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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Optical noise in a free-space quantum communications link from natural and nuclear disturbed environments*

Satellite communications at radio frequencies can experience a ‘blackout’ period following the atmospheric detonation of a nuclear weapon. The wavelengths used for free-space quantum communications will not incur the same ‘blackout’ effects from a nuclear detonation, but the optical systems will suffer from a phenomenon called redout. Redout occurs in an optical detector when ambient light scatters into the optical receiver, causing elevated background photon counts in the detector such that background noise overwhelms the signal. In this work, the duration of the redout effect is quantified from a nuclear disturbed environment on a ground-to-space quantum optical link. In addition, we comment on various techniques for reducing ambient and nuclear disturbed background counts in a quantum free-space optical link. For low-altitude nuclear detonations (i.e., under 50 km), the maximum interference time will be less than 1 min. Implementing a telescope, timing gate, and wavelength filter to the detector can reduce the background counts in the detector significantly. Aerosol levels and ground albedo are major contributors to background noise in a ground-to-satellite quantum channel, and ground station location should factor in both variables.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Mass of a weakly measured photon

Bohmian mechanics has garnered significant attention as an interpretation of quantum theory since the paradigmatic experiments which inferred the average trajectories of photons in the nonrelativistic regime. These experiments were largely motivated by Wiseman's formulation of Bohmian mechanics, which grounded these trajectories in weak measurements. Recently, Wiseman's framework was extended to the relativistic regime by expressing the velocity field of single photons in terms of weak values of the photon energy and momentum. Here, we propose an operational, weak value-based definition for the Bohmian “local mass” of relativistic single particles. For relativistic wave functions satisfying the scalar Klein-Gordon equation, this mass coincides with the effective mass defined by de Broglie in his relativistic pilot-wave theory, a quantity closely connected with the quantum potential that is responsible for Bohmian trajectory self-bending and the anomalous photoelectric effect. Here, we demonstrate the relationship between the photon trajectories and the mass in an interferometric setup.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Conformal maps of viscous electron flow in the Gurzhi crossover

Herein we investigate the impact of geometric constriction on the viscous flow of electron liquid through quantum point contacts. We provide analysis on the electric potential distribution given the setup of a slit configuration and use the method of conformal mapping to obtain analytical results. The potential profile can be tested and contrasted experimentally with the scanning tunneling potentiometry technique. We discuss intricate physics that underlies the Gurzhi effect, i.e., the enhancement of conductivity in the viscous flow, and compare results for different boundary conditions. In addition, we calculate the temperature dependence of the momentum relaxation time as a result of impurity assisted quasiballistic interference effects and discuss various correlational corrections that lead to the violation of Matthiessen's rule in the hydrodynamic regime. We caution that spatially inhomogeneous profiles of current in the Gurzhi crossover between Ohmic and Stokes flows might also appear in the nonhydrodynamic limit where nonlocality plays an important role. This conclusion is corroborated by calculation of dispersive conductivity in the weakly impure limit.

2-dimensional systems↗
DOE OSTI2021

Achieving extreme light confinement in low-index dielectric resonators through quasi-bound states in the continuum

Obtaining large field enhancement in low-refractive-index dielectric materials is highly relevant to many photonic and quantum optics applications. However, confining light in these materials is challenging, owing to light leakage through coupling to continuum modes in the surrounding environment. Here, we investigate the possibility of achieving high quality factors in low-index dielectric resonators through the bound states in the continuum (BIC). Our simulations demonstrate that destructive interference between leaky modes can be achieved by tuning the geometrical parameters of the resonator arrays, leading to the emergence of quasi-BIC in resonators that have a small index contrast to the underlying substrates. The resultant large field enhancement gives rise to giant quality factors and Purcell effects. By introducing vertical mirror symmetry, the quasi-BIC can be tuned into an ideal BIC. In addition, the quasi-BIC can modify the emission patterns of the coupled emitters, rendering highly directional and focused far-field emission. These findings may provide a path for the practical implementation of photonic and quantum devices based on low-index dielectric materials.

42 ENGINEERING↗
DOE OSTI2024

Non-Fermi liquid behaviour in a correlated flat-band pyrochlore lattice

Electronic correlation effects are manifested in quantum materials when either the on-site Coulomb repulsion is large or the electron kinetic energy is small. The former is the dominant effect in cuprate superconductors and heavy-fermion systems whereas it is the latter in twisted bilayer graphene and geometrically frustrated metals. However, the simultaneous cooperation of both effects in the same quantum material remains rare. The design aim is to produce correlated topological flat bands pinned at the Fermi level. Here, we observe a flat band at the Fermi level in a 3d pyrochlore metal CuV 2 S 4 . Our angle-resolved photoemission spectroscopy data reveal that destructive quantum interference associated with the V pyrochlore sublattice and further renormalization to the Fermi level by electron interactions induce this flat band. Consequently, we discover transport signatures that evidence a deviation from Fermi liquid behaviour as well as an enhanced Sommerfeld coefficient. Our work illustrates the combined cooperation of local Coulomb interactions and geometric frustration in a pyrochlore lattice system to induce correlated topology by constructing and pinning correlated flat bands near the Fermi level.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Analytical WKB theory for high-harmonic generation and its application to massive Dirac electrons

