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1. Enhanced cavity coupling to silicon vacancies in 4H silicon carbide using laser irradiation and thermal annealing

   https://doi.org/10.1073/pnas.2021768118  

   Gadalla, Mena N. ; Greenspon, Andrew S. ; Defo, Rodrick Kuate ; Zhang, Xingyu ; Hu, Evelyn L. ( March 2021 , Proceedings of the National Academy of Sciences)

   The negatively charged silicon monovacancy${\mathrm{V}}_{\text{Si}}^{-}$in 4H silicon carbide (SiC) is a spin-active point defect that has the potential to act as a qubit in solid-state quantum information applications. Photonic crystal cavities (PCCs) can augment the optical emission of the${\mathrm{V}}_{\text{Si}}^{-}$, yet fine-tuning the defect–cavity interaction remains challenging. We report on two postfabrication processes that result in enhancement of the$\mathrm{V}1\prime$optical emission from our PCCs, an indication of improved coupling between the cavity and ensemble of silicon vacancies. Below-bandgap irradiation at 785-nm and 532-nm wavelengths carried out at times ranging from a few minutes to several hours results in stable enhancement of emission, believed to result from changing the relative ratio of${\mathrm{V}}_{\text{Si}}^0$(“dark state”) to${\mathrm{V}}_{\text{Si}}^{-}$(“bright state”). The much faster change effected by 532-nm irradiation may result from cooperative charge-state conversion due to proximal defects. Thermal annealing at 100 °C, carried out over 20 min, also results in emission enhancements and may be explained by the relatively low-activation energy diffusion of carbon interstitials${\mathrm{C}}_{\mathrm{i}}$, subsequently recombining with other defects to create additional${\mathrm{V}}_{\text{Si}}^{-}$s. These PCC-enabled experiments reveal insights into defect modifications and interactions within a controlled, designated volume and indicate pathways tomore »improved defect–cavity interactions.

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2. The metastable Q ³ Δ ₂ state of ThO: a new resource for the ACME electron EDM search

   https://doi.org/10.1088/1367-2630/ab6a3a  

   Wu, X. ; Han, Z. ; Chow, J. ; Ang, D. G. ; Meisenhelder, C. ; Panda, C. D. ; West, E. P. ; Gabrielse, G. ; Doyle, J. M. ; DeMille, D. ( February 2020 , New Journal of Physics)

   The best upper limit for the electron electric dipole moment was recently set by the ACME collaboration. This experiment measures an electron spin-precession in a cold beam of ThO molecules in their metastable$H{(}^3{\mathrm{\Delta }}_1)$state. Improvement in the statistical and systematic uncertainties is possible with more efficient use of molecules from the source and better magnetometry in the experiment, respectively. Here, we report measurements of several relevant properties of the long-lived$Q{(}^3{\mathrm{\Delta }}_2)$state of ThO, and show that this state is a very useful resource for both these purposes. TheQstate lifetime is long enough that its decay during the time of flight in the ACME beam experiment is negligible. The large electric dipole moment measured for theQstate, giving rise to a large linear Stark shift, is ideal for an electrostatic lens that increases the fraction of molecules detected downstream. The measured magnetic moment of theQstate is also large enough to be used as a sensitive co-magnetometer in ACME. Finally, we show that theQstate has a large transition dipole moment to the$C{(}^1{\mathrm{\Pi }}_1)$state, which allows for efficient population transfer between the ground statewidth='0.50em'/>(1Σ+)and theQstate via$X-C-Q$Stimulated Raman Adiabatic Passage (STIRAP). We demonstrate 90 % STIRAP transfer efficiency. In the course of these measurements, we also determine the magnetic moment ofCstate, the$X\to C$transition dipole moment, and branching ratios of decays from theCstate.

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3. Formation and evolution of post-solitons following a high intensity laser-plasma interaction with a low-density foam target

   https://doi.org/10.1088/1361-6587/abf85c  

   Blackman, David R. ; Adak, Amitava ; Singh, Prashant K. ; Lad, Amit D. ; Chatterjee, Gourab ; Ridgers, Christopher P. ; Del Sorbo, Dario ; Trines, Raoul M. G. M. ; Robinson, A. P. L. ; Nazarov, Wigen ; et al ( May 2021 , Plasma Physics and Controlled Fusion)

   The formation and evolution of post-solitons has been discussed for quite some time both analytically and through the use of particle-in-cell (PIC) codes. It is however only recently that they have been directly observed in laser-plasma experiments. Relativistic electromagnetic (EM) solitons are localised structures that can occur in collisionless plasmas. They consist of a low-frequency EM wave trapped in a low electron number-density cavity surrounded by a shell with a higher electron number-density. Here we describe the results of an experiment in which a 100 TW Ti:sapphire laser (30 fs, 800 nm) irradiates a$0.03\mathrm{g}\mathrm{c}{\mathrm{m}}^{-3}$TMPTA foam target with a focused intensity$I_{\mathrm{l}}=9.5\times {10}^{17}\mathrm{W}\mathrm{c}{\mathrm{m}}^{-2}$. A third harmonic (${\lambda }_{\mathrm{p}\mathrm{r}\mathrm{o}\mathrm{b}\mathrm{e}}\simeq 266$nm) probe is employed to diagnose plasma motion for 25 ps after the main pulse interaction via Doppler-Spectroscopy. Both radiation-hydrodynamics and 2D PIC simulations are performed to aid in the interpretation of the experimental results. We show that the rapid motion of the probe critical-surface observed in the experiment might be a signature of post-soliton wall motion.
4. Electro-optic interface for ultrasensitive intracavity electric field measurements at microwave and terahertz frequencies

