Lifetime Reduction of Single Germanium-Vacancy Centers in Diamond via a Tunable Open Microcavity

Coupling between a single quantum emitter and an optical cavity presents a key capability for future quantum networking applications. Here, we explore interactions between individual germanium-vacancy (<a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><a:mi>Ge</a:mi></a:math>V) defects in diamond and an open microcavity at cryogenic temperatures. Exploiting the tunability of our microcavity system to characterize and select emitters, we observe a Purcell-effect-induced lifetime reduction of up to <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><d:mn>4.5</d:mn><d:mo>±</d:mo><d:mn>0.3</d:mn></d:math> and extract coherent-coupling rates up to <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><g:mn>360</g:mn><g:mo>±</g:mo><g:mn>20</g:mn></g:math> MHz. Our results indicate that the <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><j:mi>Ge</j:mi></j:math>V defect has favorable optical properties for cavity coupling, with a quantum efficiency of at least <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><m:mn>0.34</m:mn><m:mo>±</m:mo><m:mn>0.05</m:mn></m:math> and likely much higher.