Photon Source Research Articles

SN 2022oqm: A Bright and Multipeaked Calcium-rich Transient

We present the photometric and spectroscopic evolution of SN 2022oqm, a nearby multipeaked hydrogen- and helium-weak calcium-rich transient (CaRT). SN 2022oqm was detected 13.1 kpc from its host galaxy, the face-on spiral galaxy NGC 5875. Extensive spectroscopic coverage reveals an early hot (T ≥ 40,000 K) continuum and carbon features observed ∼1 day after discovery, SN Ic-like photospheric-phase spectra, and strong forbidden calcium emission starting 38 days after discovery. SN 2022oqm has a relatively high peak luminosity (M B = −17 mag) for CaRTs, making it an outlier in the population. We determine that three power sources are necessary to explain the light curve (LC), with each corresponding to a distinct peak. The first peak is powered by an expanding blackbody with a power-law luminosity, suggesting shock cooling by circumstellar material (CSM). Subsequent LC evolution is powered by a double radioactive decay model, consistent with two sources of photons diffusing through optically thick ejecta. From the LC, we derive an ejecta mass and 56Ni mass of ∼0.6 M ⊙ and ∼0.09 M ⊙. Spectroscopic modeling ∼0.6 M ⊙ of ejecta, and with well-mixed Fe-peak elements throughout. We discuss several physical origins for SN 2022oqm and find either a surprisingly massive white dwarf progenitor or a peculiar stripped envelope model could explain SN 2022oqm. A stripped envelope explosion inside a dense, hydrogen- and helium-poor CSM, akin to SNe Icn, but with a large 56Ni mass and small CSM mass could explain SN 2022oqm. Alternatively, helium detonation on an unexpectedly massive white dwarf could also explain SN 2022oqm.

Design principles for >90% efficiency and >99% indistinguishability broadband quantum dot cavities

Abstract Quantum dots have the potential to be one of the brightest deterministic single photon sources with high end applications in quantum computing and cluster state generation. In this work, we re-examine the design of simple micropillars by meticulously examining the structural effects of the decay into leaky channels beyond an atom-like cavity estimation. We show that precise control of the side losses with the diameter and avoidance of propagating Bloch modes in the distributed Bragg reflectors can result in easy-to-manufacture broadband (Q≈ 750 − 2500) micropillars, allowing for broad optical coherent control pulses necessary for high single photon purity (> 99.2 − 99.99% achievable) while simultaneously demonstrating extremely high efficiency out the top (90.5% − 96.4%). We also demonstrate that such cavities naturally decouple from the phonon sideband, with the phonon sideband reducing by a factor of 5 − 33 allowing us to predict that the photons should show 98.5% − 99.8% indistinguishability without the need for filtering.

Progress of the High Energy Photon Source construction

Progress of the High Energy Photon Source construction

Operation of the Belle II imaging Time-Of-Propagation (iTOP) detector before and after the first long shutdown

The iTOP detector is a Cherenkov detector specialized on particle identification at Belle II. The SuperKEKB accelerator collides electrons and positrons with a design luminosity of 6⋅10351cm2s. In order to exploit the high collision rate Belle II has a trigger rate of up to 30 kHz. The iTOP detector uses quartz bars as the source of Cherenkov photons. The photons are reflected inside the bars until they hit photomultipliers installed at one end. The spatial distribution and precise arrival times of the detected photons are used to reconstruct the Cherenkov angle and particle flight time. To achieve a good pion–kaon separation the photon arrival times have to be measured with a resolution of 100 ps. Microchannel plate photomultipliers together with dedicated high-speed electronics for 2.7 GSa/s waveform sampling in 8192 channels are used to achieve this requirement. After four years of operation, the experiment entered its first long shutdown phase in 2022. Aging components of iTOP were exchanged and the detector was prepared for data-taking at increasing luminosities and backgrounds after the long shutdown. In this talk the design of the iTOP detector will be shown and experience and results from operation will be discussed together with an outlook on future running conditions.

