In this work, the Stokes-anti-Stokes¿ time-correlation phenomena was studied. The timecorrelated scattering process occurs when the same vibrational quantum from a material participates in the Stokes and anti-Stokes photon generation process in the inelastic scattering of light. We demonstrate that the SaS phenomenon occurs in different bands of the Raman spectra, from different transparent liquid materials. The observation of time-correlated SaS pairs in energy bands out of the resonance region indicates the possibility of energy exchange between photons via virtual phonons, which allows drawing a parallel with the Cooper pair formation phenomenon for electrons, from the BCS superconductivity theory. In this dissertation, we discuss the fundamentals of the theory and the instrumentation related to the concepts about the discussed phenomena, as well as demonstrate that the rate of SaS pair formation exhibits a linear relation with the supertransparency gap, concept brought from the BCS superconductivity theory.
In this work, the Stokes-anti-Stokes¿ time-correlation phenomena was studied. The timecorrelated scattering process occurs when the same vibrational quantum from a material participates in the Stokes and anti-Stokes photon generation process in the inelastic scattering of light. We demonstrate that the SaS phenomenon occurs in different bands of the Raman spectra, from different transparent liquid materials. The observation of time-correlated SaS pairs in energy bands out of the resonance region indicates the possibility of energy exchange between photons via virtual phonons, which allows drawing a parallel with the Cooper pair formation phenomenon for electrons, from the BCS superconductivity theory. In this dissertation, we discuss the fundamentals of the theory and the instrumentation related to the concepts about the discussed phenomena, as well as demonstrate that the rate of SaS pair formation exhibits a linear relation with the supertransparency gap, concept brought from the BCS superconductivity theory.
The correlated Raman scattering, referred to here as the SaS process, occurs with the annihilation, within a material, of two photons of an excitation laser and the creation of a quantum correlated Stokes (S) and anti-Soktes (aS) photon pair where the phonon created in the S process is annihilated in the aS scattering. We found that, in addition to real SaS process where the energy exchange coincides with the energy of a vibrational state of the material, there is also the virtual SaS process, whose the exchange of energy and momentum between the photons of the laser, generating the S-aS photon pair, is mediated by a virtual vibrational excitation, setting up a photon-photon interaction similar to the electron-electron attraction responsible for the creation of Cooper pairs of the BCS theory of superconductivity. We observed the SaS process in transparent media in general, by measuring non-classical values of the normalized second-order cross-correlation function of the Stokes and anti-Stokes fields, 2(0). In diamond, we characterize the intensity of the virtual SaS scattering ( ) as a function of the virtual phonon energy, proving that the SaS process occurs only when the photon-photon interaction is attractive, as in the BCS theory for the Cooper pairs. We show that photons S and aS from the SaS process are scattered predominantly in the same polarization as the excitation laser of the sample and, with this, we implemented the pump-probe technique to study the lifetime of the real phonon (obtained in the diamond order 2.8 ps ) and the lifetime of the virtual excitation, which proved to be inferior to the temporal resolution of the measurement’s, characterizing one of the main differences between the two processes. We also observed that, due to the relations of energy and momentum conservation, have the same spatial intensity profile of the non-interacting laser that crosses the sample, different from the behavior observed for uncorrelated Raman scattering which spreads photons in all directions. We observed that the efficiency of the SaS scattering is proportional to the Raman scattering cross-section when we compare the process in different hydrocarbons and we generalize the observations made in the diamond to the sample of liquid decane. In water, the values of 2(0), predicted by the theoretical description of the process, corroborate the experimental data, validating the BCS theory for virtual SaS scattering, setting the pair of Stokes and anti-Stokes photons as counterparts of the Cooper pairs.
