Temperature-Controlled Entangled-Photon Absorption Spectroscopy

Abstract

Entangled two-photon absorption spectroscopy (TPA) has been widely recognized as a powerful tool for revealing relevant information about the structure of complex molecular systems. However, to date, the experimental implementation of this technique has remained elusive, mainly because of two major difficulties. First, the need to perform multiple experiments with two-photon states bearing different temporal correlations, which translates into the necessity to have at the experimenter's disposal tens, if not hundreds, of sources of entangled photons. Second, the need to have a priori knowledge of the absorbing medium's lowest-lying intermediate energy level. In this work, we put forward a simple experimental scheme that successfully overcomes these two limitations. By making use of a temperature-controlled entangled-photon source, which allows the tuning of the central frequencies of the absorbed photons, we show that the TPA signal, measured as a function of the temperature of the nonlinear crystal that generates the paired photons, and a controllable delay between them, carries all information about the electronic level structure of the absorbing medium, which can be revealed by a simple Fourier transformation.

How to optimize the absorption of two entangled photons

“…as the only solution. 3 The maximal population can thus be expressed directly in terms of N , by (30) in ( 25), together with 〈Φ|Φ〉 = 1 as imposed by the constraint in (24), or in frequency space, with (12,13,15) in ( 30) in (25), to obtain an explicit expression for N in terms of the system parameters [40]:…”

“…The factor N stems from (30), and clarifies the meaning of this equation: if N is the maximal population achievable by using the optimal state |Φ〉, then the population in the case of a shaped realistic state M 1 M 2 |Σ〉 is reduced by the overlap between these two initial states.…”

“…Such pairs can induce two-photon transitions more efficiently than laser pulses, and promise the use at low photon flux, thus preventing damage in photosensitive samples [24][25][26][27]. 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].…”

Exploring energy-time entanglement using the dynamics of two-photon absorption

“…III. As demonstrated in [17], it is then possible to extract information about the electronic level structure of the absorbing medium from the effects of a time delay in the absorption of broad band entangled photon pairs. However, this may not be the case when the resonant contributions are unphysical.…”

Hong-Ou-Mandel interferometry and spectroscopy using entangled photons

“…uantum states of light provide an exciting platform for observing and controlling matter beyond what is possible classically [1][2][3][4] . Quantum states are very sensitive to the external environment, which makes them useful probes of matter.…”