Exact Solutions for Radiative Transfer with Partial Frequency Redistribution

The construction of exact solutions for radiative transfer in a plane-parallel medium has been addressed by Hemsch and Ferziger in 1972 for a partial frequency redistribution model of the formation of spectral lines consisting in a linear combination of frequency coherent and fully incoherent scattering. The method of solution is based on an eigenfunction expansion of the radiation field, leading to two singular integral equations with Cauchy or Cauchy-type kernels, that have to be solved one after the other. We reconsider this problem, using as starting point the integral formulation of the radiative transfer equation, where the terms involving the coupling between the two scattering mechanisms are clearly displayed, as well as the primary source of photons. With an inverse Laplace transform, we recover the singular integral equations previously established and, with Hilbert transforms as in the previous work, recast them as boundary value problems in the complex plane. Their solutions are presented in detail for an infinite and a semi-infinite medium. The coupling terms are carefully analyzed and consistency with either the coherent or the incoherent limit is systematically checked. We recover the important result of the previous work that an exact solution exists for an infinite medium, whereas for a semi-infinite medium, which requires the introduction of half-space auxiliary functions, the solution is given by a Fredholm integral equation to be solved numerically. The solutions of the singular integral equations are used to construct explicit expressions providing the radiation field for an arbitrary primary source and for the Green’s function. An explicit expression is given for the radiation field emerging from a semi-infinite medium.

A new dual-thickness semi-transparent beamstop for small-angle X-ray scattering.

An innovative dual-thickness semi-transparent beamstop designed to enhance the performance of small-angle X-ray scattering (SAXS) experiments is introduced. This design integrates two absorbers of differing thicknesses side by side into a single attenuator, known as a beamstop. Instead of completely stopping the direct beam, it attenuates it, allowing the SAXS detector to measure the transmitted beam through the sample. This approach achieves true synchronization in measuring both scattered and transmitted signals and effectively eliminates higher-order harmonic contributions when determining the transmission light intensity through the sample. This facilitates and optimizes signal detection and background subtraction. This contribution details the theoretical basis and practical implementation of this solution at the SAXS station on the 1W2A beamline at the Beijing Synchrotron Radiation Facility. It also anticipates its application at other SAXS stations, including that at the forthcoming High Energy Photon Source, providing an effective solution for high-precision SAXS experiments.

Polarization-entangled photon-pair source with van der Waals 3R-WS2 crystal

Ultracompact entangled photon sources are pivotal to miniaturized quantum photonic devices. Van der Waals (vdW) nonlinear crystals promise efficient photon-pair generation and on-chip monolithic integration with nanophotonic circuitry. However, it remains challenging to generate maximally entangled Bell states of photon pairs with high purity, generation rate, and fidelity required for practical applications. Here, we realize a polarization-entangled photon-pair source based on spontaneous parametric down conversion in an ultrathin rhombohedral tungsten disulfide (3R-WS2) crystal. This vdW entangled photonic source exhibits a high photon-pair purity with a coincidence-to-accidental ratio of above 800, a generation rate of 31 Hz, and two maximally polarization-entangled Bell states with fidelities exceeding 0.93 and entanglement degree over 0.97. These results stem from scalable optical nonlinearity, enhanced second-order susceptibility by electronic transitions, and a well-defined symmetry-enabled selection rule inherent in 3R-WS2. Our polarization entangled photon source can be integrated with photonic structures for generating more complex entangled states, thus paving an avenue for advanced quantum photonic systems toward computation and metrology.

Spin-Orbit Coupling of Color Centers for Quantum Applications

Color centers in 4H-SiC and diamond are candidates for single photon sources and qubits for the implementation of quantum applications. The CI-cRPA method is able to correctly reproduce the structure of the underlying highly correlated wave functions for low and high spin multiplets. Aiming for a more complete understanding of spin-orbit mediated intersystem crossing between such states, we have extended CI-cRPA by a first order treatment of the spin-orbit interactions. We present preliminary results for intercrossing matrix elements and contributions of spin-orbit coupling to the zero field splitting of the silicon vacancy and di-vacancy in 4H-SiC, as well as the NV center in diamond using this approach.

