Guofeng Zhang, Professor, Department of Applied Mathematics, The Hong Kong Polytechnic University

Liqun Cao, Professor

Optimal Control of Flying Qubits

15:00-16:00 June 25 (Tuesday), Z301

The transmission of flying qubits carried by itinerant photons is ubiquitous in quantum communication networks. In addition to their logical states, the temporal/frequency profiles of flying qubits must also be tailored into proper shapes to match remote receiver qubits. In this talk, we report a general framework for optimal control of flying qubits. The framework is based on quantum stochastic differential equations (QSDEs) that describe the flying qubit input-output relations actuated by a standing quantum system (e.g., a superconducting qubit or quantum dot). Under the continuous time-ordered photon-number basis, the infinite-dimensional QSDE is reduced to a system of low-dimensional deterministic ordinary differential equations for the non-unitary state evolution of the standing quantum system, and the outgoing flying qubit states can be calculated in the form of randomly occurring quantum jumps. This makes it possible to analyze general cases when the number of excitations is not reserved. The proposed framework lays the foundation for the design of flying-qubit control systems from an optimal control point of view, within which advanced optimal control techniques can be incorporated for practical applications. Some examples, such as the generation, catching and steering of flying photons by two- or three- level artificial atoms, are studied.

Bio: Guofeng Zhang received his B.Sc. degree and M.Sc. degree from Northeastern University, Shenyang, China, in 1998 and 2000 respectively. He received a Ph.D. degree in Applied Mathematics from the University of Alberta, Edmonton, Canada, in 2005. During 2005–2006, he was a Postdoc Fellow in the Department of Electrical and Computer Engineering at the University of Windsor, Windsor, Canada. He joined the School of Electronic Engineering of the University of Electronic Science and Technology of China, Chengdu, Sichuan, China, in 2007. From April 2010 to December 2011, he was a Research Fellow in the School of Engineering of The Australian National University. He joined the Hong Kong Polytechnic University in December 2011 and is currently an Associate Professor in the Department of Applied Mathematics. His research interests include quantum information, quantum control, quantum algorithms, and tensor computation.