In this work we study the correlated Stokes and anti-Stokes Raman scattering, called here SaS. The SaS is an event where the same phonon participates in the of Stokes and anti-Stokes scattering processes. This process is not considered in current treatments of Raman scattering and can bring changes in the use of Raman spectroscopy for localtemperature measurements. Furthermore, these photons emerge as an important source of correlated photons pairs, widely used in quantum information, for example in implementing a quantum memory. We checked, by measurements of coincidence counting, that the Stokes and anti-Stokes photons generated in the Raman scattering from water, morespecifically the bands at }1644 1 concerning the angle variation mode between the H atoms, are quantum correlated. We get a value of 2(0) 517, much higher than what has been measured in others materials, as reported in the literature. We found that theintensity of the anti-Stokes signal has a quadratic dependence on the laser power, being another indication of the SaS occurrence. The value of 2(0) decays to high power values, in agreement with theoretical predictions. We have also obtained evidences that the SaScorrelation exhibits a dependence on the S and aS photon polarizations and can thus be exploited in future entanglement experiments.
The correlation between the Stokes and anti-Stokes components of Raman scattering has assumed an important role in the field of quantum information. When the Raman shifts match the energy of a phonon in the material, in the real-SaS, one-phonon Fock state are generated. When such resonance is not achieved, the energy exchange is mediated by virtual phonons, generating photonic Cooper pairs (PCPs). In this work, investigations of polarization correlations and scattering time dependences elucidate the fundamental difference between the real and the virtual phenomena.
O espalhamento Raman correlacionado, denominado aqui processo SaS, ocorre com a destruicao, dentro de um material, de dois fotons de um laser de excitacao e a criacao de um par de fotons Stokes (S) e anti-Soktes (aS) correlacionado quanticamente onde o fonon criado no processo S e aniquilado no espalhamento aS. Nos verificamos que, alem do processo SaS real, onde a troca de energia coincide com a energia de um estado vibracional do material, existe tambem o processo SaS virtual, cuja troca de energia e momento entre os fotons do laser, gerando o par S-aS, e mediada por uma excitacao vibracional virtual configurando uma interacao foton-foton similar a atracao eletron-eletron responsavel pela criacao dos pares de Cooper na teria BCS da supercondutividade. Observamos o processo SaS em meios transparentes em geral, via medicao de valores nao classicos da funcao de correlacao de segunda ordem normalizada dos campos Stokes e anti-Stokes, 𝑔2𝑆𝑎𝑆(0). No diamante, caracterizamos a intensidade do espalhamento SaS (𝐼𝑐𝑜𝑟𝑟𝑆𝑎𝑆 ) em funcao da energia do fonon virtual, verificando que o processo SaS ocorre somente quando a interacao foton-foton e atrativa, como acontece na teoria BCS para os pares de Cooper. Mostramos que os pares de fotons S e aS sao espalhados predominantemente na mesma polarizacao do laser de excitacao da amostra e, com isso, implementamos a tecnica de pump-probe para o estudo do tempo de vida do fonon real (obtido no diamante da ordem de 2,8 ps) e da excitacao virtual, que mostrou ser menor que a resolucao temporal da medida, caracterizando uma das principais diferencas entre os dois processos. Observamos tambem que, devido as relacoes de conservacao de energia e momento, 𝐼𝑐𝑜𝑟𝑟𝑆𝑎𝑆 segue o mesmo perfil espacial de intensidade do laser nao interagente que atravessa a amostra, diferentemente do comportamento observado para o espalhamento Raman nao correlacionado, que espalha fotons em todas as direcoes. Nos observamos que a eficiencia do espalhamento SaS e proporcional a secao de choque do espalhamento Raman quando comparamos o processo em diferentes hidrocarbonetos e generalizamos as observacoes feitas no diamante para a amostra liquida de decano. Na agua, os valores de 𝑔2𝑆𝑎𝑆(0) previstos pela
descricao teorica do processo corroboram os dados experimentais, validando a teoria BCS para espalhamento SaS virtual e colocando os pares de fotons Stokes e anti-Stokes correlacionados como analogos fotonicos aos pares de Cooper.
In this study, the correlated Stokes--anti-Stokes Raman scattering, denominated as the SaS process, is investigated in a decane sample, generalizing for a liquid the results observed in crystalline diamond. The production of SaS photon pairs is observed in both real and virtual processes by measuring nonclassical values of the second-order cross-correlation function gSaS2(0). The correlated Raman spectrum is observed only for Raman shift values below approximately $2900\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, which is equivalent to the highest vibrational mode of the decane molecule. Furthermore, despite the fact that decane is a liquid, the polarization and spatial profile of the SaS process in decane presents the same properties as those observed in diamond.