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  • Open Access

Reshaping the Quantum Arrow of Time

Luis Pedro García-Pintos1,*, Yi-Kai Liu2,3, and Alexey V. Gorshkov2,4

  • *Contact author: lpgp@lanl.gov
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Phys. Rev. X 16, 011028 – Published 19 February, 2026

DOI: https://doi.org/10.1103/l18s-9vmh

Abstract

While the microscopic laws of physics are often symmetric under time reversal, most natural processes that we observe are not. The emergent asymmetry between typical and time-reversed processes is referred to as the arrow of time. In quantum physics, an arrow of time emerges when a sequence of measurements is performed on a system. We introduce quantum control tools that can yield dynamics more consistent with time flowing backward than forward. The control tools are based on the explicit construction of a Hamiltonian that can replicate the stochastic trajectories of a monitored quantum system. Such a Hamiltonian can reverse the effect of monitoring and, via a feedback process, generate trajectories consistent with a reversed arrow of time. It can also be used to simulate the backward-in-time dynamics of an open quantum system. Finally, we design a feedback-driven continuous measurement engine powered by the energy pumped into the system by the monitoring process. We show that the engine can operate under experimentally realizable conditions with feedback delay and finite-efficiency measurements.

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Popular Summary

While the microscopic laws of physics are often symmetric under time reversal, natural processes typically follow a distinct direction known as the arrow of time. In a monitored quantum system, an arrow of time is induced by the effects of quantum measurement and their backaction. We introduce control tools that can manipulate this arrow by explicitly constructing a Hamiltonian that replicates the stochastic trajectories of a monitored quantum system. By using this Hamiltonian in a feedback process, we can cancel, amplify, or overcompensate for measurement disturbances, producing dynamics more consistent with time flowing backward than forward. These tools can also emulate the time-reversed dynamics of open systems and, by modifying the flow of energy in and out of the system, power a continuous measurement engine that extracts energy from the monitoring process, even under realistic conditions with feedback delays. This research provides a novel framework for experimenting with the perceived flow of time and utilizing measurements as a thermodynamic resource in quantum systems.

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Outline

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Phys. Rev. X 16, 011028– Published 19 February, 2026
  • Received 10 April 2025
  • Revised 3 October 2025
  • Accepted 5 January 2026
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