Entangled Photon Holes

Most experimental demonstrations of entanglement require nonclassical states and correlated measurements of single-photon detection events. It is shown here that entanglement can produce a large decrease in the rate of two-photon absorption for a classical input state that can be observed using classical detectors. These effects can be interpreted as being due to the creation of entangled photon holes that are somewhat analogous to the holes of semiconductor theory.

Figure 1

(a) Two-photon probability amplitude from parametric down-conversion, where the photons are known to be at the same location (to within the bandwidth of the source) with an equal probability amplitude for all locations, such as points A and B; (b) Two-photon probability amplitude for the entangled photon holes produced by two-photon absorption, where there is an equal probability amplitude for two photons to have been removed from any location.

Figure 2

Single-photon intensity (a) as a function of position and two-photon detection probability (b) as a function of separation in the initial state. The corresponding results after passing through five atoms are shown in (c) and (d).

Figure 3

(a) The dots indicate the probability of remaining in the initial two-photon state after passing through $n_A$ atoms, while the line represents an exponential decay curve fitted to the first two data points. (b) The integrated intensity as a function of propagation distance as calculated using semiclassical theory. (c) The probability of remaining in the initial two-photon state for the case in which the photons are traveling in opposite directions. The fluctuations in these data are due to the random choice of the positions of the atoms.