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Atomic Resonant Single-Mode Squeezed Light from Four-Wave Mixing through Feedforward

Squeezed states of light have received renewed attention due to their applicability to quantum-enhanced sensing. To take full advantage of their reduced noise properties to enhance atomic-based sensors, it is necessary to generate narrowband near or on atomic resonance single-mode squeezed states of light. We have previously generated bright two-mode squeezed states of light, or twin beams, that can be tuned to resonance with the D1 line of $^{87}$Rb with a non-degenerate four-wave mixing (FWM) process in a double-lambda configuration in a $^{85}$Rb vapor cell. Here we report on the use of feedforward to transfer the amplitude quantum correlations present in the twin beams to a single beam for the generation of single-mode amplitude squeezed light. With this technique we obtain a single-mode squeezed state with a squeezing level of $-2.9\pm0.1$ dB when it is tuned off-resonance and a level of $-2.0\pm 0.1$ dB when it is tuned on resonance with the D1 $F=2$ to $F'=2$ transition of $^{87}$Rb.