QOptCraft: A Python package for the design and study of linear optical quantum systems

The manipulation of the quantum states of light in linear optical systems has multiple applications in quantum optics and quantum computation. The package QOptCraft gives a collection of methods to solve some of the most usual problems when designing quantum experiments with linear interferometers. The methods include functions that compute the quantum evolution matrix for n photons from the classical description of the system and inverse methods that, for any desired quantum evolution, will either give the complete description of the experimental system that realizes that unitary evolution or, when this is impossible, the complete description of the linear system which approximates the desired unitary with a locally minimal error. The functions in the package include implementations of different known decompositions that translate the classical scattering matrix of a linear system into a list of beam splitters and phase shifters and methods to compute the effective Hamiltonian that describes the quantum evolution of states with n photons. The package is completed with routines for useful tasks like generating random linear optical systems, computing matrix logarithms, and quantum state entanglement measurement via metrics such as the Schmidt rank. The routines are chosen to avoid usual numerical problems when dealing with the unitary matrices that appear in the description of linear systems.

对线性光学系统中光量子态的操作在量子光学与量子计算领域具有多方面的应用。QOptCraft 软件包提供了一系列方法，用以解决在利用线性干涉仪设计量子实验时遇到的一些常见问题。这些方法包括计算从系统的经典描述中得出 n 个光子量子演化矩阵的函数，以及针对任何期望的量子演化，提供实现该幺正演化的实验系统的完整描述或当此不可能时，提供近似所需幺正演化的线性系统的完整描述，并确保误差局部最小。该软件包中的函数实现了多种已知的分解，将线性系统的经典散射矩阵转换为一系列分束器和相位移位器，以及计算描述 n 个光子状态量子演化的有效哈密顿量的方法。此外，软件包还包含生成随机线性光学系统、计算矩阵对数以及通过施密特秩等指标测量量子态纠缠等有用任务的例程。所选例程旨在避免处理线性系统描述中出现的幺正矩阵时常见的数值问题。