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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Ultrafast hole relaxation dynamics in quantum dots revealed by two-dimensional electronic spectroscopy

Elucidating the population dynamics of correlated electron-hole pairs (bound excitons) in semiconducting quantum dots (QDs) is key for developing our fundamental understanding of nanoscale photophysics as well as for the optimal design of devices, such as lasers. For decades, it was assumed that holes did not contribute to band edge bleach signals in QDs. Here, we employ two-dimensional electronic spectroscopy to monitor electron and hole dynamics in both CdSe and CdSe/CdS/ZnS QDs to probe electron and hole dynamics. Based on a combination of time and frequency resolution, we observe a previously unresolved bleaching signal in CdSe QDs on timescales faster than 30 fs due to hole cooling. Atomistic semiempirical pseudopotential calculations are used to rationalize the order of magnitude difference in the observed hole dynamics in CdSe and CdSe/CdS/ZnS QDs. This picture advances our understanding of QD excitonics past the prevailing continuum effective mass theories generally used to describe QD electronic structure and dynamics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Interplay between Chiro-Optical and Spin Transport Properties in Chiral CdSe Quantum Dots

The chiral-induced spin selectivity (CISS) effect offers compelling approaches for manipulating spin-dependent processes in both chemistry and physics, yet the physical mechanism(s) underpinning CISS are still debated. Here we present a study of structure-property relationships in chiral quantum dot assemblies to identify attributes of CISS-based phenomena. Our results show that the circular dichroism (CD) strength of chiral CdSe quantum dots’ primary exciton transition correlates with two CISS properties, the propensity to transmit pure spin currents and to produce spin-polarized charge currents. While the spin-polarized charge current reverses its sign with a change in the polarity of the CD signal, the pure spin current transport does not. The trends in both transport types can be rationalized in terms of chirality-induced splitting of spin sub-bands, which are modulated by chiral symmetry breaking under charge transport through the CdSe quantum dots.

cadmium selenide↗
NASA NTRS2003

Microscopic Modeling of Intersubband Optical Processes in Type II Semiconductor Quantum Wells: Linear Absorption

Linear absorption spectra arising from intersubband transitions in semiconductor quantum well heterostructures are analyzed using quantum kinetic theory by treating correlations to the first order within Hartree-Fock approximation. The resulting intersubband semiconductor Bloch equations take into account extrinsic dephasing contributions, carrier-longitudinal optical phonon interaction and carrier-interface roughness interaction which is considered with Ando s theory. As input for resonance lineshape calculation, a spurious-states-free 8-band kp Hamiltonian is used, in conjunction with the envelop function approximation, to compute self-consistently the energy subband structure of electrons in type II InAs/AlSb single quantum well structures. We demonstrate the interplay of nonparabolicity and many-body effects in the mid-infrared frequency range for such heterostructures.

Li, Jian-Zhong↗
DOE OSTI2014

High-accuracy calculations of sixteen collision integrals for Lennard-Jones (12–6) gases and their interpolation to parameterize neon, argon, and krypton

The inverse problem of parameterizing intermolecular potentials given macroscopic transport and thermodynamic data is addressed. Procedures are developed to create arbitrary-precision algorithms for transport collision integrals, using the Lennard-Jones (12–6) potential as an example. Interpolation formulas are produced that compute these collision integrals to four-digit accuracy over the reduced-temperature range 0.3≤T{sup ⁎}≤400, allowing very fast computation. Lennard-Jones parameters for neon, argon, and krypton are determined by simultaneously fitting the observed temperature dependences of their viscosities and second virial coefficients—one of the first times that a thermodynamic and a dynamic property have been used simultaneously for Lennard-Jones parameterization. In addition to matching viscosities and second virial coefficients within the bounds of experimental error, the determined Lennard-Jones parameters are also found to predict the thermal conductivity and self-diffusion coefficient accurately, supporting the value of the Lennard-Jones (12–6) potential for noble-gas transport-property correlation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Hidden quantum criticality and entanglement in quench dynamics

Entanglement exhibits universal behavior near the ground-state critical point where correlations are long ranged and the thermodynamic entropy is vanishing. On the other hand, a quantum quench imparts extensive energy and results in a build up of entropy, hence no critical behavior is expected at long times. In this work, we present a new paradigm in the quench dynamics of integrable spin chains which exhibit a ground-state order-disorder phase transition at a critical line. Specifically, we consider a quench along the critical line which displays a volume-law behavior of the entropy and exponentially decaying correlations; however, we show that quantum criticality is hidden in higher-order correlations and becomes manifest via measures such as the mutual information and logarithmic negativity. Furthermore, we showcase the scale invariance of the Rényi mutual information between disjoint regions as further evidence for genuine critical behavior. We attribute the emergent quantum criticality to the soft mode not getting excited in spite of the quench. Moreover, the results presented here are universal to models whose low-energy or long-wavelength dynamics are well described by a free-fermionic field theory. Our results are amenable to an experimental realization on different quantum simulator platforms, particularly the Rydberg simulators. Published by the American Physical Society 2024

