Fig. 1: Overcoming detection loss in squeezing-assisted interferometry.
From: Overcoming detection loss and noise in squeezing-based optical sensing
Panels a, c, e show the experimental schemes and panels b, d, f, the calculated Wigner functions of the output states for five equidistant phases. a This ideal Mach-Zehnder interferometer fed with a coherent state \(\left|\alpha \right\rangle\) has the best phase sensitivity at ϕ = 0, the detector seeing the `dark fringe', where the output states for different phases are most distinguishable (b). c If, additionally, the second input port is fed with squeezed vacuum (SV) \(\left|\xi \right\rangle\), the neighboring states are squeezed and better distinguishable; however loss or imperfect detection efficiency η makes them overlap (d). e To overcome the loss, a degenerate optical parametric amplifier (DOPA) amplifies the state before detection. f The output states are now anti-squeezed in the quadrature carrying the phase information; the latter is therefore protected against loss. In the calculation, α = 3, η = 0.5, \(\left|\xi \right\rangle\) is 6 dB squeezed, and DOPA provides 9.6 dB quadrature anti-squeezing.
