Two-Photon Interaction of Atoms with Broadband Squeezed Vacuum

We analyze the resonance two-photon interaction of atomic subsystem with broadband squeezed vacuum relative to dipole-forbidden transitions. We suppose that the bandwidth of the squeezed vacuum with carrier frequency W O is assumed to be sufficiently broad 0 < w S 2wu so that 20" ji io2, where 0 2 , is the atomic transition frequency between dipole-forbidden 12) and 11) states. As the broadband squeezed vacuum consists from the coherent pairs of photons (biphotons) [I] at short times the atomic subsystem undergo the nonlinear nutation in process of two-photon interaction with squeezed light, like one photon cooperative interactions with a single mode coherent field. Here the atomic subsystem inversion oscillates with Rabi frequency 2 0 that is proportionally with product of positive frequency amplitude pans of squeezed EMF strength. Moreover in process of two-photon deexcitation of atomic subsystem the cooperative scattering effect with generation of photons with frequency larger than the bandwidth of the squeezed vacuum mr2 = 2w0 + oil can predominate. For higher Rabi frequency in process of two-photon interaction of atomic subsystem with broadband squeezed vacuum is possible the resonance fluorescence in the spectrum of emitted biphotons. We show that in resonance case in the fluorescence spectrum is possible the generation of three bands of biphotons w!hich consist from photon pairs with. energy h o ~ l + hm~? = Zho,, MO, AmLl + Rwu = 2Rwo. This effect is similar to Mollow effect and the mean difference between this effect and Mollow's consists in fact that the triplet appears in the biphoton resonance fluorescence spectrum We also discuss the possibility of generation of the second order square amplitude squeezed light in fluorescence spectrum. It is important to mention that two-photon interaction of broadband squeezed vacuum with dipole-forbidden two-level system have the similar property as resonance interaction of coherent light with dipole active two-level system [Z]. For instance, the condition of generation of second order square amplitude squeezed light in process of two-photon resonance fluorescence is similar to generatton of first order squeezed light in process of one photon resonance fluorescence.