Isolation of individual Er quantum emitters in anatase TiO2 on Si photonics

Defects and dopant atoms in solid state materials are a promising platform for realizing single photon sources and quantum memories, which are the basic building blocks of quantum repeaters needed for long distance quantum networks. In particular, trivalent erbium (Er3+) is of interest because it couples C-band telecom optical transitions with a spin-based memory platform. In order to produce quantum repeaters at the scale required for quantum networks it is imperative to integrate these necessary building blocks with mature and scalable semiconductor processes. In this work, we demonstrate the optical isolation of single Er3+ ions in CMOS-compatible titanium dioxide (TiO2) thin films monolithically integrated on a silicon-on-insulator photonics platform. Our results demonstrate an initial step toward the realization of a monolithically integrated and scalable quantum photonics package based on Er3+ doped thin films.

From π-Conjugated Rods to Shape-Persistent Rings, Wheels, and Ladders: The Question of Rigidity.

ConspectusRigid-rod oligomers and polymers are mostly based on (hetero)aromatic rings connected with each other, either directly or via ethynylene or butadiynylene linkers, or by a combination of both structural elements. Although they are much more rigid than vinyl polymers, they exhibit considerable structural flexibility, often more than would be expected merely from their chemical structure. This disparity holds for both linear as well as for cyclic structures. The flexibility of rigid-rod polymers, which is directly observable for defined oligomers of different lengths at the solid-liquid interface by means of scanning-tunneling microscopy, also impacts their optical and electronic properties. The flexibility can be used, for example, to control whether an oligomer with two different fluorescent end-groups emits from either the one or the other. The flexibility of shape-persistent macrocycles also has an impact on the overall thermal stability of mechanically interlocked molecular architectures. However, the degree of flexibility can be reduced when rigid struts are covalently mounted into the inside of the rings, leading to the formation of so-called molecular spoked wheels. The combination of these two elements─rings and rods─stiffens both of them: the ring perimeter is prevented from collapsing and the internal rods from bending. These compounds have been further developed as platform molecules, where three spokes stiffen the ring and together form a tripod-like platform, while a fourth arm points─after adsorption to a solid substrate─above the plane of the molecule. This pillar makes it possible to decouple a functional group at the end of the arm from the surface. Rigidity enhancement by the introduction of rigid spacer elements can also be applied to the case of rigid-rod polymers and is visualized by sophisticated molecular dynamics simulations. In this case, formation of single-stranded oligomers and polymers, and a subsequent zipping reaction to form ladder-like structures, directly allows, by means of single-molecule fluorescence spectroscopy, a comparison of the single- and double-stranded molecules. In particular in the case of the polymers, which can be up to 100 nm in length, the enhancement of rigidity is quite remarkable. Overall, the covalent connection of two or more rigid molecular entities has a self-reinforcing effect: all parts of the molecule gain rigidity. Since overall synthetic yields for such complex high-molecular weight covalently bound shape-persistent structures can still be low, scanning tunneling microscopy and single-molecule fluorescence spectroscopy are the methods of choice for structural analyses. Preliminary results illustrate how these compounds can serve as versatile sources of deterministic single photons on demand, since rigidity also enhances the intramolecular flow of excitation energy, and suggest a range of applications in optoelectronic devices.

