Single and Double Hole Quantum Dots in Strained Ge/SiGe Quantum Wells

Even as today's most prominent spin-based qubit technologies are maturing in terms of capability and sophistication, there is growing interest in exploring alternate material platforms that may provide advantages, such as enhanced qubit control, longer coherence times, and improved extensibility. Recent advances in heterostructure material growth have opened new possibilities for employing hole spins in semiconductors for qubit applications. Undoped, strained Ge/SiGe quantum wells are promising candidate hosts for hole spin-based qubits due to their low disorder, large intrinsic spin-orbit coupling strength, and absence of valley states. Here, we use a simple one-layer gated device structure to demonstrate both a single quantum dot as well as coupling between two adjacent quantum dots. The hole effective mass in these undoped structures, $m$* ~ 0.08 $m$$_0$, is significantly lower than for electrons in Si/SiGe, pointing to the possibility of enhanced tunnel couplings in quantum dots and favorable qubit-qubit interactions in an industry-compatible semiconductor platform.