Noisy Quantum Simulation Using Tracking, Uncomputation and Sampling

Abstract: Quantum computers have grown in size and qubit quality in recent years, enabling the execution of complex quantum circuits. However, for most researchers, access to compute time on quantum hardware is limited. This necessitates the need to build simulators that mimic the execution of quantum circuits on noisy quantum hardware accurately and scalably. In this work, we propose TUSQ - Tracking, Uncomputation, and Sampling for Noisy Quantum Simulation. To represent the stochastic noisy channels accurately, we average the output of multiple quantum circuits with fixed noisy gates sampled from the channels. However, this leads to a substantial increase in circuit overhead, which slows down the simulation. To eliminate this overhead, TUSQ uses two modules: the Error Characterization Module (ECM), and the Tree-based Execution Module (TEM). The ECM tracks the number of unique circuit executions needed to accurately represent the noise. That is, if initially we needed $n_{1}$ circuit executions, ECM reduces that number to $n_{2}$ by eliminating redundancies so that $n_{2} < n_{1}$. This is followed by the TEM, which reuses computation across these $n_{2}$ circuits. This computational reuse is facilitated by representing all $n_{2}$ circuits as a tree. We sample the significant leaf nodes of this tree and prune the remaining ones. We traverse this tree using depth-first search. We use uncomputation to perform rollback-recovery at several stages which reduces simulation time. We evaluate TUSQ for a total of 186 benchmarks and report an average speedup of $52.5\times$ and $12.53\times$ over Qiskit and CUDA-Q, which goes up to $7878.03\times$ and $439.38\times$ respectively. For larger benchmarks (more than than 15 qubits), the average speedup is $55.42\times$ and $23.03\times$ over Qiskit and CUDA-Q respectively