoparticle structure, where through strong local field with high helicity, the rate of circularly polarized photons emitting into photonic crystal waveguide is one order larger than that without the nanoparticle and the linewidth of Rabi splitting spectra is about one-tenth of that with only the nanoparticle, both with ∼\sim∼ 95%\%% photons propagating unidirectionally, which can be utilized in directional quantum light sources.
The study of optical effects in active media is rich with unexpected consequences. For instance, one may imagine that absorption and amplification in a dielectric medium will exhibit some sort of symmetry because both are related to the same imaginary part of the dielectric constant, except for a sign change. It turns out that such a symmetry does not exist [1]. This issue has also been investigated in detail for random or disordered gain media, with varying viewpoints [2]. Traditionally, much of the research on amplifying media has considered the interaction of light within the entire volume of such a medium. Recent interest in metamaterials and other esoteric structures in which plasmons are used to manipulate optical signals has brought attention to the role of surface waves in active dielectrics [3, 4]. From a fundamental perspective, the main difference between active and passive media is that spontaneous emission cannot be avoided in gain media. As a result, a rigorous analysis of gain media demands a quantum-mechanical treatment. Spontaneous emission in a gain medium depends not only on the material properties of that medium but also on the optical modes supported by the structure containing that material [5]. By a clever design of this structure (e.g., photonic crystals or microdisk resonators with a metallic cladding), it is possible to control the local density of optical modes and the spontaneous emission process itself. In Chapter 4, we discuss how to model a gain medium under such conditions by deploying optical Bloch equations.
We demonstrate that light propagation in reciprocal chiral photonic media admits a unified description in terms of an emergent Dirac structure in helicity space. Starting from Maxwell's equations, we reformulate the electromagnetic field as a four-component spinor governed by an effective non-Hermitian optical Dirac equation. In this representation, the magnetoelectric response of the chiral medium appears as a helicity-dependent background that modifies the spectrum and eigenmodes, while the breaking of the spin-degenerate condition generates the intrinsic spin-orbit coupling between helicity and orbital degrees of freedom. After projection onto the positive-frequency sector, the theory reduces to an exact two-level helicity-orbital model. This model is found to have an analytical solution and describes coherent Rabi-like oscillations between spin-orbit-coupled vector modes. Chirality controls the helicity splitting and detuning, whereas the electromagnetic mismatch of the medium determines the coupling strength responsible for oscillatory spin-orbit conversion. The resulting dynamics is constrained by exact conservation of the total angular momentum, leading to reversible conversion between spin and orbital angular momentum with well-defined selection rules. Our work establishes an optical Dirac framework for structured light in chiral media, and provides experimentally accessible predictions for chirality-controlled oscillations, polarization dynamics, and orbital angular momentum conversion in structured optical fields.
Chiral materials possess some unusual properties for which they have attracted tremendous interest in recent research. In this paper, we discuss the interaction of electromagnetic fields with an initially isotropic material, making it anisotropic chiral by inducing magnetoelectric cross coupling. We consider a four-level double Λ -type configuration of an atomic ensemble, which is simultaneously sensitive to relative phase of the applied fields due to its closed-loop nature, providing an extra degree of freedom for controlling the birefringent nature of the medium. We show that the material splits a linearly polarized probe field into left- (LCP) and right-circularly polarized (RCP) components, and their angular divergence can be related to the optical activity of the medium. This leads to efficient modulation of the probe field, which may be helpful in accurate position detection of the transmitted beams and images. Next, we demonstrate that such a medium can be used to couple incident light with surface plasmons (SPs) in two ways: (1) as a prism-like coupler, in either Otto- or Kretschmann-type geometry, where excitation of SPs can be achieved beyond a certain incident angle of the interacting pulse in a plasmonic waveguide placed closed to it; and (2) direct excitation of SPs by a LCP or RCP beam from the chiral medium in a particular slit-type plasmonic waveguide. We find that the coupled modes in the latter case are unidirectional and highly tunable. Further, we show that the birefringent nature of the medium as well as the plasmonic field intensities can be efficiently manipulated with a number of controlling parameters. Our results may find applications in image coding, plasmonic sensors, and bio-photonics.