Fine-Structure Qubit Encoded in Metastable Strontium Trapped in an Optical Lattice

We demonstrate coherent control of the fine-structure qubit in neutral strontium atoms. This qubit is encoded in the metastable <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mmultiscripts><a:mrow><a:msub><a:mrow><a:mi>P</a:mi></a:mrow><a:mrow><a:mn>2</a:mn></a:mrow></a:msub></a:mrow><a:mprescripts/><a:none/><a:mrow><a:mn>3</a:mn></a:mrow></a:mmultiscripts></a:mrow></a:math> and <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mrow><c:mmultiscripts><c:mrow><c:msub><c:mrow><c:mi>P</c:mi></c:mrow><c:mrow><c:mn>0</c:mn></c:mrow></c:msub></c:mrow><c:mprescripts/><c:none/><c:mrow><c:mn>3</c:mn></c:mrow></c:mmultiscripts></c:mrow></c:math> states, coupled by a Raman transition. Using a magnetic quadrupole transition, we demonstrate coherent state initialization of this THz qubit. We show Rabi oscillations with more than 60 coherent cycles and single-qubit rotations on the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mi mathvariant="normal">μ</e:mi><e:mi mathvariant="normal">s</e:mi></e:math> scale. With spin echo, we demonstrate coherence times of tens of ms. Our results pave the way for fast quantum information processors and highly tunable quantum simulators with two-electron atoms.