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All sources NASA NTRS DOE OSTI

DOE OSTI2022

Probing electron-hole coherence in strongly driven 2D materials using high-harmonic generation

Under strong electromagnetic excitation, electron–hole (e-h) pairs may be generated in solids, which are subsequently driven to high energy and high momentum, producing high harmonics (HH) of the driving field. The HH efficiency depends on the degree of coherence between the driven electron and hole created by the laser field. Here, we disrupt this e-h coherence in an atomically thin semiconductor by photodoping via incoherent e-h pairs. We observe a strong, systematic harmonic order-dependent intensity reduction. This trend is explained by an exponential decay of the inter-band polarization, proportional to the sub-cycle excursion time of the e-h pair. Our study provides a platform to probe the importance of many-body effects, such as excitation density-dependent decoherence time for strongly driven electrons without the need of ultrashort laser pulses.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2021

Improving probabilistic infectious disease forecasting through coherence

With an estimated $10.4 billion in medical costs and 31.4 million outpatient visits each year, influenza poses a serious burden of disease in the United States. To provide insights and advance warning into the spread of influenza, the U.S. Centers for Disease Control and Prevention (CDC) runs a challenge for forecasting weighted influenza-like illness (wILI) at the national and regional level. Many models produce independent forecasts for each geographical unit, ignoring the constraint that the national wILI is a weighted sum of regional wILI, where the weights correspond to the population size of the region. We propose a novel algorithm that transforms a set of independent forecast distributions to obey this constraint, which we refer to as probabilistically coherent. Enforcing probabilistic coherence led to an increase in forecast skill for 79% of the models we tested over multiple flu seasons, highlighting the importance of respecting the forecasting system’s geographical hierarchy.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2022

Defect identification in simulated Bragg coherent diffraction imaging by automated AI

X-ray Bragg coherent diffraction imaging is a powerful technique for operando and in situ materials characterization and provides a unique means of quantifying the influence of one-dimensional (1D) and two-dimensional (2D) material defects on material response. However, obtaining full images from raw x-ray diffraction data is nontrivial and computationally intensive, precluding real-time experimental feedback. Here, we present a machine learning approach to identify the presence of crystalline line defects (edge and screw) in samples from the raw, 2D, coherent diffraction data without the need for image reconstruction through iterative phase retrieval. Further, we compare different approaches to designing neural networks for this application and demonstrate the potential of automated ML (autoML) approaches.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Back-Azimuth Estimation of Air-to-Ground Coupled Infrasound from Transverse Coherence Minimization

We present the transverse coherence minimization method (TCM)—an approach to estimate the back–azimuth of infrasound signals that are recorded on an infrasound microphone and a colocated three–component seismometer. Accurate back–azimuth information is important for a variety of monitoring efforts, but it is currently only available for infrasound arrays and for seismoacoustic sensor pairs separated by 10 s of meters. Our TCM method allows for the analysis of colocated sensor pairs, sensors located within a few meters of each other, which may extend the capabilities of existing seismoacoustic networks and supplement operating infrasound arrays. This approach minimizes the coherence of the transverse component of seismic displacement with the infrasound wave to estimate the infrasound back–azimuth. After developing an analytical model, we investigate seismoacoustic signals from the August 2012 Humming Roadrunner experiment and the 26 May 2021 eruption of Great Sitkin Volcano, Alaska, U.S.A., at the ranges of 6.5–185 km from the source. We discuss back–azimuth estimates and potential sources of deviation (1°–15°), such as local terrain effects or deviation from common analytical models. This practical method complements existing seismoacoustic tools and may be suitable for routine application to signals of interest.

58 GEOSCIENCES↗

DOE OSTI2020

Coherent Processing of Up/Down Linear Frequency Modulated Chirps

A useful and popular waveform for high-performance radar systems is the Linear Frequency Modulated (LFM) chirp. The chirp may have a positive frequency slope with time (up-chirp) or a negative frequency slope with time (down-chirp). There is no inherent advantage to one with respect to the other, except that the receiver needs to be matched to the proper waveform. However, if up-chirps and down-chirps are employed on different pulses in the same Coherent Processing Interval (CPI), then care must be taken to maintain coherence in the range-compressed echo signals. We present the mathematics for doing so, for both correlation processing and stretch processing.

