What if the direction of time isn’t as fixed as it seems? While our everyday experience tells us that time moves relentlessly forward, the microscopic laws governing quantum systems are far less restrictive. In fact, many of the equations of quantum mechanics work just as well if time runs in reverse.
Now, researchers reporting in Physical Review X have developed quantum control protocols that can make certain processes appear more consistent with time flowing backward than forward. By carefully combining measurements, feedback, and tailored control fields, the team showed that they can suppress a quantum system’s arrow of time—or even invert its apparent direction. The work not only offers a new way to explore one of physics’ most fundamental concepts but could also lead to novel methods for extracting energy from quantum systems and preparing quantum states.
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