Using Inherent Qubit Decoherence To Simulate Thermal Relaxation in Spin Chemistry Systems on NISQ Machines*

Current and near-term quantum computers (i.e. NISQ devices) are limited in their computational power in part due to qubit decoherence. Here we seek to take advantage of qubit decoherence as a resource for simulating the behavior of real-world quantum systems, which are always subject to decoherence, with no additional computational overhead. We show how to use the natural qubit decoherence to accurately simulate experimental results of quantum beats in radical ion pairs undergoing thermal relaxation on a quantum computer. We further implement our method to simulate two interesting chemical systems that are run on a quantum computer made available by IBM Quantum, and compare against directly implementing the decoherence channels using ancilla qubits. Using error mitigation techniques, we are able to achieve very good agreement with both theoretical and experimental data.