Paul, Sanku↗
DOE OSTI2020

Ultrafast Electron Correlations and Memory Effects at Work: Femtosecond Demagnetization in Ni

Experimental observations of the ultrafast (less than 50 fs) demagnetization of Ni have so far defied theoretical explanations particularly since its spin-flipping time is much less than that resulting from spin-orbit and electron-lattice interactions. Through the application of an approach that benefits from spin-flip time-dependent density-functional theory and dynamical mean-field theory, we show that proper inclusion of electron correlations and memory (time dependence of electron-electron interaction) effects leads to demagnetization at the femtosecond scale, in good agreement with experimental observations. Furthermore, our calculations reveal that this ultrafast demagnetization results mainly from spin-flip transitions from occupied to unoccupied orbitals implying a dynamical reduction of exchange splitting. In this work, these conclusions are found to be valid for a wide range of laser pulse amplitudes. They also pave the way for ab initio investigations of ultrafast charge and spin dynamics in a variety of quantum materials in which electron correlations may play a definitive role.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Electronic in-plane symmetry breaking at field-tuned quantum criticality in CeRhIn5

Electronic nematicity appears in proximity to unconventional high-temperature superconductivity in the cuprates and iron-arsenides, yet whether they cooperate or compete is widely discussed. While many parallels are drawn between high-T c and heavy fermion superconductors, electronic nematicity was not believed to be an important aspect in their superconductivity. We have found evidence for a field-induced strong electronic in-plane symmetry breaking in the tetragonal heavy fermion superconductor CeRhIn 5 . At ambient pressure and zero field, it hosts an anti-ferromagnetic order (AFM) of nominally localized 4f electrons at TN=3.8K(1). Moderate pressure of 17kBar suppresses the AFM order and a dome of superconductivity appears around the quantum critical point. Similarly, a density-wave-like correlated phase appears centered around the field-induced AFM quantum critical point. In this phase, we have now observed electronic nematic behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Quantum materials for nanosensing and fault-tolerant quantum computing

New concepts of symmetry related to topological order emerged from the discovery of the fractional quantum Hall effect and high-temperature superconductivity in strongly correlated electron systems. This led to the study of quantum materials-- materials exhibiting emergent quantum phenomena with no classical analogues. While these materials have engendered exciting basic materials science and physics, realizing novel devices is a key challenge in the field. The goal of this proposal is to harness the unique properties of topological materials for quantum computing and quantum sensing applications. In this project, we investigated a variety of topological superconducting platforms and identified three technologies that can benefit from their quantum properties: quantum memory, single-photon detection, and non reciprocal electronics. The platforms developed in this work will be broadly useful to National Security and Basic Science.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Universal Spreading of Conditional Mutual Information in Noisy Random Circuits

For this work, we study the evolution of conditional mutual information (CMI) in generic open quantum systems, focusing on one-dimensional random circuits with interspersed local noise. Unlike in noiseless circuits, where CMI spreads linearly while being bounded by the light cone, we find that noisy random circuits with an error rate 𝑝 exhibit superlinear propagation of CMI, which diverges far beyond the light cone at a critical circuit depth 𝑡 𝑐 ∝ 𝑝 −1 . We demonstrate that the underlying mechanism for such rapid spreading is the combined effect of local noise and a scrambling unitary, which selectively removes short-range correlations while preserving long-range correlations. To analytically capture the dynamics of CMI in noisy random circuits, we introduce a coarse-graining method, and we validate our theoretical results through numerical simulations. Furthermore, we identify a universal scaling law governing the spreading of CMI.

