Associate Prof.Jun Zhang has made big progress in the research on quantum identification. A recent paper of his titled “Quantum Hamiltonian identification from measurement time traces”  coauthored with Dr. Mohan Sarovar of Sandia National Laboratories, U.S.A., has been published by the famous international journal, Physical Review Letters.
In the past two decades, numerous areas of the quantum technology, such as quantum computing, quantum communication, and precision measurements, have made ​​tremendous progress. The series of important applications often requires the capabilities to build quantum devices on the nanometer scale and to accurately characterize and control the quantum dynamics. Because quantum devices are typically very sensitive to the environmental impact and the quantum properties can easily be destroyed, the dynamic model to quantitatively describe quantum systems is a challenging task.
Quantum system dynamics is mainly portrayed by Hamiltonian quantity, but there is not yet an effective method to identify Hamiltonian quantity in the quantum system. Currently the main approach to establish a dynamic model of unknown quantum system is ‘process tomography,’ the major problem of which is the need to consume a lot of resources. To solve the problem, Zhang and Sarovar propose a completely different approach from process tomography. They measured the observed quantities provided by the system at multiple time points, resulting in a continuous time series. Based on the basic principles of quantum physics, such equations can be determined dynamically by the time series. On this basis, by using the controllability and identification algorithm of the classical control theory, the system can derive the unknown parameters to satisfy the algebraic equations. These can be obtained by solving algebraic equations of the system parameters to be identified. This method can effectively utilize priori knowledge of the system and can be applied to limited resources, thereby very helpful for experiments.
Prof. Zhang and Dr. Sarovar had been working at the Quantum Information Center of UC Berkeley. They both are interested in the control and optimization of the quantum process and have teamed up in research. This paper is a critical beginning of their collaborative project on quantum identification. They plan to further explore the physics system and other complicated situations.
Prof. Jun Zhang obtained a Ph.D. in EECS from UC Berkeley in 2003 and joined the UM-SJTU Joint Institute in 2010. He was voted one of SJTU Outstanding Teachers in 2013.
The abstract of the paper: