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

Understand

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.