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1. (2D+1) pendulum beams: non-diffracting optical spatial wavepackets that simulate quantum pendulum dynamics

   https://doi.org/10.1117/12.2627732  

   Nguyen, Thao; Rodríguez-Fajardo, Valeria; Galvez, Enrique J. (March 2022, Complex Light and Optical Forces XVI, 1201704)

   Andrews, David L.; Galvez, Enrique J.; Rubinsztein-Dunlop, Halina (Ed.)

   The similarity between the 2D Helmholtz equation in elliptical coordinates and the Schr¨odinger equation for the simple mechanical pendulum inspires us to use light to mimic this quantum system. When optical beams are prepared in Mathieu modes, their intensity in the Fourier plane is proportional to the quantum mechanical probability for the pendulum. Previous works have produced a two-dimensional pendulum beam that oscillates as a function of time through the superpositions of Mathieu modes with phases proportional to pendulum energies. Here we create a three-dimensional pendulum wavepacket made of a superposition of Helical Mathieu-Gaussian modes, prepared in such a way that the components of the wave-vectors along the propagation direction are proportional to the pendulum energies. The resulting pattern oscillates or rotates as it propagates, in 3D, with the propagation coordinate playing the role of time. We obtained several different propagating beam patterns for the unbound-rotor and the bound-swinging pendulum cases. We measured the beam intensity as a function of the propagation distance. The integrated beam intensity along elliptical angles plays the role of quantum pendulum probabilities. Our measurements are in excellent agreement with numerical simulations. 

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2. Generation of extreme-ultraviolet beams with time-varying orbital angular momentum

   https://doi.org/10.1126/science.aaw9486  

   Rego, Laura; Dorney, Kevin M.; Brooks, Nathan J.; Nguyen, Quynh L.; Liao, Chen-Ting; San Román, Julio; Couch, David E.; Liu, Allison; Pisanty, Emilio; Lewenstein, Maciej; et al (June 2019, Science)

   Light fields carrying orbital angular momentum (OAM) provide powerful capabilities for applications in optical communications, microscopy, quantum optics, and microparticle manipulation. We introduce a property of light beams, manifested as a temporal OAM variation along a pulse: the self-torque of light. Although self-torque is found in diverse physical systems (i.e., electrodynamics and general relativity), it was not realized that light could possess such a property. We demonstrate that extreme-ultraviolet self-torqued beams arise in high-harmonic generation driven by time-delayed pulses with different OAM. We monitor the self-torque of extreme-ultraviolet beams through their azimuthal frequency chirp. This class of dynamic-OAM beams provides the ability for controlling magnetic, topological, and quantum excitations and for manipulating molecules and nanostructures on their natural time and length scales. 

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3. Observation of Boyer-Wolf Gaussian modes

   https://doi.org/10.1038/s41467-024-49456-x  

   Tschernig, Konrad; Guacaneme, David; Mhibik, Oussama; Divliansky, Ivan; Bandres, Miguel A (December 2024, Nature Communications)

   Abstract Stable laser resonators support three fundamental families of transverse modes: the Hermite, Laguerre, and Ince Gaussian modes. These modes are crucial for understanding complex resonators, beam propagation, and structured light. We experimentally observe a new family of fundamental laser modes in stable resonators: Boyer-Wolf Gaussian modes. By studying the isomorphism between laser cavities and quadratic Hamiltonians, we design a laser resonator equivalent to a quantum two-dimensional anisotropic harmonic oscillator with a 2:1 frequency ratio. The generated Boyer-Wolf Gaussian modes exhibit a parabolic structure and show remarkable agreement with our theoretical predictions. These modes are also eigenmodes of a 2:1 anisotropic gradient refractive index medium, suggesting their presence in any physical system with a 2:1 anisotropic quadratic potential. We identify a transition connecting Boyer-Wolf Gaussian modes to Weber nondiffractive parabolic beams. These new modes are foundational for structured light, and open exciting possibilities for applications in laser micromachining, particle micromanipulation, and optical communications. 

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4. Induced transparency by interference or polarization

   https://doi.org/10.1073/pnas.2012982118  

   Wang, Changqing; Jiang, Xuefeng; Sweeney, William R.; Hsu, Chia Wei; Liu, Yiming; Zhao, Guangming; Peng, Bo; Zhang, Mengzhen; Jiang, Liang; Stone, A. Douglas; et al (January 2021, Proceedings of the National Academy of Sciences)

   null (Ed.)

   Polarization of optical fields is a crucial degree of freedom in the all-optical analogue of electromagnetically induced transparency (EIT). However, the physical origins of EIT and polarization-induced phenomena have not been well distinguished, which can lead to confusion in associated applications such as slow light and optical/quantum storage. Here we study the polarization effects in various optical EIT systems. We find that a polarization mismatch between whispering gallery modes in two indirectly coupled resonators can induce a narrow transparency window in the transmission spectrum resembling the EIT lineshape. However, such polarization-induced transparency (PIT) is distinct from EIT: It originates from strong polarization rotation effects and shows a unidirectional feature. The coexistence of PIT and EIT provides additional routes for the manipulation of light flow in optical resonator systems. 

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5. Isolating the classical and quantum coherence of a multiphoton system

   https://doi.org/10.1186/s43074-024-00153-4  

   You, Chenglong; Hong, Mingyuan; Mostafavi, Fatemeh; Ferdous, Jannatul; León-Montiel, Roberto de J; Dawkins, Riley B; Magaña-Loaiza, Omar S (December 2024, PhotoniX)

   Abstract The classical properties of thermal light fields were instrumental in shaping our early understanding of light. Before the invention of the laser, thermal light was used to investigate the wave-particle duality of light. The subsequent formulation of the quantum theory of electromagnetic radiation later confirmed the classical nature of thermal light fields. Here, we fragment a pseudothermal field into its multiparticle constituents to demonstrate that it can host multiphoton dynamics mediated by either classical or quantum properties of coherence. This is shown in a forty-particle system through a process of scattering mediated by twisted paths endowed with orbital angular momentum. This platform enables accurate projections of the scattered pseudothermal system into isolated multiphoton subsystems governed by quantum dynamics. Interestingly, the isolated multiphoton subsystems exhibiting quantum coherence produce interference patterns previously attributed to entangled optical systems. As such, our work unveils novel mechanisms to isolate quantum systems from classical fields. This possibility opens new paradigms in quantum physics with enormous implications for the development of robust quantum technologies. 

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