A regular switch clicks, and current either flows or it doesn't. Now imagine a material that switches itself between 'conducts without loss' and 'resists' under the influence of a magnet. That's exactly the sandwich physicists built: a thin lead film on top of a superconductor made of bismuth, strontium, calcium, copper, and oxygen.

Between the layers, a hair-thin layer of lead oxide grew on its own — an insulator. It doesn't hinder; it helps: inside the superconductor, vortices form — tiny magnetic 'whirlpools,' like funnels in water. These funnels get stuck in the insulator, and the lead film stops being superconducting. Remove the field — the funnels stay put, and the state persists. That gives you a memory cell: field on (one, field off) zero.

The scientists also saw other oddities: resistance would suddenly drop or jump as the field changed, and heating returned the device to its original superconducting state. All of this is a trace of how vortices interact across the boundary between the two superconductors.

For now, it's a lab prototype, but it shows a simple way to make energy-efficient memory for future quantum devices.