Here we propose an analytical approach to high-harmonic generation (HHG) for nonperturbative low-frequency and high-intensity fields based on the (Jeffreys-)Wentzel-Kramers-Brillouin (WKB) approximation. By properly taking into account Stokes phenomena of WKB solutions, we obtain wave functions that systematically include the repetitive dynamics of production and acceleration of electron-hole pairs and quantum interference due to phase accumulation between different pair production times (Stückelberg phase). Using the obtained wave functions without relying on any phenomenological assumptions, we explicitly compute electric current (including intra- and interband contributions) as the source of HHG for a massive Dirac system in (1+1) dimensions under an ac electric field. We demonstrate that the WKB approximation agrees well with numerical results obtained by solving the time-dependent Schrödinger equation and point out that the quantum interference is important in HHG. We also predict in the deep nonperturbative regime that (1) harmonic intensities oscillate with respect to electric-field amplitude E 0 and frequency Ω with a period determined by the Stückelberg phase, (2) the cutoff order of HHG is determined by 2eE 0 ℏΩ 2 , with e being the electron charge, and that (3) noninteger harmonics, controlled by the Stückelberg phase, appear as a transient effect. Our WKB theory is particularly suited for a parameter regime, where the Keldysh parameter γ = (Δ/2)Ω/eE 0 ,with Δ being the gap size, is small. This parameter regime corresponds to intense lasers in the terahertz regime for realistic massive Dirac materials. Our analysis implies that the so-called HHG plateau can be observed at the terahertz frequency within the current technology.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Current-Phase Relations of Superconducting PtSi Constriction Josephson Junctions

Here, we study the current-phase relations of superconductor–constriction–superconductor Josephson junctions made from platinum silicide thin films by fabricating dc-superconducting quantum interference devices incorporating pairs of junctions and measuring their magnetic-field-dependent electrical transport. By comparing the supercurrent interference patterns with numerical Ginzburg–Landau simulations, we extract the current-phase relations of individual junctions and quantify the degree of nonlinearity. These measurements show that while the constrictions themselves sustain substantial nonlinearity, the effect is moderated by the kinetic inductance of the device leads, which is an important consideration for practical superconducting circuit applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Asymmetries in ionization of atomic superposition states by ultrashort laser pulses

Abstract Progress in ultrafast science allows for probing quantum superposition states with ultrashort laser pulses in the new regime where several linear and nonlinear ionization pathways compete. Interferences of pathways can be observed in the photoelectron angular distribution and in the past they have been analyzed for atoms and molecules in a single quantum state via anisotropy and asymmetry parameters. Those conventional parameters, however, do not provide comprehensive tools for probing superposition states in the emerging research area of bright and ultrashort light sources, such as free-electron lasers and high-order harmonic generation. We propose a new set of generalized asymmetry parameters which are sensitive to interference effects in the photoionization and the interplay of competing pathways as the laser pulse duration is shortened and the laser intensity is increased. The relevance of the parameters is demonstrated using results of state-of-the-art numerical solutions of the time-dependent Schrödinger equation for ionization of helium atom and neon atom.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Vortex-induced anomalies in the superconducting quantum interference patterns of topological insulator Josephson junctions

The superconducting quantum interference (SQI) patterns of Josephson junctions fabricated from hybrid structures that interface an s-wave superconductor with a topological insulator can be used to detect signatures of novel quasiparticle states. Here, we compare calculated and experimental SQI patterns obtained from hybrid junctions fabricated on cadmium arsenide, a two-dimensional topological insulator. The calculations account for the effects of Abrikosov (anti-) vortices in the superconducting contacts. They describe the experimentally observed deviations of the SQI from an ideal Fraunhofer pattern, including anomalous phase shifts, node lifting, even/odd modulations of the lobes, irregular lobe spacing, and an asymmetry in the positive/negative magnetic field. We also show that under a current bias, these vortices enter the electrodes even if there is no intentionally applied external magnetic field. The results show that Abrikosov vortices in the electrodes of the junctions can explain many of the observed anomalies in the SQI patterns of topological insulator Josephson junctions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Mixed quantum–classical approach to model non-adiabatic electron–nuclear dynamics: Detailed balance and improved surface hopping method