decoherence↗
DOE OSTI2026

Geometric decoherence time in Lindbladian dynamics

The onset of decoherence in open many-body systems lacks a dynamical timescale grounded in the loss of bipartite entanglement. Here, we introduce the geometric decoherence time, defined as the earliest moment the monotone relation between logarithmic negativity and Rényi-$\frac{1}{2}$ entropy—exactly equal across any bipartition for pure states—breaks down under open-system evolution, signaling entropy growth without accompanying entanglement growth. We establish this criterion in both single-particle Gaussian dynamics and many-body Lindbladian evolution. We show that quantum mutual information provides a complementary long-time diagnostic: Its asymptotic vanishing is equivalent to factorization of the steady state across the bipartition, a condition strictly stronger than separability, and whenever a product steady state is approached exponentially in trace norm, negativity and mutual information share the same decay rate. In the presence of a strong symmetry, this tracking can fail—residual classical correlations can survive after entanglement has vanished. In the Kitaev chain with balanced gain and loss, we derive a closed-form solution and show that the topological phase sustains longer coherence times than the trivial phase at identical dissipation, with a local minimum at the chiral-symmetric point. In the interacting XXZ chain, exact many-body evolution shows that local 𝑍 dephasing preserves residual classical correlations, whereas gain and loss restore the mutual-information tracking of negativity. Furthermore, our results establish the geometric decoherence time as a dynamical scale tracking the onset of decoherence.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Multireference linearized coupled cluster theory for strongly correlated systems using matrix product states

We propose a multireference linearized coupled cluster theory using matrix product states (MPSs-LCC) which provides remarkably accurate ground-state energies, at a computational cost that has the same scaling as multireference configuration interaction singles and doubles, for a wide variety of electronic Hamiltonians. These range from first-row dimers at equilibrium and stretched geometries to highly multireference systems such as the chromium dimer and lattice models such as periodic two-dimensional 1-band and 3-band Hubbard models. The MPS-LCC theory shows a speed up of several orders of magnitude over the usual Density Matrix Renormalization Group (DMRG) algorithm while delivering energies in excellent agreement with converged DMRG calculations. Also, in all the benchmark calculations presented here, MPS-LCC outperformed the commonly used multi-reference quantum chemistry methods in some cases giving energies in excess of an order of magnitude more accurate. As a size-extensive method that can treat large active spaces, MPS-LCC opens up the use of multireference quantum chemical techniques in strongly correlated ab initio Hamiltonians, including two- and three-dimensional solids.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Determining topological order from infinite projected entangled pair states

In this work, we present a method of extracting information about the topological order from the ground state of a strongly correlated two-dimensional system computed with the infinite projected entangled pair state (iPEPS). For topologically ordered systems, the iPEPS wrapped on a torus becomes a superposition of degenerate, locally indistinguishable ground states. Projectors in the form of infinite matrix product operators onto states with well-defined anyon flux are used to compute topological S and T matrices (encoding mutual and self-statistics of emergent anyons). The algorithm is shown to be robust against a perturbation driving string-net toric code across a phase transition to a ferromagnetic phase. Our approach provides accurate results near quantum phase transition, where the correlation length is prohibitively large for other numerical methods. Moreover, we used numerically optimized iPEPS describing the ground state of the Kitaev honeycomb model in the toric code phase and obtained topological data in excellent agreement with theoretical prediction.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Novel quantum states of matter in moiré materials (2023 Aspen Winter Conference)

This report is to summarize the proceedings of the conference “Novel Quantum States of Matter in Moiré Materials,” which was held at the Aspen Center for Physics, March 12 – 17, 2023. The conference organizers thank the Department of Energy (DOE) for providing funding support for the conference. The advent of moiré quantum materials has opened a highly tunable platform for exploring the interplay between electronic structure, interactions, symmetry, and topology. Since the discovery of correlated insulator states and superconductivity in magic-angle twisted bilayer graphene (MATBG), a growing variety of moiré systems have emerged, revealing novel correlated and topological phenomena such as quantum anomalous Hall systems, generalized Wigner crystals, and fractional Chern insulators. This rich phenomenology continues to attract intense theoretical and experimental interest.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Spin Dynamics of SCRPs in ZnO Quantum Dot–Organic Molecule Conjugates Studied with Pulsed EPR

Photogenerated spin-correlated radical pairs (SCRPs) are emerging as promising new candidates for Quantum Information Science applications, where they act as electron spin qubit pairs (SQPs). Historically, these pairs have been mostly investigated in natural photosynthesis and in molecular organic donor–(linker)–acceptor systems. Recently, we have shown that these spin pairs can also be observed by time-resolved electron-paramagnetic resonance (EPR) spectroscopy in hybrid inorganic–organic conjugates. The current study builds on recent work (ACS Nano, 2025, 19, 12194–12207), in which we systematically prepared hybrid inorganic–organic molecule systems with tunable geometries that can host SCRPs/SQPs. Here, we demonstrate using pulsed EPR spectroscopy that we can generate, study, and manipulate the spins in these photogenerated SCRPs hosted on highly tailorable inorganic–organic hybrid systems. Microwave pulse-based spin manipulation is the first step toward developing quantum computing and quantum sensing applications with these promising spin-based qubit materials, which can be reversibly photogenerated in highly spin-polarized states at moderate temperatures. An attractive feature of this new class of hybrid materials is that the g-factor of the unpaired electron spin in the ZnO QD (as part of the SCRP/SQP) can be adjusted using the quantum size effect in these QDs, which allows for the selective addressability of each spin in the SCRP using microwave pulses. Additionally, we also observed a difference between the g-values of the unpaired electron in the ZnO QD in the transient SCRP state and stable photoreduced state. We hypothesize that the unpaired electron in the SCRP is delocalized as a band-like conduction electron, while in the stable photoreduced state, the electron is delocalized in a shallow electron trap state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Many-Electron System on Helium and Color Center Spectroscopy

