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DOE OSTI2016

Wave function continuity and the diagonal Born-Oppenheimer correction at conical intersections

We demonstrate that though exact in principle, the expansion of the total molecular wave function as a sum over adiabatic Born-Oppenheimer (BO) vibronic states makes inclusion of the second-derivative nonadiabatic energy term near conical intersections practically problematic. In order to construct a well-behaved molecular wave function that has density at a conical intersection, the individual BO vibronic states in the summation must be discontinuous. When the second-derivative nonadiabatic terms are added to the Hamiltonian, singularities in the diagonal BO corrections (DBOCs) of the individual BO states arise from these discontinuities. In contrast to the well-known singularities in the first-derivative couplings at conical intersections, these singularities are non-integrable, resulting in undefined DBOC matrix elements. Though these singularities suggest that the exact molecular wave function may not have density at the conical intersection point, there is no physical basis for this constraint. Instead, the singularities are artifacts of the chosen basis of discontinuous functions. We also demonstrate that continuity of the total molecular wave function does not require continuity of the individual adiabatic nuclear wave functions. We classify nonadiabatic molecular dynamics methods according to the constraints placed on wave function continuity and analyze their formal properties. Based on our analysis, it is recommended that the DBOC be neglected when employing mixed quantum-classical methods and certain approximate quantum dynamical methods in the adiabatic representation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2016

Interface structure in nanoscale multilayers near continuous-to-discontinuous regime

Interfacial atomic diffusion, reaction, and formation of microstructure in nanoscale level are investigated in W/B{sub 4}C multilayer (ML) system as functions of thickness in ultrathin limit. Hard x-ray reflectivity (XRR) and x-ray diffuse scattering in conjunction with x-ray absorption near edge spectroscopy (XANES) in soft x-ray and hard x-ray regimes and depth profiling x-ray photoelectron spectroscopy (XPS) have been used to precisely evaluate detailed interfacial structure by systematically varying the individual layer thickness from continuous-to-discontinuous regime. It is observed that the interfacial morphology undergoes an unexpected significant modification as the layer thickness varies from continuous-to-discontinuous regime. The interfacial atomic diffusion increases, the physical density of W layer decreases and that of B{sub 4}C layer increases, and further more interestingly the in-plane correlation length decreases substantially as the layer thickness varies from continuous-to-discontinuous regime. This is corroborated using combined XRR and x-ray diffused scattering analysis. XANES and XPS results show formation of more and more tungsten compounds at the interfaces as the layer thickness decreases below the percolation threshold due to increase in the contact area between the elements. The formation of compound enhances to minimize certain degree of disorder at the interfaces in the discontinuous region that enables to maintain the periodic structure in ML. The degree of interfacial atomic diffusion, interlayer interaction, and microstructure is correlated as a function of layer thickness during early stage of film growth.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2018

Continuous roll-to-roll fabrication of organic photovoltaic cells via interconnected high-vacuum and low-pressure organic vapor phase deposition systems

We demonstrate continuous roll-to-roll (R2R) fabrication of single junction and tandem organic photovoltaic (OPV) cells on flexible plastic substrates employing a system that integrates organic deposition by high vacuum thermal evaporation (VTE) and low pressure organic vapor phase deposition (OVPD). By moving the substrate from chamber to chamber and then depositing films on stationary substrates, we achieve power conversion efficiencies of PCE = 8.6 ± 0.3% and 8.9 ± 0.2% for the single junction and tandem cells, respectively. Single junction OPVs are also fabricated on a continuously translating substrate at 0.3 cm/s, to achieve PCE = 8.5 ± 0.2%. Thin films grown on translating substrates by OVPD show <3% thickness non-uniformity and 0.66 nm root mean square surface roughness, similar to that obtained by VTE. Our results suggest that R2R film deposition comprising multiple vapor deposition technologies is a promising method for rapid speed and continuous manufacturing of high quality, small molecular weight organic electronic materials.

