TRIM: crossTalk-awaRe qubIt Mapping for multiprogrammed quantum systems

The challenge of mapping logical qubits to physical qubits in quantum systems has been addressed in prior proposals that optimize the Probability of Successful Trial (PST) by considering the coherence and gate error rates. However, these proposals do not account for crosstalk errors, which occur when active qubits interact during execution. The reason for this is that crosstalk only appears after the initial mapping, while previous strategies allocate qubits based on program and quantum system characteristics using one-step mapping methods. Scheduling-based solutions have been created to address this problem by inserting barriers between gates to reduce crosstalk, but at the expense of increased execution time and coherence error rates, ultimately decreasing overall accuracy. This paper presents and evaluates TRIM, a novel strategy that characterizes crosstalk and eliminates it in an iterative fashion using a multi-step greedy search method, which can be applied to any qubit mapping to reduce crosstalk while keeping execution time and coherence errors in check. Evaluations of TRIM using multiple workloads show PST improvements of 7.3% for single-programmed execution and 7.7% for multiprogramming scenarios, while reducing or keeping the number of gates, compared to a state-of-the-art mapping scheme. Additionally, TRIM achieves 5.4% and 3.3% PST improvements for single-programmed and multiprogrammed executions, respectively, compared to a state-of-the-art scheduling strategy.