Indistinguishable photons from an artificial atom in silicon photonics

Silicon is the ideal material for building electronic and photonic circuits at scale. Integrated photonic quantum technologies in silicon offer a promising path to scaling by leveraging advanced semiconductor manufacturing and integration capabilities. However, the lack of deterministic quantum light sources and strong photon-photon interactions in silicon poses a challenge to scalability. In this work, we demonstrate an indistinguishable photon source in silicon photonics based on an artificial atom. We show that a G center in a silicon waveguide can generate high-purity telecom-band single photons. We perform high-resolution spectroscopy and time-delayed two-photon interference to demonstrate the indistinguishability of single photons emitted from a G center in a silicon waveguide. Our results show that artificial atoms in silicon photonics can source single photons suitable for photonic quantum networks and processors.

CMOS photonic integrated source of broadband polarization-entangled photons

We showcase a fully on-chip CMOS-fabricated silicon photonic integrated circuit employing a bidirectionally pumped microring and polarization splitter-rotators tailored for the generation of broadband (>9 THz), high-fidelity (90–98%) polarization-entangled photons. Spanning the optical C+L-band and producing over 116 frequency-bin pairs on a 38.4-GHz-spaced grid, this source is ideal for flex-grid wavelength-multiplexed entanglement distribution in multiuser networks.

(Invited) Next-Generation Photonic Source Based on Lateral GaAs/AlgaAs Heterostructure Devices

Quantum communications and remote sensing protocols rely on preparing individual quanta of light, or photons, as carriers of quantum information. While it is easy to generate many-photon classical states of light (e.g., a light bulb or a laser), it is challenging to generate single quanta or pairs of entangled quanta on-demand. Yet, only in this latter regime can the fundamentally quantum nature of light be exploited to achieve performance exceeding classical bounds.We are developing a single-photon source based on combining a one-parameter single electron pump (Figure 1a,b) – an electrically controlled, on-demand, high-fidelity emitter of single electrons [1] – with a lateral p-n junction [2] (Figure 1c,d) in which injected single electrons recombine with holes to produce single photons. These devices are realized in undoped GaAs/AlGaAs heterostructures and designed to be ambipolar. Such a quantum light source could lead to a paradigm shift in metrology, providing a quantum redefinition of two of the seven SI base units, the ampere and the candela. It is also possible in principle to realize scalable source arrays on a single chip. I will discuss progress towards realizing and characterizing these sources, including work on optimizing collection efficiency and Purcell enhancement using a lateral distributed Bragg reflector in a concentric ring geometry. Beyond fundamental studies, the proposed photon source will find practical use in quantum communications protocols (QKD), where it can offer fast data transmission rates, and quantum sensing with LiDAR, where it could outperform laser-based systems in the few-photon regime for low-power, stealth applications.[1] B. Buonacorsi et al, “Non-adiabatic single-electron pumps in a dopant-free GaAs/AlGaAs 2DEG”, Appl. Phys. Lett. 119, 114001 (2021).[2] L. Tian et al, “Stable electroluminescence in ambipolar dopant-free lateral p-n junctions”, Appl. Phys. Lett. 123, 061102 (2023). Figure 1

Gaseous Nitric Oxide As Probe Molecule for Fe-N-C ORR Electrocatalysts

Iron nitrogen carbon (Fe-N-C) electrocatalysts remain the most promising platinum group metal-free (PGM-free) catalysts for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs). Although significant progress has been made in recent years in improving both the ORR activity and stability of the Fe-N-C catalysts, further enhancement in the catalyst durability while maintaining the activity is imperative for the practical applications. One of the major factors that hinders the further enhancement of the catalysts is the lack of clear understanding of the nature of the active sites and density of the active sites in the Fe-N-C catalysts due to the complexity of the Fe-N-C catalysts’ composition and structure. Gaseous nitric oxide was proven to be a suitable probe molecule that can bond to Fe and impede the ORR of the Fe-N-C catalysts. In recent years, we have studied the effects of gas-phase adsorption and desorption of nitric oxide on the redox features and ORR activity on Fe-N-C catalysts synthesized by different methods. We have used various characterization tools to quantify the amount of nitric oxide adsorbed and to identify the adsorption sites and geometry, including electrochemical stripping, temperature programmed desorption, and in situ X-ray techniques. The corresponding results obtained will be summarized in this talk. The implication of these results on the nature of the ORR active sites of the Fe-N-C catalysts will be discussed.AcknowledgementsThis work was supported by the U.S. Department of Energy (DOE), Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (HFTO) under the auspices of the Electrocatalysis Consortium (ElectroCat 2.0). This work utilized the resources of the Advanced Photon Source, a U.S. DOE Office of Science user facility operated by Argonne National Laboratory for DOE Office. This work was partially authored by Argonne, a U.S. Department of Energy (DOE) Office of Science laboratory operated for DOE by UChicago Argonne, LLC under contract no. DE-AC02-06CH11357.

