SEARCH · Search NASA
Results for “Quantum embedding”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Portobello - Quantum embedding in correlated materials made accessible
Not provided.
Robust, Accurate, and Efficient: Quantum Embedding Using the Huzinaga Level-Shift Projection Operator for Complex Systems
Using wave function (WF) in density functional theory (DFT) embedding methods provides a framework for performing localized, high-accuracy WF calculations on a system, while not incurring the full computational cost of the WF calculation on the full system. To effectively partition a system into localized WF and DFT subsystems, we utilize the Huzinaga level-shift projection operator within an absolutely localized basis. In this work, we study the ability of the absolutely localized Huzinaga level-shift projection operator method to study complex WF and DFT partitions, including partitions between multiple covalent bonds, a double bond, and transition-metal–ligand bonds. We find that our methodology can accurately describe all of these complex partitions. Additionally, we study the robustness of this method with respect to the WF method, specifically where the embedded systems were described using a multiconfigurational WF method. We found that the method is systematically improvable with respect to both the number of atoms in the WF region and the size of the basis set used, with energy errors less than 1 kcal/mol. Additionally, we calculated the adsorption energy of H2 to a model of an iron metal–organic framework (Fe-MOF-74) to within 1 kcal/mol compared to CASPT2 calculations performed on the full model while incurring only a small fraction of the full computational cost. In conclusion, this work demonstrates that the absolutely localized Huzinaga level-shift projection operator method is applicable to very complex systems with difficult electronic structures.
Projector-Based Quantum Embedding for Molecular Systems: An Investigation of Three Partitioning Approaches
Projector-based embedding is a relatively recent addition to the collection of methods that seek to utilize chemical locality to provide improved computational efficiency. This work considers the interactions between the different proposed procedures for this method and their effects on the accuracy of the results. The interplay between the embedded background, projector type, partitioning scheme, and level of atomic orbital (AO) truncation are investigated on a selection of reactions from the literature. The Huzinaga projection approach proves to be more reliable than the level-shift projection when paired with other procedural options. Active subsystem partitioning from the subsystem projected AO decomposition (SPADE) procedure proves slightly better than the combination of Pipek-Mezey localization and Mulliken population screening (PMM). Along with these two options, a new partitioning criteria is proposed based on subsystem von Neumann entropy and the related subsystem orbital occupancy. This new method overlaps with the previous PMM method, but the screening process is computationally simpler. Finally, AO truncation proves to be a robust option for the tested systems when paired with the Huzinaga projection, with satisfactory results being acquired at even the most severe truncation level.
CO Inversion on a NaCl(100) Surface: A Multireference Quantum Embedding Study
Not Available
Quantum embedding description of the Anderson lattice model with the ghost Gutzwiller approximation
Not Available
Spectral functions of strongly correlated extended systems via an exact quantum embedding
Not Available
Bypassing the computational bottleneck of quantum-embedding theories for strong electron correlations with machine learning
Not Available
Testing the applicability and potential impact of rigorous quantum embedding methods for the study and characterization of metal organic frameworks
The rational design of molecular photosystems is a challenge of paramount scientific, industrial, and societal importance. Computational research has the potential to contribute in this area by allowing for detailed investigations of biological photosystems, by revealing key insights into fundamental photochemical processes, and by allowing for fast and inexpensive screening of candidate photosystems. However, major theoretical obstacles currently hinder the reliable and efficient computational modeling of photocatalytic processes. We are developing new methods that overcome the intrinsic challenges of simulating and understanding the dynamics of processes that are central to solar photocatalysis and basic energy science, including proton-coupled electron transfer (PCET) dynamics. Furthermore, we are using these new methods to elucidate the fundamental chemical processes at the heart of the photocatalytic water splitting, which will yield fundamental insights into natural photosynthesis, as well as new strategies for the design of biomimetic photocatalysts.
Advances in Quantum Defect Embedding Theory
Quantum defect embedding theory (QDET) is a many-body embedding method designed to describe condensed systems with strongly correlated electrons localized within a given region of space, for example spin defects in semiconductors and insulators. Although the QDET approach has been successful in predicting the electronic properties of several point defects, several limitations of the method remain. Here, in this work, we propose multiple advances to the QDET formalism. We derive a doublecounting correction that consistently treats the frequency dependence of the screened Coulomb interaction, and we illustrate the effect of including unoccupied orbitals in the active space. In addition, we propose a method to describe hybridization effects between the active space and the environment, and we compare the results of several impurity solvers, providing further insights into improving the reliability and applicability of the method. We present results for defects in diamond and for molecular qubits, including a detailed comparison with experiments.
