Optimal encoding of two dissipative interacting qubits

• Main Authors: Di Bello, G, De Filippis, G, Hamma, A, Perroni, C. A
• Format: Journal Article
• Language: English
• Published: 18-01-2024
• Subjects: Physics - Mesoscale and Nanoscale Physics; Physics - Other Condensed Matter; Physics - Quantum Physics
• DOI: 10.48550/arxiv.2310.05561

Phys. Rev. B, 109, 014304 (2024) We investigate a system of two coupled qubits interacting with an Ohmic bath
as a physical model for the implementation of one logical qubit. In this model,
the interaction with the other qubit represents unitary noise while the Ohmic
bath is responsible for finite temperature. In the presence of a
one-dimensional decoherence-free subspace (DFS), we show that, while this is
not sufficient to protect a qubit from decoherence, it can be exploited to
encode one logical qubit with greater performance than the physical one. We
show different possible strategies for the optimal encoding of a logical qubit
through a numerical analysis based on matrix product states. This method
reproduces faithfully the results of perturbative calculations, but it can be
extended to cases of crucial interest for physical implementations, e.g., in
the case of strong coupling with the bath. As a result, a logical qubit encoded
in the subspace which is the direct sum of the antiferromagnetic states in Bell
basis, the DFS and the one in the triplet, is the optimally robust one, as it
takes advantage of both the anchoring to the DFS and the protection from the
antiferromagnetic interaction. These authors contributed equally to this work,
and their names are listed in alphabetical order.