(Invited) Visualizing Electrode Assembly Movement and Lithiation Gradients in Lithium-Metal Batteries

In this presentation we will introduce dilatometry and profilometry using Operando Energy Dispersive X-Ray Diffraction conducted at the Advanced Photon Source, Argonne National Laboratory. This approach is applied to a Li metal battery with a high-voltage NMC811 cathode but the method is suitable for any and all materials and electrodes.In the technique, micrometer-wide collimated X-rays traverse the electrode assembly, and the Bragg peaks from different crystalline phases are used to track the hard edges of the solid materials as they move due to volume changes in the cell. We visualize, with submicron resolution, the movement of the oxide cathode and microporous separator: the latter is observed through the diffraction of X-rays off the lamellae in the polymer matrix. One can map movement of the cathode and also compression in the porous separator – a task that is beyond the capabilities of mechanical dilatometers. We use our approach to show periodic expansion and contraction of metallic lithium during delithiation and relithiation of the cathode and to quantify formation of mossy lithium on the metal surface. The method is universal, easy to implement in-operando, and is selective in distinguishing between different phases in materials.Another dividend of this method is that it allows the profiling of lithiation gradients in the layered-oxide cathode. In our NMC811/Li cells, the cathode gradients are seen even with weak currents, they occur only during relithiation of the cathode, and they persist as the currents abate during constant-voltage discharge.Other particulars of our experimental approach and observations will also be discussed during the talk.Acknowledgement: This document has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357.

(Invited) Bragg Coherent Diffraction Imaging Studies of Composition Distribution and Strain in Catalytic Alloy Nanoparticles

Compositional distribution, strain, and defects in alloy nanoparticles significantly affect the catalytic properties for a wide range of applications such as gas reforming, fuel cells, electrolysis, etc. while various alloy compositions of nanoparticles have been investigated to improve performance and reduce the amount of precious metals used. It was reported that the composition distribution of the alloy particles, expectedly homogeneous in the whole particle, changed dynamically depending on the operating environment, resulting in altering the catalytic activity [1]. Furthermore, defects such as dislocations, grain boundaries, and elastic strain of the crystalline lattice also significantly affect catalytic properties. Since these factors dynamically change and evolve under operating environments, in situ measurements are essential to reveal these factors and ultimately to exploit them to enhance the catalytic properties. Bragg coherent diffraction imaging (BCDI) is a lens-less imaging method that measures speckle patterns near Bragg diffraction from a crystalline sample and reconstructs the 3D particle images. Since Bragg diffraction is inherently sensitive to displacements of the crystal lattice, BCDI yields the displacement field within the sample as well as the electron density, i.e., the “shape” of the particle. This displacement field information further allows us to evaluate strain distribution, dislocations, and composition distribution in the particle. BCDI is also advantageous for in situ measurements because the 3D image can be obtained by rotating the sample by only a few degrees, which eases the geometrical constraint of an electrochemical cell for the measurement. This is in contrast to conventional 3D imaging techniques such as X-ray CT, which usually requires 180 degrees of sample rotation.Furthermore, it is expected that the measurement capabilities of BCDI will be rapidly advanced by upgrading synchrotron radiation facilities such as APS-U, which delivers high-flux coherent X-rays. This should expand the applications of BCDI to wider electrochemical materials. In this presentation, we will briefly overview the principle of BCDI followed by specific examples of in situ measurements of catalytic alloy particles [2-4] conducted at 34-ID-C at Advanced Photon Source.[1] F. Tao et al., Science 322, 932 (2008).[2] T. Kawaguchi et al., Phys. Rev. Lett. 123, 246001 (2019).[3] T. Kawaguchi et al., Nano Lett. 21, 5945 (2021).[4] D. Sheyfer, R. G. Mariano, T. Kawaguchi, et al., Nano Lett. 23, 1 (2023).

