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1. Multi-sideband interference structures by high-order photon-induced continuum-continuum transitions in helium

   https://doi.org/10.1103/PhysRevA.109.023110  

   Bharti, D; Srinivas, H; Shobeiry, F; Bondy, A T; Saha, S; Hamilton, K R; Moshammer, R; Pfeifer, T; Bartschat, K; Harth, A (February 2024, Physical Review A)

   Following up on a previous paper on two-color photoionization of Ar(3p) [D. Bharti et al., Phys. Rev. A 103, 022834 (2021)], we present measurements and calculations for a modified three-sideband (3-SB) version of the reconstruction of attosecond beating by interference of two-photon transitions (RABBITT) configuration applied to He(1s). The 3-SB RABBITT approach allows us to explore interference effects between pathways involving different orders of transitions within the continuum. The relative differences in the retrieved oscillation phases of the three sidebands provide insights into the continuum-continuum transitions. The ground state of helium has zero orbital angular momentum, which simplifies the analysis of oscillation phases and their angle dependence within the three sidebands. We find qualitative agreement between our experimental results and the theoretical predictions for many cases but also observe some significant quantitative discrepancies. 

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2. Influence of final state interactions in attosecond photoelectron interferometry

   https://doi.org/10.1103/PhysRevResearch.6.043271  

   Luo, S; Weissenbilder, R; Laurell, H; Bello, R Y; Marante, C; Ammitzböll, M; Neoričić, L; Ljungdahl, A; Squibb, R J; Feifel, R; et al (December 2024, Physical Review Research)

   Fano resonances are ubiquitous phenomena appearing in many fields of physics, e.g., atomic or molecular photoionization, or electron transport in quantum dots. Recently, attosecond interferometric techniques have been used to measure the amplitude and phase of photoelectron wave packets close to Fano resonances in argon and helium, allowing for the retrieval of the temporal dynamics of the photoionization process. In this work, we study the photoionization of argon atoms close to the $3s^{1}3p^{6}4p$autoionizing state using an interferometric technique with high spectral resolution. The phase shows a monotonic $2\pi$variation across the resonance or a nonmonotonic less than $\pi$variation depending on experimental conditions, e.g., the probe laser bandwidth. Using three different, state-of-the-art calculations, we show that the measured phase is influenced by the interaction between final states reached by two-photon transitions. Published by the American Physical Society2024 

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3. On-chip spin-orbit locking of quantum emitters in 2D materials for chiral emission

   https://doi.org/10.1364/OPTICA.463481  

   Ma, Yichen; Zhao, Haoqi; Liu, Na; Gao, Zihe; Mohajerani, Seyed_Sepehr; Xiao, Licheng; Hone, James; Feng, Liang; Strauf, Stefan (August 2022, Optica)

   Light carries both spin angular momentum (SAM) and orbital angular momentum (OAM), which can be used as potential degrees of freedom for quantum information processing. Quantum emitters are ideal candidates towards on-chip control and manipulation of the full SAM–OAM state space. Here, we show coupling of a spin-polarized quantum emitter in a monolayer ${\mathrm{W}\mathrm{S}\mathrm{e}}_2$with the whispering gallery mode of a ${\mathrm{S}\mathrm{i}}_3{\mathrm{N}}_4$ring resonator. The cavity mode carries a transverse SAM of $\mathrm{\sigma <\#comment/>}=\pm <\#comment/>1$in the evanescent regions, with the sign depending on the orbital power flow direction of the light. By tailoring the cavity–emitter interaction, we couple the intrinsic spin state of the quantum emitter to the SAM and propagation direction of the cavity mode, which leads to spin–orbit locking and subsequent chiral single-photon emission. Furthermore, by engineering how light is scattered from the WGM, we create a high-order Bessel beam which opens up the possibility to generate optical vortex carrying OAM states. 

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4. Femtosecond timing synchronization at megahertz repetition rates for an x-ray free-electron laser

   https://doi.org/10.1364/OPTICA.396728  

   Sato, Tokushi; Letrun, Romain; Kirkwood, Henry_J; Liu, Jia; Vagovič, Patrik; Mills, Grant; Kim, Yoonhee; Takem, Cedric_M_S; Planas, Marc; Emons, Moritz; et al (June 2020, Optica)

   A critical challenge of pump-probe experiments with x-ray free-electron lasers (XFELs) is accurate synchronization of x-ray and optical pulses. At the European XFEL we observed megahertz rate timing jitter of $24.0\pm <\#comment/>12.4\mathrm{f}\mathrm{s}$. 

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5. Partons as unique ground states of quantum Hall parent Hamiltonians: The case of Fibonacci anyons

   https://doi.org/10.21468/SciPostPhys.15.2.043  

   Tanhayi Ahari, Mostafa; Bandyopadhyay, Sumanta; Nussinov, Zohar; Seidel, Alexander; Ortiz, Gerardo (January 2023, SciPost Physics)

   We present microscopic, multiple Landau level, (frustration-free and positive semi-definite) parent Hamiltonians whose ground states, realizing different quantum Hall fluids, are parton-like and whose excitations display either Abelian or non-Abelian braiding statistics. We prove ground state energy monotonicity theorems for systems with different particle numbers in multiple Landau levels, demonstrate S-duality in the case of toroidal geometry, and establish complete sets of zero modes of special Hamiltonians stabilizing parton-like states, specifically at filling factor\nu=2/3 $\nu =2/3$. The emergent Entangled Pauli Principle (EPP), introduced in [Phys. Rev. B 98, 161118(R) (2018)] and which defines the “DNA” of the quantum Hall fluid, is behind the exact determination of the topological characteristics of the fluid, including charge and braiding statistics of excitations, and effective edge theory descriptions. When the closed-shell condition is satisfied, the densest (i.e., the highest density and lowest total angular momentum) zero-energy mode is a unique parton state. We conjecture that parton-like states generally span the subspace of many-body wave functions with the two-bodyM $M$-clustering property within any given number of Landau levels, that is, wave functions withM $M$th-order coincidence plane zeroes and both holomorphic and anti-holomorphic dependence on variables. General arguments are supplemented by rigorous considerations for theM=3 $M=3$case of fermions in four Landau levels. For this case, we establish that the zero mode counting can be done by enumerating certain patterns consistent with an underlying EPP. We apply the coherent state approach of [Phys. Rev. X 1, 021015 (2011)] to show that the elementary (localized) bulk excitations are Fibonacci anyons. This demonstrates that the DNA associated with fractional quantum Hall states encodes all universal properties. Specifically, for parton-like states, we establish a link with tensor network structures of finite bond dimension that emerge via root level entanglement. 

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