Controls developed to reshape quantum arrow of time

Scientists at Los Alamos National Laboratory have developed quantum control protocols that generate processes more consistent with time flowing backward than forward. The protocols modify a quantum system's arrow of time. The research appears in Physical Review X. A quantum system such as a collection of qubits follows the laws of quantum mechanics. The protocols can prevent the emergence of the arrow of time or invert its direction. In one application the team designed a measurement engine that extracts energy from quantum measurements performed on the system. Unlike classical physics, quantum measurements stochastically change the system's state and induce an arrow of time. The researchers used measurements and feedback to engineer time-reversed stochastic trajectories. They also designed a control Hamiltonian that emulates the effects of measurements and can cancel, amplify or overcompensate for measurement disturbances. Physicist Luis Pedro García-Pintos of Los Alamos National Laboratory said the fundamental laws of physics at the microscopic level treat forward and backward movement in time as physically possible. The tools manipulate the perceived arrow of time and create new ways to control quantum systems. The approach parallels the Maxwell's demon thought experiment by using knowledge of a system's state to drive processes that reverse the natural order. The protocols can modify the flow of energy in and out of the system. They support a continuous measurement engine that treats quantum measurements as a thermodynamic resource. Future work includes experimental demonstrations in superconducting qubits and the design of quantum state preparation protocols.