Scientists have developed a new way to control quantum systems, which can make their behavior more closely match time running backwards than forwards. Research published in the journal Physical Review X introduces quantum control protocols that change the so-called arrow of time, or the idea that time naturally flows in only one direction.
Quantum systems, like groups of qubits, do not behave according to the rules of classical physics, but according to the laws of quantum mechanics. The new protocols allow researchers to suppress the usual appearance of the arrow of time or even reverse its apparent direction, making processes appear to run backwards.
Quantum time can change direction with precise measurement control
As a proof of concept, the team also created a measurement mechanism that can extract energy from the very act of quantum measurement.
Physicist Luis Pedro García-Pintos of Los Alamos National Laboratory explains that at the microscopic level, many of the basic laws of physics can be described just as well when time is turned back. In other words, the equations also work in the reverse direction, which opens up space for unusual methods of controlling quantum systems.
In classical physics, measurement generally does not significantly change the object being observed. In the quantum world, the situation is different: the measurement itself randomly changes the state of the system and thus naturally creates the direction of time.
The researchers tried to reverse that effect by combining measurement and feedback. Thus, they obtained quantum trajectories that act in concert with time flowing backwards.
For this purpose, a control Hamiltonian was used, a precisely planned sequence of fields and pulses that can mimic the effects of quantum measurements. When incorporated into a feedback control system, it can cancel, amplify, or overcorrect measurement disturbances.
The paper also builds on the well-known thought experiment Maxwell’s Demon, in which a hypothetical observer separates hot and cold particles and seemingly reduces entropy. A quantum version of this “demon” uses information about the system’s state and measurement results to induce time-reversal-like behavior.
The most interesting part of the research is the possibility of managing the flow of energy in a quantum system. The measurement could thus become a thermodynamic resource, from which useful energy is obtained for starting another quantum process or charging a quantum battery.
The researchers now plan to test these processes experimentally using superconducting qubits. Such systems enable fast feedback control and efficient reading, which is why they are suitable for the development of more powerful quantum computers, quantum batteries and new methods of preparing quantum states, writes Science Daily.