An ordinary field-effect transistor is like a faucet with a very sensitive handle: turn it slightly, and water flows. In the cold depths of a quantum computer, where everything is chilled to near absolute zero, such a faucet must open strictly on command. But the engineers in this work found their faucet had a trick: if you press the handle harder and then shine light on it, it sticks in a new position and holds on its own, without constant effort.
The secret lies at the interface between silicon and germanium layers. There, a host of microscopic defects accumulate (trap density exceeds 1.6 trillion per square centimeter per electron-volt). These defects act like potholes on a slippery road: electrons fall in and get stuck. By applying a voltage to the gate, you can push charge into these potholes, and a short flash of light helps it settle in. As a result, the transistor's threshold shifts, and stays shifted even after power is removed. That's non-volatile memory.
The device endured more than a thousand write-erase cycles and held its state for over ten thousand seconds — almost three hours. For silicon quantum circuits, this means memory can be built right on the same chip, from the same materials, and at the same temperature, without bulky add-on systems.
Ten thousand seconds at room temperature is less than three hours. But in the quantum world, where operations last nanoseconds, that's nearly an eternity, comparable to years of storage in a regular flash drive.