Researchers understand time variation through nondeterministic inputs and outputs

A research team has built a coherent bidirectional quantum evolution superposition in a photonic system and confirmed its advantage in characterizing input-output nondeterminism. The study was published in Physical review papers.

The notion that time flows inexorably from the past to the future is deeply ingrained in people’s minds. However, the laws of physics that govern the motion of objects in the microscopic world do not intentionally distinguish the direction of time.

To be more specific, the basic equations of motion of classical and quantum mechanics are reversible, and changing the direction of the time coordinate system of a dynamical process (perhaps along with the direction of some other parameters) still constitutes a valid evolution process .

This is known as time-reversal symmetry. In quantum information science, time reversal has attracted great interest due to its applications in multi-temporal quantum states, simulations of closed time curves, and inversion of unknown quantum evolutions. However, time reversal is difficult to realize experimentally.

To tackle this problem, the team, led by academician Guo Guangcan, Prof. Li Chuanfeng and Prof. Liu Biheng from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS), collaborating with Prof. Chiribella from the University of Hong Kong, built a class of quantum evolution processes in a photonic configuration by extending the time reversal in the input-output reversal of a quantum device.

When exchanging the input and output ports of a quantum device, the resulting evolution satisfied the time-varying properties of the initial evolution, thus obtaining a time-reversal simulator for quantum evolution.

On this basis, the team further quantized the time direction of evolution, achieving the coherent superposition of quantum evolution and its inverse evolution. They also characterized the structures using quantum witness techniques.

Compared to the scenario of a fixed time direction of evolution, time direction quantization showed significant advantages in quantum channel identification.

In this study, the researchers used the device to distinguish two sets of quantum channels with a 99.6% success probability, while the maximum success probability of a given timing strategy was only 89% with the same resource consumption.

The study reveals the potential of input-output indeterminacy as a valuable resource for advances in quantum information and quantum photonic technologies.