China News Service, Hefei, March 30 (Reporter Wu Lan) The University of Science and Technology of China has made important progress in the study of quantum entanglement - it has been discovered that experimental data that originally only detected the presence or absence of entanglement can be used to estimate the size of entanglement.
This discovery was made by Yu Sixia, Sun Liangliang, and Zhou Xiang of the school in collaboration with Xu Zhenpeng of Anhui University, Armin Tavakoli of Lund University, and others. The relevant results were recently published in Physical Review Letters.
According to reports, the team used the average of commonly used entanglement witnesses and under three common experimental conditions to provide estimates of the lower limits of almost all commonly used entanglement measurements, and upgraded the experiment of detecting entanglement to an experiment of estimating entanglement size at zero cost.
Quantum entanglement is the basic concept of quantum theory and the core resource in quantum information. The two basic tasks of quantum entanglement research are the detection and measurement of entanglement. In experiments, effective detection and estimation of entanglement size is a prerequisite for completing various information tasks. In particular, estimation of the size of entanglement determines the effectiveness of the precious resource of entanglement. To date, all entanglement witnesses have generally only been used to detect the presence or absence of entanglement and have remained silent on estimates of its size.
The research team found that entangled witnesses can be appropriately normalized to a distance that can characterize the difference between experimental data generated by a given quantum state and experimental data generated by a separable state under the same measurement. Distinguishability, which is at the core of quantified entanglement, can be related to various common entanglement measures.
Ultimately, no matter what kind of experimental conditions the entangled witnesses are used in the experiment, as long as entanglement can be detected, the experimenter can calculate the lower bound of various entanglement measures based on the average value of the entangled witnesses, and the entangled witnesses will no longer be silent. For many-body systems, the normalized entanglement witness can also be used to estimate the entanglement depth, that is, at least how many particles of the system are entangled. Under the asymptotic condition that the number of particles approaches infinity, this method gives a strict lower bound for the entanglement measure based on trace distance for some systems, that is, it gives an accurate entanglement size.
The reviewers spoke highly of the method proposed by the team, saying that it "solves an important problem in a comprehensive way, making entanglement experiments touch upon many entanglement measures." (End)