Scientists Have Found a Way to Make Time Flow Backward Inside a Quantum System
This is not time travel. That part needs to be said upfront. But what researchers at Los Alamos National Laboratory published in Physical Review X in July 2026 is strange enough that the distinction nearly does not matter: they built a system where, through careful manipulation of quantum measurements, a quantum process appears to run in reverse. Time, for these particles, flows backward.
What the arrow of time actually means
In classical physics, eggs do not uncrack and heat does not flow from cold objects to hot ones. That one-way directionality is what physicists call the arrow of time — the concept that entropy increases, disorder grows, and you cannot rewind the process. It shapes nearly every aspect of physical reality as we experience it.
Quantum systems do not share this constraint so neatly. The equations of quantum mechanics work equally well running forward or backward. What creates the arrow of time in quantum systems is the act of measurement — the moment of observation that collapses a quantum state and introduces irreversibility. That is the mechanism the Los Alamos team targeted.
How the breakthrough works
The researchers — Luis Pedro Garcia-Pintos, Yi-Kai Liu, and Alexey V. Gorshkov — developed what they call quantum control protocols. At the center is a carefully designed "control Hamiltonian": a programmed sequence of fields and pulses that can mimic the effect of quantum measurements. By feeding that Hamiltonian into a feedback system, they were able to cancel, strengthen, or overcorrect the disturbances that measurements cause.
The result is quantum trajectories that correspond to a stretched, blurred, or outright inverted arrow of time. The system behaves as if time is running in reverse. "The tools we have constructed can manipulate the perceived arrow of time," Garcia-Pintos said. The equations work both ways, he explained. Human intuition just defaults to the forward direction.
The Maxwell Demon connection
The work connects to a famous 19th-century thought experiment. In it, a hypothetical observer sorts fast and slow particles into separate chambers, apparently reducing entropy and violating the second law of thermodynamics. Physicists later showed the law was not actually broken once you account for the energy cost of the observer's information processing.
The Los Alamos protocol is a quantum version of this idea. By using information from measurements to drive the system's behavior, the researchers built a "measurement engine" — a device that harvests energy from the act of observing a quantum system. Quantum measurements, normally an obstacle to precise computation, become a thermodynamic resource. A continuous measurement engine could, in principle, extract work from simply monitoring a quantum process, and store it in a quantum battery.
Why this matters beyond the headline
The practical applications are further out than press coverage suggests, but they are real. Better control over the quantum arrow of time could improve how quantum computers prepare and maintain quantum states — a persistent challenge that limits their stability and usefulness. The energy-harvesting side could eventually contribute to quantum battery research.
The immediate challenge is precision. Kater Murch, an experimental physicist at UC Berkeley not involved in the study, noted the approach requires near-perfect measurement of quantum systems. Current measurement efficiency sits around 50%, which means details are lost and the Hamiltonian cannot be constructed with full accuracy. Getting measurement fidelity up is the next technical hurdle before these protocols can run in real hardware.
The team plans to test their methods using superconducting qubits, which support rapid feedback and have already been used in earlier Maxwell Demon experiments. Whether the results hold in physical hardware is the next question. For now, what the research demonstrates is that time, at the quantum scale, is far more elastic than our daily experience suggests.