Suppression of macroscopic quantum tunneling in a large Josephson junction coupled to a resonator

We employ a functional integral technique to calculate the macroscopic quantum tunneling rate at zero temperature of a current-biased Josephson junction weakly coupled to a resonator. We allow for the effects of environmental dissipation on both the junction and the resonator via baths of harmonic oscillators, and we consider both cases of weak and strong junction damping. The resonator can be, in principle, any quantum harmonic oscillator that couples to the junction bilinearly in either the coordinate or the velocity. The Josephson phase difference ϕ is the tunneling variable in this system, and the low-lying bound states in the junction’s potential energy well are weakly metastable due to tunneling through a finite-width energy barrier. There has been some interest in using such biased junctions as qubits with the resonator providing multiqubit coupling. The main result of this work is that coupling to the resonator has a suppressive effect on the junction’s tunneling: the stronger the coupling strength between the junction and resonator, the greater the reduction of the tunneling rate. Including damping to the junction also suppresses tunneling, a well-known result, but damping of the resonator actually reduces the magnitude of suppression; i.e., damping the resonator partially counteracts the suppression provided directly by the junction-resonator coupling. Details of the junction-resonator coupling yield interesting variations on this theme that may be useful for qubit design. For example, the coupling Uint between a current-biased junction and an AlN dilatational resonator should depend on the angular frequency of the resonator ωR in a power-law fashion [A. N. Cleland and M. R. Geller, Phys. Rev. Lett. 93, 070501 (2004)], specifically Uint∝(ωR)n, where n=1∕2. We find that for any value of n in the range

Designing Studies to Evaluate Parent-Mediated Interventions for Toddlers With Autism Spectrum Disorder

Given recent advances in science, policy, and practice of early identification in autism spectrum disorder (ASD), questions about the effectiveness of early intervention have far-reaching service and policy implications. However, rigorous research evaluating the efficacy and effectiveness of intervention programs for toddlers with ASD faces a multitude of novel scientific challenges. The Autism Speaks Toddler Treatment Network (ASTTN) was formed in 2007 to provide an infrastructure for ongoing communication between the investigators of eight research projects evaluating parent-mediated interventions for toddlers with ASD. The present article describes and compares the research studies of the ASTTN; highlights specific challenges with regard to research design, participants, recruitment, eligibility criteria, enrollment, and intervention approach; and outlines practical considerations that may guide the next generation of parent-mediated intervention studies involving toddlers with ASD