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:2509.03970

A Diagrammatic Method for Non-Gaussian Photon Correlations in Weakly Coupled Atomic Ensembles

Yangming Wang, Sahand Mahmoodian

quant-phphysics.opticsSubmitted Sep 4, 2025• Announced Sep 5, 2025• Revised Oct 30, 2026 (v3)
v1 · Sep 4, 2025v2 · Mar 3, 2026v3 · Oct 30, 2026
arXivHTMLPDF

Abstract

We develop a scattering-theory formalism and use it to predict that a resonantly driven atomic ensemble weakly coupled to an optical mode can generate light with non-Gaussian correlations. Our approach---based on a perturbative diagrammatic expansion of multi-photon interactions---shows that photon-photon interaction mediated by the emitters causes the transmitted light to have a connected third-order correlation function $g_c^{(3)}$ containing non-Gaussian field correlations. The temporal pattern of $g_c^{(3)}$ is explained using the microscopic transport processes in terms of our diagrams. We derive an optical-depth-dependent bound on the perturbative truncation error and benchmark our predictions against cascaded master-equation and quantum trajectory simulations for small ensembles with $\mathrm{OD}\leq 2$, identifying a regime of controlled accuracy under weak driving. Our predictions can be experimentally demonstrated in state-of-the-art nanofibre-coupled atomic ensembles.

Comments
5 pages, 3 figures

Related papers

Theory of Three-Photon Transport Through a Weakly Coupled Atomic Ensemble

Yangming Wang, Noé Demazure, Sahand Mahmoodian

Understanding multi-photon interactions in non-equilibrium quantum systems is an outstanding challenge in quantum optics. In this work, we develop an analytical and diagrammatic framework to explore three-photon interactions in atomic ensembles weakly coupled to a one-dimensional waveguide. Taking advantage of the weak coupling, we use our diagrammatic framework to perform perturbation theory and calculate the leading-order contributions to the three-photon wavefunction, which would otherwise be intractable. We then compute the outgoing photon wavefunction of a resonantly driven atomic ensemble, with photon-photon interactions truncated up to three photons. Our formulation not only captures the individual transmission of photons but also isolates the connected S-matrix elements that embody genuine photon-photon correlations. Through detailed analysis, we obtain the analytic expressions of the connected third-order correlation function and the third-order electric-field-quadrature cumulant, which reveal non-Gaussian signatures emerging from the interplay of two- and three-photon processes. We also calculate the optical depth where non-Gaussian photon states can be observed. Numerical simulations based on a cascaded master equation validate our analytical predictions on a small-scale system. These results provide a formalism to further explore non-equilibrium quantum optics in atomic ensembles and extend this to the regime of non-Gaussian photon transport.

arXiv:2507.03428•Jul 4, 2025•0 citations

Correlating photons using the collective nonlinear response of atoms weakly coupled to an optical mode

Arno Rauschenbeutel

Typical schemes for generating correlated states of light require a highly nonlinear medium that is strongly coupled to an optical mode. However, unavoidable dissipative processes, which cause photon loss and blur nonlinear quantum effects, often impede such methods. In this talk, I will report on our experimental implementation of the opposite approach. Using a strongly dissipative, weakly coupled medium, we generate and study strongly correlated states of light. Specifically, we study the transmission of resonant light through an ensemble of non-interacting atoms that weakly couple to a guided optical mode. Dissipation removes uncorrelated photons while preferentially transmitting highly correlated photons, created through collectively enhanced nonlinear interactions. As a result, the transmitted light constitutes a strongly correlated many-body state of light, revealed in the second-order correlation function. The latter exhibits strong antibunching or bunching, depending on the optical depth of the atomic ensemble. The demonstrated mechanism opens a new avenue for generating nonclassical states of light and for exploring correlations of photons in non-equilibrium systems using a mix of nonlinear and dissipative processes.

