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Du, Weijie

Publications and source records attributed to Du, Weijie.

13 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

An efficient quantum circuit for block encoding a pairing Hamiltonian

We present an efficient quantum circuit for block encoding a pairing Hamiltonian often studied in nuclear physics. Our block encoding scheme does not require mapping the creation and annihilation operators to the Pauli operators and representing the Hamiltonian as a linear combination of unitaries. Instead, we show how to encode the Hamiltonian directly using controlled swap operations. We analyze the gate complexity of the block encoding circuit and show that it scales polynomially with respect to the number of qubits required to represent a quantum state associated with the pairing Hamiltonian. We also show how the block encoding circuit can be combined with the quantum singular value transformation to construct an efficient quantum circuit for approximating the density of states of a pairing Hamiltonian. The techniques presented can be extended to encode more general second-quantized Hamiltonians.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2023

Multinucleon structure and dynamics via quantum computing

We propose a framework for computing the structure and dynamics for second-quantized many-nucleon Hamiltonians on quantum computers. We develop an oracle-based Hamiltonian input model that computes the many-nucleon states and nonzero Hamiltonian matrix elements of the many-nucleon system. With our Fock-state based input model, we show how to implement the sparse matrix simulation algorithms to calculate the dynamics of the second-quantized many-nucleon Hamiltonian. Based on the dynamics simulation methods, we also present the methodology for structure calculations of the many-nucleon system. In this work, we provide an explicit circuit design of our input model of the second-quantized Hamiltonian within a direct encoding scheme that maps the occupation of each available single-particle state in the many-nucleon state to the state of specific qubit in a quantum register. Here, we analyze our method and provide the asymptotic cost in computing resources for structure and dynamics calculations of many-nucleon systems. For pedagogical purposes, we demonstrate our input model with two model problems in restricted model spaces.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Calculations of the $np→dγ$ reaction in chiral effective field theory

Here, we present a calculation of the radiative capture cross section of the $np→dγ$ reaction in the low-energy range, where the M⁢1 reaction channel dominates. Employing the LENPIC nucleon-nucleon interaction up to the fifth order (N4LO) that is regularized by the semilocal coordinate space regulators, we obtain the initial and final state wave functions, and evaluate the phase shifts of the scattering state and deuteron properties. We derive the transition operator from the chiral effective field theory up to the next-to-next-to leading order (N2LO), where we also regularize the transition operator using regulators consistent with those of the interactions. We compute the capture cross sections, and the results show a converging pattern with the chiral-order expansion of the nucleon-nucleon interaction, where the regulator dependence of the results is weak when higher-order nucleon-nucleon interactions are employed. We quantify the uncertainties of the cross-section results due to the chiral-order truncation. The chirally complete and consistent cross-section results are calculated up to N2LO and they compare well with the experiments and other theoretical predictions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Sub Coulomb barrier d+ 208 Pb scattering in the time-dependent basis function approach

We employ the non-perturbative time-dependent basis function (tBF) approach to study the scattering of the deuteron on 208 Pb below the Coulomb barrier. We obtain the bound and discretized scattering states of the projectile, which form the basis representation of the tBF approach, by diagonalizing a realistic Hamiltonian in a large harmonic oscillator basis. We find that the higher-order inelastic scattering effects are noticeable for sub barrier scatterings with the tBF method. We have successfully reproduced experimental sub Coulomb barrier elastic cross section ratios with the tBF approach by considering only the electric dipole (E1) component of the Coulomb interaction between the projectile and the target during scatterings. Here, we find that the correction of the polarization potential to the Rutherford trajectory is dominant in reproducing the data at very low bombarding energies, whereas the role of internal transitions of the deuteron projectile induced by the E1 interaction during the scattering becomes increasingly significant at higher bombarding energies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Quantum simulation of nuclear inelastic scattering

