Engineering topics
Xue, Sha
Publications and source records attributed to Xue, Sha.
Silicon carbide detectors for high flux neutron monitoring at near-core locations
Not provided.
Analysis of superfast encoding performance for electronic structure simulations
In our recent work, we examined various fermion-to-qubit mappings in the context of quantum simulation including the original Bravyi-Kitaev superfast encoding (OSE) as well as a generalized version (GSE). We return to OSE and compare it against the Jordan-Wigner (JW) transform for quantum chemistry considering the number of qubits required, the Pauli weight of terms in the transformed Hamiltonians, and the L 1 norm of the Hamiltonian. We considered a test set of molecular systems known as the Atomization Energy 6 (AE6) as well as hydrogen lattices. Our results showed that the resource efficiency of OSE is strongly affected by the spatial locality of the underlying single-particle basis. We find that OSE is outperformed by JW when the orbitals in the underlying single-particle basis are highly overlapping, which limits its applicability to near-term quantum chemistry simulations utilizing standard basis sets. In contrast, when orbitals are overlapping with only few others, as is the case of hydrogen lattices with very tight orbitals, OSE fares comparatively better. Furthermore, our results illustrate the importance of choosing the right combination of basis sets and fermion-to-qubit mapping to get the most out of a quantum device when simulating physical systems.
Ab initio calculations for crystalline PEO6:LiPF6 polymer electrolytes
Dry polymer electrolytes have been studied extensively because of their enhanced mechanical properties. Experimental studies have demonstrated that crystalline PEO6:LiPF6 has higher ionic conductivity than that of the amorphous phase, which seemingly contradicts the prevailing theory that amorphous polymer electrolytes have higher conduction performance. Also, the underlying mechanism at the atomic scale has remained elusive. In this work, the atomic and electronic structures of crystalline PEO6:LiPF6 are studied using ab initio density-functional theory. The results agree with experimental measurements. Additionally, the atomic-scale mechanisms of lithium ion transport in the polymer electrolytes are investigated with the climbing nudged elastic band method. The diffusion pathway and activation energy (∼0.87 eV) of lithium ions in crystalline PEO6:LiPF6 are determined.
Monitoring of Actinide Concentrations in Molten LiCl-KCl Salt using Alpha Spectroscopy: Final Progress Report
This project addresses the need for real time monitoring of actinide concentrations for spent fuel reprocessing utilizing alpha spectroscopy. This project specifically focuses on spent fuel reprocessing with the pyroprocessing technique that uses high temperature molten salt. Pyroprocessing uses molten salt such as lithium chloride and potassium chloride to separate out uranium and plutonium from spent fuel. To prevent any possible diversion of high purity plutonium in this process, monitoring of the actinide concentrations within the refinery are essential for safeguards and non-proliferation efforts. Alpha spectroscopy enables the identification and quantification of actinide isotopic concentrations. However, current assay methods involving intrusive sampling and ex-suit measurement require weeks to provide accurate information. A near real-time and in-situ measurement system is required to quickly quantify actinide isotopic concentrations within the salt. Semiconductor radiation detectors provide a compact, high energy resolution option for completing these measurement needs. Silicon carbide (SiC) has been shown to operate effectively at high temperatures and high chemical stability in the molten salt environment. 4H-SiC Schottky diode alpha particle detectors were fabricated and tested to determine their alpha spectroscopy capabilities. The detectors need to operate at the elevated temperatures, survive the molten salt environment, be radiation hard, and have sufficient energy resolution under all these conditions to determine isotopic concentrations. Along with the detector, a method of producing samples of the actinides in the salt is required. To produce a thin film of the actinides on the detector, which is a necessity for alpha spectroscopy, electrodeposition can be used. Electrodeposition uses an electric potential difference to selectively deposit uranium or other actinides from the salt using an anode and cathode. Deposition of the material directly onto the sensor would produce a thin film of material that would enable materials accountability measurements to be taken in real time.