47 OTHER INSTRUMENTATION↗

DOE OSTI2022

Coherent wiggler radiation impedance at the storage ring cooler for the EIC project

The Electron Ion Collider project is presently under design at Brookhaven National Laboratory. One of the options how to achieve an electron-proton high-luminosity of 10 34 cm –2 s –1 range, is the storage ring cooler concept, which is based on employing a significant amount of the damping wigglers. One of the main concerns, in achieving the required beam parameters, is the collective effects, especially the coherent synchrotron radiation impedance produced by the damping wigglers and its effect on the longitudinal beam dynamics. Low energy of the electrons, E o =149.6 MeV, small vacuum chamber aperture, b=15 mm, small bending radius and a big number of poles make the coherent synchrotron radiation simulations for the damping wiggler with D. Zhou’s CSRZ code, pretty challenging. The obtained numerical results have been compare with a theoretical approach of Stupakov and Zhou. The strong narrow-band impedance, due to a presence of the periodic poles and the vacuum chamber, have been identified and classified. To suppress or detune the high-Q resonance peaks, a design of the damping wiggler with a varied period of length is presented and discussed.

43 PARTICLE ACCELERATORS↗

DOE OSTI2023

Coherent Neutrino-Nucleus Scattering: A Tool to Search for New Physics

The Neutrino is a well-understood particle in the models of particle physics. Even so, it is electrically neutral, and has a very small mass. As such, it’s interaction probability is extremely small. Detecting neutrinos has always been a challenge for particle physics. Over 40 years ago, Daniel Freedman predicted a new type of interaction that neutrinos could undergo that would be much more frequent. This has since been called Coherent Elastic Neutrino Nucleus Scattering (CEvNS). While this process occurred more frequently than the traditionally used interaction process (called inverse beta decay) it was more challenging to detect. Interestingly, though, if you could detect the CEvNS process, you would be sensitive to many new studies of fundamental particle physics. A researcher may also be able to use this process to study neutrinos in more applied settings, for instance by more easily monitoring the neutrinos given off during the nuclear reaction processes in nuclear reactors. The aim of this project was to observe coherent neutrino scattering for the first time, and begin to use it as a tool both to study new types of physics models, and to study the feasibility of this concept for applied situations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Coherent Wavelength Switched Co-Packaged Optics to Disrupt Datacenters/HPC (AKA "QRock") (Final Report)

This project resulted in multiple first-of-a-kind demonstrations, including two generations of transmitters, a receiver, and a complete coherent link. The transmitter architecture, based on EAMs to generate QPSK modulation was first demonstrated in InP, which has limitations for scaling up to chips with multiple channels for full WDM architectures, and implementing the densities and level of integration needed to implement co-packaging with electronics. Our work resulted in the first demonstration of this architecture on a Si platform compatible with copackaging, and our working prototypes illustrated the potential of the approach. The link demonstration was also the first coherent optical link realized in a multi-micron waveguide platform. For the transmitters, integrating efficient III-V EAM devices into the large waveguide Si platform simultaneously enables significant reduction in driver power consumption while minimizing optical losses in routing and fiber coupling. On the receiver side, optical coupling and propagation losses are also minimized in the multi-micron platform, reducing required laser optical power which improves link energy efficiency. The measurement results presented in the final report demonstrate that we achieved the speed objectives for the program (112Gb/s: 56Gbaud QPSK), albeit at a higher BER than targeted. The report provides assessments of the low-powercoherent link architecture and associated components developed under the program from both technological and commercial viewpoints.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2023

Exploring the Effects of Environmental Radiation on Superconducting Qubit Coherence (Final Scientific/Technical Report)

