Dynamical decoupling and dephasing in interacting two-level systems

TL;DR

This paper demonstrates how dynamical decoupling techniques can significantly improve the coherence and lifetime of entangled states in superconducting qubits by mitigating dephasing noise, with implications for fault-tolerant quantum computing.

Contribution

The study introduces a method of applying rapid refocusing pulses to enhance coherence in coupled two-level systems, validated with a superconducting flux qubit and microscopic two-level system.

Findings

Refocusing pulses reduce dephasing and extend entangled state lifetime.

Multiple pulses further improve coupling coherence, consistent with a $1/f$ noise model.

Applicable to any two-qubit system with transverse coupling.

Abstract

We implement dynamical decoupling techniques to mitigate noise and enhance the lifetime of an entangled state that is formed in a superconducting flux qubit coupled to a microscopic two-level system. By rapidly changing the qubit's transition frequency relative to the two-level system, we realize a refocusing pulse that reduces dephasing due to fluctuations in the transition frequencies, thereby improving the coherence time of the entangled state. The coupling coherence is further enhanced when applying multiple refocusing pulses, in agreement with our $1/f$ noise model. The results are applicable to any two-qubit system with transverse coupling, and they highlight the potential of decoupling techniques for improving two-qubit gate fidelities, an essential prerequisite for implementing fault-tolerant quantum computing.