Single-Photon Scattering Can Account for the Discrepancies among Entangled Two-Photon Measurement Techniques

Abstract

Entangled photon pairs are predicted to linearize and increase the efficiency of two-photon absorption, allowing continuous wave laser diodes to drive ultrafast time-resolved spectroscopy and nonlinear processes. Despite a range of theoretical studies and experimental measurements, inconsistencies persist about the value of the entanglement enhanced interaction cross section. A spectrometer is constructed that can temporally and spectrally characterize the entangled photon state before, during, and after any potential two-photon excitation event. For the molecule Rhodamine 6G, which has a virtual state pathway, any entangled two-photon interaction is found to be equal to or lower than classical, single photon scattering events. This result can account for the discrepancies between the wide variety of entangled two-photon absorption cross sections reported from different measurement techniques. The reported instrumentation can unambiguously separate classical and entangled effects and therefore is of importance for the growing field of nonlinear and multiphoton entangled spectroscopy.TOC GRAPHICS KEYWORDS (Word Style "BG_Keywords"). Entangled two-photon absorption, Rhodamine 6G, entangled light matter interactions, virtual state pathways, off-resonant scattering

Entangled Photon Correlations Allow a Continuous-Wave Laser Diode to Measure Single-Photon, Time-Resolved Fluorescence

“…Broadband entangled pairs are generated in a periodically poled crystal whose design and characterization, as well as its use in studying entangled light-matter interactions, have been reported previously. 25,46 In short, photon pairs are generated by Type-0 spontaneous parametric down-conversion in a thirdorder periodically poled 8% MgO-doped congruent lithium tantalate (CLT) bulk crystal (HC Photonics). The crystal is pumped with a CW diode laser with a maximum power of 400 mW at 402.5 nm and fwhm line width of 1 nm (Coherent OBIS).…”

Progress towards on-chip entangled photon spectroscopy and bioimaging

“…While multiple theoretical predictions on ETPA cross sections have been made, [102][103][104][105][106] the predicted values vary by orders of magnitude, and the formulations emphasize different parameters of the excitation flux. Although reported ETPA cross sections could be as high as 1 × 10 −17 cm 2 /molecule, [107][108][109] recent measurements of ETPA cross sections reported values lower than 1 × 10 −21 cm 2 /molecule for organic molecules with virtual intermediate states, even in dyes with near-unity quantum yields which facilitate fluorescence detection such as rhodamine 6G (R6G), 10,35,[110][111][112] and quantum dot systems with large classical two-photon absorption (TPA) cross sections. 39 The measured fluorescence signals from ETPA are usually in the tens per second to tens per hour count rate range, which hinders many potential applications in imaging and sensing.…”

“…6,7 These entangled photon sources are compact and powered by CW lasers, while also exhibiting femtosecond temporal correlations comparable to classical ultrafast lasers. Second, we have systematically investigated the feasibility of entanglement-enabled microscopy techniques such as entangled fluorescence lifetime measurements 8 and ETPA microscopy, 9,10 and have identified entangled-FLIM as a major future development focus that will enable scalable, on-chip, nonlinear bioimaging and sensing.…”

Photon Pair Source based on PPLN‐Waveguides for Entangled Two‐Photon Absorption

“…The detection of these coupled photons is done by the same detector configuration as described in Section 3.2 to maintain the comparability to other publications which already used this configuration. [ 13,23,24 ] Additionally, the pump power will be limited to $${P}_{\mathrm{pump}}^{\max}\approx 600\;\text{\ensuremath{\umu}W}$$ by inserting a ND filter (Thorlabs NE20A‐A) directly after the laser to avoid the saturation of the detectors and set the condition that mainly anti‐bunched photon pairs arrive at the sample. The generated photon pair rate with the given pump power is approximately $$1.62\cdot {10}^{7}\text{C.C.}/\text{s}$$.…”