Fig. 2: Interaction-free quantum sensing with undetected photons.
From: Interaction-free, single-pixel quantum imaging with undetected photons
a By adjusting the phase \(\theta\) of the signal photons, we obtain the residual interference of the signal photon in the absence of the object with a visibility of 11.3 ± 1.9%. b When the object is present, the idler photon performs a successful IFM and induces the interference of the signal photon. The experimental visibility is 22.3 ± 1.8%. The relative phase \(\theta\) can be tuned by adjusting optical path difference of two arms in the nonlinear interferometer with motorized translation stages mounted on the mirrors R1. c Counting histogram of the signal photon fitted by two Gaussian distributions. The width of each bin is 20 counts per second. The mean counts per second for sensing the presence (purple) and absence (blue) of the object are about 3,500 and 2,950, respectively. By setting a threshold (vertical black dash line), we clearly distinguish whether the object is present or not. d The confidence of the sensing is obtained by integrating the two Gaussian distributions shown in panel (c); a confidence level above 99.93% at the 3.4-sigma threshold is obtained. Error bars in panels (a and b) indicate two standard errors of the mean.
