Photon-photon Interactions Research Articles

Study of the measurement of the τ lepton anomalous magnetic moment in high energy lead-lead collisions at the LHC

The τ lepton anomalous magnetic moment aτ=gτ−22 was measured, so far, with a precision of only several percents, despite its high sensitivity to physics beyond the Standard Model such as compositeness or supersymmetry. A new study is presented to improve the sensitivity of the aτ measurement with photon-photon interactions from ultraperipheral lead-lead collisions at the LHC. The theoretical approach used in this work is based on an effective Lagrangian and on a photon flux implemented in the adraph5 Monte Carlo simulation. Using a multivariate analysis to discriminate the signal from the background processes, a sensitivity to the anomalous magnetic moment aτ=0+0.015−0.019 is obtained at 95% confidence level with a dataset corresponding to an integrated luminosity of 2 nb−1 of lead-lead collisions and assuming a conservative 10% systematic uncorrelated uncertainty for signal and background. The present results using multivariate analysis are compared to similar results obtained using sequential cuts, as done in previous measurements, showing an improvement of about 35% in the sensitivity to aτ. Published by the American Physical Society 2024

Indistinguishable photons from an artificial atom in silicon photonics

Silicon is the ideal material for building electronic and photonic circuits at scale. Integrated photonic quantum technologies in silicon offer a promising path to scaling by leveraging advanced semiconductor manufacturing and integration capabilities. However, the lack of deterministic quantum light sources and strong photon-photon interactions in silicon poses a challenge to scalability. In this work, we demonstrate an indistinguishable photon source in silicon photonics based on an artificial atom. We show that a G center in a silicon waveguide can generate high-purity telecom-band single photons. We perform high-resolution spectroscopy and time-delayed two-photon interference to demonstrate the indistinguishability of single photons emitted from a G center in a silicon waveguide. Our results show that artificial atoms in silicon photonics can source single photons suitable for photonic quantum networks and processors.

Loss-Assisted Anomalous Hong-Ou-Mandel Interference Based on Nonunitary Multilayer Graphene.

Hong-Ou-Mandel interference is an intrinsic quantum phenomenon that goes beyond the possibilities of classical physics, and enables numerous applications in quantum information science. While the photon-photon interaction is fundamentally limited to the bosonic nature of photons and the restricted phase responses from commonly used unitary optical elements, we present that a nonunitary material provides an alternative degree of freedom to control the two-photon quantum interference, even revealing anomalous quantum interference paths that do not exist in a unitary configuration. An elaborate lossy multilayer graphene that can work as a nonunitary beam splitter is used to explore its tunability over the effective photon-photon interaction in spatial modes, and to verify the particle exchange statistics by its experimental implementation in quantum state filter. This scheme is further extended to observe four-dimensional quantum interference patterns on the lossless and lossy beam splitters, and thus show its applicability even in higher-dimensional Hilbert space.

Anomalous coherent and dissipative coupling in dual photon-magnon hybrid resonators

We explored the distinctive behavior of coherent and dissipative photon-magnon coupling (PMC) in dual hybrid resonators, each incorporating an Inverted Split-Ring Resonator (ISRR) paired with a Yttrium Iron Garnet (YIG) film, positioned in close proximity but with varying relative split-gap orientations. These orientations led to notable shifts in the dispersion spectra, characterized by level repulsion and attraction, signaling coherent and dissipative coupling, respectively, in single ISRR/YIG hybrids at certain orientations. Through analytical modeling, we determined that the observed shifts in coupling types are primarily due to the effect of photon-photon (ISRR-ISRR) interactions altering the phase difference between the coupled ISRR and magnon modes. Our findings highlight that precise manipulation of the relative split-gap orientations in the ISRR resonators enables controlled coherent and dissipative coupling within planar PMC systems. This capability opens new avenues for applications in quantum information technologies and quantum materials.

Photon superfluidity through dissipation

Superfluidity—frictionless flow—has been observed in various physical systems such as liquid helium, cold atoms, and exciton polaritons. Superfluidity is usually realized by cooling and suppressing all dissipation. Here we challenge this paradigm by demonstrating signatures of superfluidity, enabled by dissipation, in the flow of light within a room-temperature oil-filled cavity. Dissipation in the oil mediates effective photon-photon interactions which are noninstantaneous and nonlocal. Such interactions were expected to severely limit the emergence of superfluidity in conservative photonic systems. Surprisingly, when launching a photon fluid with sufficiently high density and low velocity against an obstacle in our driven-dissipative cavity, we observe a record suppression of backscattering. Our experiments also reveal the reorganization dynamics of photons into a nonscattering steady state and a qualitatively changing behavior of the optical phase as light propagates around the obstacle. The phase is locked between the laser and the obstacle but evolves with the intensity in the wake of the obstacle where the density of the photon fluid and its mean-field interaction energy decrease. Using a generalized Gross–Pitaevskii equation for photons coupled to a thermal field, we model our experiments and elucidate how the noninstantaneous and nonlocal character of interactions influences the suppression of scattering associated with superfluidity. Beyond providing the first signatures of cavity photon superfluidity, and of any superfluid both at room temperature and in steady state, our results pave the way for probing photon hydrodynamics in arbitrary potential landscapes using structured mirrors. Published by the American Physical Society 2024