Photonics for Quantum (PfQ)•Aug 2, 2024•0 citations

Light-scattering properties beyond weak-field excitation in atomic ensembles

Chung-Hsien Wang, Nai-Yu Tsai, Yi-Cheng Wang +1 more

In the study of optical properties of large atomic systems, a weak laser driving is often assumed to simplify the system dynamics by linearly coupled equations. Here we investigate the light-scattering properties of atomic ensembles beyond weak-field excitation through the cumulant expansion method. By progressively incorporating higher-order correlations into the steady-state equations, an enhanced accuracy can be achieved in comparison to the exact solutions obtained by solving a full density matrix. Our analysis reveals that, in the regime of weak dipole-dipole interaction, the first-order expansion yields satisfactory predictions for optical depth, while denser atomic configurations necessitate consideration of higher-order correlations. As the intensity of incident light increases, atom saturation effects become noticeable, giving rise to significant changes in light transparency, energy shift, and decay rate. This saturation phenomenon extends to subradiant atom arrays even under weak driving conditions, leading to substantial deviations from the linear model. Our findings demonstrate that the mean-field model is a good extension to linear models as it balances both accuracy and computational complexity. However, the crucial role of higher-order cumulants in large and dense atom systems remains unclear, since it is challenging theoretically owing to the exponentially increasing Hilbert space in such light-matter interacting systems.

arXiv:2310.17106•Physical Review A•Jul 22, 2024•3 citations

Simple analytical model describing the collective nonlinear response of an ensemble of two-level emitters weakly coupled to a waveguide

Max Schemmer, Martin Cordier, Lucas Pache +3 more

We model and investigate the collective nonlinear optical response of an ensemble of two-level emitters that are weakly coupled to a waveguide featuring a single spatial mode. Our approach generalizes the insight that photon-photon correlations in the light scattered by a single two-level emitter result from two-photon interference to the case of many emitters. Using our model, developed for coherent driving in the weak-saturation regime, we study different configurations for probing the nonlinear response of the ensemble, e.g., through the waveguide or via external illumination, and derive analytical expressions for the second-order quantum coherence function, g ( 2 ) ( τ ) , as well as for the squeezing spectrum of the output light in the waveguide, S θ ( ω ) . For the transmission of resonant guided light, we recover the same predictions as previously made with more involved theoretical models when analyzing experimental results regarding g ( 2 ) ( τ ) [Prasad , ] and S θ ( ω ) [Hinney , ]. We also study the transmission of light that is detuned from the transition of the two-level emitter, a situation that we recently studied experimentally [Cordier , ]. Our model predictions show how the collectively enhanced nonlinear response of weakly coupled emitters can be harnessed to generate nonclassical states of light using ensembles ranging from a few to many emitters.

arXiv:2410.21202•Physical Review A•Apr 27, 2026•0 citations

Photon scattering by an atomic ensemble coupled to a one-dimensional nanophotonic waveguide

Guo‐Zhu Song, Ewan Munro, Wei Nie +3 more

We theoretically investigate the quantum scattering of a weak coherent input field interacting with an ensemble of $\mathrm{\ensuremath{\Lambda}}$-type three-level atoms coupled to a one-dimensional waveguide. With an effective non-Hermitian Hamiltonian, we study the collective interaction between the atoms mediated by the waveguide mode. In our scheme, the atoms are randomly placed in the lattice along the axis of the one-dimensional waveguide. Many interesting optical properties occur in our waveguide-atom system, such as electromagnetically induced transparency. We quantify the influence of decoherence originating from both dephasing and population relaxation, and analyze the effect of the inhomogeneous broadening on the transport properties of the incident field. Moreover, we observe that strong photon-photon correlation with quantum beats can be generated in the off-resonant case, which provides an effective method for producing nonclassical light in experiment. With remarkable progress in waveguide-emitter systems, our scheme may be experimentally feasible in the near future.

arXiv:1703.09375•Physical Review A•Oct 31, 2017•35 citations

Strongly Correlated Photon Transport in Waveguide Quantum Electrodynamics with Weakly Coupled Emitters