Quantum annealing correction with minor embedding
Quantum annealing provides a promising route for the development of quantum optimization devices, but the usefulness of such devices will be limited in part by the range of implementable problems as dictated by hardware constraints. To overcome constraints imposed by restricted connectivity between qubits, a larger set of interactions can be approximated using minor embedding techniques whereby several physical qubits are used to represent a single logical qubit. However, minor embedding introduces new types of errors due to its approximate nature. Here we introduce and study quantum annealing correction schemes designed to improve the performance of quantum annealers in conjunction with minor embedding, thus leading to a hybrid scheme defined over an encoded graph. We argue that this scheme can be efficiently decoded using an energy minimization technique provided the density of errors does not exceed the per-site percolation threshold of the encoded graph. We test the hybrid scheme using a D-Wave Two processor on problems for which the encoded graph is a two-level grid and the Ising model is known to be NP-hard. The problems we consider are frustrated Ising model problem instances with “planted” (a priori known) solutions. Applied in conjunction with optimized energy penalties and decoding techniques, we find that this approach enables the quantum annealer to solve minor embedded instances with significantly higher success probability than it would without error correction. Our work demonstrates that quantum annealing correction can and should be used to improve the robustness of quantum annealing not only for natively embeddable problems but also when minor embedding is used to extend the connectivity of physical devices.
Impact of capping layer type on emission of InAs quantum dots embedded in InGaAs/In{sub x}Al{sub y}Ga{sub z}As/GaAs quantum wells
The optical and structural properties of In{sub 0.15}Ga{sub 0.85}As/In{sub x}Al{sub y}Ga{sub z}As/GaAs quantum wells with embedded InAs quantum dots (QDs) were investigated by the photoluminescence (PL), its temperature dependence, X-ray diffraction (XRD), and high resolution (HR-XRD) methods in dependence on the composition of capping In{sub x}Al{sub y}Ga{sub z}As layers. Three types of capping layers (Al{sub 0.3}Ga{sub 0.7}As, Al{sub 0.10}Ga{sub 0.75}In{sub 0.15}As, and Al{sub 0.40}Ga{sub 0.45}In{sub 0.15}As) have been used and their impact on PL parameters has been compared. Temperature dependences of PL peak positions in QDs have been analyzed in the range of 10–500 K and to compare with the temperature shrinkage of band gap in the bulk InAs crystal. This permits to investigate the QD material composition and the efficiency of Ga(Al)/In inter diffusion in dependence on the type of In{sub x}Al{sub y}Ga{sub z}As capping layers. XRD and HR-XRD used to control the composition of quantum well layers. It is shown that QD material composition is closer to InAs in the structure with the Al{sub 0.40}Ga{sub 0.45}In{sub 0.15}As capping layer and for this structure the emission 1.3 μm is detected at 300 K. The thermal decay of the integrated PL intensity has been studied as well. It is revealed the fast 10{sup 2}-fold thermal decay of the integrated PL intensity in the structure with the Al{sub 0.10}Ga{sub 0.75}In{sub 0.15}As capping layer in comparison with 10-fold decay in other structures. Finally, the reasons of PL spectrum transformation and the mechanism of PL thermal decay for different capping layers have been analyzed and discussed.
Controllable quantum spin glasses with magnetic impurities embedded in quantum solids
Not Available
Quantum-classical embedding via ghost Gutzwiller approximation for enhanced simulations of correlated electron systems
Simulating correlated materials on present-day quantum hardware remains challenging due to limited quantum resources. Quantum embedding methods offer a promising route by reducing computational complexity through the mapping of bulk systems onto effective impurity models, allowing more feasible simulations on pre- and early-fault-tolerant quantum devices. Here, this work develops a quantum-classical embedding framework based on the ghost Gutzwiller approximation to enable quantum-enhanced simulations of ground-state properties and spectral functions of correlated electron systems. Circuit complexity is analyzed using an adaptive variational quantum algorithm on a statevector simulator, applied to the infinite-dimensional Hubbard model with increasing ghost mode numbers from 3 to 5, resulting in circuit depths growing from 16 to 104. Noise effects are examined using a realistic error model, revealing significant impact on the spectral weight of the Hubbard bands. To mitigate these effects, the Iceberg quantum error detection code is employed, achieving up to 40% error reduction in simulations. Finally, the accuracy of the density matrix estimation and the derived spectral function is benchmarked on IBM and Quantinuum quantum hardware, featuring distinct qubit-connectivity and employing multiple levels of error mitigation techniques.