42 ENGINEERING↗

DOE OSTI2023

Computational optimal transport for molecular spectra: The fully continuous case

Computational optimal transport is used to analyze the difference between pairs of continuous molecular spectra. It is demonstrated that transport distances which are derived from this approach may be a more appropriate measure of the difference between two continuous spectra than more familiar measures of distance under many common circumstances. Associated with the transport distances is the transport map which provides a detailed analysis of the difference between two molecular spectra and is a key component of our study of quantitative differences between two continuous spectra. The use of optimal transport for comparing molecular spectra is developed in detail here with a set of model spectra, so that the discussion is self-contained. The difference between the transport distance and more common definitions of distance is elucidated for some well-chosen examples and it is shown where transport distances may be very useful alternatives to standard definitions of distance. The transport distance between a theoretical and experimental electronic absorption spectrum for SO 2 is studied and it is shown how the theoretical spectrum can be modified to fit the experimental spectrum better adjusting the theoretical band origin and the resolution of the theoretical spectrum. In conclusion, this analysis includes the calculation of transport maps between the theoretical and experimental spectra suggesting future applications of the methodology.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2019

Continuous-wave laser diodes based on epitaxially integrated InGaAs/AlGaAs/GaAs heterostructures

We report the results of the development and investigation of the main characteristics of integrated laser emitters for the spectral range from 1040 to 1080 nm. These devices are fabricated using epitaxially integrated InGaAs/AlGaAs/GaAs heterostructures with one or two emitting regions, and measurements are performed in pulsed, quasi-continuous, and continuous-wave pump regimes. It is found that along with the obvious advantage of integrated emitters − an increase in the output optical power, they also have a significant limitation, which consists in increasing the amount of released heat. Despite this, it is shown that such integrated double laser diodes operate efficiently in the continuous-wave generation regime (P{sub max} ∼ 6 W), demonstrating a 1.7-fold increase in the differential quantum efficiency as compared to single laser diodes. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2012

PRACTICAL METHODS FOR CONTINUOUS GRAVITATIONAL WAVE DETECTION USING PULSAR TIMING DATA

Gravitational waves (GWs) are tiny ripples in the fabric of space time predicted by Einstein's general relativity. Pulsar timing arrays (PTAs) are well poised to detect low-frequency (10{sup -9}-10{sup -7} Hz) GWs in the near future. There has been a significant amount of research into the detection of a stochastic background of GWs from supermassive black hole binaries (SMBHBs). Recent work has shown that single continuous sources standing out above the background may be detectable by PTAs operating at a sensitivity sufficient to detect the stochastic background. The most likely sources of continuous GWs in the pulsar timing frequency band are extremely massive and/or nearby SMBHBs. In this paper we present detection strategies including various forms of matched filtering and power spectral summing. We determine the efficacy and computational cost of such strategies. It is shown that using an optimal matched filter explicitly including the poorly constrained pulsar distances with a grid-based method is computationally infeasible. We show that an Earth-term-matched filter constructed using only the correlated signal terms is robust, computationally viable and highly sensitive to GW signals. We further show that a simple power spectral summing technique is nearly equivalent to the Earth-term-matched filter in terms of the minimum detectable amplitude. Both of these techniques are only a factor of two less sensitive than the computationally unrealizable optimal matched filter. We also show that a pairwise matched filter, taking the pulsar distances into account, is comparable to the optimal matched filter for the single template case and comparable to the Earth-term-matched filter for many search templates. Finally, using simulated data optimal quality, we place a theoretical minimum detectable strain amplitude of h > 2 Multiplication-Sign 10{sup -15} from continuous GWs at frequencies on the order {approx}1/T{sub obs}.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

