Past Returns: Entrance and Exit Uncertainty Spins Time

A team of researchers created a coherent superposition of quantum evolution with two opposite directions in the photon system and confirmed its advantage in characterizing the uncertainty of the entrance-exit. The study was published in the journal Physical Review Letters.

The idea that time is inexorably flowing from the past to the future is deeply rooted in the minds of people. However, the laws of physics that control the movement of objects in the microscopic world do not make clear differences in the direction of time.

The basic equations of the movement of both classical and quantum mechanics are reversible, and a change in the direction of the temporary coordinate of the dynamic process (possibly, along with the direction of some other parameters) is still an allowable evolutionary process. This is known as a symmetry of temporary inversion. In quantum information science, temporary inversion attracts great attention due to its applications in multi-time quantum states, modeling closed temporary curves, and inversions of unknown quantum evolutions. Nevertheless, it is extremely difficult to realize temporary inversion.

To solve this problem, the team led by academician Go Guangtsan, Professors Lee Chuanfan and Liu Bichen from the Chinese University of Science and Technology (USTC) of the Chinese Academy of Sciences (CAS), in collaboration with Professor Julio Chiribell from the University of Hong Kong, created a class of processes Quantum evolution in a photographic installation, expanding temporary inversion before the inversion of the input-output of the quantum device.

When the input ports of the quantum device, the resulting evolution satisfied the properties of a temporary inversion of initial evolution, thus a temporary inversion simulator for quantum evolution was obtained. On this basis, the team further quantized the direction of evolution, reaching the coherent superposition of quantum evolution and its reverse evolution. They also described structures using the techniques of quantum witnesses.

Compared to the script with a certain direction of evolution, the quantization of the direction of time showed significant advantages in the identification of quantum channels. In this study, researchers used a device to distinguish between two sets of quantum channels with a probability of success of 99.6%, while the maximum probability of the success of a strategy with a certain direction of time was only 89% at the same cost of resources.

The study reveals the potential for the uncertainty of entry-output as a valuable resource for achievements in quantum information and photon quantum technologies.

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