  Quantum computers promise to solve several categories of problems faster than
classical computers ever could. Current research mostly focuses on qubits,
i.e., systems where the unit of information can assume only two levels.
However, the underlying physics of most (if not all) of the technological
platforms supports more than two levels, commonly referred to as qudits.
Performing computations with qudits increases the overall complexity while, at
the same time, reducing the number of operations and providing a lower error
rate. Furthermore, qudits with different number of levels can be mixed in one
system to ease the experimental control and keep representations as compact as
possible. Exploiting these capabilities requires dedicated software support to
tackle the increased complexity in an automated and efficient fashion. In this
paper, we present a qudit simulator that handles mixed-dimensional systems
based on Decision Diagrams (DDs). More precisely, we discuss the type of
decision diagram introduced as underlying data structure as well as the
resulting implementation. Experimental evaluations demonstrate that the
proposed solution is capable of efficiently simulating mixed-dimensional
quantum circuits, with specific use cases including more than 100 qudits in one
circuit. The source code of the simulator is available via
github.com/cda-tum/MiSiM under the MIT~license.