OPTIMAL STRATEGIES FOR CONTINUOUS GRAVITATIONAL WAVE DETECTION IN PULSAR TIMING ARRAYS

Supermassive black hole binaries (SMBHBs) are expected to emit a continuous gravitational wave signal in the pulsar timing array (PTA) frequency band (10{sup -9} to 10{sup -7} Hz). The development of data analysis techniques aimed at efficient detection and characterization of these signals is critical to the gravitational wave detection effort. In this paper, we leverage methods developed for LIGO continuous wave gravitational searches and explore the use of the F-statistic for such searches in pulsar timing data. Babak and Sesana have used this approach in the context of PTAs to show that one can resolve multiple SMBHB sources in the sky. Our work improves on several aspects of prior continuous wave search methods developed for PTA data analysis. The algorithm is implemented fully in the time domain, which naturally deals with the irregular sampling typical of PTA data and avoids spectral leakage problems associated with frequency domain methods. We take into account the fitting of the timing model and have generalized our approach to deal with both correlated and uncorrelated colored noise sources. We also develop an incoherent detection statistic that maximizes over all pulsar-dependent contributions to the likelihood. To test the effectiveness and sensitivity of our detection statistics, we perform a number of Monte Carlo simulations. We produce sensitivity curves for PTAs of various configurations and outline an implementation of a fully functional data analysis pipeline. Finally, we present a derivation of the likelihood maximized over the gravitational wave phases at the pulsar locations, which results in a vast reduction of the search parameter space.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

CONTINUOUS MID-INFRARED STAR FORMATION RATE INDICATORS: DIAGNOSTICS FOR 0 < z < 3 STAR-FORMING GALAXIES

We present continuous, monochromatic star formation rate (SFR) indicators over the mid-infrared wavelength range of 6–70 μm. We use a sample of 58 star-forming galaxies (SFGs) in the Spitzer–SDSS–GALEX Spectroscopic Survey at z < 0.2, for which there is a rich suite of multi-wavelength photometry and spectroscopy from the ultraviolet through to the infrared. The data from the Spitzer Infrared Spectrograph (IRS) of these galaxies, which spans 5–40 μm, is anchored to their photometric counterparts. The spectral region between 40–70 μm is interpolated using dust model fits to the IRS spectrum and Spitzer 70 and 160 μm photometry. Since there are no sharp spectral features in this region, we expect these interpolations to be robust. This spectral range is calibrated as a SFR diagnostic using several reference SFR indicators to mitigate potential bias. Our band-specific continuous SFR indicators are found to be consistent with monochromatic calibrations in the local universe, as derived from Spitzer, WISE, and Herschel photometry. Our local composite template and continuous SFR diagnostics are made available for public use through the NASA/IPAC Infrared Science Archive (IRSA) and have typical dispersions of 30% or less. We discuss the validity and range of applicability for our SFR indicators in the context of unveiling the formation and evolution of galaxies. Additionally, in the era of the James Webb Space Telescope this will become a flexible tool, applicable to any SFG up to z ∼ 3.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

The continuous readout stream of the MicroBooNE liquid argon time projection chamber for detection of supernova burst neutrinos

The MicroBooNE continuous readout stream is a parallel readout of the MicroBooNE liquid argon time projection chamber (LArTPC) which enables detection of non-beam events such as those from a supernova neutrino burst. The low energies of the supernova neutrinos and the intense cosmic-ray background flux due to the near-surface detector location makes triggering on these events very challenging. Instead, MicroBooNE relies on a delayed trigger generated by SNEWS (the Supernova Early Warning System) for detecting supernova neutrinos. The continuous readout of the LArTPC generates large data volumes, and requires the use of real-time compression algorithms (zero suppression and Huffman compression) implemented in an FPGA (field-programmable gate array) in the readout electronics. In this paper we present the results of the optimization of the data reduction algorithms, and their operational performance. To demonstrate the capability of the continuous stream to detect low-energy electrons, a sample of Michel electrons from stopping cosmic-ray muons is reconstructed and compared to a similar sample from the lossless triggered readout stream.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2025

Noise-aware circuit compilations for a continuously parameterized two-qubit gateset