We present a time-dependent quantum algorithm for nuclear inelastic scattering in the time-dependent basis function on qubits approach. This algorithm aims to quantum simulate a subset of the nuclear inelastic scattering problems that are of physical interest in which the internal degrees of freedom of the reaction system are excited by time-dependent external interactions. We expect that our algorithm will enable an exponential speedup in simulating the dynamics of the subset of the inelastic scattering problems, which would also be advantageous for the applications to more complicated scattering problems. For a demonstration problem, we solve for the Coulomb excitation of the deuteron, where the quantum simulations are performed with IBM Qiskit.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Basis light-front quantization for a chiral nucleon-pion Lagrangian

We present the first application of the basis light-front quantization method to a simple chiral model of the nucleon-pion system as a relativistic bound state for the physical proton. In this work, the light-front mass-squared matrix of the nucleon-pion system is obtained within a truncated basis. The mass and the corresponding light-front wave function (LFWF) of the proton are computed by numerical diagonalization of the resulting mass-squared matrix. With the boost-invariant LFWF, we calculate the probability density distribution of the pion's longitudinal momentum fraction and the Dirac form factor of the proton.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Effective operators in two-nucleon systems

Effective Hamiltonians and effective electroweak operators are calculated with the Okubo-Lee-Suzuki formalism for two-nucleon systems. Working within a harmonic oscillator basis, first without and then with a confining harmonic oscillator trap, we demonstrate the effects of renormalization on observables calculated for truncated basis spaces. We illustrate the renormalization effects for the root-mean-square point-proton radius, electric quadrupole moment, magnetic dipole moment, Gamow-Teller transition and neutrinoless double-beta decay operator using nucleon-nucleon interactions from chiral Effective Field Theory. Renormalization effects tend to be larger in the weaker traps and smaller basis spaces suggesting applications to heavier nuclei with transitions dominated by weakly-bound nucleons would be subject to more significant renormalization effects within achievable basis spaces.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Influence of air exposure duration and a-Si capping layer thickness on the performance of p-BaSi{sub 2}/n-Si heterojunction solar cells

Fabrication of p-BaSi{sub 2}(20 nm)/n-Si heterojunction solar cells was performed with different a-Si capping layer thicknesses (d{sub a-Si}) and varying air exposure durations (t{sub air}) prior to the formation of a 70-nm-thick indium-tin-oxide electrode. The conversion efficiencies (η) reached approximately 4.7% regardless of t{sub air} (varying from 12–150 h) for solar cells with d{sub a-Si} = 5 nm. In contrast, η increased from 5.3 to 6.6% with increasing t{sub air} for those with d{sub a-Si} = 2 nm, in contrast to our prediction. For this sample, the reverse saturation current density (J{sub 0}) and diode ideality factor decreased with t{sub air}, resulting in the enhancement of η. The effects of the variation of d{sub a-Si} (0.7, 2, 3, and 5 nm) upon the solar cell performance were examined while keeping t{sub air} = 150 h. The η reached a maximum of 9.0% when d{sub a-Si} was 3 nm, wherein the open-circuit voltage and fill factor also reached a maximum. The series resistance, shunt resistance, and J{sub 0} exhibited a tendency to decrease as d{sub a-Si} increased. These results demonstrate that a moderate oxidation of BaSi{sub 2} is a very effective means to enhance the η of BaSi{sub 2} solar cells.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Evaluation of band offset at amorphous-Si/BaSi{sub 2} interfaces by hard x-ray photoelectron spectroscopy

The 730 nm-thick undoped BaSi{sub 2} films capped with 5 nm-thick amorphous Si (a-Si) intended for solar cell applications were grown on Si(111) by molecular beam epitaxy. The valence band (VB) offset at the interface between the BaSi{sub 2} and the a-Si was measured by hard x-ray photoelectron spectroscopy to understand the carrier transport properties by the determination of the band offset at this heterointerface. We performed the depth-analysis by varying the take-off angle of photoelectrons as 15°, 30°, and 90° with respect to the sample surface to obtain the VB spectra of the BaSi{sub 2} and the a-Si separately. It was found that the barrier height of the a-Si for holes in the BaSi{sub 2} is approximately −0.2 eV, whereas the barrier height for electrons is approximately 0.6 eV. This result means that the holes generated in the BaSi{sub 2} layer under solar radiation could be selectively extracted through the a-Si/BaSi{sub 2} interface, promoting the carrier separation in the BaSi{sub 2} layer. We therefore conclude that the a-Si/BaSi{sub 2} interface is beneficial for BaSi{sub 2} solar cells.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

