Squeezing in two photon absorption from a strong coherent beam

Ming-Chiang Li

R. Loudon

Peng Zhou, S. Swain

We examine the response of a coherently driven two-level atom interacting with a broadband squeezed vacuum to a probe beam of arbitrary intensity. The equations of motion for the reduced density matrix elements are numerically solved by nonperturbative matrix inversion methods. For large driving intensities, the absorption spectrum exhibits a number of multiphoton absorption peaks with increasing probe strength in a standard vacuum and in a squeezed vacuum with small photon numbers, while the multiphoton absorption peaks are wiped out for large squeezed photon numbers. Strong gain without inversion at line center can be obtained in the presence of the squeezed vacuum when the probe strength does not exceed the driving one. The absorption spectrum is phase sensitive. We also find the presence of remarkable, very narrow structures at line center. In general, the spectrum is symmetric when \ensuremath{\Phi}=0 and \ensuremath{\pi}; otherwise, it is asymmetric and displays a dispersivelike profile at line center.

NILOY KUMAR DUTTA

P. Kochan, H. J. Carmichael

Under usual laboratory conditions the absorption of a beam of light by a dilute two-level medium depends on the intensity and spectrum of the incident light. If the incident photon flux is small compared to the decay rate of the absorber’s excited state, saturation effects can be neglected and only the spectrum of the light is important; thus, weak-field absorption depends only on the firstorder correlation function of the incident light. This result relies, however, on a requirement that the incident beam cross-section be much larger than the absorption cross-section of an atom. Then individual atoms act as low efficiency scatterers and the statistics of the scattering process is governed by the law of large numbers applied to many scattering sites. In contrast, if it is arranged that just one atom significantly absorbs (scatters) a beam of photons, correlation functions of the incident light beyond the first-order must be considered. For a beam that is focused within an absorption cross-section, we might naively predict that every photon will be scattered and none transmitted. In fact, even for a very weak beam there is a finite probability for two photons to arrive at the atom within the excited state lifetime, and in this event at least one of them will be transmitted (statistical saturation). In this paper we calculate the transmitted photon flux for a weak beam of photons focussed strongly onto a single, resonant two-state atom. We study the dependence of the transmitted flux on the statistics of the incident photons. Photon beams derived from sources of coherent, chaotic, squeezed, coherent-antibunched, and broadband-antibunched light are considered. our calculations are based on a recently developed theory of cascaded open systems,1,2 and serve to illustrate the usefulness of this theory.

Klaus M. Gheri, Daniel F. Walls

We show that significant squeezing in a strong signal light field can be generated with three-level atoms in a ghost-transition setup by tuning a weak probe beam inside the Autler-Townes doublet created by the strong signal light. Close to the Rabi level, i.e., within the absorption line, processes involving both amplitude quadratures become important. Significant atomic two-photon coherence provides a vehicle for signal-amplitude fluctuations to trigger fluctuations in the probe amplitude. Subsequently, atomic coherence will feed these probe fluctuations back into the signal and enable substantial noise suppression.