State-of-the-art noisy-intermediate-scale quantum processors are currently implemented across a variety of hardware platforms, each with their own distinct gatesets. As such, circuit compilation should not only be aware of but also deeply connect to the native gateset and noise properties of each. Trapped-ion processors are one such platform that provides a gateset that can be continuously parameterized across both one- and two-qubit gates. Here we use the Quantum Scientific Computing Open User Testbed to study noise-aware compilations focused on continuously parameterized two-qubit 𝑍⁢𝑍 gates (based on the Mølmer-Sørensen interaction) using $\scriptsize{SUPERSTAQ}$, a quantum software platform for hardware-aware circuit compiler optimizations. We discuss the realization of 𝑍⁢𝑍 gates with arbitrary angle on the all-to-all connected trapped-ion system. Then we discuss a variety of different compiler optimizations that innately target these 𝑍⁢𝑍 gates and their noise properties. These optimizations include moving from a restricted maximally entangling gateset to a continuously parameterized one, swap mirroring to further reduce the total entangling angle of the operations, focusing the heaviest 𝑍⁢𝑍 angle participation on the best-performing gate pairs, and circuit approximation to remove the least impactful 𝑍⁢𝑍 gates. We demonstrate these compilation approaches on the hardware with randomized quantum volume circuits, observing the potential to realize a larger quantum volume as a result of these optimizations. Using differing yet complementary analysis techniques, we observe the distinct improvements in system performance provided by these noise-aware compilations and study the role of stochastic and coherent error channels for each compilation choice.

Noise↗

DOE OSTI2026

Monte Carlo Event Generation with Continuous Normalizing Flows

We apply continuous normalizing flows trained with the flow matching method to the problem of phase-space sampling in Monte Carlo event generation for high-energy collider physics. Focusing on lepton-pair and top-quark pair production with multiple jets, the two computationally most expensive processes at the Large Hadron Collider, we train helicity-conditioned continuous normalizing flows to remap the random numbers used in matrix element evaluation. Compared to standard methods, we achieve unweighting efficiency improvements by factors of up to 184 and 25 for the two processes at their respective highest jet number, at the cost of an increased evaluation time. When combining the advantages of continuous normalizing flows with the fast evaluation times of coupling-layer-based flows, using the RegFlow approach, we find parton-level unweighted event generation walltime gains of about a factor of 10 at the highest jet numbers. These substantial gains highlight the promise of samplers based on machine learning for next-generation collider experiments.

Bothmann, Enrico [CERN; Gottingen U.] (ORCID:00000↗

DOE OSTI2025

Cheaper and more noise-resilient quantum state preparation using eigenvector continuation

Subspace methods are powerful, noise-resilient methods that can effectively prepare ground states on quantum computers. The challenge is to get a subspace with a small condition number that spans the states of interest using minimal quantum resources. In this work, we will use eigenvector continuation to build a subspace from the low-lying states of a set of Hamiltonians. The basis vectors are prepared using truncated versions of standard state preparation methods such as imaginary-time evolution (ITE), adiabatic state preparation (ASP), and variational quantum eigensolver. By using these truncated methods combined with eigenvector continuation, we can directly improve upon them, obtaining more accurate ground-state energies at a reduced cost. We use several spin systems to demonstrate convergence even when methods like ITE and ASP fail, such as ASP in the presence of level crossings and ITE with vanishing energy gaps. We also showcase the noise resilience of this approach beyond the gains already made by having shallower quantum circuits. Furthermore, our findings suggest that eigenvector continuation can be used to improve existing state preparation methods in the near term.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

Quantum simulation of quantum field theory using continuous variables

Much progress has been made in the field of quantum computing using continuous variables over the last couple of years. This includes the generation of extremely large entangled cluster states (10,000 modes, in fact) as well as a fault tolerant architecture. This has lead to the point that continuous-variable quantum computing can indeed be thought of as a viable alternative for universal quantum computing. With that in mind, we present a new algorithm for continuous-variable quantum computers which gives an exponential speedup over the best known classical methods. Specifically, this relates to efficiently calculating the scattering amplitudes in scalar bosonic quantum field theory, a problem that is known to be hard using a classical computer. Thus, we give an experimental implementation based on cluster states that is feasible with today's technology.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2019

Fluctuation theorems for continuous quantum measurements and absolute irreversibility

Fluctuation theorems are relations constraining the out-of-equilibrium fluctuations of thermodynamic quantities like the entropy production that were initially introduced for classical or quantum systems in contact with a thermal bath. Here we show, in the absence of thermal bath, the dynamics of continuously measured quantum systems can also be described by a fluctuation theorem, expressed in terms of a recently introduced arrow of time measure. Furthermore, this theorem captures the emergence of irreversible behavior from microscopic reversibility in continuous quantum measurements. From this relation, we demonstrate that measurement-induced wave-function collapse exhibits absolute irreversibility, such that Jarzynski-like equalities are violated, and that this property is inherent to quantum information acquisition. We apply our results to different continuous measurement schemes on a qubit: dispersive measurement, homodyne, and heterodyne detection of qubit's fluorescence.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2017

