While superconducting qubits are renowned for their superior scalability and programmability, achieving fault-tolerant quantum computing remains elusive, primarily due to the prevalent issue of qubit decoherence. In our group, we explore how the symmetry properties in certain quantum many-body spin systems can be used in superconducting circuits to engineer qubits that are intrinsically protected from local noises. We have discovered specific spin models with ground states that adhere to Translation and Inversion symmetries and conserve the total number of excitations within the system. Intriguingly, these states demonstrate immunity to all forms of local Pauli noise and display no dephasing or relaxation attributable to local noises.
By mapping this spin model to Circuit QED systems, we have proposed a new qubit design: the Magenium qubit. Using the quantization and exact diagonalization of the circuit Hamiltonian, we can calculate the ground states and evaluate the qubit’s coherence performance. The relaxation time T1 is estimated to be 5 ms, primarily restricted by quasiparticle tunneling. The dephasing time T2 limited by charge noise and flux noise is estimated to be 2.9 ms and 5.2 ms, respectively. Currently, we are developing an improved design that reduces the number of Josephson junctions and bridges required to construct the qubit. Preliminary findings suggest that this new design is not only more feasible from a practical perspective but also shows potential to further enhance qubit coherence.
- Protection of Quantum Information in a Chain of Josephson Junctions P. Brookes, T. Chang, M. H. Szymanska, E. Grosfeld, E. Ginossar, and M. Stern Phys. Rev. Applied. 17(2), 024057. (2022)
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