CHARACTERIZATION OF CURRENT SPIN QUBIT DEVICES AND A PROPOSED NEW QUBIT DESIGN

Abstract

We characterize the performance of current quantum dot spin qubit devices for small quantum simulations, demonstrate a new theoretical framework for the modeling of the qubit charge stability diagram, and propose a new qubit design to extend coherence times and reduce leakage errors in exchange qubits. First, we show that silicon quantum dot spin qubits can effectively simulate discrete time crystals with clear signatures that appear even in small arrays, where charge noise—typically detrimental to qubit performance—actually stabilizes the time-translation symmetry breaking phase. Second, we develop full configuration interaction methods to accurately model multi-electron quantum dots, revealing significant many-body effects that enhance tunneling couplings and improve device characterization beyond single-electron approximations. Finally, we introduce the Singlet-only Always-on Gapless Exchange (SAGE) qubit architecture, a four-electron encoding that eliminates sensitivity to local magnetic fields while maintaining all-electrical baseband control, and suppressing leakage. The SAGE qubit offers a promising pathway toward ultra-scalable quantum computation with spin qubits.