In new research published in Physical Review X, scientists have designed quantum control protocols that generate processes more consistent with time flowing backward than forward. The protocols—techniques to control quantum systems—modify a quantum system’s “arrow of time,” the concept of time as moving in one forward direction. The work opens up possibilities for energy extraction from quantum systems and for quantum state preparation.

A quantum system, such as a collection of qubits, is governed by the laws of quantum mechanics. The team’s control protocols can prevent the emergence of the arrow of time in a quantum system or even invert its direction—that is, cause quantum time to appear to flow in reverse.

As an application of their research, the team leveraged their control protocols to design a measurement engine that extracts energy from quantum measurements performed on the system.