In the classical Universe, the arrow of time flies one way – but in the quantum realm, where classical physics breaks down, could even time's direction be ripe for the tweaking?
The ability to manipulate the direction of quantum evolution could offer new ways to process information – with implications especially for quantum computing.
And it may be within reach.
Korean physicists have demonstrated a qubit whose processes can be run backward in time… and the deliciously ironic twist is that they had to go back in time to find it.
In a new preprint, physicist Tai Hyun Yoon of Korea University developed a theory describing what he calls a quantum vacuum-seeded single-photon time qubit – and showed that an experiment he and colleagues conducted in 2018 for an entirely different purpose had inadvertently already shown it in action.
The notion of a time qubit is a relatively recent one, arising in a preprint penned by physicist Yakov Bloch of Tel Aviv University, uploaded to arXiv in November 2025.
It's not actually a qubit that can travel backward in time; rather, as Bloch explains it, it's a quantum system that can evolve in two opposite temporal directions at once.
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