Squeezed spin states

Abstract

The basic concept of squeezed spin states is established and the principles for their generation are discussed. Two proposed mechanisms, referred to as one-axis twisting and two-axis countertwisting, are shown to reduce the standard quantum noise S/2 of the coherent S-spin state down to -(S/3) and 2, respectively. Implementations of spin squeezing in interferometers are also discussed. 42.50.Dv, 03.65.Bz

Quantum Fisher information and spin squeezing in one-axis twisting model

“…Below, we introduce two popular spin squeezing parameters: ξ 2 K proposed by Kitagawa and Ueda in analogy to photon squeezing [9], and ξ 2 W by Wineland in Ramsey experiments [11]. Besides, there are various definitions of spin squeezing which were introduced for certain considerations, and one can refer to reference [19] for detailed discussion.…”

“…It means that for SSS, its fluctuation of the collective angular momentum is squeezed in one direction and inflated in the another direction, and the fluctuation in the squeezed direction is smaller than the sub-short limit. It is believed that spin squeezing which is aroused from quantum correlation effect among individual particles, is closely related to multipartite entanglement [9,11,16,41]. One of the main applications of the SSSs is used to reduce quantum noise and increase the signal-to-noise ratio in spectroscopy [10,11,42,43].…”

“…By submitting those solutions into equation (42), one can exactly obtain V − and ξ 2 K . χ 2 for the state of (47) can be numerically calculated based on equations (8) and (9).…”

“…Equation (1) shows that a quantum state with the APEP-enhancing must be entangled. Besides entangled states, it has been theoretically and experimentally demonstrated that spin squeezed states (SSSs) can also be used to improve the accuracy of estimation [8,9,10,11,12,13,14,15,16,17,18,19]. The concept of SSSs was first established by Kitagawa and Ueda [9].…”

“…We first derive the analytical expressions for the maximal QFI and spin squeezing parameter ξ 2 K [9] in this model. Furthermore, we investigate the dependence of the APEP χ 2 and ξ 2 K on the polar angle θ 0 and the azimuth angle φ 0 of the initial CSS.…”