Parallel Quantum Sensing with Spatially Multimode Twin Beams of Light*

Quantum sensing with light takes advantage of optical quantum correlated states, such as two-mode squeezed states (twin beams) with reduced noise properties, to enhance the sensitivity of compatible measurements beyond the shot noise limit (SNL). In addition to temporal correlations, twin beams can also exhibit spatial quantum correlations that lead to localized and independently correlated spatial regions known as the coherence area.  We show that the presence of multiple correlated coherence areas in twin beams can enable a parallel quantum sensing configuration.  Building on our previous work on quantum enhanced plasmonic sensing~[1], we designed and fabricated a quadrant array of plasmonic sensors that we probe with one of the twin beams to simultaneously and independently detect local refractive index modulations below the SNL. With an initial level of $-5.2$~dB of squeezing, we obtain a quantum based enhancement for each plasmonic sensor of $\sim17\%$ with respect to the SNL. The degree of quantum enhancement is limited by optical losses and the finite size of the coherence area in the twin beam. The implemented parallel quantum plasmonic sensing configuration provides a proof-of-principle application for squeezed states of light with quantum correlations in multiple degrees of freedom and represents a first step towards spatially resolved quantum sensing architectures.

[1] M. Dowran, A. Kumar, B. Lawrie, R. Pooser, and A. Marino, ``Quantum-enhanced plasmonic sensing,'' \textit{Optica} \textbf{5} 628--633 (2018)