Previous experiments at MIT have shown that ionizing radiation reduces the average coherence of superconducting qubit coherence. Recently, others have observed spatiotemporally correlated errors in superconducting qubit arrays and suggested ionizing radiation as the source of these error events. The spatiotemporally correlated errors observed in superconducting qubit arrays have been speculated to originate from ionizing radiation, but it has not been shown that ionizing radiation is the source of these events. During the past year of our research under program DE-SC0021181 we demonstrated that ionizing radiation is a source of spatiotemporally correlated qubit relaxation events.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2021

Understanding Spin Coherence in Polyoxometalate-Based Molecular Qubits

This research advances the understanding of spin decoherence mechanisms and addresses the grand challenges in quantum information science of generating and stabilizing quantum states that may be manipulated with single-atom precision. It is accomplished using unique capabilities developed at PNNL for ion soft landing and spatially resolved vibrational spectroscopy of well-defined supported molecular qubit (MQ) arrays. It addresses knowledge gaps impeding the development of MQ-based quantum devices by answering two scientific questions: 1) Can we minimize spin-lattice relaxation rates by tuning the substrate-MQ interface? 2) What is the optimum number of spin centers that enables sufficient coherent signal generation prior to decoherence through inter-MQ and MQ-support interactions? The objective is to develop predictive design principles for prolonging spin coherence lifetimes in arrays of optically-addressable MQs for quantum computing applications.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2024

Removing Coherent ZZ Crosstalk Via a Simple Driven Coupling Resonator

The interaction between computational and non-computational states of nearby coupled qubits in popular NISQ-era superconducting qubit chip platforms, gives rise to an unwanted static ZZ interaction. This always-on term is a common source of coherent errors, in turn limiting the computational potential of such chips. However, it is still unclear how to eliminate such crosstalk noise efficiently and without added complexity. We here discuss experimental results from a recently-proposed technique addressing this issue: using a simple high-coherence coupling resonator, driven so as to induce a controllable phase interaction between the qubits, the inherent crosstalk can be cancelled. Coupled with cross-resonance gates, such a scheme is a potential avenue towards high fidelity entangling operations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

GENERATING CORCOS-COHERENT SIGNAL SERIES USING PHASE PERTURBATION

Phase perturbations are used to simulate the time-domain behavior of pressure loads from turbulent boundary layers while faithfully representing the coherence decay behaviors of turbulence-generated pressure fields. Turbulence "evolves" as it proceeds downstream, and coherence decays as the decaying exponential of the product of a flow-related constant with frequency and distance. Time domain methods for a line, a plane, a closed cyclic surface, and most of a cone were given.

Swift, Stephen Hales↗

DOE OSTI2025

Understanding and Mitigating Coherence and Frequency Fluctuations in Superconducting Transmon Qubits

Transmon qubits are a cornerstone of superconducting quantum computing platforms. However‚ their frequency and coherence properties exhibit temporal fluctuations‚ leading to performance degradation in quantum processors over time. A common mitigation approach involves frequent recalibration‚ which‚ while effective‚ results in increased system downtime. Enhancing the long-term stability of transmon qubits is therefore critical for scalable and reliable quantum computing. In this study‚ we develop novel techniques for understanding the underlying mechanisms driving frequency and coherence fluctuations in fixed-frequency transmon qubits. We further explore strategies to mitigate these instabilities‚ aiming to improve overall system robustness. Our findings provide insights into optimizing superconducting quantum hardware for practical applications.

Roy, Tanay [Fermilab]↗

DOE OSTI2026

Quantum Zeno Control of Superconducting Qubit Coherence

The Quantum Zeno Effect (QZE) dictates how the dynamics of a quantum system can be modified through continuous or discrete measurements [1]. It has gained increasing attention in quantum computing community in recent years, both due to its inevitable implications for qubit readout as well as for its promise for enabling new methods of quantum state control such as reservoir engineering and Zeno-dragging. Here, we investigate Zeno effects implemented via weak measurements for controlling superconducting-qubit coherence during gate and readout operations in a multi-qubit setup. Building on prior observations [2] that measurement backaction can both suppress and enhance qubit relaxation, we predict and measure QZE-altered qubit coherence times by manipulating the spectral overlap of qubit spectrum with background noise sources. We also discuss modifications and opportunities for controllable QZE due to anharmonic effects in multi-level superconducting atoms. [1] S. Greenfield, A. Kamal, J. Dressel, E. Levenson-Falk, arXiv:2506.12679 (2025) [2] Thorbeck, Z. Xiao, L. Govia, A. Kamal, Phys. Rev. Lett. 132, 090602 (2024)