(Invited) From Inside Out: How Synthesis-Structure Correlations Conspire to Determine Photoluminescence Traits and Operational Robustness in Non-Blinking Giant Quantum Dots

“Giant” or thick-shell core/shell quantum dots (gQDs) are an important class of solid-state quantum emitter. Without any encapsulation gQDs are characterized by strongly suppressed blinking, or even non-blinking behavior, and resistance to photobleaching at room temperature. In addition, non-radiative Auger processes are significantly reduced in this class of luminescent nanomaterial. Together, these qualities lead to novel functionality as photon sources for a range of ensemble and single-emitter applications, including down-conversion phosphors, direct excitation light-emitting diodes, single-biomolecule tracking, and single-photon generation. For many applications, operation at elevated temperature and under intense photon flux is also desired, and we have shown that gQDs outperform other emitters in this key metric of operational robustness. Interestingly, performance under these conditions is strongly dependent on the synthetic method employed for shell growth. Previously we revealed the mechanistic pathways responsible for thermally-assisted photodegradation, distinguishing effects of hot-carrier trapping and QD charging (ACS Nano 2018, 12, 5, 4206), and subsequently used solid-state spectroscopy to obtain kinetic and thermodynamic parameters of the photothermal degradation process (ACS Appl. Mater. Interfaces 2020, 12, 27, 30695). Here, I will discuss a comprehensive analysis of gQD structural properties from the inside of the nanocrystal to its surface and demonstrate correlations between specific structural features and both causal synthetic parameters and resulting performance metrics. Two synthetic methods—successive-ionic-layer-adsorption-and-reaction and high-temperature continuous-injection—will be compared. Investigated structural features will include interfacial alloying, stacking-fault density and surface-ligand identity, while correlated functionalities will address quantum yield, single-gQD photoluminescence under thermal/photo-stress, charging behavior and quantum-optical properties. I will show several unexpected conclusions, including the surprising finding that while interfacial alloying is the strongest indicator of gQD stability under stress, the parameter is not the determining factor for Auger suppression. Furthermore, quantum yield is strongly influenced by surface chemistry and can approach unity even in the case of a gQD comprising a thick shell with a high defect density with proper choice of excitation wavelength. Interestingly, we find a strong correlation between the existence of zinc-blende stacking faults and whether the gQD exhibits charged-state or purely excitonic emission, and the interplay between charged emission and excitonic emission can be precisely tuned by “mixing” shell-growth methods (Small Sci. 2023,3, 2300092).

