  We present version 2 of QuTiP, the Quantum Toolbox in Python. Compared to the
preceding version [Comput. Phys. Comm. 183 (2012) 1760], we have introduced
numerous new features, enhanced performance, made changes in the Application
Programming Interface (API) for improved functionality and consistency within
the package, as well as increased compatibility with existing conventions used
in other scientific software packages for Python. The most significant new
features include efficient solvers for arbitrary time-dependent Hamiltonians
and collapse operators, support for the Floquet formalism, and new solvers for
Bloch-Redfield and Floquet-Markov master equations. Here we introduce these new
features, demonstrate their use, and give a summary of the important
backward-incompatible API changes introduced in this version.
