  We describe a new approach to spin squeezing based on a double-pass Faraday
interaction between an optical probe and an optically dense atomic sample. A
quantum eraser is used to remove residual spin-probe entanglement, thereby
realizing a single-axis twisting unitary map on the collective spin. This
interaction can be phase-matched, resulting in exponential enhancement of
squeezing. In practice the scaling and peak squeezing depends on decoherence,
technical loss, and noise. A simplified model indicates ~10 dB of squeezing
should be achievable with current laboratory parameters.