   https://doi.org/10.1364/OPTICA.384160  

   Benea-Chelmus, Ileana-Cristina ; Salamin, Yannick ; Settembrini, Francesca Fabiana ; Fedoryshyn, Yuriy ; Heni, Wolfgang ; Elder, Delwin L. ; Dalton, Larry R. ; Leuthold, Juerg ; Faist, Jérôme ( May 2020 , Optica)

   Electro-optic quantum coherent interfaces map the amplitude and phase of a quantum signal directly to the phase or intensity of a probe beam. At terahertz frequencies, a fundamental challenge is not only to sense such weak signals (due to a weak coupling with a probe in the near-infrared) but also to resolve them in the time domain. Cavity confinement of both light fields can increase the interaction and achieve strong coupling. Using this approach, current realizations are limited to low microwave frequencies. Alternatively, in bulk crystals, electro-optic sampling was shown to reach quantum-level sensitivity of terahertz waves. Yet, the coupling strength was extremely weak. Here, we propose an on-chip architecture that concomitantly provides subcycle temporal resolution and an extreme sensitivity to sense terahertz intracavity fields below 20 V/m. We use guided femtosecond pulses in the near-infrared and a confinement of the terahertz wave to a volume of$V_{\mathrm{T}\mathrm{H}\mathrm{z}}\sim <\#comment/>{10}^{-<\#comment/>9}({\mathrm{\lambda <\#comment/>}}_{\mathrm{T}\mathrm{H}\mathrm{z}}/2{)}^3$in combination with ultraperformant organic molecules ($r_{33}=170\mathrm{p}\mathrm{m}/\mathrm{V}$) and accomplish a record-high single-photon electro-optic coupling rate ofmathvariant='normal'>Hz, 10,000 times higher than in recent reports of sensing vacuum field fluctuations in bulk media. Via homodyne detection implemented directly on chip, the interaction results into an intensity modulation of the femtosecond pulses. The single-photon cooperativity is$C_0=1.6\times <\#comment/>{10}^{-<\#comment/>8}$, and the multiphoton cooperativity is$C=0.002$at room temperature. We show$><\#comment/>70\mathrm{d}\mathrm{B}$dynamic range in intensity at 500 ms integration under irradiation with a weak coherent terahertz field. Similar devices could be employed in future measurements of quantum states in the terahertz at the standard quantum limit, or for entanglement of subsystems on subcycle temporal scales, such as terahertz and near-infrared quantum bits.

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5. Microphysics of Relativistic Collisionless Electron-ion-positron Shocks

   https://doi.org/10.3847/1538-4357/ac713e  

   Grošelj, Daniel ; Sironi, Lorenzo ; Beloborodov, Andrei M. ( July 2022 , The Astrophysical Journal)

   We perform particle-in-cell simulations to elucidate the microphysics of relativistic weakly magnetized shocks loaded with electron-positron pairs. Various external magnetizationsσ≲ 10⁻⁴and pair-loading factorsZ_±≲ 10 are studied, whereZ_±is the number of loaded electrons and positrons per ion. We find the following: (1) The shock becomes mediated by the ion Larmor gyration in the mean field whenσexceeds a critical valueσ_Lthat decreases withZ_±. Atσ≲σ_Lthe shock is mediated by particle scattering in the self-generated microturbulent fields, the strength and scale of which decrease withZ_±, leading to lowerσ_L. (2) The energy fraction carried by the post-shock pairs is robustly in the range between 20% and 50% of the upstream ion energy. The mean energy per post-shock electron scales as${\overline{E}}_{\mathrm{e}}\propto {\left(Z_{\pm }+1\right)}^{-1}$. (3) Pair loading suppresses nonthermal ion acceleration at magnetizations as low asσ≈ 5 × 10⁻⁶. The ions then become essentially thermal with mean energy${\overline{E}}_{\mathrm{i}}$, while electrons form a nonthermal tail, extending from$E\sim {\left(Z_{\pm }+1\right)}^{-1}{\overline{E}}_{\mathrm{i}}$to${\overline{E}}_{\mathrm{i}}$. Whenσ= 0, particle acceleration is enhanced by the formation of intense magnetic cavities that populate the precursor during the late stages of shock evolution. Here,more »the maximum energy of the nonthermal ions and electrons keeps growing over the duration of the simulation. Alongside the simulations, we develop theoretical estimates consistent with the numerical results. Our findings have important implications for models of early gamma-ray burst afterglows.

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