Quantum-Enhanced Absorption Spectroscopy with Bright Squeezed Frequency Combs.

Absorption spectroscopy is a widely used technique that permits the detection and characterization of gas species at low concentrations. We propose a sensing strategy combining the advantages of frequency modulation spectroscopy with the reduced noise properties accessible by squeezing the probe state. A homodyne detection scheme allows the simultaneous measurement of the absorption at multiple frequencies and is robust against dispersion across the absorption profile.

Advantage of Coherent States in Ring Resonators over Any Quantum Probe Single-Pass Absorption Estimation Strategy.

Quantum states of light have been shown to enhance precision in absorption estimation over classical strategies. By exploiting interference and resonant enhancement effects, we show that coherent-state probes in all-pass ring resonators can outperform any quantum probe single-pass strategy even when normalized by the mean input photon number. We also find that under optimal conditions coherent-state probes equal the performance of arbitrarily bright pure single-mode squeezed probes in all-pass ring resonators.

Generating path entangled states in waveguide systems with second-order nonlinearity.

Spontaneous parametric down-conversion in coupled nonlinear waveguides is a flexible approach for generating tunable path entangled states. We describe a formalism based on the Cayley-Hamilton theorem to compute the quantum states generated by waveguide arrays for arbitrary system parameters. We find that all four Bell states can be generated in directional couplers with non-degenerate photons.