CMB spectral distortions from an axion-dark photon-photon interaction

The presence of a plethora of light spin 0 and spin 1 fields is motivated in a number of BSM scenarios, such as the axiverse. The study of the interactions of such light bosonic fields with the Standard Model has focused mostly on interactions involving only one such field, such as the axion (ϕ) coupling to photons, \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi F\\widetilde{F}$$\\end{document}, or the kinetic mixing between photon and the dark photon, FFD. In this work, we continue the exploration of interactions involving two light BSM fields and the standard model, focusing on the mixed axion-photon-dark-photon interaction \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi F{\\widetilde{F}}_{D}$$\\end{document}. If either the axion or dark photon are dark matter, we show that this interaction leads to conversion of the CMB photons into a dark sector particle, leading to a distortion in the CMB spectrum. We present the details of these unique distortion signatures and the resulting constraints on the \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi F{\\widetilde{F}}_{D}$$\\end{document} coupling. In particular, we find that for a wide range of masses, the constraints from these effect are stronger than on the more widely studied axion-photon coupling.

Strongly Interacting Photons in 2D Waveguide QED.

One-dimensional confinement in waveguide quantum electrodynamics (QED) plays a crucial role to enhance light-matter interactions and to induce a strong quantum nonlinear optical response. In two or higher-dimensional settings, this response is reduced since photons can be emitted within a larger phase space, opening the question whether strong photon-photon interaction can be still achieved. In this study, we positively answer this question for the case of a 2D square array of atoms coupled to the light confined into a two-dimensional waveguide. More specifically, we demonstrate the occurrence of long-lived two-photon repulsive and bound states with genuine 2D features. Furthermore, we observe signatures of these effects also in free-space atomic arrays in the form of weakly subradiant in-band scattering resonances. Our findings provide a paradigmatic signature of the presence of strong photon-photon interactions in 2D waveguide QED.

Micro-optical Maximization of Photon-photon Interaction

In the “Star Wars” movies, Jedi knights engage in dazzling duels with lightsabers that confine light and push it against each other. However, confining photons or enabling their interaction in reality, especially in free space, is extremely challenging. Photon-photon interactions, which are only possible through optical nonlinearity, are difficult to achieve with conventional materials. The quest to confine photons in a specific space for as long as possible, and to allow individual photons to interact with each other, is a major challenge for researchers in physics and optics. Since the invention of the laser, the study of optical nonlinearity has been the foundation of various modern scientific and technological advances that contribute significantly to our daily lives. Recently, optical nonlinearity has become a central platform for quantum information, computing, and sensing research, highlighting its growing importance. This article discusses a new turning point in optical nonlinearity based on micro-resonators, and presents efforts and future perspectives to realize photon-photon interactions.

Universal and Ultrafast Quantum Computation Based on Free-Electron-Polariton Blockade

Cavity QED, wherein a quantum emitter is coupled to electromagnetic cavity modes, is a powerful platform for implementing quantum sensors, memories, and networks. However, due to the fundamental trade-off between gate fidelity and execution time, as well as limited scalability, the use of cavity QED for quantum computation was overtaken by other architectures. Here, we introduce a new element into cavity QED—a free charged particle, acting as a flying qubit. Using free electrons as a specific example, we demonstrate that our approach enables ultrafast, deterministic, and universal discrete-variable quantum computation in a cavity-QED-based architecture, with potentially improved scalability. Our proposal hinges on a novel excitation blockade mechanism in a resonant interaction between a free-electron and a cavity polariton. This nonlinear interaction is faster by several orders of magnitude with respect to current photon-based cavity-QED gates, enjoys wide tunability and can demonstrate fidelities close to unity. Furthermore, our scheme is ubiquitous to any cavity nonlinearity, either due to light-matter coupling as in the Jaynes-Cummings model or due to photon-photon interactions as in a Kerr-type many-body system. In addition to promising advancements in cavity-QED quantum computation, our approach paves the way towards ultrafast and deterministic generation of highly entangled photonic graph states and is applicable to other quantum technologies involving cavity QED. Published by the American Physical Society 2024

Correlations of dihadron polarization in central, peripheral, and ultraperipheral heavy-ion collisions