(Invited) Simple and Optimized Silicon Nano-Antennas for Quantum Emitter Control

Improving the brightness and efficiency of single photon sources by the mean of optically resonant nanostructures is a major stake for the development of efficient nanodevices for quantum communications.For a couple of decades, these resonant nanostructures have mainly been made of noble metal that sustain strong localized resonances (LSPR) that can be used to manipulate, concentrate or redirect visible light. Such properties have led to numerous actual or potential applications in integrated optics, sensors, nonlinear optics, field-enhanced spectroscopies, or photovoltaics. Recently, an alternative emerged with high refractive index dielectric nanostructures, which offer the same range of applications as plasmonics by manipulating Mie optical resonances instead of LSPR [1].These resonances can be efficiently tuned by modifying the size, shape, and material of those nanostructures (e.g. silicon, n ~ 4) [2]. Furthermore, high index dielectric nanostructures offer several key advantages when compared to their metallic counterparts: absorption losses are far weaker for wavelengths longer than the direct band gap, access to semiconductor (CMOS) technology for nanostructure fabrication, and presence of intrinsic strong magnetic and electric resonances, providing an unique opportunity to spatially separate and redistribute the energy of the magnetic and electric parts of the electromagnetic field in the near field, otherwise inextricably connected in the far field [3].We discuss here the effect of simple high-index dielectric nanoantennas on the spontaneous emission of model quantum emitters. First, we accurately positioned arrays of nanodiamonds hosting NV colored centers in the gap of silicon dimer nanoantennas, using atomic force microscopy (AFM – [4]) nanoxerography [5]. The NV center is an ideal model system exhibiting single photon emission properties at room temperature, which is well adapted for proof of concept experiments in quantum nano-optics. Since the local density of photonic states (LDOS) is modified by the nanostructure, we show by the mean of time-resolved photoluminescence acquisitions that the photodynamics of these quantum emitters can be enhanced by the coupling to the nanoantenna, down to the single photon emission regime [5]. Our experimental results are in good agreement with multipolar analysis and numerical simulations based on the Green Dyadic Method - GDM.Second, in order to go a step further, we explore the control of the directive emission from quantum dipolar sources by the mean of complex silicon antennas. The latter, made of a given number of building (nano)blocks, are optimized by an Evolutionary Algorithm (EA) coupled to full-field electrodynamical GDM simulations. The geometries obtained allow to tailor the emission direction of a single dipolar source, maximizing the intensity of the emitted light within a given solid angle. Our numerical and preliminary experimental results demonstrate the efficiency of such compact EA-optimized antennas for the control of quantum nanosources. Acknowledgements : This work was supported by Programme Investissements d’Avenir through the grants ANR-10-LABX-0037-NEXT (MILO) and NanoX n° ANR-17-EURE- 0009 (Q-META), by the HiLight ANR project ANR-19-CE24-0026, by LAAS-CNRS micro and nanotechnologies platform member of the French Renatech network, by the CNRS and INSA (PhD grant), by the Région Midi-Pyrénées via the Institute for Quantum technologies in Occitanie (IQO), and by the computing facility center CALMIP of the University of Toulouse under grants P12167 and P1107. References : Kallel et al, Tunable enhancement of light absorption and scattering in Si1xGex nanowires, Phys. Rev. B 12: 085318, 2012.P.R. Wiecha et al., Strongly directional scattering from dielectric nanowires, ACS Photonics 4: pp 2036–2046, 2017.Montagnac et al., Control of light emission of quantum emitters coupled to silicon nanoantenna using cylindrical vector beams, Light : Science and Applications 12 (1), 239, 2023.Humbert et al., Versatile, rapid and robust nanopositioning of single-photon emitters by AFM-nanoxerography, Nanotechnology 33, 215301, 2022.Humbert et al., Large-scale controlled coupling of single-photon emitters to high index dielectric nanoantennas using AFM nanoxerography, Nanoscale 15, 599-608, 2023. Figure 1

PGM-Free Oxygen Evolution Reaction Catalyst for PEM Water Electrolysis – a Mechanistic Study on Activity and Durability for Practical Applications

