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1. Observation of muonic Dalitz decays of chib mesons and precise spectroscopy of hidden-beauty states

   https://doi.org/10.1007/JHEP10(2024)122  

   Aaij, R; Abdelmotteleb, A_S W; Abellan_Beteta, C; Abudinén, F; Ackernley, T; Adefisoye, A A; Adeva, B; Adinolfi, M; Adlarson, P; Agapopoulou, C; et al (October 2024, Journal of High Energy Physics)

   A<sc>bstract</sc> The decays of the χ_b1(1P), χ_b2(1P), χ_b1(2P) and χ_b2(2P) mesons into the Υ(1S)μ⁺μ⁻final state are observed with a high significance using proton-proton collision data collected with the LHCb detector and corresponding to an integrated luminosity of 9 fb⁻¹. The newly observed decays together with the Υ(2S) → Υ(1S)π⁺π⁻and Υ(3S) → Υ(2S)π⁺π⁻decay modes are used for precision measurements of the mass and mass splittings for the hidden-beauty states. 

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2. General framework for ultrafast nonlinear photonics: unifying single and multi-envelope treatments [Invited]

   https://doi.org/10.1364/OE.513856  

   Phillips, C_R; Jankowski, M.; Flemens, N.; Fejer, M_M (February 2024, Optics Express)

   Numerical modeling of ultrashort pulse propagation is important for designing and understanding the underlying dynamical processes in devices that take advantage of highly nonlinear interactions in dispersion-engineered optical waveguides. Once the spectral bandwidth reaches an octave or more, multiple types of nonlinear polarization terms can drive individual optical frequencies. This issue is particularly prominent inχ⁽²⁾devices where all harmonics of the input pulse are generated and there can be extensive spectral overlap between them. Single-envelope approaches to pulse propagation have been developed to address these complexities; this has led to a significant mismatch between the strategies used to analyze moderate-bandwidth devices (usually involving multi-envelope models) and those used to analyze octave-spanning devices (usually involving models with one envelope per waveguide mode). Here we unify the different strategies by developing a common framework, applicable to any optical bandwidth, that allows for a side-by-side comparison between single- and multi-envelope models. We include bothχ⁽²⁾andχ⁽³⁾interactions in these models, with emphasis onχ⁽²⁾interactions. We show a detailed example based on recent supercontinuum generation experiments in a thin-film LiNbO₃on sapphire quasi-phase-matching waveguide. Our simulations of this device show good agreement between single- and multi-envelope models in terms of the frequency comb properties of the electric field, even for multi-octave-spanning spectra. Building on this finding, we explore how the multi-envelope approach can be used to develop reduced models that help build physical insights about new ultrafast photonics devices enabled by modern dispersion-engineered waveguides, and discuss practical considerations for the choice of such models. More broadly, we give guidelines on the pros and cons of the different modeling strategies in the context of device design, numerical efficiency, and accuracy of the simulations. 

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3. Degenerate optical parametric amplification in CMOS silicon

   https://doi.org/10.1364/OPTICA.478702  

   Heydari, David; Cătuneanu, Mircea; Ng, Edwin; Gray, Dodd_J; Hamerly, Ryan; Mishra, Jatadhari; Jankowski, Marc; Fejer, M_M; Jamshidi, Kambiz; Mabuchi, Hideo (March 2023, Optica)

   Silicon is a common material for photonics due to its favorable optical properties in the telecom and mid-wave IR bands, as well as compatibility with a wide range of complementary metal–oxide semiconductor (CMOS) foundry processes. Crystalline inversion symmetry precludes silicon from natively exhibiting second-order nonlinear optical processes. In this work, we build on recent works in silicon photonics that break this material symmetry using large bias fields, thereby enablingχ⁽²⁾interactions. Using this approach, we demonstrate both second-harmonic generation (with a normalized efficiency of 0.20%W⁻¹cm⁻²) and, to our knowledge, the first degenerateχ⁽²⁾optical parametric amplifier (with an estimated normalized gain of 0.6dBW^−1/2cm⁻¹) using silicon-on-insulator waveguides fabricated in a CMOS-compatible commercial foundry. We expect this technology to enable the integration of novel nonlinear optical devices such as optical parametric amplifiers, oscillators, and frequency converters into large-scale, hybrid photonic–electronic systems by leveraging the extensive ecosystem of CMOS fabrication. 

