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Self-induced transparency in a resonant two-level system creates a 2^-soliton pulse, which produces large optical nonlinearities with a very fast response time and an extremely small loss. The self-phase modulation of a 2/r soliton and the mutual-phase modulation by the collision of two In solitons in the excitonic range of the spectrum in CdS can achieve an effective % i3) coefficient of 10 ~~6 to 10 ~4 5 esu for a pulse duration of 1 to 3 ps. The quantum theory of In solitons predicts this new nonlinear process can realize squeezed states and quantum nondemolition measurement 20 dB below the standard quantum limit.PACS numbers: 42.50.Qg, 32.90.+a, 42.50.Dv Optical nonlinear processes can be divided into two categories: nonresonant coherent and resonant incoherent. ] If a field frequency is well detuned from the atomic transition frequency, the response time is fast and the absorption loss is negligible, but the # (3) coefficient is usually small. On the other hand, when the field frequency is close to the atomic frequency, the / (3) coefficient is enhanced, but the response time becomes slow and the absorption loss is high. These tradeoffs between the x coefficient and the response time or the absorption loss impose a serious limitation on both nonlinear optical switches in classical optics 2 and squeezed-state generation and quantum nondemolition measurement in quantum optics. 3 This Letter demonstrates the possibility of new optical nonlinearities based on the resonant and coherent coupling between the field and the atoms.j Suppose the pulse duration T is much shorter than the energy and phase decay time constants T\ y T2 and the area A=(p2\/h)jEdt of a secant-hyperbolic shaped pulse is a multiple of 2/r. Here pi\\% the atomic dipole moment and E is the electric field envelope. The pulse propagates without being absorbed irrespective of the pulse frequency detuning from the atomic frequency and the inhomogeneous broadening of the atomic frequen- cies. 4 This is a so-called 2K soliton. The Maxwell-Bloch equations for self-induced transparency (SIT) can be solved by the inverse scattering method formula. 5 The 2/r-soliton solution is uniquely determined by the complex eigenvalue $=a + ip of the inverse scattering (Zakharov-Shabat) equations. 5 The field envelope function for the 2K soliton, except for an exp[/(p) Pi\ cosh{2pv[t -(z/v)(l + n 2 /4v 2 K { )]}Here Ci 2ss conp2\/2he, e^e^nl is the dielectric constant, n is the atomic density, v =*c/n$ is the nonresonant light velocity, a = (2\), then the coefficients K: O and K\, the group velocity K, and the ph...

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Absorption spectra of cold Cs atoms in a magneto-optical trap under the influence of a strong external pump laser field with arbitrary detuning and intensity have been systematically investigated. The spectra featured the Rabi sidebands of each transition, and their behavior was nicely fitted by the dressed-atom theory. A pronounced dispersion-type profile with sub-natural linewidth at the pump frequency may be attributable to the stimulated Raman process by sublevels that are lightshifted and optically pumped by the pump laser.

We analyze the time evolution of solutions of nonlinear Schrödinger equations that describe a condensate composed of atoms with negative scattering lengths in a harmonic potential trap. It is theoretically demonstrated that if an initial condensate has negative energies due to negative scattering lengths, then the solutions diverge in a finite time that is determined by the condensate's energy, its initial phase, and the trap parameter.