While jet quenching in relativistic heavy-ion collisions has been extensively studied over decades, the polarization of quenched hadrons has rarely been discussed. It has recently been proposed that the correlations of dihadron polarization in e+e− and pp collisions provide a novel probe of the longitudinal spin transfer from hard partons to hadrons without requiring the colliding beams to be polarized. To support realistic experimental measurement of dihadron polarization with sufficient luminosity, we extend the aforementioned study to relativistic heavy-ion collisions by convoluting the vacuum fragmentation of partons with their energy loss inside the quark-gluon plasma. We find that while the correlation functions of Λ−Λ (or Λ−Λ¯) polarization in peripheral collisions is consistent with those in pp collisions, clear enhancement can be seen in central collisions. These correlation functions appear sensitive to different assumptions in the de Florian-Stratmann-Vogelsang (DSV) of parton fragmentation functions and, therefore, could place additional constraints on the spin-dependent fragmentation functions of quarks and gluons. The correlation of dihadron polarization has also been explored in ultraperipheral heavy-ion collisions, which provides a cleaner probe of fragmentation functions of quarks produced by energetic photon-photon and photon-Pomeron interactions. Published by the American Physical Society 2024

Overview of recent CMS results

Recent results from the CMS Collaboration are presented. These measurements include a full physics program using ultraperipheral collisions such as photon-photon and photon-ion interactions, small collision systems including proton-proton and proton-lead collisions, and many measurements of hadronic ion-ion collisions. The properties of the quark-gluon plasma produced in ion-ion collisions are studied in detail. The measurements examine the number of degrees of freedom of the medium, the strength of jet quenching effects in the medium, the role of heavy flavor in hadronization processes, and more.

Control of photon-photon interaction via a cavity.

Controlling the interaction between photons is one of the important technologies applied to quantum information processing at the few-photon level. We investigate the two-photon interaction via a Ξ-type atom, where one atomic transition is coupled to a one-dimensional waveguide, and the other transition is coupled to a cavity field. Whether the cavity is initially in the vacuum state or not, determines the effective configuration of the quantum emitter. When the cavity is in the vacuum state, only one bound state appears. We further found that the joint probability of transmitted photons oscillates with their spatial separation due to the coexistence of two bound states, if the cavity is in fock state |n〉 (n ≠ 0). With the incoming wave function consists entirely of plane waves, we present the exact out-state function that exhibit the bunching and antibunching behaviors. And, we discuss in detail with the behaviors of varying both the photon pair energy(E) and the energy difference between the two photons (Δ). Moreover, the spatial attraction and repulsion between the two transmitted photons can be controlled by the parameters of the cavity.

On the Wave-Particle Duality of the Photons and the Matter-Photon Particle Mixture Model

Relativistic quantum mechanics and many experimental results and observations show that electron-positron annihilation can produce photons; photon-matter and photon-photon interaction can also create electrons and positrons. The photons have no rest mass, e.g. relative to Lab frame, and always travel at the speed of light in the vacuum. In this paper, a rotational moving electric dipole model with negative and positive charges was proposed for photons. In a vacuum, the electric dipoles are moving in a twisted helical motion around their propagation axis (their center of mass). Photon particles are traveling at the speed of light along the propagation axis. This pair of negative and positive charged particles exerts both electrostatic and magnetic force on each other. Both forces are attractive and act as a centripetal force to keep the electric dipole in a continuous helical motion around the axis of rotation. With this model, the wave-particle duality of photons can be described simultaneously. The space is filled by matter (having rest mass relative to Lab frame) and photons (without rest mass); it is a multicomponent mixture fluid. In "vacuum", though there is no rest matter particle, but there are still photon gas particles, the total energy-momentum tensor should include rest matter particles and photon gas particles.

Ultra-Peripheral Collisions physics with ATLAS

Exclusive production of dilepton pairs, γγ → ℓℓ, ℓ = e, μ, τ, is studied using data from ultraperipheral collisions (UPC) of lead nuclei at TeV recorded by the ATLAS detector [1] at the LHC. The process of interest proceeds via photon-photon interactions in the strong electromagnetic fields of relativistic lead nuclei. In the case of the dielectron production, within experimental uncertainties the measured integrated cross section is in good agreement with the QED predictions from the Monte Carlo programs STARlight and SuperChic, confirming the broad features of the initial photon fluxes. The differential cross section shows systematic differences from these predictions which are more pronounced at high absolute rapidity, |yee | and scattering angle, |cosθ*|. In the dimuon production case, the measured cross sections at large absolute rapidity |yμμ | is found to be about 10-20% larger in data than in the calculations, suggesting the presence of larger fluxes of photons in the initial state. The γγ → ττ process is observed in the UPCs with a significance exceeding 5 standard deviations. This observation can be turned into a constraint on the τ-lepton anomalous magnetic moment. Measurement of light-by-light scattering data are also performed during the LHC Run 2. The diphoton invariant mass distribution is used to set limits on the production of axion-like particles. This result provides the most stringent limits to date on axion-like particle production for masses in the range 6-100 GeV.

