Optical communications links using entangled two-photon light sources
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quantum entanglement non diffraction limited↗
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Machine learning assisted quantum super-resolution microscopy
One of the main characteristics of optical imaging systems is spatial resolution, which is restricted by the diffraction limit to approximately half the wavelength of the incident light. Along with the recently developed classical super-resolution techniques, which aim at breaking the diffraction limit in classical systems, there is a class of quantum super-resolution techniques which leverage the non-classical nature of the optical signals radiated by quantum emitters, the so-called antibunching super-resolution microscopy. This approach can ensure a factor of $\sqrt{n}$ improvement in the spatial resolution by measuring the n -th order autocorrelation function. The main bottleneck of the antibunching super-resolution microscopy is the time-consuming acquisition of multi-photon event histograms. We present a machine learning-assisted approach for the realization of rapid antibunching super-resolution imaging and demonstrate 12 times speed-up compared to conventional, fitting-based autocorrelation measurements. The developed framework paves the way to the practical realization of scalable quantum super-resolution imaging devices that can be compatible with various types of quantum emitters.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Semi-empirical quantum optics for mid-infrared molecular nanophotonics
Nanoscale infrared (IR) resonators with sub-diffraction limited mode volumes and open geometries have emerged as new platforms for implementing cavity quantum electrodynamics at room temperature. The use of IR nanoantennas and tip nanoprobes to study strong light–matter coupling of molecular vibrations with the vacuum field can be exploited for IR quantum control with nanometer spatial and femtosecond temporal resolution. In order to advance the development of molecule-based quantum nanophotonics in the mid-IR, we propose a generally applicable semi-empirical methodology based on quantum optics to describe light–matter interaction in systems driven by mid-IR femtosecond laser pulses. The theory is shown to reproduce recent experiments on the acceleration of the vibrational relaxation rate in infrared nanostructures. It also provides physical insights on the implementation of coherent phase rotations of the near-field using broadband nanotips. We then apply the quantum framework to develop general tip-design rules for the experimental manipulation of vibrational strong coupling and Fano interference effects in open infrared resonators. We finally propose the possibility of transferring the natural anharmonicity of molecular vibrational levels to the resonator near-field in the weak coupling regime to implement intensity-dependent phase shifts of the coupled system response with strong pulses and develop a vibrational chirping model to understand the effect. The semi-empirical quantum theory is equivalent to first-principles techniques based on Maxwell’s equations, but its lower computational cost suggests its use as a rapid design tool for the development of strongly coupled infrared nanophotonic hardware for applications ranging from quantum control of materials to quantum information processing.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
In-plane multi-q magnetic ground state of Na 3 Co 2 SbO 6
We report Na 3 Co 2 SbO 6 is a potential Kitaev magnet with a monoclinic layered crystal structure. Recent investigations of the C3-symmetric sister compound Na 2 Co 2 TeO 6 have uncovered a unique triple-q magnetic ground state, as opposed to a single-q (zigzag) one, prompting us to examine the influence of the reduced structural symmetry of Na 3 Co 2 SbO 6 on its ground state. Neutron diffraction data obtained on a twin-free crystal reveal that the ground state remains a multi-q state, despite the system's strong non-C 3 -symmetric anisotropy. This robustness of multi-q orders suggests that they are driven by a common mechanism in the honeycomb cobaltates, such as interactions beyond the bilinear order. Spin-polarized neutron diffraction results show that the ordered moments are entirely in plane, with each staggered component orthogonal to the propagating wave vector. The inferred ground state appears more compatible with the so-called XXZ easy-plane anisotropy than the Kitaev anisotropy, and features unequal ordered moments reduced by strong quantum fluctuations.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Metal Side Reflectors for Trapping Light in QWIPs
Focal-plane arrays of quantum-well infrared photodetectors (QWIPs) equipped with both light-coupling diffraction gratings and metal side reflectors have been proposed, and prototypes are expected to be fabricated soon. The purpose served by the metal side reflectors is to increase quantum efficiency by helping to trap light in the photosensitive material of each pixel. The reasons for using diffraction gratings were discussed in several prior NASA Tech Briefs articles. To recapitulate: In an array of QWIPs, the quantum-well layers are typically oriented parallel to the focal plane and therefore perpendicular or nearly perpendicular to the direction of incidence of infrared light. By virtue of the applicable quantum selection rules, light polarized parallel to the focal plane (as normally incident light is) cannot excite charge carriers and, hence, cannot be detected. Diffraction gratings scatter normally or nearly normally incident light into directions more nearly parallel to the focal plane, so that a significant portion of the light attains a component of polarization normal to the focal plane and, hence, can excite charge carriers. Unfortunately, light scattered in directions parallel or nearly parallel to the focal plane can escape sideways from the QWIP of a given pixel, as illustrated in Figure 1. The escaped light has made only a single pass through the interior photosensitive volume of the QWIP. The quantum efficiency of the QWIP would be increased by trapping light so that it makes multiple passes through the photosensitive volume. As shown in Figure 2, the sides of the QWIP of each pixel would be coated with gold to reflect escaping light back into the interior.
