# Long-lasting Quantum Memories: Extending the Coherence Time of Superconducting Artificial Atoms in the Ultrastrong-Coupling Regime

## TL;DR

This paper theoretically demonstrates that in the ultrastrong-coupling regime, superconducting artificial atoms can be protected against decoherence, significantly extending their coherence times for quantum memory applications.

## Contribution

It introduces a method to protect superconducting qubits from decoherence by exploiting ultrastrong coupling regimes and dynamical decoupling techniques.

## Key findings

- Protection against relaxation in longitudinal coupling regime
- Protection against pure dephasing in transverse coupling regime
- Enhanced coherence times for quantum memory applications

## Abstract

Quantum systems are affected by interactions with their environments, causing decoherence through two processes: pure dephasing and energy relaxation. For quantum information processing it is important to increase the coherence time of Josephson qubits and other artificial two-level atoms. We show theoretically that if the coupling between these qubits and a cavity field is longitudinal and in the ultrastrong-coupling regime, the system is strongly protected against relaxation. Vice versa, if the coupling is transverse and in the ultrastrong-coupling regime, the system is protected against pure dephasing. Taking advantage of the relaxation suppression, we show that it is possible to enhance their coherence time and use these qubits as quantum memories. Indeed, to preserve the coherence from pure dephasing, we prove that it is possible to apply dynamical decoupling. We also use an auxiliary atomic level to store and retrieve quantum information.