p-BaSi{sub 2}/n-Si heterojunction solar cells with conversion efficiency reaching 9.0%

p-BaSi{sub 2}/n-Si heterojunction solar cells consisting of a 20 nm thick B-doped p-BaSi{sub 2} epitaxial layer (p = 2.2 × 10{sup 18 }cm{sup −3}) on n-Si(111) (ρ = 1–4 Ω cm) were formed by molecular beam epitaxy. The separation of photogenerated minority carriers is promoted at the heterointerface in this structure. Under AM1.5 illumination, the conversion efficiency η reached 9.0%, which is the highest ever reported for solar cells with semiconducting silicides. An open-circuit voltage of 0.46 V, a short-circuit current density of 31.9 mA/cm{sup 2}, and a fill factor of 0.60 were obtained. These results demonstrate the high potential of BaSi{sub 2} for solar cell applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Measurement of valence-band offset at native oxide/BaSi{sub 2} interfaces by hard x-ray photoelectron spectroscopy

Undoped n-type BaSi{sub 2} films were grown on Si(111) by molecular beam epitaxy, and the valence band (VB) offset at the interface between the BaSi{sub 2} and its native oxide was measured by hard x-ray photoelectron spectroscopy (HAXPES) at room temperature. HAXPES enabled us to investigate the electronic states of the buried BaSi{sub 2} layer non-destructively thanks to its large analysis depth. We performed the depth-analysis by varying the take-off angle (TOA) of photoelectrons as 15°, 30°, and 90° with respect to the sample surface and succeeded to obtain the VB spectra of the BaSi{sub 2} and the native oxide separately. The VB maximum was located at −1.0 eV from the Fermi energy for the BaSi{sub 2} and −4.9 eV for the native oxide. We found that the band bending did not occur near the native oxide/BaSi{sub 2} interface. This result was clarified by the fact that the core-level emission peaks did not shift regardless of TOA (i.e., analysis depth). Thus, the barrier height of the native oxide for the minority-carriers in the undoped n-BaSi{sub 2} (holes) was determined to be 3.9 eV. No band bending in the BaSi{sub 2} close to the interface also suggests that the large minority-carrier lifetime in undoped n-BaSi{sub 2} films capped with native oxide is attributed not to the band bending in the BaSi{sub 2}, which pushes away photogenerated minority carriers from the defective surface region, but to the decrease of defective states by the native oxide.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Influence of grain size and surface condition on minority-carrier lifetime in undoped n-BaSi{sub 2} on Si(111)

We have fabricated approximately 0.5-μm-thick undoped n-BaSi{sub 2} epitaxial films with various average grain areas ranging from 2.6 to 23.3 μm{sup 2} on Si(111) by molecular beam epitaxy, and investigated their minority-carrier lifetime properties by the microwave-detected photoconductivity decay method at room temperature. The measured excess-carrier decay curves were divided into three parts in terms of decay rate. We characterized the BaSi{sub 2} films using the decay time of the second decay mode, τ{sub SRH}, caused by Shockley-Read-Hall recombination without the carrier trapping effect, as a measure of the minority-carrier properties in the BaSi{sub 2} films. The measured τ{sub SRH} was grouped into two, independently of the average grain area of BaSi{sub 2}. BaSi{sub 2} films with cloudy surfaces or capped intentionally with a 3 nm Ba or Si layer, showed large τ{sub SRH} (ca. 8 μs), whereas those with mirror surfaces much smaller τ{sub SRH} (ca. 0.4 μs). X-ray photoelectron spectroscopy measurements were performed to discuss the surface region of the BaSi{sub 2} films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