Improving QuIDD-based Simulation

This chapter describes some ways to speed up QuIDD-based simulation that are facilitated by the QuIDDPro language. These techniques apply to QuIDD matrix multiplication, the tensor product, and the partial trace, which are key operations for simulation with and without errors. First, we describe algorithms for efficiently applying controlled- and 1-qubit gates to QuIDD state vectors. The simulator uses these algorithms when processing particular source-code expressions in its input. Next, we show how one can selectively tensor and remove, via the partial trace operation, qubits that do not affect a computation's final outcome. Although this technique cannot be used in every case, it can exponentially reduce simulation complexity in important special cases. We illustrate this by simulating a circuit with several types of continuous errors and evaluating the effectiveness of “bang-bang” error correction.