This review covers recent theoretical and experimental efforts to extend the application of the continuous-variable quantum technology of light beyond "Gaussian" quantum states, such as coherent and squeezed states, into the domain of "non-Gaussian" states with negative Wigner functions. Starting with basic Gaussian nonclassicality associated with single- and two-mode vacuum states produced by means of parametric down-conversion and applying a set of standard tools, such as linear interferometry, coherent state injection, and conditional homodyne and photon number measurements, one can implement a large variety of optical states and processes that are relevant in fundamental quantum physics as well as quantum optical information processing. We present a systematic review of these methods, paying attention to both fundamental and practical aspects of their implementation, as well as a comprehensive overview of the results achieved therewith.
Informational steady-states and conditional entropy production in continuously monitored systems: the case of Gaussian systems
测量一个系统的行为具有动力学和热力学性质的深刻后果。特别是，从非平衡过程中产生的不可逆性的程度受到旨在获取感兴趣的系统状态信息的测量的强烈影响：有条件和无条件的熵产生，量化了开放系统动态的不可逆性的程度，通过明确解释的信息量相互关联。基于最近提出的碰撞模型框架[G. T. Landi { \it等人}，arXiv：2103.06247]，我们研究了在高斯态中制备的连续可变信息载体并经历高斯过程的情况。我们建立了一个工具箱，充分表征了连续测量的非平衡高斯系统和过程的热力学，说明了在此引入的仪器如何为最近的介观量子系统实验提供关键见解[Phys. Rev. Lett，{ \bf 125}，080601（2020）]。