Low temperature proton exchange membrane water electrolyzer (PEMWE) represents a critical technology for green hydrogen production. It offers the advantages of significantly higher current density and higher H2 purity, rendering it a preferred technology when high energy efficiency and low footprint are essential. Working in the oxidative and acidic environment under high polarization voltage, however, adds substantial demand to the electrode catalyst and the support. This is particularly the case at anode where the oxygen evolution reaction (OER) takes place. At present, the platinum group metal (PGM) materials such as Ir black or Ir oxide are catalysts of choice. Their high cost and limited reserve add a significant cost barrier to PEM electrolyzer, which contributes to the overall expense of hydrogen production next only to the cost of electricity. Replacing Ir with earth-abundant transition metal oxides could help to reduce the electrolyzer system cost.For PEMWE application, a PGM-free anodic catalyst must be highly active to match the performance of Ir. Furthermore, it must be stable against oxidative acid corrosion. At Argonne National Laboratory, we recently developed a new PGM-free OER of a nanofibrous cobalt spinel catalyst co-doped with lanthanum and manganese (LMCF). [1] The catalyst was synthesized from the precursor of cobalt zeolitic methyl-imidazolate framework (Co-ZIF) doped with manganese and lanthanum. The Co-ZIF was mixed with a polymer solution and electrospun into nanofiber before being converted to fibrous cobalt spinel under low temperature oxidation to remove all the organics and carbon. The new PGM-free catalyst demonstrated a low overpotential of 353 mV (RHE) at 10 mA/cm2 and a low OER degradation over 360 hours in acidic electrolyte. A PEMWE containing this catalyst at its anode at ~2.0 mg/cm2 demonstrated a current density of 2000 mA/cm2 at 2.47 volts (Nafion® 115 membrane) or 4000 mA/cm2 at 3.00 volt (Nafion® 212 membrane). The membrane electrode was also subjected to accelerated-stress-test (AST) in both voltage cycling and galvanostatic run at different current densities. Low degradation rates under both ASTs were observed.In addition to catalyst design and synthesis, we also conducted extensive structural characterizations, stability measurement, as well as computational modeling. Our in situ study found that the OER process involves significant lattice oxygen movement, leading to lowering instead of raising the cobalt oxidation state during the electrolysis. The measurement of the stability number, combined with computational Pourbaix diagram, elucidated the importance of the operating potential in reducing catalyst dissolution. These findings offer in-depth understanding and direction of future development for PGM-free OER catalyst in PEM water electrolyzer. Acknowledgement: This work is supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewal Energy, Hydrogen and Fuel Cell Technologies Office, and by Laboratory Directed Research and Development funding of Argonne National Laboratory, provided by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DEAC02-06CH11357. Work performed at the Center for Nanoscale Materials and Advanced Photon Source, both U.S. Department of Energy Office of Science User Facilities, was supported by the U.S. DOE, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.[1] “La- and Mn-doped cobalt spinel oxygen evolution catalyst for proton exchange membrane electrolysis” Lina Chong, Guoping Gao, Jianguo Wen, Haixia Li, Haiping Xu, Zach Green, Joshua D. Sugar, A. Jeremy Kropf, Wenqian Xu, Xiao-Min Lin, Hui Xu, Lin-Wang Wang, Di-Jia Liu, Science 380, 609–616 (2023)

Loophole-Free Test of Local Realism via Hardy's Violation.

Bell's theorem states that the quantum mechanical description of physical quantities cannot be fully explained by local realistic theories, laying a solid basis for various quantum information applications. Hardy's paradox is celebrated as the simplest form of Bell's theorem concerning its "All versus Nothing" approach to test local realism. However, due to experimental imperfections, existing tests of Hardy's paradox require additional assumptions of the experimental systems, and these assumptions constitute potential loopholes for faithfully testing local realistic theories. Here, we experimentally demonstrate Hardy's nonlocality through a photonic entanglement source. By achieving a detection efficiency of 82.2%, a quantum state fidelity of 99.10%, and applying high-speed quantum random number generators for the measurement setting switching, the experiment is implemented in a loophole-free manner. During 6h of running, a strong violation of P_{Hardy}=4.646×10^{-4} up to 5 standard deviations is observed with 4.32×10^{9} trials. A null hypothesis test shows that the results can be explained by local realistic theories with an upper bound probability of 10^{-16348}. These testing results provide affirmative evidence against local realism, and establish an advancing benchmark for quantum information applications based on Hardy's paradox.