2023/02/21 by Imoto, Takashi, Susa, Yuki, Miyazaki, Ryoji +1
#FOS: Physical sciences #Quantum Physics (quant-ph)
paper · doi:10.48550/arxiv.2302.10486
Quantum annealing has been demonstrated with superconducting qubits. Such a quantum annealer has been used to solve combinatorial optimization problems. Moreover, it serves as a quantum simulator for investigating the properties of quantum many-body systems. However, the coherence properties of multi-qubit states provided by D-Wave Quantum Inc. have not been explored sufficiently. Here, using the D-Wave device, we measure the energy relaxation rate of superconducting qubits and find long-lived multi-qubit states. Specifically, we investigate the energy relaxation rate of the first excited states of a fully connected Ising model with a transverse field. We find that the decay rate of the excited states of such a system with four qubits is orders of magnitude smaller than that of the excited state of a single qubit, which demonstrates the existence of long-lived multi-qubit states. We elucidate the mechanism using an independent decoherence model that qualitatively describes the phenomenon. In addition, by using such a mechanism, we theoretically predict a long-lived entangled state whose energy relaxation rate is smaller than that of the separable states.