Gunapala, Sarath↗
Probing electronic dead layers in homoepitaxial n-SrTiO 3 (001) films
We combine state-of-the-art oxide epitaxial growth by hybrid molecular beam epitaxy with transport, x-ray photoemission, and surface diffraction, along with classical and first-principles quantum mechanical modeling to investigate the nuances of insulating layer formation in otherwise high-mobility homoepitaxial n-SrTiO 3 (001) films. Our analysis points to charge immobilization at the buried n-SrTiO 3 /undoped SrTiO 3 (001) interface as well as within the surface contamination layer resulting from air exposure as the drivers of electronic dead-layer formation. As Fermi level equilibration occurs at the surface and the buried interface, charge trapping reduces the sheet carrier density (n 2D ) and renders the n-STO film insulating if n 2D falls below the critical value for the metal-to-insulator transition.
36 MATERIALS SCIENCE↗
On the possibility of laser ektacytometry measurement of the kurtosis for erythrocyte deformability distribution
The problem of measuring red blood cell deformability by laser diffractometry in shear flow (ektacytometry) is considered. An algorithm has been developed for measuring the four central parameters of the erythrocyte deformability distribution, i.e. mean value, variance, asymmetry coefficient and kurtosis. The algorithm is designed to work with the peripheral part of the diffraction pattern and serves to analyse weakly inhomogeneous ensembles of red blood cells. (paper)
62 RADIOLOGY AND NUCLEAR MEDICINE↗
Magneto-transport study on Sn-rich Sn 1–x Ge x thin films enabled by CdTe buffer layer
α-Sn, generally known as gray tin, has attracted significant scientific interest due to its potential to host novel topological phases. Studying the transport properties of α-Sn thin films grown on the InSb substrate has been challenging, as the InSb substrate also significantly contributes to the transport properties. In this article, we report a novel approach to epitaxially grow α-Sn thin films on an InSb substrate with a resistive buffer layer of CdTe. Thin films of α–Sn 1–x Ge x (x = 0, 0.025) alloy of 15 nm thickness have been grown using molecular beam epitaxy. The high quality of the samples has been determined through high-resolution x-ray diffraction. The CdTe buffer layer has high resistance and acts as an insulating virtual substrate, which significantly suppresses contribution from InSb. Magnetotransport measurements show clear Shubnikov–de Hass oscillations in α–Sn 1–x Ge x (x = 0, 0.025) thin films. A change in oscillation frequency is observed upon alloying with Ge, implying a modification in the electronic structure and demonstrating the effectiveness of the CdTe buffer layer approach. Furthermore, this work provides a new approach that enables the electronic transport characterization of the α–Sn 1–x Ge x alloy system, which enables the study of the topological quantum states using electronic transport and their device applications.
