Role of hyperfine interaction for cavity-mediated coupling between spin qubits

We consider two qubits interacting by means of an optical cavity, where each qubit is represented by a single electron spin confined to a quantum dot. It is known that electron spins in III-V semiconductor quantum dots are affected by the decoherence due to the hyperfine interaction with nuclear spins. Here we show that the interaction between two qubits is influenced by the Overhauser field as well. Starting from an unpolarizied nuclear ensemble, we investigate the dependance of the fidelities for two-qubit gates on the Overhauser field. We include the hyperfine interaction perturbatively to second order in our analytical results, and to arbitrary precision numerically.Comment: 7 pages, 7 figure

The Republic of The Philippines: Epidemiology and Epigenetics

A brief, yet concise investigation was conducted on the Republic of the Philippines, with a keen interest in the epidemiology of the current urban areas of the nation (+150,000 inhabitants), as well as possible epigenetic change that may be induced from disease or environmental stressors upon these same groups of people. G6PD deficiency, a common disorder among persons in urban dwellings within the Republic of the Philippines (Hsia 1993) was found to have a strong correlation of incidence with members of other nations in localized proximity to the equator. Additionally, low birth weight in infants has been identified as a potential epigenetic cue in those of the emerging, current population (Kuzawa 2012).https://scholarscompass.vcu.edu/uresposters/1111/thumbnail.jp

Weak measurement of quantum dot spin qubits

The theory of weak quantum measurements is developed for quantum dot spin qubits. Building on recent experiments, we propose a control cycle to prepare, manipulate, weakly measure, and perform quantum state tomography. This is accomplished using a combination of the physics of electron spin resonance, spin blockade, and Coulomb blockade, resulting in a charge transport process. We investigate the influence of the surrounding nuclear spin environment, and find a regime where this environment significantly simplifies the dynamics of the weak measurement process, making this theoretical proposal realistic with existing experimental technology. We further consider spin-echo refocusing to combat dephasing, as well as discuss a realization of "quantum undemolition", whereby the effects of quantum state disturbance are undone.Comment: 8 pages, 2 figure

Datta-Das transistor with enhanced spin control

We consider a two-channel spin transistor with weak spin-orbit induced interband coupling. We show that the coherent transfer of carriers between the coupled channels gives rise to an \textit{additional} spin rotation. We calculate the corresponding spin-resolved current in a Datta-Das geometry and show that a weak interband mixing leads to enhanced spin control.Comment: Added ref. + corrected typo

Lesbian, Gay, and Bisexual Supervisees’ Experiences of LGB-Affirmative and Nonaffirmative Supervision

Lesbian, gay, and bisexual (LGB) supervisees were interviewed regarding their experiences of LGB affirmative and nonaffirmative supervision. Supervisees were asked to describe one of each type of event (i.e., affirmative, nonaffirmative) from their past supervision. In LGB-affirmative supervision, all supervisees felt supported in their LGB-affirmative work with clients. Supervisees perceived that the affirming events also positively affected the supervision relationship, client outcomes, and themselves as supervisees. In LGB nonaffirming supervision, supervisees perceived supervisors to be biased or oppressive toward supervisees’ clients or themselves on the basis of LGB concerns or identity. From supervisees’ perspectives, the nonaffirming events negatively affected the supervision relationship, client outcomes, and supervisees. Implications for research and supervision are discussed

Low-damping transmission of spin waves through YIG/Pt-based layered structures for spin-orbit-torque applications

We show that in YIG-Pt bi-layers, which are widely used in experiments on the spin transfer torque and spin Hall effects, the spin-wave amplitude significantly decreases in comparison to a single YIG film due to the excitation of microwave eddy currents in a Pt coat. By introducing a novel excitation geometry, where the Pt layer faces the ground plane of a microstrip line structure, we suppressed the excitation of the eddy currents in the Pt layer and, thus, achieved a large increase in the transmission of the Damon-Eshbach surface spin wave. At the same time, no visible influence of an external dc current applied to the Pt layer on the spin-wave amplitude in the YIG-Pt bi-layer was observed in our experiments with YIG films of micrometer thickness

Spin-Orbit Coupling and Time-Reversal Symmetry in Quantum Gates

We study the effect of spin-orbit coupling on quantum gates produced by pulsing the exchange interaction between two single electron quantum dots. Spin-orbit coupling enters as a small spin precession when electrons tunnel between dots. For adiabatic pulses the resulting gate is described by a unitary operator acting on the four-dimensional Hilbert space of two qubits. If the precession axis is fixed, time-symmetric pulsing constrains the set of possible gates to those which, when combined with single qubit rotations, can be used in a simple CNOT construction. Deviations from time-symmetric pulsing spoil this construction. The effect of time asymmetry is studied by numerically integrating the Schr\"odinger equation using parameters appropriate for GaAs quantum dots. Deviations of the implemented gate from the desired form are shown to be proportional to dimensionless measures of both spin-orbit coupling and time asymmetry of the pulse.Comment: 10 pages, 3 figure