English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

We present a variational method to calculate the exchange interactions amongdonor clusters in a semiconductor. Such clusters are candidates for a so-calledcontrol-qubit architecture for quantum information, where the effectiveexchange coupling between two atoms is controlled by the electronic state of athird. We use a combination of the effective-mass approximation and the quantumdefect method; our variational ansatz is particularly suited to cases where anexcited state of one of the donors (control) is partially delocalised overseveral different centres, forming an analogue of an extended molecularorbital. Our method allows calculations of the "on/off" ratios of exchangeinteractions in such cases. We compare exchange interactions when the controlis in the "on" and "off" states, and find that both the magnitude and sign ofthe exchange interactions may be changed. To rationalize the sign-change, wecarry out a simple Green's function perturbation-theory calculation. Thissimple model qualitatively explains the sign change and illustrates its originsboth in ring-exchange processes and in the delocalization of the controlelectron. We also compute probability distributions for the coupling strengthsover the ensemble of clusters, and show that excitation of the control causesnarrowing of the distributions along with shifts to larger magnitudes and fromanti-ferromagnetic to ferromagnetic coupling.

Exchange in multi-defect semiconductor clusters: assessment of `control-qubit' architectures