Seidel, Olivia [Texas U., Arlington; Fermilab]↗

DOE OSTI2026

Probing the Coherence of Metal Absorbers toward Background Quasar Pairs

Abstract We investigate the spatial coherence of metal absorption lines in the circumgalactic medium using 4115 quasar pairs from Sloan Digital Sky Survey DR16. We identify 184 Mg ii (15 with dual detections) and 50 C iv (11 with dual detections) absorber pairs. The fraction of pairs with fractional equivalent width difference δW r ≤ 0.5 declines with projected separation: for Mg ii , it drops from ∼52% at 0–25 kpc to ∼7% at 100–200 kpc, while for C iv , it decreases from ∼100% to ∼21% over 0–200 kpc. In every separation bin, C iv absorbers with δW r ≤ 0.5 maintain a higher fraction than Mg ii absorbers. Similar results are obtained when the nondetections are treated as 2 σ W r upper limits in a survival analysis. The transverse autocorrelation function shows strong Mg ii clustering within 0–25 kpc, whereas the C iv excess remains relatively flat out to ∼100 kpc. These findings suggest that high-ionization C iv gas retains coherence over larger transverse scales than low-ionization Mg ii gas, in agreement with previous lensed quasar and high-resolution studies.

Li, Jing [Guangxi University] (ORCID:0009000148751↗

DOE OSTI2025

Modeling the effects of active wake mixing on wake behavior through large-scale coherent structures

The use of active wake mixing (AWM) to mitigate downstream turbine wakes has created new opportunities for reducing power losses in wind farms. However, many current analytical or semi-empirical wake models do not capture the flow instabilities that are excited through the blade pitch actuation. In this work, we develop a framework, which accounts for the impacts of the large-scale coherent structures and turbulence on the mean flow, for modeling AWM. The framework uses a triple-decomposition approach for the unsteady flow field and models the mean flow and fine-scale turbulence with a parabolized Reynolds-averaged Navier–Stokes (RANS) system. The wave components are modeled using a simplified spatial linear stability formulation that captures the growth and evolution of the coherent structures. Comparisons with high-fidelity large eddy simulations (LESs) of the turbine wakes showed that this framework was able to capture the additional wake mixing and faster wake recovery in the far-wake regions for both the pulse and helix AWM strategies with minimal computational expense. In the near-wake region, some differences are observed in both the RANS velocity profiles and initial growth of the large-scale structures, which may be due to some simplifying assumptions used in the model.

17 WIND ENERGY↗

DOE OSTI2020

Cosmological Constant in Coherent Quantum Gravity

It is argued that quantum states of geometry, like those of particles, should be coherent on light cones of any size. An exact classical solution, the gravitational shock wave of a relativistic point particle, is used to estimate gravitational drag from coherent energy flows, and the expected gravitational effect of virtual transverse vacuum energy fluctuations on surfaces of causal diamonds. It is proposed that the appropriately spacetime-averaged gravitational effect of the Standard Model vacuum state leads to the observed small nonzero value of the cosmological constant, dominated by gravitational drag of virtual gluonic strings at the strong interaction scale.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Simultaneous classical and quantum communication scheme based on coherent detection

An improved coherent communication scheme is provided. The coherent communication scheme encodes both classical and quantum information simultaneously using isolated groups of states: classical information is represented by different groups and can be decoded deterministically; and quantum information is represented by highly overlapped states within the same group, thus guaranteeing security. Decoding includes projecting the detection results at the receiver to one of the distinguishable encoding groups first, which allows the classical information to be read out, and then generating a quantum key from the residual randomness. This communications scheme enables simultaneous classical communication and QKD over the same communication channel using the same transmitter and receiver, opening the door to operate QKD in the background of classical communication and at negligible costs.

Qi, Bi↗