Quantifying the Energy Relaxation Rate of Quantum States Using D-Wave Device and the Discovery of Long-Lived Multiqubit States

TL;DR

This paper uses a D-Wave quantum annealer to measure energy relaxation rates, revealing long-lived multi-qubit states and predicting entangled states with enhanced coherence properties, advancing understanding of quantum state stability.

Contribution

It provides the first experimental measurement of multi-qubit relaxation rates on a D-Wave device and introduces a decoherence model explaining long-lived states and predicting stable entangled states.

Findings

Multi-qubit excited states have decay rates much lower than single-qubit states.

Long-lived multi-qubit states are experimentally observed.

A theoretical model predicts stable entangled states with reduced relaxation rates.

Abstract

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.