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Ultrafast Coherent Dynamics of Microring Modulators arxiv.org/abs/2412.17986

Ultrafast Coherent Dynamics of Microring Modulators

Next-generation computing clusters require ultra-high-bandwidth optical interconnects to support large-scale artificial-intelligence applications. In this context, microring modulators (MRMs) emerge as a promising solution. Nevertheless, their potential is curtailed by inherent challenges, such as pronounced frequency chirp and dynamic non-linearity. Moreover, a comprehensive understanding of their coherent dynamics is still lacking, which further constrains their applicability and efficiency. Consequently, these constraints have confined their use to spectrally inefficient intensity-modulation direct-detection links. In this work, we present a thorough study of MRM coherent dynamics, unlocking phase as a new dimension for MRM-based high-speed data transmission in advanced modulation formats. We demonstrate that the phase and intensity modulations of MRMs exhibit distinct yet coupled dynamics, limiting their direct application in higher-order modulation formats. This challenge can be addressed by embedding a pair of MRMs within a Mach-Zehnder interferometer in a push-pull configuration, enabling a bistable phase response and unchirped amplitude modulation. Furthermore, we show that its amplitude frequency response exhibits a distinct dependency on frequency detuning compared to phase and intensity modulations of MRMs, without strong peaking near resonance. Harnessing the ultra-fast coherent dynamics, we designed and experimentally demonstrated an ultra-compact, ultra-wide-bandwidth in-phase/quadrature (I/Q) modulator on a silicon chip fabricated using a CMOS-compatible photonic process. Achieving a record on-chip shoreline bandwidth density exceeding 5Tb/s/mm, our device enabled coherent transmission for symbol rates up to 180Gbaud and a net bit rate surpassing 1Tb/s over an 80km span, with modulation energy consumption as low as 10.4fJ/bit.

arXiv.org

Dependence of convective precipitation extremes on near-surface relative humidity arxiv.org/abs/2412.16306

Dependence of convective precipitation extremes on near-surface relative humidity

Precipitation extremes produced by convection have been found to intensify with near-surface temperatures at a Clausius-Clapeyron rate of $6$ to $7\%$ K$^{-1}$ in simulations of radiative-convective equilibrium (RCE). However, these idealized simulations are typically performed over an ocean surface with a high near-surface relative humidity (RH) that stays roughly constant with warming. Over land, near-surface RH is lower than over ocean and is projected to decrease by global climate models. Here, we investigate the dependence of precipitation extremes on near-surface RH in convection-resolving simulations of RCE. We reduce near-surface RH by increasing surface evaporative resistance while holding free-tropospheric temperatures fixed by increasing surface temperature. This ``top-down'' approach produces an RCE state with a deeper, drier boundary layer, which weakens convective precipitation extremes in three distinct ways. First, the lifted condensation level is higher, leading to a small thermodynamic weakening of precipitation extremes. Second, the higher lifted condensation level also reduces positive buoyancy in the lower troposphere, leading to a dynamic weakening of precipitation extremes. Third, precipitation re-evaporates more readily when falling through a deeper, drier boundary layer, leading to a substantial decrease in precipitation efficiency. These three effects all follow from changes in near-surface relative humidity and are physically distinct from the mechanism that underpins the Clausius-Clapeyron scaling rate. Overall, our results suggest that changes in relative humidity must be taken into account when seeking to understand and predict changes in convective precipitation extremes over land.

arXiv.org

Development of large Micromegas readout planes for experiments searching for rare events arxiv.org/abs/2412.16313

Development of large Micromegas readout planes for experiments searching for rare events

The use of Time Projection Chambers (TPCs) in particle physics experiments has been growing since their invention, reaching sizes equivalent to buildings (ALICE or ATLAS at CERN). However, their application in another class of experiments, commonly referred to as rare event experiments, has been more recent. This work focuses on two such experiments aimed at searching for rare events: the search for neutrinoless double beta decay (PandaX-III experiment) and the search for WIMPs (TREX-DM experiment). Both utilize a large-sized gaseous TPC, necessitating that the corresponding readout plane is also large. Both also employ microbulk Micromegas readout planes. This technology has become established in recent years and is continuously improving. Due to the size limitation during manufacturing and the concurrent increase in the size of double beta experiments, there arose a need to develop a tiled readout plane, using a mosaic of modules with microbulk Micromegas, conforming the first part of this thesis, in the context of the PandaX-III experiment. The second part, featuring a single readout plane of 25 x 25 cm2 installed in TREX-DM, focuses on the specifications that define a Micromegas and its response in a high-pressure gaseous detector. Additionally, during the work on TREX-DM, the need to reduce the energy threshold of the experiment emerged, leading to the development of another composite readout plane, the GEM-Micromegas system, in which a GEM specifically manufactured for this system was installed above the Micromegas. Finally, leveraging the development of the Micromegas for TREX-DM, a new gaseous detector for the detection of surface alpha particles, called AlphaCAMM, is planned, designed, and implemented, addressing all the requirements of a low-background detector with a projection beyond the TREX-DM experiment.