We develop a density matrix formalism to describe coupled electron–nuclear dynamics. To this end, we introduce an effective Hamiltonian formalism that describes electronic transitions and small (quantum) nuclear fluctuations along a classical trajectory of the nuclei. Using this Hamiltonian, we derive equations of motion for the electronic occupation numbers and for the nuclear coordinates and momenta. We show that, in the limit, when the number of nuclear degrees of freedom coupled to a given electronic transition is sufficiently high (i.e., the strong decoherence limit), the equations of motion for the electronic occupation numbers become Markovian. Furthermore, the transition rates in these (rate) equations are asymmetric with respect to the lower-to-higher energy transitions and vice versa. In thermal equilibrium, such asymmetry corresponds to the detailed balance condition. We also study the equations for the electronic occupations in the non-Markovian regime and develop a surface hopping algorithm based on our formalism. To treat the decoherence effects, we introduce additional “virtual” nuclear wave packets whose interference with the “real” (physical) wave packets leads to the reduction in coupling between the electronic states (i.e., decoherence) as well as to the phase shifts that improve the accuracy of the numerical approach. Remarkably, the same phase shifts lead to the detailed balance condition in the strong decoherence limit.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Condensation of indirect excitons

An indirect exciton (IX), also known as an interlayer exciton, is a bound pair of an electron and a hole confi ned in spatially separated layers. Due to their long lifetimes, IXs can cool below the temperature of quantum degeneracy. This provides an opportunity to experimentally study cold composite bosons. This article provides an overview of our studies of cold IXs, presenting spontaneous coherence and Bose–Einstein condensation of IXs and phenomena observed in the IX condensate, including the spatially ordered exciton state, commensurability effect of exciton density wave, spin textures, Pancharatnam–Berry phase, long-range coherent spin transport, and interference dislocations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Early-Time Exponential Instabilities in Nonchaotic Quantum Systems

The majority of classical dynamical systems are chaotic and exhibit the butterfly effect: a minute change in initial conditions has exponentially large effects later on. But this phenomenon is difficult to reconcile with quantum mechanics. One of the main goals in the field of quantum chaos is to establish a correspondence between the dynamics of classical chaotic systems and their quantum counterparts. In isolated systems in the absence of decoherence, there is such a correspondence in dynamics, but it usually persists only over a short time window, after which quantum interference washes out classical chaos. In this work, we demonstrate that quantum mechanics can also play the opposite role and generate exponential instabilities in classically nonchaotic systems within this early-time window. Our calculations employ the out-of-time-ordered correlator (OTOC)—a diagnostic that reduces to the Lyapunov exponent in the classical limit but is well defined for general quantum systems. We show that certain classically nonchaotic models, such as polygonal billiards, demonstrate a Lyapunov-like exponential growth of the OTOC at early times with Planck’s-constant-dependent rates. This behavior is sharply contrasted with the slow early-time growth of the analog of the OTOC in the systems’ classical counterparts. These results suggest that classical-to-quantum correspondence in dynamics is violated in the OTOC even before quantum interference develops.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Interference effects in the high-order harmonic amplification process in the active medium of a plasma-based X-ray laser modulated by an optical field

We study the process of propagation of high harmonics of optical radiation in an active medium of a plasma-based X-ray laser, simultaneously irradiated by an intense optical field of fundamental frequency. It is shown that for moderate plasma dispersion of the active medium at the frequency of the modulating optical field, the energy and relative amplitudes of the harmonics at the output of the medium are determined by their phases at the entrance to the medium, as well as by the time-delay of the harmonics with respect to the modulating field. These dependences are due to interference of high-order harmonics with a set of multi-frequency fields generated by each of the harmonics in the process of coherent scattering in a modulated active medium. The possibilities of using these effects to increase the efficiency of harmonic amplification, to control the harmonic spectrum, and determine the relative phases at the entrance to the medium are discussed on the example of the active medium of hydrogen-like Li{sup 2+} ions (with a 13.5 nm wavelength of an inverted transition). (paper)

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Theory of resonant x-ray scattering with ultrafast intense pulses

Here, we present a time-dependent Schrödinger equation approach within a nonrelativistic quantum electrodynamics framework to investigate resonant x-ray scattering driven by intense x-ray pulses. This method enables us to explore how coherent x-ray electron dynamics influence scattering signals from Ne + . We account for both resonance fluorescence and elastic scattering channels, while also considering competing photoionization and inner-shell decay processes. By computing the angular distribution and energy spectrum of scattered photons, we uncover interference effects between elastic scattering and resonance fluorescence pathways. Notably, this interference results in a small asymmetry in the energy spectrum. We discuss the experimental potential for detecting signatures of interference. Our findings demonstrate that the x-ray Rabi dynamics can be used to control scattering responses and provide insights into interference mechanisms and scattering efficiency in high-intensity x-ray regimes.

