Researchers from the University of Messina in Italy, Adam Mickiewicz University in Poland, Fuzhou University in China, and The University of Michigan, Ann Arbor, Michigan, USA have theoretically investigated a system to extend the coherence of quantum bits. The work investigates a chain of superconducting qubits arranged with alternating XX and YY ultrastrong interactions, utilizing the two lowest energy states as a single logical qubit. The authors demonstrate that increasing interaction strength or the number of qubits in the chain suppresses the logical qubit’s pure dephasing rate to zero, and reduces its relaxation rate to half that of a single physical qubit, demonstrating the feasibility of high-fidelity single and two-qubit gates. Ultrastrong Qubit Interactions Enhance Logical Qubit Coherence A logical qubit constructed from a chain of superconducting qubits can maintain coherence significantly longer than its constituent physical qubits, according to theoretical work focused on novel qubit arrangements. Researchers detailed a system where alternating XX and YY ultrastrong interactions between qubits suppress decoherence, a critical step toward building fault-tolerant quantum computers. The study, involving collaboration between institutions in Italy, Poland, China, and The University of Michigan, Ann Arbor, Michigan, USA, theoretically investigates a pathway to extend both pure dephasing and relaxation times, key measures of qubit stability, beyond the limitations of individual qubits. This approach differs from previous hardware-level qubit protection strategies, which typically rely on either a small number of complex elements or a large number of simpler ones. The team’s model utilizes a chain of qubits, leveraging the specific pattern of interactions to create a more robust logical qubit. The theoretical framework centers on understanding how environmental interactions affect qubit coherence. The researchers define global susceptibilities for pure dephasing and relaxation, representing the system’s sensitivity to noise. They explain that ideally, a system would be fully protected if these