Exploring the superconducting grid-states qubit

Quantum information is inevitably susceptible to decoherence mechanisms imposed by the environment, leading to imprecision that hinders the progress in quantum computing. One promising approach to correct information loss is to encode a finite-dimensional subspace non-locally into the infinite-dimensional Hilbert space of a continuous-variable system, forming a periodic grid where error can be efficiently detected and suppressed. Alternatively, the information can be protected if it is hardware-encoded into the grid-like eigenstates of a superconducting circuit with dual nonlinearity in charge and phase. Here, we present an approach to implement such a qubit by combining the quasicharge element with the double-Cooper-pair tunneling element. We discuss the concepts, design principles, and expected behaviors of the circuit. We then showcase the experimental progress toward implementing the qubit.