Cavity-enhanced emission and absorption of color centers in a diamond membrane with selectable strain

Group IV color centers in diamond are among the most promising optically active electron-spin systems with strong optical transitions and long spin coherences. The orbital ground-state splitting of the center is particularly important to suppress the interaction with coherence-limiting phonons. A higher orbital ground-state splitting improves the spin-coherence properties and sets the upper limit for the operating temperature. Negatively charged silicon-vacancy centers have an ordinary ground-state splitting from spin-orbit coupling of only <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><a:mn>48</a:mn><a:mspace width="0.1em"/><a:mrow><a:mi mathvariant="normal">G</a:mi><a:mi>Hz</a:mi></a:mrow></a:math>, resulting in required temperatures below 1 K, which can only be achieved by dilution refrigerators. Here, we increase the orbital ground-state splitting by up to an order of magnitude by induced strain in a single-crystal diamond membrane. The characterized orbital ground-state splitting in highly strained regions could allow for electron-spin-coherence times of milliseconds at <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><f:mrow><f:mn>1.5</f:mn></f:mrow><f:mspace width="0.1em"/><f:mrow><f:mrow><f:mi mathvariant="normal">K</f:mi></f:mrow></f:mrow></f:math>. We demonstrate cavity-assisted spectroscopy enabled by coupling the emitter ensemble with a selectable strain to the mode of a Fabry-Perot microcavity. Calculation of the absorption cross section yields <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><k:msubsup><k:mi>σ</k:mi><k:mi>abs</k:mi><k:mi>ens</k:mi></k:msubsup><k:mo>≈</k:mo><k:mn>4.9</k:mn><k:mo>⋅</k:mo><k:msup><k:mn>10</k:mn><k:mrow><k:mo>−</k:mo><k:mn>11</k:mn></k:mrow></k:msup><k:mspace width="0.1em"/><k:msup><k:mi>cm</k:mi><k:mn>2</k:mn></k:msup></k:math>. Furthermore, temperature-dependent lifetime measurements reveal a Purcell enhanced twofold reduction in emitter lifetime below <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><o:mn>1</o:mn><o:mspace width="0.1em"/><o:mi>ns</o:mi></o:math> at <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><s:mn>4</s:mn><s:mspace width="0.1em"/><s:mrow><s:mrow><s:mi mathvariant="normal">K</s:mi></s:mrow></s:mrow></s:math>.