A reversal of time
A team of researchers from the University of Science and Technology of China, collaborating with Professor Giulio Chiribella of the University of Hong Kong, has made a significant advance in quantum information science.
The study published in Physical Review Letters explores time reversal symmetry and is particularly relevant for its applications in multi-time quantum states and simulations of closed timelike curves.
In quantum mechanics, a superposition is when a system exists in multiple states at once. Coherence means these states are combined in a precise, predictable way that maintains their quantum characteristics, such as phase relationships. Quantum evolution describes how the state of a quantum system changes over time according to the principles of quantum mechanics. A photonic system is an arrangement of devices and components that use light particles (photons) to process information, transmit signals, or perform computations.
The team from USTC and HKU successfully constructed a coherent superposition of quantum evolution in two opposite directions within a photonic system. In their experiment, the team created a class of quantum evolution processes by extending time reversal to the input-output inversion of a quantum device. By exchanging the input and output ports, they achieved a time-reversal simulator for quantum evolution.
Input-output indefiniteness refers to a condition in quantum systems where the relationship between the input and output is not fixed or definite. It means that the input and output of a quantum device can be swapped or reversed, and the system can still function correctly. This concept leverages the principles of quantum mechanics, where the direction of time and processes can be reversible, unlike in classical systems where processes typically have a fixed direction from cause to effect.
This study underscores the potential of input-output indefiniteness as a valuable resource for advancements in quantum information and photonic quantum technologies, paving the way for new innovations in these fields.
Chiribella, a professor in the Department of Computer Science at the University of Hong Kong, won a Croucher Senior Research Fellowship in 2018. His Croucher profile is here.