Even the most chaotic quantum systems keep a permanent mark of their own past—a “quantum birthmark”—that never fades. Researchers from Tampere University, Harvard University and TU Dresden discovered the feature in their recent study. Their findings shed new light on the elusive relationship between classical and quantum mechanics. Looking ahead, these quantum birthmarks, along with related phenomena known as “scars,” could eventually be harnessed to power next-generation nanoelectronics.

Stir a drop of milk into a cup of tea and it is gone for good. The swirl blurs, spreads and evens out, and no amount of staring at the cup will tell you where the drop first landed. Physicists refer to this kind of unpredictable, memory-erasing behavior simply as chaos, and it underpins much of how we explain the everyday world: heat spreading through a room, smoke filling the air, a pinball rattling away from wherever it was launched.

The new study shows that the quantum realm—the world of atoms and electrons—does not play by that rule. There, the earliest moments leave a signature that never washes out. The study “Quantum Birthmarks: Ergodicity Breaking Beyond Scarring” was published in Physical Review X on Sept. 10, 2026.