Experimental feasibility of molecular two-photon absorption with isolated time-frequency-entangled photon pairs

How to optimize the absorption of two entangled photons

“…6 In panels (a,b), we observe a monotonic increase of E q with S, and a plateau of the achievable entanglement and quantum enhancement emerges for large values of the detuning ∆, which we address in the next subsection. The increase of S with ∆ and as δ → −2 can be attributed to a narrowing of the frequency-sum distribution (33), in unison with a broad single frequency distribution (34) (due to its composition by two distant peaks). This distribution signifies strong frequency anti-correlations, and indeed, since we are here considering pure quantum states of light, correspond to a strongly entangled wave function [19].…”

“…4(c). The delta function stems from a narrowband continuous-wave (cw) pump laser and replaces the Lorentzian distribution of the sum frequencies we encountered in (33). The cw nature of the pump pulse implies that the arrival time of the entangled photon pair is completely undetermined.…”

“…The former determines the width of the pump pulse, and hence should be compared to the deviation δ, which sets the width of the optimal two-photon wave function (32), see Fig. 1(b) and (33). The latter determines the frequency difference between the two down-converted photons, and thus should be compared to the deviation ∆ between the transition frequencies |g〉 → |e〉 and |e〉 → | f 〉, see Fig.…”

“…In addition, quantum correlations may help to further manipulate optical signals [28][29][30]. Yet, a key problem in the practical application, currently, is the low absorption cross section of many samples [31][32][33][34], unless the two-photon transition can proceed through near-resonant intermediate states [35]. In this case [36], the shaping of entangled photonic wave functions [37][38][39] can enhance the absorption probability.…”

“…We carefully examine the optimal pulse shapes, as well as the relation between quantum correlations and the achievable enhancement. The insight obtained from this basic three-level (33,34). The widths of the local maxima give a qualitative impression of the nonclassical frequency correlation between both incoming photons.…”