arXiv subjects

Andrew J. Miller

Publications and source records attributed to Andrew J. Miller.

5 recordsLinked to original sources

arXiv2024

Using a high-fidelity numerical model to infer the shape of a few-hole Ge quantum dot

The magnetic properties of hole quantum dots in Ge are sensitive to their shape due to the interplay between strong spin-orbit coupling and confinement. We show that the split-off band, surrounding SiGe layers, and hole-hole interactions have a strong influence on calculations of the effective $g$ factor of a lithographic quantum dot in a Ge/SiGe heterostructure. Comparing predictions from a model including these effects to raw magnetospectroscopy data, we apply maximum-likelihood estimation to infer the shape of a quantum dot with up to four holes. We expect that methods like this will be useful in assessing qubit-to-qubit variability critical to further scaling quantum computing technologies based on spins in semiconductors.

cond-mat.mes-hall↗

arXiv2022

Thermal activation of low-density Ga implanted in Ge

The nuclear spins of low-density implanted Ga atoms in Ge are interesting candidates for solid state-based qubits. To date, activation studies of implanted Ga in Ge have focused on high densities. Here we extend activation studies into the low-density regime. We use spreading resistance profiling and secondary ion mass spectrometry to derive electrical activation of Ga ions implanted into Ge as a function of rapid thermal anneal temperature and implant density. We show that for our implant conditions the activation is best for anneal temperatures between 400 and 650 $^\circ$C, with a maximum activation of 64% at the highest fluence. Below 400 $^\circ$C, remaining implant damage results in defects that act as superfluous carriers, and above 650 $^\circ$C, surface roughening and loss of Ga ions are observed. The activation increased monotonically from 10% to 64% as the implant fluence increased from $6\times10^{10}$ to $6\times10^{12}$ cm$^{-2}$. The results provide thermal anneal conditions to be used for initial studies of using low-density Ga atoms in Ge as nuclear spin qubits.

cond-mat.mtrl-sci↗

arXiv2021

Effective out-of-plane g-factor in strained-Ge/SiGe quantum dots

Recently, lithographic quantum dots in strained-Ge/SiGe have become a promising candidate for quantum computation, with a remarkably quick progression from demonstration of a quantum dot to qubit logic demonstrations. Here we present a measurement of the out-of-plane $g$-factor for single-hole quantum dots in this material. As this is a single-hole measurement, this is the first experimental result that avoids the strong orbital effects present in the out-of-plane configuration. In addition to verifying the expected $g$-factor anisotropy between in-plane and out-of-plane magnetic ($B$)-fields, variations in the $g$-factor dependent on the occupation of the quantum dot are observed. These results are in good agreement with calculations of the $g$-factor using the heavy- and light-hole spaces of the Luttinger Hamiltonian, especially the first two holes, showing a strong spin-orbit coupling and suggesting dramatic $g$-factor tunability through both the $B$-field and the charge state.

cond-mat.mes-hall↗

arXiv2020

A $4π$ Fluorescence Detection Region for Collinear Laser Spectroscopy

We report on a novel detection system for collinear laser spectroscopy which provides an almost $4π$ solid angle for fluorescence photon detection by employing curved surface mirrors. Additional parabolic angular filters offer passive stray light suppression and can be configured to match the experimental conditions. The mirror surfaces have an excellent reflectivity over a broad band of wavelengths in the optical spectrum and can be substituted to expand the wavelength acceptance range even further. Experiments with this system were performed at two collinear laser spectroscopy setups, including the laser spectroscopic investigation of $^{36}$Ca using rates of 25/s at NSCL, MSU.

physics.ins-det↗

arXiv2014

Implementing a search for aligned-spin neutron star -- black hole systems with advanced ground based gravitational wave detectors

We study the effect of spins on searches for gravitational waves from compact binary coalescences in realistic simulated early advanced LIGO data. We construct a detection pipeline including matched filtering, signal-based vetoes, a coincidence test between different detectors, and an estimate of the rate of background events. We restrict attention to neutron star--black hole (NS-BH) binary systems, and we compare a search using non-spinning templates to one using templates that include spins aligned with the orbital angular momentum. To run the searches we implement the binary inspiral matched-filter computation in PyCBC, a new software toolkit for gravitational-wave data analysis. We find that the inclusion of aligned-spin effects significantly increases the astrophysical reach of the search. Considering astrophysical NS-BH systems with non-precessing black hole spins, for dimensionless spin components along the orbital angular momentum uniformly distributed in $(-1, 1)$, the sensitive volume of the search with aligned-spin templates is increased by $\sim 50\%$ compared to the non-spinning search; for signals with aligned spins uniformly distributed in the range $(0.7,1)$, the increase in sensitive volume is a factor of $\sim 10$.

gr-qc↗