Friday, November 30, 10:50am, CSE 3941


Title: On the Perfect Distinguishability of Unitary Operations

Speaker: Runyao Duan, Tsinghua University


Abstract:

Unitary operation (or quantum logical gate) is one of the most basic ingredients of Quantum Mechanics as well as Quantum Information Theory. The study of various properties of unitary operations lies at the heart of many important quantum information processing tasks. Recently the problem of distinguishing unitary operations has received considerable attention. Most notably, it has been demonstrated that a perfect discrimination between two unitary operations can always be achieved by taking a suitable entangled state as input and then applying only a finite number of runs of the unknown unitary operation.

In this talk we first review some related results on this topic. Then we present a new scheme to show that entanglement or any joint quantum operations are not necessary for the perfect discrimination between unitary operations, which makes this task actually feasible in experiment. Furthermore, we give an analytical formula for the number of the runs needed for the perfect discrimination between two untiary operations and rigorously prove its optimality.

We also consider the discrimination of multipartite unitary operations by local quantum operations and classical communication (LOCC) only. Remarkably, our result indicates that any two different multipartite unitary operations, no matter entangled or not, can also be perfectly discriminated by LOCC. Intuitively, this result means that the lost identity of a nonlocal unitary operation can be recovered locally. To the best of my knowledge, this is the first result about the local distinguishability of multipartite quantum operations.


References:

1. Runyao Duan, Yuan Feng, and Mingsheng Ying, Entanglement is Not Necessary for Perfect Discrimination between Unitary operations, Physical Review Letters 98, 100503, 2007. Available online: http://www.arxiv.org/abs/quant-ph/0601150.

2. Runyao Duan, Yuan Feng, and Mingsheng Ying, Local Distinguishability of Multipartite Unitary Operations, 2007. Available online: http://www.arxiv.org/abs/0705.1424.