Optical and Magnetic Response by Design in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>Ga</mml:mi><mml:mi>As</mml:mi></mml:mrow></mml:math> Quantum Dots

Quantum networking technologies use spin qubits and their interface to single photons as core components of a network node. This necessitates the ability to co-design the magnetic- and optical-dipole response of a quantum system—a capability that has been notably absent in solid-state platforms where spin-orbit coupling and the crystalline environment lead to inhomogeneity of electronic <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>g</a:mi></a:math>-factors and optically active states. Here, we demonstrate the ability to design both the optical and magnetic response of a solid-state quantum emitter . We show that <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mrow><c:mi>Ga</c:mi><c:mi>As</c:mi></c:mrow></c:math> quantum dots (QDs), obtained via local droplet etching epitaxy and already known as exceptionally coherent and efficient quantum light sources, also exhibit spin and optical properties that follow directly from assuming the highest possible system symmetry. Our measurements of electron and hole <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mi>g</e:mi></e:math>-tensors—using a new sign-sensitive measurement protocol based on the hyperfine interaction—and of transition dipole moment orientations for charged excitons agree with our predictions from a multiband <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mi mathvariant="bold-italic">k</g:mi><g:mo>⋅</g:mo><g:mi mathvariant="bold-italic">p</g:mi></g:math> simulation constrained only by a single atomic-force-microscopy reconstruction of QD morphology. This agreement is verified across multiple wavelength-specific growth runs at different facilities within the range of 730 to 790 nm for the exciton emission. Remarkably, our measurements and simulations track the in-plane electron <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mi>g</k:mi></k:math>-factors through a zero-crossing from <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mo>−</m:mo><m:mn>0.1</m:mn></m:math> to 0.3 and linear optical dipole moment orientations fully determined by an external magnetic field. The robustness and generality of these results establish a fundamentally new paradigm for solid-state spin-photon interfaces: one in which the properties of a spin qubit and its tunable optical interface can be designed—prior to growth—for a target magnetic and photonic environment, with direct applications to scalable and high-fidelity spin-photon entanglement.