Experimental detection of entanglement polytopes via local filters

• Published in: npj quantum information Vol. 3; no. 1; pp. 1 - 7
• Main Authors: Zhao, Yuan-Yuan, Grassl, Markus, Zeng, Bei, Xiang, Guo-Yong, Zhang, Chao, Li, Chuan-Feng, Guo, Guang-Can
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 20-03-2017; Nature Publishing Group; Nature Portfolio
• Subjects: 639/624/400; 639/766/483/481; Classical and Quantum Gravitation; Filters; Physics; Physics and Astronomy; Quantum Computing; Quantum Field Theories; Quantum Information Technology; Quantum Physics; Quantum theory; Relativity Theory; Spintronics; Stochasticity; String Theory
• ISSN: 2056-6387; 2056-6387
• DOI: 10.1038/s41534-017-0007-5

Quantum entanglement, resulting in correlations between subsystems that are stronger than any possible classical correlation, is one of the mysteries of quantum mechanics. Entanglement cannot be increased by any local operation, and for a sufficiently large many-body quantum system there exist infinitely many different entanglement classes, i.e., states that are not related by stochastic local operations and classical communications. On the other hand, the method of entanglement polytopes results in finitely many coarse-grained types of entanglement that can be detected by only measuring single-particle spectra. We find, however, that with high probability the local spectra lie in more than one polytope, hence providing only partial information about the entanglement type. To overcome this problem, we propose to additionally use so-called local filters, which are non-unitary local operations. We experimentally demonstrate the detection of entanglement polytopes in a four-qubit system. Using local filters we can distinguish the entanglement type of states with the same single particle spectra, but which belong to different polytopes.
Entanglement polytopes: An effective way to distinguish entanglement types
An experiment-friendly method has been proposed to detect the entanglement type of multi-particle states. The way of characterizing entanglement types is a central question in studying entanglement. Entanglement polytopes serve as an elegant method to solve this issue by using the information of single particles alone, namely their local spectra. However, classifying states via entanglement polytopes is limited due to the large overlap of different polytopes. Here an international group of scientists proposed to use SLOCC (stochastic local operation and classical communication operations to overcome this difficulty. They experimentally detected the entanglement polytopes for two four-qubit states having the same local spectra by using SLOCC operations to move them to a non-overlapping region. Their method sheds light on experimental detection of entanglement in a general way.