36 MATERIALS SCIENCE↗
Structural Asymmetry and Chiral-Induced Spin Selectivity in Chiral Palladium-Halide Semiconductors
Chiral Pb-free metal-halide semiconductors (MHSs) have attracted considerable attention in the field of spintronics due to various interesting spin-related properties and chiral-induced spin selectivity (CISS) effect. Despite their excellent chemical and structural tunability, the material scope and crystal structure of Pb-free chiral MHSs exhibiting the CISS effect are still limited; chiral MHSs that have metal-halide structures of octahedra and tetrahedra are only reported. Here, we report a new class of chiral MHSs, of which palladium (Pd)-halides are formed in 1D square-pyramidal structures or 0D square-planar structures, with a general formula of ((R/S-MBA) 2 PdBr 4 ) 1-x ((R/S-MBA) 2 PdCl 4 ) x (MBA = methylbenzylammonium; x = 0, 0.25, 0.5, 0.75, and 1) for the first time. The crystals adopt the 1D helical chain of Pd-halide square-pyramid (for x = 0, 0.25, 0.5, and 0.75) and 0D structure of Pd-halide square-plane (for x = 1). All the Pd-halides are distorted by the interaction between the halide and the chiral organic ammonium and arranged in a noncentrosymmetric position. Circular dichroism (CD) for ((R/S-MBA) 2 PdBr 4 ) 1-x ((R/S-MBA) 2 PdCl 4 ) x indicates that chirality was transferred from chiral organic ammonium to Pd-halide inorganics. ((R-MBA) 2 PdBr 4 ) 1-x ((R-MBA) 2 PdCl 4 ) x (x = 0, 0.25, 0.5, and 0.75) shows a distortion index of 0.127-0.128, which is the highest value among the previously reported chiral MHSs to the best of our knowledge. We also find that (R/S-MBA) 2 Pd(Br 1-x Cl x ) 4 crystals grow along the out-of-plane direction during spin coating and have high c-axis orientation and crystallinity, and (R/S-MBA) 2 Pd(Br 1-x Cl x ) 4 (x = 0 and 0.5) crystals exhibit a CISS effect in polycrystalline bulk films. In conclusion, these results demonstrate the possibility of a new metal-halide series with square-planar structures or square-pyramidal structures for future spintronic applications.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Robust atom optics for Bragg atom interferometry
Multi-photon Bragg diffraction is a powerful method for fast, coherent momentum transfer of atom waves. However, laser noise, Doppler detunings, and cloud expansion limit its efficiency in large momentum transfer (LMT) pulse sequences. We present simulation studies of robust Bragg pulses developed through numerical quantum optimal control. Optimized pulse performance under noise and cloud inhomogeneities is analyzed and compared to analogous Gaussian and adiabatic rapid passage pulses in simulated LMT Mach–Zehnder interferometry sequences. The optimized pulses maintain robust population transfer and phase response over a broader range of noise, resulting in superior contrast in LMT sequences with thermal atom clouds and intensity inhomogeneities. Large optimized LMT sequences use lower pulse area than Gaussian pulses, making them less susceptible to spontaneous emission loss. The optimized sequences maintain over five times better contrast with tens of momentum separation and offer more improvement with greater LMT. Such pulses could allow operation of Bragg atom interferometers with unprecedented sensitivity, improved contrast, and hotter atom sources.
74 ATOMIC AND MOLECULAR PHYSICS↗
Anharmonic Bloch oscillations in a coupler composed of two parallel optical fibre arrays
The effects of laser beam propagation in a coupler composed of two parallel optical-fibre arrays are studied by the coupled-mode method taking into account the interaction of a given fibre with the nearest neighbours and the linear dependence of the propagation constant on the fibre number. It is shown that, due to the complex structure of each subsystem, the structure of light intensity spatial distribution becomes significantly complicated in the system under study. The occurrence of space limited transverse light diffraction is predicted. (paper)
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Incommensurate Spiral Spin Order in CaMn 2 Bi 2 Observed via High-Pressure Neutron Diffraction
Here, high-pressure neutron diffraction is employed to investigate the magnetic behavior of CaMn 2 Bi 2 in extreme conditions. In contrast to antiferromagnetic ordering on Mn atoms reported at ambient pressure, our results reveal that at high pressure, incommensurate spiral spin order emerges due to the interplay between magnetism on the Mn atoms and strong spin–orbit coupling on the Bi atoms: sinusoidal spin order is observed at pressures as high as 7.4 GPa. First-principles calculations with a noncollinear spin orientation demonstrate band crossing behavior near the Fermi level as a result of strong hybridization between the d orbitals of Mn and the p orbitals of Bi atoms. Competing antiferromagnetic order is observed at different temperatures in the partially frustrated lattice. Theoretical models have been developed to investigate spin dynamics. This research provides a unique toolbox for conducting experimental and theoretical magnetic and spin dynamics studies of magnetic quantum materials via high-pressure neutron diffraction.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Hyperconjugation Promotes Catalysis in a Pyridoxal 5'-Phosphate-Dependent Enzyme
