We propose an all-optical approach for quantum erasure. Unwanted atom-light entanglement in spin squeezing is removed by destructive interference of three successive atom-light interaction process, with only the desired atom-atom interaction left. This scheme allows implementation of unitary one-axis and two-axis twisting spin squeezing using coherent light and cold or warm atomic ensemble. Calculations show that substantial spin squeezing is attainable under moderate experiment conditions. This proposal provides a new angle in using light to eciently create manybody entanglement state with simple setups, and thus is promising for advancing technologies in quantum metrology and quantum information procession.
Spin squeezing, as a crucial quantum resource, plays a pivotal role in quantum metrology, enabling us to achieve high-precision parameter estimation schemes. Here, we investigate the spin squeezing and the quantum phase transition in an anisotropic central spin system. We find that this kind of central spin system can be mapped to the anisotropic Lipkin-Meshkov-Glick model in the limit where the ratio of transition frequencies between the central spin and the spin bath tends towards infinity. This property can induce a one-axis twisting interaction and provides another possibility for generating spin squeezing. We consider the generation of spin-squeezed states through the ground state and the dynamical evolution of the central spin model, respectively. The results show that the dynamical approach is more effective, and the spin-squeezing parameter improves as the anisotropy parameter decreases, while its value scales with system size as ${N}^{\ensuremath{-}2/3}$. Furthermore, we obtain the critical exponent of the quantum Fisher information around the critical point by numerical simulation, and find its value tends to
4/3 as the frequency ratio and the system size approach infinity. This paper offers a promising scheme for generating spin-squeezed state and paves the way for potential advancements in quantum sensing.
In this work we analyze two axis twisting in the presence of depolarizing channel dissipation. We find that spin squeezing is only possible if the dissipation is parametrically weaker than the squeezing coupling. Squeezing may be used for meteorologically useful decrease of spin noise but only in the case where the squeezing occurs before measurement, in the case one squeezes as one measures one also squeezes the signal thereby making spin squeezing ineffective for metrological gain. The key mathematical advance made in this work is the observation that TACT in the presence of depolarizing noise is equivalent to TACT with reduced polarization and no noise. We find an exponential gain in signal to noise with the exponent proportional to the ratio between the squeezing strength and the depolarization rate.