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4. Spindown of Pulsars Interacting with Companion Winds: The Impact of Magnetospheric Compression

   https://doi.org/10.3847/1538-4357/ad6840  

   Zhong, Yici; Spitkovsky, Anatoly; Mahlmann, Jens_F; Hakobyan, Hayk (September 2024, The Astrophysical Journal)

   Abstract Pulsars in binary systems with strong companion winds can have the magnetopause separating their magnetosphere from the wind located well within their light cylinder. This bow-like enclosure effectively creates a waveguide that confines the pulsar’s electromagnetic fields and can significantly alter its spindown. In this paper, we study the spindown of compressed pulsar magnetospheres in such systems. We parameterize the confinement as the ratio between the equatorial position of the magnetopause (or standoff distance)R_mand the pulsar’s light cylinderR_LC. Using particle-in-cell simulations, we quantify the pulsar spindown for a range of compressions,R_m/R_LC= 1/3–1, and inclination angles,χ= 0°…90°, between magnetic and rotation axes. Our strongly confined models (R_m/R_LC= 1/3) show two distinct limits. Forχ= 0°, the spindown of a compressed pulsar magnetosphere is enhanced by approximately a factor of three compared to an isolated pulsar due to the increased number of open magnetic field lines. Conversely, forχ= 90°, the compressed pulsar spins down at less than 40% of the rate of an isolated reference pulsar due to the mismatch between the pulsar wind stripe wavelength and the waveguide size. We apply our analysis to the 2.77 s oblique rotator (χ= 60°) in the double-pulsar system PSR J0737-3039. With the numerically derived spindown estimate, we constrain its surface magnetic field toB_*≈ (7.3 ± 0.2) × 10¹¹G. We discuss the time modulation of its period derivative, the effects of compression on its braking index, and implications for the radio eclipse in PSR J0737-3039. 

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5. Ultrafast second-order nonlinear photonics—from classical physics to non-Gaussian quantum dynamics: a tutorial

   https://doi.org/10.1364/AOP.495768  

   Jankowski, Marc; Yanagimoto, Ryotatsu; Ng, Edwin; Hamerly, Ryan; McKenna, Timothy P; Mabuchi, Hideo; Fejer, M M (June 2024, Advances in Optics and Photonics)

   Photonic integrated circuits with second-order (χ⁽²⁾) nonlinearities are rapidly scaling to remarkably low powers. At this time, state-of-the-art devices achieve saturated nonlinear interactions with thousands of photons when driven by continuous-wave lasers, and further reductions in these energy requirements enabled by the use of ultrafast pulses may soon push nonlinear optics into the realm of single-photon nonlinearities. This tutorial reviews these recent developments in ultrafast nonlinear photonics, discusses design strategies for realizing few-photon nonlinear interactions, and presents a unified treatment of ultrafast quantum nonlinear optics using a framework that smoothly interpolates from classical behaviors to the few-photon scale. These emerging platforms for quantum optics fundamentally differ from typical realizations in cavity quantum electrodynamics due to the large number of coupled optical modes. Classically, multimode behaviors have been well studied in nonlinear optics, with famous examples including soliton formation and supercontinuum generation. In contrast, multimode quantum systems exhibit a far greater variety of behaviors, and yet closed-form solutions are even sparser than their classical counterparts. In developing a framework for ultrafast quantum optics, we identify what behaviors carry over from classical to quantum devices, what intuition must be abandoned, and what new opportunities exist at the intersection of ultrafast and quantum nonlinear optics. Although this article focuses on establishing connections between the classical and quantum behaviors of devices withχ⁽²⁾nonlinearities, the frameworks developed here are general and are readily extended to the description of dynamical processes based on third-orderχ⁽³⁾nonlinearities. 

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