A qubit is like a tenant in a tiny apartment: it usually takes the ground floor to avoid distractions from upstairs neighbors. In germanium quantum dots, where spin qubits live, this tenant is a hole: that is, a missing electron. The hole has a spin that acts like a tiny magnetic needle. When an external magnetic field is switched on, this needle starts to precess at a certain rate — known as the g-factor. This parameter determines how the qubit is controlled.

But germanium has a quirk: spin and orbit (the floor the hole sits on) are strongly coupled. So the g-factor changes from floor to floor and depends on how many neighbors the hole has. The scientists measured the g-factor in two ways: by looking at how a single hole behaves (excitation spectrum) and how several holes behave together (addition spectrum). Previously, these methods gave different numbers, and it was unclear which to trust.

Moreover, the g-factor can be changed by 15% simply with an electric field, without touching the magnetic one. This is important because for a quantum computer, it's more convenient to control qubits with electrical signals rather than bulky magnets. Now engineers can design control circuits more precisely: they just need to know which floor the hole sits on and how many holes are in the dot.

So germanium dots are not just tiny apartments for qubits, but houses with very flexible layouts. Understanding their internal order brings quantum computers closer to reality, where each qubit can be tuned to its own task.