Quantum vortices of strongly interacting photons

Vortices are topologically nontrivial defects that generally originate from nonlinear field dynamics. All-optical generation of photonic vortices—phase singularities of the electromagnetic field—requires sufficiently strong nonlinearity that is typically achieved in the classical optics regime. We report on the realization of quantum vortices of photons that result from a strong photon-photon interaction in a quantum nonlinear optical medium. The interaction causes faster phase accumulation for copropagating photons, producing a quantum vortex-antivortex pair within the two-photon wave function. For three photons, the formation of vortex lines and a central vortex ring confirms the existence of a genuine three-photon interaction. The wave function topology, governed by two- and three-photon bound states, imposes a conditional phase shift of π per photon, a potential resource for deterministic quantum logic operations.

Time Translation Symmetry Breaking in an Isolated Spin-Orbit-Coupled Fluid of Light.

We study the interplay between intrinsic spin-orbit coupling and nonlinear photon-photon interactions in a nonparaxial, elliptically polarized fluid of light propagating in a bulk Kerr medium. We find that in situations where the nonlinear interactions induce birefringence, i.e., a polarization-dependent nonlinear refractive index, their interplay with spin-orbit coupling results in an interference between the two polarization components of the fluid traveling at different wave vectors, which entails the breaking of translation symmetry along the propagation direction. This phenomenon leads to a Floquet band structure in the Bogoliubov spectrum of the fluid, and to characteristic oscillations of its intensity correlations. We characterize these oscillations in detail and point out their exponential growth at large propagation distances, revealing the presence of parametric resonances.

Quantum nonlinear metasurfaces from dual arrays of ultracold atoms

Atoms in a sub-wavelength lattices have remarkable optical properties that have become of high scientific and technological significance. Here, we show how the coupling of light to more than a single atomic array can expand these perspectives into the domain of quantum nonlinear optics. While a single array transmits and reflects light in a largely linear fashion, the combination of two arrays is found to induce strong photon-photon interactions that can convert an incoming classical beam into highly antibunched light. Such quantum metasurfaces open up new possibilities for coherently generating and manipulating nonclassical light, from optical quantum information processing to exploring quantum many-body phenomena in two-dimensional systems of strongly interacting photons.

Observation of photon-photon thermodynamic processes under negative optical temperature conditions.

Statistical mechanics demands that the temperature of a system is positive provided that its internal energy has no upper bound. Yet if this condition is not met, it is possible to attain negative temperatures for which higher-order energy states are thermodynamically favored. Although negative temperatures have been reported in spin and Bose-Hubbard settings as well as in quantum fluids, the observation of thermodynamic processes in this regime has thus far remained elusive. Here, we demonstrate isentropic expansion-compression and Joule expansion for negative optical temperatures, enabled by purely nonlinear photon-photon interactions in a thermodynamic microcanonical photonic system. Our photonic approach provides a platform for exploring new all-optical thermal engines and could have ramifications in other bosonic systems beyond optics, such as cold atoms and optomechanics.

HEWES: Heisenberg–Euler weak-field expansion simulator

Vacuum polarization, a key prediction of quantum theory, can cause a variety of intriguing phenomena that can be triggered by high-intensity laser pulses. The Heisenberg-Euler theory of the quantum vacuum supplements Maxwell's theory of electromagnetism with nonlinear photon-photon interactions mediated by vacuum fluctuations. This work presents a numerical solver for the leading weak-field Heisenberg-Euler corrections. The present code implementation reaches an accuracy of order thirteen in the numerical scheme and takes into account up to six-photon interactions. Since theoretical approaches are limited to approximations and the experimental requirements for signal detection are high, the need for support from the numerical side is apparent.

Impact parameter dependence of photon-photon interactions in relativistic heavy-ion collisions

The Lorentz-boosted electromagnetic fields surrounding relativistic heavy ions with large charges can be treated as a flux of linearly polarized quasireal photons, which can interact via the photon-photon scattering to produce lepton antilepton pairs. Those photon-photon interactions can happen even in heavy-ion collisions with hadronic overlap, making an opportunity to probe the electromagnetic properties of the produced deconfined quark-gluon plasma. In this paper, we review the recent experimental progress of the impact parameter dependent photon-photon interactions in heavy-ion collisions, and discuss their essential role in probing the possible electromagnetic properties of quark-gluon plasma produced in hadronic heavy-ion collisions.