Spin squeezing in internal bosonic Josephson junctions via enhanced shortcuts to adiabaticity

Abstract: We investigate a time-efficient and robust preparation of spin-squeezed states -- a class of states of interest for quantum-enhanced metrology -- in internal bosonic Josephson junctions with a time-dependent nonlinear coupling strength between atoms in two different hyperfine states. We treat this state-preparation problem, which had previously been addressed using shortcuts to adiabaticity (STA), using the recently proposed analytical modification of this class of quantum-control protocols that became known as the enhanced STA (eSTA) method. We characterize the state-preparation process by evaluating the time dependence of the coherent spin-squeezing and number-squeezing parameters and the target-state fidelity. We show that the state-preparation times obtained using the eSTA method compare favourably to those found in previously proposed approaches. We also demonstrate that the increased robustness of the eSTA approach -- compared to its STA counterpart -- leads to additional advantages for potential experimental realizations of strongly spin-squeezed states in bosonic Josephson junctions.