Venkatesh, Akilesh [Argonne National Laboratory (A↗
DOE OSTI2020

Signatures of possible surface states in TaAs

In this work, we study Shubnikov-de Haas oscillations in single crystals of TaAs and find a previously undetected two-dimensional quantum oscillation that does not belong to the bulk Fermi surface. We cannot find an impurity phase consistent with our observations, and extensive diffraction measurements have not shown the presence of known impurity phases. We conjecture that the frequency originates from surface states that are sensitive to surface disorder. One candidate is the interference of coherent quasiparticles traversing two distinct Fermi arcs on the [001] crystallographic surface. The frequency and effective mass quantitatively agree with predictions of density functional theory and previous angle-resolved photoemission spectroscopy measurements of the Fermi arcs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Oscillating paramagnetic Meissner effect and Berezinskii-Kosterlitz-Thouless transition in underdoped Bi2Sr2CaCu2O8+δ

ABSTRACT Superconducting phase transitions in two dimensions lie beyond the description of the Ginzburg-Landau symmetry-breaking paradigm for three-dimensional superconductors. They are Berezinskii-Kosterlitz-Thouless (BKT) transitions of paired-electron condensate driven by the unbinding of topological excitations, i.e. vortices. The recently discovered monolayers of layered high-transition-temperature (${{{T}}}_{{\rm C}}$) cuprate superconductor Bi2Sr2CaCu2O8+δ (Bi2212) meant that this 2D superconductor promised to be ideal for the study of unconventional superconductivity. But inhomogeneity posed challenges for distinguishing BKT physics from charge correlations in this material. Here, we utilize the phase sensitivity of scanning superconducting quantum interference device microscopy susceptometry to image the local magnetic response of underdoped Bi2212 from the monolayer to the bulk throughout its phase transition. The monolayer segregates into domains with independent phases at elevated temperatures below ${{{T}}}_{{\rm C}}$. Within a single domain, we find that the susceptibility oscillates with flux between diamagnetism and paramagnetism in a Fraunhofer-like pattern up to ${{{T}}}_{{\rm C}}$. The finite modulation period, as well as the broadening of the peaks when approaching ${{{T}}}_{{\rm C}}$ from below, suggests well-defined vortices that are increasingly screened by the dissociation of vortex-antivortex plasma through a BKT transition. In the multilayers, the susceptibility oscillation differs in a small temperature regime below ${{{T}}}_{{\rm C}}$, consistent with a dimensional crossover led by interlayer coupling. Serving as strong evidence for BKT transition in the bulk, we observe a sharp jump in phase stiffness and paramagnetism at small fields just below ${{{T}}}_{{\rm C}}$. These results unify the superconducting phase transitions from the monolayer to the bulk underdoped Bi2212, and can be collectively referred to as the BKT transition with interlayer coupling.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Time-reversed Young’s experiment: Deterministic, diffractionless second-order interference effect

The classic Young’s double-slit experiment exhibits first-order interference, producing alternating bright and dark fringes shaped by the diffraction effect of the slits. In contrast, here we demonstrate that its time-reversed configuration generates an ideal, deterministic second-order ‘ghost’ interference pattern free from diffraction and first-order effects with the use of only a position-fixed detector. The pattern’s size is governed by the dimensions of the ‘effectively extended light source’ formed by point emitter(s). Beyond highlighting the nonreciprocal physics between the two configurations, this system unlocks a range of novel phenomena inaccessible in traditional double-slit experiments. These include fully programmable, digitized interference fringe formations and the ability to align the pattern plane with the source plane on the same side of the setup. Remarkably, our proposed experiment achieves these outcomes without relying on nonclassical correlations or quantum entanglement. Here, by restoring time-reversal symmetry and eliminating diffraction, our theoretical analysis reveals that this approach offers exciting potential for advancing optical imaging and sensing technologies with improved transverse and longitudinal phase-shift sensitivity and resolution limit beyond current limitations.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2026

Flux trapping in NbTiN strips

We use scanning superconducting quantum interference device (SQUID) microscopy to image vortices in superconducting structures fabricated from NbTiN thin films. We repeatedly cool superconducting strips with different width in an applied magnetic field and image the individual vortices. From these images we determine the threshold field at which the first vortex enters a strip and the number and configuration of vortices beyond this threshold field. We model the behavior of the vortices with and without considering the effect of pinning using numerical methods to minimize the Gibbs free energy of vortices in the strips. Our measurements provide a first benchmark to investigate the flux trapping properties of NbTiN thin films directly relevant to NbTiN-based superconducting digital circuits.

Bai, Ruiheng [Cornell University] (ORCID:000000025↗