Parity-symmetric phase sensing in one- and two-axis twisting spin systems
Guang-Ri Jin, Yi Yang, Hang Li +2 more
Abstract We investigate spin squeezing and optimal phase sensing in parity-conserving one-axis twisting (OAT) and two-axis twisting (TAT) spin systems. For the OAT model, we analytically identify a plateau regime where the quantum Fisher information (QFI) reaches 0.5 N 2 with a fixed y -axis sensing direction—a configuration well-suited for standard interferometry. For an even number of particles N , it is essential to switch the sensing direction from the y -axis to the z -axis to further enhance the QFI to N 2 . In contrast, for odd N , the y -axis remains nearly optimal without such a directional transition. We analytically demonstrate that this transition in the optimal sensing direction is exclusive to the even- N case. For the TAT model, we demonstrate a discontinuous jump in the optimal sensing direction from the anti-squeezing direction to the z -axis, enabling the QFI to reach a peak value ∼ 0.93 N 2 , thereby exceeding the earlier benchmark of 0.64 N 2 . Our results reveal the important role of the sensing direction transition in achieving a high-precision quantum phase estimation.
Communications in Theoretical Physics•Jul 23, 2026•0 citations