Electrons on the helium surface display sharp resonant absorption lines related to the transitions between the subbands of quantized motion transverse to the surface. A magnetic field parallel to the surface strongly affects the absorption spectrum.We show that the effect results from admixing the intersubband transitions to the in-plane quantum dynamics of the strongly correlated electron liquid or a Wigner crystal. This is similar to the admixing of electron transitions in color centers to phonons. Furthermore, the spectrum permits a direct characterization of the many-electron dynamics and also enables testing the theory of color centers in a system with controllable coupling.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Predicting Quantum Criticality in Single-Crystalline Ce 2 Ru 3 Ge 5

Strongly correlated f-electron systems are known to host exotic quantum states, such as quantum criticality, complex order parameters, and unconventional superconductivity. However, the appearance of these exotic states is difficult to predict, making the study of quantum critical behavior challenging, especially in ferromagnetic materials. Herein, we report a structure–property map for Ce 2 M 3 X 5 (M = transition metal; X = main group element) that aids in the targeted design of materials likely to exhibit quantum criticality. Guided by this map, we report on the synthesis of single-crystalline Ce 2 Ru 3 Ge 5 and provide, for the first time, magnetic susceptibility, heat capacity, resistivity, and magnetoresistance measurements on single crystals. Here, we observe a weak ferromagnetic-like response at 7.5 K, which is contrasted with the bulk ferromagnetic ordering that appears in polycrystalline samples. Non-Fermi liquid behavior is seen in the temperature dependent electrical resistivity and heat capacity of the single crystals, suggesting proximity to a ferromagnetic quantum critical point without chemical or physical pressure. Given the contrast with previous reports of polycrystals, these results lead us to propose that single crystalline Ce 2 Ru 3 Ge 5 is intrinsically tuned into the vicinity of a ferromagnetic quantum critical point.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Local spectroscopy of a gate-switchable moiré quantum anomalous Hall insulator

Abstract In recent years, correlated insulating states, unconventional superconductivity, and topologically non-trivial phases have all been observed in several moiré heterostructures. However, understanding of the physical mechanisms behind these phenomena is hampered by the lack of local electronic structure data. Here, we use scanning tunnelling microscopy and spectroscopy to demonstrate how the interplay between correlation, topology, and local atomic structure determines the behaviour of electron-doped twisted monolayer–bilayer graphene. Through gate- and magnetic field-dependent measurements, we observe local spectroscopic signatures indicating a quantum anomalous Hall insulating state with a total Chern number of ±2 at a doping level of three electrons per moiré unit cell. We show that the sign of the Chern number and associated magnetism can be electrostatically switched only over a limited range of twist angle and sample hetero-strain values. This results from a competition between the orbital magnetization of filled bulk bands and chiral edge states, which is sensitive to strain-induced distortions in the moiré superlattice.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Recent advancements in atomic many-body methods for high-precision studies of isotope shifts

The development of atomic many-body methods, capable of incorporating electron correlation effects accurately, is required for isotope shift (IS) studies. In combination with precise measurements, such calculations help to extract nuclear charge radii differences, and to probe for signatures of physics beyond the Standard Model of particle physics. Here, we review here a few recently-developed methods in the relativistic many-body perturbation theory (RMBPT) and relativistic coupled-cluster (RCC) theory frameworks for calculations of IS factors in the highly charged ions (HCIs), and neutral or singly-charged ions, respectively. The results are presented for a wide range of atomic systems in order to demonstrate the interplay between quantum electrodynamics (QED) and electron correlation effects. In view of this, we start our discussions with the RMBPT calculations for a few HCIs by rigorously treating QED effects; then we outline methods to calculate IS factors in the one-valence atomic systems using two formulations of the RCC approach. Then we present calculations for two valence atomic systems, by employing the Fock-space RCC methods. For completeness, we briefly discuss theoretical input required for the upcoming experiments, their possibilities to probe nuclear properties and implications to fundamental physics studies.

QED effects↗