arXiv subjects

Justin Copenhaver

Publications and source records attributed to Justin Copenhaver.

3 recordsLinked to original sources

arXiv2023

Microwave spectroscopy of Majorana vortex modes

The observation of zero-bias conductance peaks in vortex cores of certain Fe-based superconductors has sparked renewed interest in vortex-bound Majorana states. These materials are believed to be intrinsically topological in their bulk phase, thus avoiding potentially problematic interface physics encountered in superconductor-semiconductor heterostructures. However, progress toward a vortex-based topological qubit is hindered by our inability to measure the topological quantum state of a non-local vortex Majorana state, i.e., the charge of a vortex pair. In this paper, we theoretically propose a microwave-based charge parity readout of the Majorana vortex pair charge. A microwave resonator above the vortices can couple to the charge allowing for a dispersive readout of the Majorana parity. Our technique may also be used in vortices in conventional superconductors and allows one to probe the lifetime of vortex-bound quasiparticles, which is currently beyond existing scanning tunneling microscopy capabilities.

cond-mat.supr-con↗

arXiv2022

Edge spin transport in the disordered two-dimensional topological insulator WTe$_2$

The spin conductance of two-dimensional topological insulators (2D TIs) is not expected to be quantized in the presence of perturbations that break the spin-rotational symmetry. However, the deviation from the pristine-limit quantization has yet to be studied in detail. In this paper, we define the spin current operator for the helical edge modes of a 2D TI and introduce a four-terminal setup to measure spin conductances. Using the developed formalism, we consider the effects of disorder terms that break spin-rotational symmetry or give rise to edge-to-edge coupling. We identify a key role played by spin torque in an out-of-equilibrium edge. We then utilize a tight-binding model of topological monolayer WTe$_2$ and scattering matrix formalism to numerically study spin transport in a four-terminal 2D TI device. In particular, we calculate the spin conductances and characteristic spin decay length in the presence of magnetic disorder. In addition, we study the effects of inter-edge scattering in a quantum point contact geometry. We find that the spin Hall conductance is surprisingly robust to spin symmetry-breaking perturbations, as long as time-reversal symmetry is preserved and inter-edge scattering is weak.

cond-mat.mes-hall↗

arXiv2020

Using Quantum Annealers to Calculate Ground State Properties of Molecules

Quantum annealers are an alternative approach to quantum computing which make use of the adiabatic theorem to efficiently find the ground state of a physically realizable Hamiltonian. Such devices are currently commercially available and have been successfully applied to several combinatorial and discrete optimization problems. However, the application of quantum annealers to problems in chemistry remains a relatively sparse area of research due to the difficulty in mapping molecular systems to the Ising model Hamiltonian. In this paper we review two different methods for finding the ground state of molecular Hamiltonians using Ising model-based quantum annealers. In addition, we compare the relative effectiveness of each method by calculating the binding energies, bond lengths, and bond angles of the H+3and H2O molecules and mapping their potential energy curves. We also assess the resource requirements of each method by determining the number of qubits and computation time required to simulate each molecule using various parameter values. While each of these methods is capable of accurately predicting the ground state properties of small molecules, we find that they are still outperformed by modern classical algorithms and that the scaling of the resource requirements remains a challenge.

quant-ph↗