## Not Quite an Alternate World

The rules of the quantum realm, which explain how subatomic particles move, can be truly mind-boggling because they defy traditional logic. But briefly: Particles as small as electrons and protons don’t just exist in one point in space, they can occupy many at a time. The mathematical framework of quantum mechanics tries to explain the motion of these particles.

The laws of quantum mechanics can also be applied to quantum computers. These are very different from computers we use today, and can solve certain problems exponentially faster than normal computers can because they adhere to these completely different laws of physics. A standard computer uses bits with a value of either 0 or 1. A quantum computer uses qubits, which can attain a kind of combined state of 0 or 1, a unique characteristic of quantum systems — for example, an electron — called “superposition.”

## Information Preservation

In a quantum system, small changes to qubits — even looking at or measuring them — can have immense effects. So in the new study, the researchers wanted to see what would happen when they simulated sending a qubit back in time while also damaging it. Researchers constructing quantum experiments often use the stand-ins “Alice” and “Bob” to illustrate their theoretical process. In this case, they let Alice bring her qubit back in time, scrambling the information as part of what they call “reverse evolution.” Once in the past, Bob, an intruder, measures Alice’s qubit, changing it. Alice brings her qubit forward in time.

If the butterfly effect had held, the original information in Alice’s qubit would have been exponentially changed. But instead, the evolution forward in time allowed Alice to recover the original information, even though Bob’s intrusion had destroyed all the connections between her qubit and others that travelled with hers.