Pyridoxal 5'-phosphate (PLP)-dependent enzymes facilitate reaction specificity by aligning the scissile σ-bond of the PLP-substrate covalent complex perpendicular to the ring of the cofactor. Current models propose that this alignment causes a destabilization of the ground state. To test this hypothesis, quantum chemical calculations, utilizing our recent neutron diffraction models of aspartate aminotransferase, were performed. The calculations reveal that the scissile σ-bond orbital overlaps significantly with the π* orbital of the Schiff base. Here, this σ → π* hyperconjugation interaction stabilizes the ground state of the external aldimine and substantially contributes to transition-state stabilization by withdrawing electron density from the Cα-H σ bond into the π system of PLP, enhancing the rate of catalysis.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Floquet engineering of optical lattices with spatial features and periodicity below the diffraction limit
Floquet engineering or coherent time-periodic driving of quantum systems has been successfully used to synthesize Hamiltonians with novel properties. In ultracold atomic systems, this has led to experimental realizations of artificial gauge fields, topological band structures, and observation of dynamical localization, to name a few. Here we present a Floquet-based framework to stroboscopically engineer Hamiltonians with spatial features and periodicity below the diffraction limit of light used to create them by time averaging over various configurations of a 1D optical Kronig–Penney (KP)lattice. The KP potential is a lattice of narrow subwavelength barriers spaced by half the optical wavelength (λ/2) and arises from the nonlinear optical response of the atomic dark state. Stroboscopic control over the strength and position of this lattice requires time-dependent adiabatic manipulation of the dark-state spin composition. We investigate adiabaticity requirements and shape our time-dependent light fields to respect the requirements. We apply this framework to show that aλ/4-spaced lattice can be synthesized using realistic experimental parameters as an example, discuss mechanisms that limit lifetimes in these lattices, explore candidate systems and their limitations, and treat adiabatic loading into the ground band of these lattices.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Magnetic Properties of Co-doped Bismuth Oxide (δ-Bi{sub 2}O{sub 3}) at Low Temperature
The (Bi{sub 2}O{sub 3}){sub 1−x−y}(Gd{sub 2}O{sub 3}){sub x}(Lu{sub 2}O{sub 3}){sub y} material compounds were prepared by using the solid-state reaction technique under normal air conditions. The heat treatments of the ternary samples were performed firstly at 800 °C for 48 h and then at 750 °C for 100 h. The structural, morphological, and magnetic properties of the materials were characterized by X-ray powder diffraction (XRD), scanning electron microscope, and a Quantum Design PPMS-9T system, respectively. From the XRD results, it was found that the phases of all of the samples consisted of the fluorite-type face-centered cubic δ-Bi{sub 2}O{sub 3} phase. It was observed that the microstructure of the samples is uniformly distributed on the samples’ surface. The temperature dependence of magnetization (M–T) measurements showed that the magnetization rose sharply at the critical temperature. The calculated critical temperature values vary from 22.19 to 56.61 K for the samples. All of the samples displayed the paramagnetic behavior. The paramagnetic behavior started from 300 K to very low temperature which varied from 22.19 to 56.61 K. The coercive rise on the magnetization below 22.19 K or 56.61 K with decreasing temperature causes a phase transformation in the δ-Bi{sub 2}O{sub 3} system. This sudden increment was considered as a ferromagnetic or ferrimagnetic phase transition.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Generation regimes of an Nd : YAG laser with mode locking by a travelling-wave acousto-optic modulator and spherical mirror
The lasing regimes of a diode-pumped Nd : YAG laser with mode locking by a spherical mirror and a travelling-wave acousto-optic modulator (SMAOM method) are investigated. The lasing dynamics at mode spacing detuning from the doubled operating modulator frequency and with a change in the diffraction modulator efficiency is studied. The results of measuring the pulse duration and the frequency spectrum of output radiation are presented. (paper)
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Laguerre–Gauss and Hermite–Gauss soft X-ray states generated using diffractive optics
Light’s capacity to carry angular momentum is integral to our knowledge of physics and ability to probe matter. In addition to spin, photons can occupy free-space orbital angular momentum eigenstates. Visible light orbital angular momentum is used in quantum information experiments, super-resolution microscopy, optical tweezers and angular momentum transfer to atoms in optical lattices. Soft X-ray orbital angular momentum applications, slowed by the lack of suitable optics and the rarity of coherent X-ray sources, could enable the direct alteration of atomic states through orbital angular momentum exchange, and methods to study the electronic properties of quantum materials. We have made soft X-ray diffractive optics that generate single Laguerre–Gauss modes, observed carrying up to 30$\hbar$ angular momentum per photon, or their superpositions. We also present Hermite–Gauss diffractive optics and a soft X-ray orbital angular momentum analyser. Finally, these tools could enable both the manipulation and finer characterization of topologically complex electronic matter, such as magnetic skyrmions.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Diffraction-limited GaAs laser with external resonator
GaAs injection laser operated with external optical resonator for diffraction-limited radiation, considering peak power and quantum efficiency
Edmonds, H. D.↗