Low-crosstalk silicon-fabricated optical waveguides for laser delivery to matter qubits

Reliable control of quantum information in matter-based qubits requires precisely applied external fields, and unaccounted-for spatial crosstalk of these fields between adjacent qubits leads to loss of fidelity. We report a CMOS foundry-produced microfabricated silicon nitride ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msub> <a:mi>Si</a:mi> <a:mn>3</a:mn> </a:msub> </a:math> <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:msub> <c:mrow> <c:mrow> <c:mi mathvariant="normal">N</c:mi> </c:mrow> </c:mrow> <c:mn>4</c:mn> </c:msub> </c:math> ) optical waveguide for addressing a chain of eight unequally spaced trapped barium ions, with crosstalk compatible with scalable quantum information processing. The crosstalk-mitigation techniques incorporated into the chip design result in a reduction of the measured optical field by at least 50.8(1.3) dB between adjacent waveguide outputs near 650 nm and similar behavior for devices designed for 493 nm and 585 nm. The waveguide outputs near 650 nm, along with a global laser near 493 nm, have been used to laser cool a chain of eight <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"> <f:msup> <f:mi/> <f:mn>138</f:mn> </f:msup> </f:math> <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"> <h:mi>Ba</h:mi> </h:math> <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"> <j:msup> <j:mi/> <j:mo>+</j:mo> </j:msup> </j:math> ions, and a camera has imaged the resulting fluorescence at 493 nm.