量子信息报告

报告人： You Zhou (University of Science and Technology of China)

题  目： Multipartite entanglement structure and its efficient  detection based on graph states

时  间： 2019.08.06（星期二），15:00-16:00

地  点： 数学院南楼N702室

摘  要： Recently, there are tremendous developments on the number of controllable qubits in several quantum computing systems. For these implementations, it is crucial to determine the entanglement structure of the prepared multipartite quantum state as a basis for further information processing tasks. In reality, evaluation of a multipartite state is in general a very challenging task owing to the exponential increase of the Hilbert space with respect to the number of system components. In this work, we propose a systematic method using very few local measurements to detect multipartite entanglement structures based on the graph state — one of the most important classes of quantum states for quantum information processing. Thanks to the close connection between the Schmidt coe？cient and quantum entropy in graph states, we develop a family of e？cient witness operators to detect the entanglement between subsystems under any partitions and hence the entanglement intactness. We show that the number of local measurements equals to the chromatic number of the underlying graph, which is a constant number, independent of the number of qubits. In reality, the optimization problem involved in the witnesses can be challenging with large system size. For several widely-used graph states, such as 1-D and 2-D cluster states and the Greenberger-Horne-Zeilinger state, by taking advantage of the area law of entanglement entropy, we derive analytical solutions for the witnesses, which only employ two local measurements. Our method o？ers a standard tool for entanglement structure detection to benchmark multipartite quantum systems.

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报告人：Youwei Zhao (University of Science and Technology of China)

题  目：Experimental verification of five-qubit quantum error correction with superconducting qubits

时  间：2019.08.08（星期四），15:00-16:00

地  点：数学院南楼N702室

摘  要：Quantum error correction is an essential ingredient for universal quantum computing. Despite tremendous experimental efforts in the study of quantum error correction, to date, there has been no demonstration in the realization of universal quantum error correction code (QECC), with the subsequent verification of all key features including the identification of an arbitrary physical error, the capability for transversal manipulation of the logical state, and state decoding. To address this notoriously difficult challenge, we experimentally realize the five-qubit QECC by demonstrating each key aspect of this code. Our work establishes the viability of experimental quantum error correction with superconducting qubits and paves the route to fault-tolerant quantum computing.