Self-learning Monte Carlo method: Continuous-time algorithm

The recently introduced self-learning Monte Carlo method is a general-purpose numerical method that speeds up Monte Carlo simulations by training an effective model to propose uncorrelated configurations in the Markov chain. We implement this method in the framework of a continuous-time Monte Carlo method with an auxiliary field in quantum impurity models. We introduce and train a diagram generating function (DGF) to model the probability distribution of auxiliary field configurations in continuous imaginary time, at all orders of diagrammatic expansion. Furthermore, by using DGF to propose global moves in configuration space, we show that the self-learning continuous-time Monte Carlo method can significantly reduce the computational complexity of the simulation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2020

From canyons to valleys: Numerically continuing sticky-hard-sphere clusters to the landscapes of smoother potentials

Here, we study the energy landscapes of particles with short-range attractive interactions as the range of the interactions increases. Starting with the set of local minima for 6 ≤ $\textit{N}$ ≤ 12 hard spheres that are “sticky,” i.e., they interact only when their surfaces are exactly in contact, we use numerical continuation to evolve the local minima (clusters) as the range of the potential increases, using both the Lennard-Jones and Morse families of interaction potentials. As the range increases, clusters merge, until at long ranges only one or two clusters are left. We compare clusters obtained by continuation with different potentials and find that for short and medium ranges, up to about 30% of particle diameter, the continued clusters are nearly identical, both within and across families of potentials. For longer ranges, the clusters vary significantly, with more variation between families of potentials than within a family. We analyze the mechanisms behind the merge events and find that most rearrangements occur when a pair of nonbonded particles comes within the range of the potential. An exception occurs for nonharmonic clusters, i.e., those that have a zero eigenvalue in their Hessian, which undergo a more global rearrangement.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2014

PLAStiCC: Predictive Look-Ahead Scheduling for Continuous dataflows on Clouds

Scalable stream processing and continuous dataflow systems are gaining traction with the rise of big data due to the need for processing high velocity data in near real time. Unlike batch processing systems such as MapReduce and workflows, static scheduling strategies fall short for continuous dataflows due to the variations in the input data rates and the need for sustained throughput. The elastic resource provisioning of cloud infrastructure is valuable to meet the changing resource needs of such continuous applications. However, multi-tenant cloud resources introduce yet another dimension of performance variability that impacts the application’s throughput. In this paper we propose PLAStiCC, an adaptive scheduling algorithm that balances resource cost and application throughput using a prediction-based look-ahead approach. It not only addresses variations in the input data rates but also the underlying cloud infrastructure. In addition, we also propose several simpler static scheduling heuristics that operate in the absence of accurate performance prediction model. These static and adaptive heuristics are evaluated through extensive simulations using performance traces obtained from public and private IaaS clouds. Our results show an improvement of up to 20% in the overall profit as compared to the reactive adaptation algorithm.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2019

Continuous Data Acquisition for Liquid Argon Time Projection Chamber Neutrino Detectors Using FPGA-Based Real-Time Compression Algorithms

Liquid argon time projection chambers (LArTPCs) have been proposed as neutrino detectors that combine both large sizes to maximize the number of neutrino interactions and detailed recording of the interaction. The readout of thousands of channels at MHz sampling rates produce images of the neutrino-nucleus interaction with millimeter-scale resolution, enabling the identification of the resulting particles and offering multiple handles to measure their energies at the expense of large data rates. Continuous acquisition of the LArTPC data is required to enable the use of high-latency triggers for capturing non-accelerator-beam events. We describe the case of the continuous readout of the MicroBooNE LArTPC, that grants the possibility of acquiring the neutrino burst from a supernova using the SNEWS (Supernova Early Warning System) alert as delayed trigger. The continuous data acquisition is accomplished by using real-time compression algorithms (zero suppression and Huffman compression) implemented in an FPGA in the readout electronics.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