Figure 1. Principle of single-photon decision maker: single photon and polarization.

(i) Light polarized 45° with respect to the horizontal axis is incident on a polarizing beam splitter (PBS). The single photon travels down to one of the output channels (Ch.0 or Ch.1) with a probability of 0.5 for each channel. However, the probability of a single photon to travel down one of the channels is unity; thus, the selected channel is immediately associated with a decision. (ii) Nearly horizontally polarized light is highly likely to be detected in Ch.1, leading to the decision of selecting slot machine R. (iii) Nearly vertically polarized light is highly likely to be detected in Ch.0, leading to the decision of selecting slot machine L.