System identification is a key enabling component for the implementation of quantum technologies, including quantum control. In this paper, we consider the class of passive linear input-output systems, and investigate several basic questions: (1) which parameters can be identified? (2) Given sufficient input-output data, how do we reconstruct the system parameters? (3) How can we optimize the estimation precision by preparing appropriate input states and performing measurements on the output? We show that minimal systems can be identified up to a unitary transformation on the modes, and systems satisfying a Hamiltonian connectivity condition called "infecting" are completely identifiable. We propose a frequency domain design based on a Fisher information criterion, for optimizing the estimation precision for coherent input state. As a consequence of the unitarity of the transfer function, we show that the Heisenberg limit with respect to the input energy can be achieved using non-classical input states.
Fock majorization in bosonic quantum channels with a passive environment
我们引入了一类称为被动环境玻色子信道的量子信道。从量子力学的观点来看，这些通道是相关的，因为它们对应于玻色子系统与处于被动状态的玻色子环境的能量保持线性耦合（通过使用幺正变换不能从其中提取能量），然后丢弃环境。在[New J. Phys. 18，073047（2016）]中定义的福克优序关系在这种情况下特别有用，因为与常规优序不同，它将状态的无序与其能量联系在一起。我们的主要结果是在所有被动环境玻色子通道的福克优化的保存。这意味着在被动状态的集合上的规则优化具有类似的保持属性，并且它还扩展到被动环境通道，其Stinespring膨胀涉及主动高斯酉。除了玻色子系统之外，引入的被动环境操作类自然地概括了热操作，并有望为量子系统的热力学提供新的见解。
Classical simulation and model concentration in passive linear optics
School of Informatics, University of Edinburgh（爱丁堡大学信息学院）；Terra Quantum AG；Laboratoire d’Informatique de Paris 6, CNRS, Sorbonne Université（巴黎第六大学计算机实验室，法国国家科学研究中心，索邦大学）；Quandela；DIENS, École Normale Supérieure, PSL University, CNRS, INRIA（高等师范学院计算机科学系，巴黎文理研究大学，法国国家科学研究中心，法国国家信息与自动化研究所）；Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL)（洛桑联邦理工学院物理研究所）；Centre for Quantum Science and Engineering, École Polytechnique Fédérale de Lausanne (EPFL)（洛桑联邦理工学院量子科学与工程中心）
A two-disk approach to the synthesis of coherent passive equalizers for linear quantum systems
School of Engineering and Technology, University of New South Wales（新南威尔士大学工程与技术学院）；School of Engineering, Australian National University（澳大利亚国立大学工程学院）