Sahand Mahmoodian, Mantas Čepulkovskis, Sumanta Das +3 more

We show that strongly correlated photon transport can be observed in waveguides containing optically dense ensembles of emitters. Remarkably, this occurs even for weak coupling efficiencies. Specifically, we compute the photon transport properties through a chirally coupled system of N two-level systems driven by a weak coherent field, where each emitter can also scatter photons out of the waveguide. The photon correlations arise due to an interplay of nonlinearity and coupling to a loss reservoir, which creates a strong effective interaction between transmitted photons. The highly correlated photon states are less susceptible to losses than uncorrelated photons and have a power-law decay with N. This is described using a simple universal asymptotic solution governed by a single scaling parameter which describes photon bunching and power transmission. We show numerically that, for randomly placed emitters, these results hold even in systems without chirality. The effect can be observed in existing tapered fiber setups with trapped atoms.

arXiv:1803.02428•Physical Review Letters•Oct 3, 2018•109 citations
We develop a scattering-theory formalism and use it to predict that a resonantly driven atomic ensemble weakly coupled to an optical mode can generate light with non-Gaussian correlations. Our approach---based on a perturbative diagrammatic expansion of multi-photon interactions---shows that photon-photon interaction mediated by the emitters causes the transmitted light to have a connected third-order correlation function gc(3)g_c^{(3)}gc(3)​ containing non-Gaussian field correlations. The temporal pattern of gc(3)g_c^{(3)}gc(3)​ is explained using the microscopic transport processes in terms of our diagrams. We derive an optical-depth-dependent bound on the perturbative truncation error and benchmark our predictions against cascaded master-equation and quantum trajectory simulations for small ensembles with OD≤2\mathrm{OD}\leq 2OD≤2, identifying a regime of controlled accuracy under weak driving. Our predictions can be experimentally demonstrated in state-of-the-art nanofibre-coupled atomic ensembles.
Understanding multi-photon interactions in non-equilibrium quantum systems is an outstanding challenge in quantum optics. In this work, we develop an analytical and diagrammatic framework to explore three-photon interactions in atomic ensembles weakly coupled to a one-dimensional waveguide. Taking advantage of the weak coupling, we use our diagrammatic framework to perform perturbation theory and calculate the leading-order contributions to the three-photon wavefunction, which would otherwise be intractable. We then compute the outgoing photon wavefunction of a resonantly driven atomic ensemble, with photon-photon interactions truncated up to three photons. Our formulation not only captures the individual transmission of photons but also isolates the connected S-matrix elements that embody genuine photon-photon correlations. Through detailed analysis, we obtain the analytic expressions of the connected third-order correlation function and the third-order electric-field-quadrature cumulant, which reveal non-Gaussian signatures emerging from the interplay of two- and three-photon processes. We also calculate the optical depth where non-Gaussian photon states can be observed. Numerical simulations based on a cascaded master equation validate our analytical predictions on a small-scale system. These results provide a formalism to further explore non-equilibrium quantum optics in atomic ensembles and extend this to the regime of non-Gaussian photon transport.
Typical schemes for generating correlated states of light require a highly nonlinear medium that is strongly coupled to an optical mode. However, unavoidable dissipative processes, which cause photon loss and blur nonlinear quantum effects, often impede such methods. In this talk, I will report on our experimental implementation of the opposite approach. Using a strongly dissipative, weakly coupled medium, we generate and study strongly correlated states of light. Specifically, we study the transmission of resonant light through an ensemble of non-interacting atoms that weakly couple to a guided optical mode. Dissipation removes uncorrelated photons while preferentially transmitting highly correlated photons, created through collectively enhanced nonlinear interactions. As a result, the transmitted light constitutes a strongly correlated many-body state of light, revealed in the second-order correlation function. The latter exhibits strong antibunching or bunching, depending on the optical depth of the atomic ensemble. The demonstrated mechanism opens a new avenue for generating nonclassical states of light and for exploring correlations of photons in non-equilibrium systems using a mix of nonlinear and dissipative processes.
In the study of optical properties of large atomic systems, a weak laser driving is often assumed to simplify the system dynamics by linearly coupled equations. Here we investigate the light-scattering properties of atomic ensembles beyond weak-field excitation through the cumulant expansion method. By progressively incorporating higher-order correlations into the steady-state equations, an enhanced accuracy can be achieved in comparison to the exact solutions obtained by solving a full density matrix. Our analysis reveals that, in the regime of weak dipole-dipole interaction, the first-order expansion yields satisfactory predictions for optical depth, while denser atomic configurations necessitate consideration of higher-order correlations. As the intensity of incident light increases, atom saturation effects become noticeable, giving rise to significant changes in light transparency, energy shift, and decay rate. This saturation phenomenon extends to subradiant atom arrays even under weak driving conditions, leading to substantial deviations from the linear model. Our findings demonstrate that the mean-field model is a good extension to linear models as it balances both accuracy and computational complexity. However, the crucial role of higher-order cumulants in large and dense atom systems remains unclear, since it is challenging theoretically owing to the exponentially increasing Hilbert space in such light-matter interacting systems.
We model and investigate the collective nonlinear optical response of an ensemble of two-level emitters that are weakly coupled to a waveguide featuring a single spatial mode. Our approach generalizes the insight that photon-photon correlations in the light scattered by a single two-level emitter result from two-photon interference to the case of many emitters. Using our model, developed for coherent driving in the weak-saturation regime, we study different configurations for probing the nonlinear response of the ensemble, e.g., through the waveguide or via external illumination, and derive analytical expressions for the second-order quantum coherence function, g ( 2 ) ( τ ) , as well as for the squeezing spectrum of the output light in the waveguide, S θ ( ω ) . For the transmission of resonant guided light, we recover the same predictions as previously made with more involved theoretical models when analyzing experimental results regarding g ( 2 ) ( τ ) [Prasad , ] and S θ ( ω ) [Hinney , ]. We also study the transmission of light that is detuned from the transition of the two-level emitter, a situation that we recently studied experimentally [Cordier , ]. Our model predictions show how the collectively enhanced nonlinear response of weakly coupled emitters can be harnessed to generate nonclassical states of light using ensembles ranging from a few to many emitters.
We theoretically investigate the quantum scattering of a weak coherent input field interacting with an ensemble of $\mathrm{\ensuremath{\Lambda}}$-type three-level atoms coupled to a one-dimensional waveguide. With an effective non-Hermitian Hamiltonian, we study the collective interaction between the atoms mediated by the waveguide mode. In our scheme, the atoms are randomly placed in the lattice along the axis of the one-dimensional waveguide. Many interesting optical properties occur in our waveguide-atom system, such as electromagnetically induced transparency. We quantify the influence of decoherence originating from both dephasing and population relaxation, and analyze the effect of the inhomogeneous broadening on the transport properties of the incident field. Moreover, we observe that strong photon-photon correlation with quantum beats can be generated in the off-resonant case, which provides an effective method for producing nonclassical light in experiment. With remarkable progress in waveguide-emitter systems, our scheme may be experimentally feasible in the near future.
We show that strongly correlated photon transport can be observed in waveguides containing optically dense ensembles of emitters. Remarkably, this occurs even for weak coupling efficiencies. Specifically, we compute the photon transport properties through a chirally coupled system of N two-level systems driven by a weak coherent field, where each emitter can also scatter photons out of the waveguide. The photon correlations arise due to an interplay of nonlinearity and coupling to a loss reservoir, which creates a strong effective interaction between transmitted photons. The highly correlated photon states are less susceptible to losses than uncorrelated photons and have a power-law decay with N. This is described using a simple universal asymptotic solution governed by a single scaling parameter which describes photon bunching and power transmission. We show numerically that, for randomly placed emitters, these results hold even in systems without chirality. The effect can be observed in existing tapered fiber setups with trapped atoms.