arXiv.org

A multiscale radiation biophysical stochastic model describing the cell survival response at ultra-high dose rate arxiv.org/abs/2412.16322

A multiscale radiation biophysical stochastic model describing the cell survival response at ultra-high dose rate

Ultra-high dose-rate (UHDR) radiotherapy, characterized by an extremely high radiation delivery rate, represents one of the most recent and promising frontier in radiotherapy. UHDR radiotherapy, addressed in the field as FLASH radiotherapy, is a disruptive treatment modality with several benefits, including significantly shorter treatment times, unchanged effectiveness in treating tumors, and clear reductions in side effects on normal tissues. While the benefits of UHDR irradiation have been well highlighted experimentally, the biological mechanism underlying the FLASH effect is still unclear and highly debated. Nonetheless, to effectively use UHDR radiotherapy in clinics, understanding the driving biological mechanism is paramount. Since the concurrent involvement of multiple scales of radiation damage has been suggested, we developed the MultiScale Generalized Stochastic Microdosimetric Model (MS-GSM2), a multi-stage extension of the GSM2, which is a probabilistic model describing the time evolution of the DNA damage in an irradiated cell nucleus. The MS-GSM2 can investigate several chemical species combined effects, DNA damage formation, and time evolution. We demonstrate that the MS-GSM2 can predict various in-vitro UHDR experimental results across various oxygenation levels, radiation types, and energies. The MS-GSM2 can accurately describe the empirical trend of dose and dose rate-dependent cell sensitivity over a wide range, consistently describing multiple aspects of the FLASH effect and reproducing the main evidence from the in-vitro experimental data. Our model also proposes a consistent explanation for the differential outcomes observed in normal tissues and tumors, in-vivo and in-vitro.

arXiv.org

Non-Linearities In Atomic Quantum Receivers: Harmonic And Intermodulation Distortion arxiv.org/abs/2412.16366

Non-Linearities In Atomic Quantum Receivers: Harmonic And Intermodulation Distortion

Rydberg sensors offer a unique approach to radio frequency (RF) detection, leveraging the high sensitivity and quantum properties of highly-excited atomic states to achieve performance levels beyond classical technologies. Non-linear responses and distortion behavior in Rydberg atom receivers are critical to evaluating and establishing performance metrics and capabilities such as spur-free dynamic range and tolerance to unwanted interfering signals. We report here on the measurement and characterization of non-linear behavior and spurious response of a Rydberg atomic heterodyne receiver. Single-tone and two-tone testing procedures are developed and implemented for measurement of harmonic and inter-modulation distortion in Rydberg atomic receivers based on multi-photon Rydberg spectroscopy and radio-frequency heterodyne signal detection and demodulation in an atomic vapor. For a predetermined set of atomic receiver parameters and RF carrier wave in the SHF band near-resonant to a cesium Rydberg transition, we measure and characterize atomic receiver selectivity, bandwidth, roll-off, compression point (P1dB), second-order (IP2) and third-order (IP3) intercepts, and spur-free dynamic range. Receiver intermodulation distortion is characterized for the case of an interfering signal wave applied at two frequency offsets relative to the near-resonant reference local oscillator, $ΔF/F= 10^{-4}$ at 6dB and $10^{-6}$ at 22dB single-tone bandwidths, respectively. We observe that under suitable operating conditions the atomic receiver can exhibit a suppression of harmonic and inter-modulation distortion relative to that of classical receiver mixer amplifiers. Finally, we describe how the non-linear behaviors of atomic receivers can provide unique, controllable RF signatures inaccessible by classical counterparts and propose their use to realize secure communication modalities and applications.

arXiv.org

Systematic discrepancies between reference methods for non-covalent interactions within the S66 dataset arxiv.org/abs/2412.16405

