Pump-Probe Measurements with Entangled Photons

Oleksiy Roslyak, Shaul Mukamel

We show that entangled photons may be used in coherent multidimensional nonlinear spectroscopy to provide information on matter by scanning photon wave function parameters (entanglement time and delay of twin photons), rather than frequencies and time delays, as is commonly done with classical pulses. Signals are expressed and interpreted intuitively in terms of products of matter and field correlation functions using a diagrammatic close time path loop formalism which reveals the entangled quantum pathways of the fields and matter. The pump-probe signal measured when the pump and the probe are in a twin entangled state shows two-photon resonant contributions which scale linearly rather than quadratically with the incident beam intensity and reveal frequencies of off-resonant transitions. Two-dimensional spectrograms obtained by double Fourier transform of the signal with respect to the entanglement time and delay of the twins could provide detailed information on correlations among states and dynamical processes with high temporal resolution. The analogy with multidimensional time-domain optical techniques which use sequences of short classical pulses and pulse shaping algorithms is pointed out.

Otgonbaatar Myagmar, Duger Ulam-Orgikh, Purevdorj Munkhbaatar

Zeenat Baig, Zoya Shafique, Sean J. Bentley

Aiman Khan, Francesco Albarelli, Animesh Datta

Abstract It depends. For a single molecule interacting with one mode of a biphoton probe, we show that the spectroscopic information has three contributions, only one of which is a genuine two-photon contribution. When all the scattered light can be measured, solely this contribution exists and can be fully extracted using unentangled measurements. Furthermore, this two-photon contribution can, in principle, be matched by an optimised but unentangled single-photon probe. When the matter system spontaneously emits into inaccessible modes, an advantage due to entanglement can not be ruled out. In practice, time-frequency entanglement does enhance spectroscopic performance of the oft-studied weakly-pumped spontaneous parametric down conversion (PDC) probes. For two-level systems and coupled dimers, more entangled PDC probes yield more spectroscopic information, even in the presence of emission into inaccessible modes. Moreover, simple, unentangled measurements can capture between 60% and 90% of the spectroscopic information. We thus establish that biphoton spectroscopy using source-engineered PDC probes and unentangled measurements can provide tangible quantum enhancement. Our work underscores the intricate role of entanglement in single-molecule spectroscopy using quantum light.

P Munkhbaatar, Duger Ulam-Orgikh, J Vanchinkhuu

We propose an excitation-probe measurement method utilizing entangled photon pulses. The excitation-probe signal is dominated by stimulated Raman scattering as well as two-photon absorption when the time delay between the excitation pulse and the probe pulse is shorter than the pulseduration. This paper demonstrates that the two-photon-absorption signal can be suppressed when the photons of the pulses are entangled. The stimulated Raman scattering signal can be composed of many peaks distributed over broad photon energies owing to the transitions between numerous quantum states in complex materials. We also show that the desired peaks among the many peaks can be selected by controlling the thickness of the nonlinear crystal, the pump pulse center frequency,and the polarization of the excitation pulse and probe pulse.

Todd S. Larchuk