Systematic discrepancies between reference methods for non-covalent interactions within the S66 dataset

The accurate treatment of non-covalent interactions is necessary to model a wide range of applications, from molecular crystals to surface catalysts to aqueous solutions and many more. Quantum diffusion Monte Carlo (DMC) and coupled cluster theory with single, double and perturbative triple excitations [CCSD(T)] are considered two widely-trusted methods for treating non-covalent interactions. However, while they have been well-validated for small molecules, recent work has indicated that these two methods can disagree by more than $7.5\,$kcal/mol for larger systems. The origin of this discrepancy remains unknown. Moreover, the lack of systematic comparisons, particularly for medium-sized complexes, has made it difficult to identify which systems may be prone to such disagreements and the potential scale of these differences. In this work, we leverage the latest developments in DMC to compute interaction energies for the entire S66 dataset, containing 66 medium-sized complexes with a balanced representation of dispersion and electrostatic interactions. Comparison to previous CCSD(T) references reveals systematic trends, with DMC predicting stronger binding than CCSD(T) for electrostatic-dominated systems, while the binding becomes weaker for dispersion-dominated systems. We show that the relative strength of this discrepancy is correlated to the ratio of electrostatic and dispersion interactions, as obtained from energy decomposition analysis methods. Finally, we pinpoint systems in the S66 dataset where these discrepancies are particularly prominent, offering cost-effective benchmarks to guide future developments in DMC, CCSD(T) as well as the wider electronic structure theory community.

arXiv.org

Rapid Climate Model Downscaling to Assess Risk of Extreme Rainfall in Bangladesh in a Warming Climate arxiv.org/abs/2412.16407

Rapid Climate Model Downscaling to Assess Risk of Extreme Rainfall in Bangladesh in a Warming Climate

As climate change drives an increase in global extremes, it is critical for Bangladesh, a nation highly vulnerable to these impacts, to assess future risks for effective adaptation and mitigation planning. Downscaling coarse-resolution climate models to finer scales is essential for accurately evaluating the risk of extremes. In this study, we apply our downscaling method, which integrates data, physics, and machine learning, to quantify the risks of extreme precipitation in Bangladesh. The proposed approach successfully captures the observed spatial patterns and risks of extreme rainfall in the current climate while generating risk and uncertainty estimates by efficiently downscaling multiple models under future climate scenarios. Our findings project that the risk of extreme rainfall rises across the country, with the most significant increases in the northeastern hilly and southeastern coastal areas. Projections show that the daily maximum rainfall for a 100-year return period could increase by approximately 50 mm/day by mid-century and around 100 mm/day by the end of the century. However, substantial uncertainties remain due to variations across multiple climate models and scenarios.

arXiv.org

Room-temperature Distributed Feedback CsPbBr$_3$ Perovskite Laser Integrated on a Silicon Nitride Waveguide Platform arxiv.org/abs/2412.15245

Room-temperature Distributed Feedback CsPbBr$_3$ Perovskite Laser Integrated on a Silicon Nitride Waveguide Platform

Silicon photonic integrated circuits (PICs) require cost-effective laser sources that can be monolithically integrated. The low cost and low-temperature solution processability of metal halide perovskites (MHPs) make them attractive alternatives to established III-V compound semiconductors for on-chip laser sources in PICs. Cesium lead bromide (CsPbBr$_3$) perovskites are emerging materials for green light-emitting diodes and lasers. To date, amplified spontaneous emission (ASE) at room temperature has been frequently achieved in CsPbBr$_3$ thin films, while reports on lasing are more limited. Here, we demonstrate a first-order grating distributed feedback (DFB) CsPbBr$_3$ thin-film laser operating at room temperature. Planar hot-pressed (PHP)-CsPbBr$_}$, with a low ASE threshold of 14.5 $μ$Jcm$^{-2}$ under 0.3 nanosecond (ns) pump pulses, was monolithically integrated into a silicon nitride (Si$_3$N$_4$) waveguide platform via a compatible top-down patterning process. The first-order grating DFB PHP-CsPbBr$_3$ thin-film laser operated at 540 nm in the green spectral region, where III-V lasers have limitations, and exhibited a lasing threshold of 0.755 mJcm$^{-2}$ at room temperature. This work marks a significant step toward utilizing MHPs for on-chip green lasers in PICs for commercial applications.

arXiv.org
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