G. Adam

Exact Equations of Motion and Numerical Results for Two-atom Spontaneous Emission in a Damped Cavity

By using a new technique developed recently, exact closed equations of motion for expectation values for the spontaneous emission from two two-level atoms in a resonant damped cavity are derived. These equations are solved numerically for different values of the cavity damping. Moreover, different atom and field fluctuations are calculated numerically. A comparison is made with results obtained by Bonifacio, Schwendimann and Haake in the case of strong damping.

Reconstruction of quantum states of spin systems via the Jaynes principle of maximum entropy

We apply the Jaynes principle of maximum entropy for the partial reconstruction of correlated spin states. We determine the minimum set of observables which is necessary for the complete reconstruction of the most correlated states of systems composed of spins 1/2 (e.g. the Bell and the Greenberger-Horne-Zeilinger states). We investigate to what extent an incomplete measurement can reveal non-classical features of correlated spin states.

Density matrix elements and moments for generalized Gaussian state fields

Abstract A single-mode radiation field with Gaussian Wigner functions (Gaussian state field) is studied. The single-mode Gaussian-field generating function for both the density matrix elements and the moments of the creation and annihilation operators is calculated. It is shown that the matrix elements as well as the moments of different orders can be expressed in terms of Hermitian polynomials of two variables. Furthermore, the cumulants of the Gaussian state field are calculated. Finally, we generalize the Gaussian state field and compute the corresponding moments and density matrix elements.

Multilevel coherence effects in a two-level atom driven by a trichromatic field

We study the absorption and dispersion properties of a weak probe field monitoring a two-level atom driven by a trichromatic field. We calculate the steady-state linear susceptibility and find that the system can produce a number of multilevel coherence effects predicted for atoms composed of three and more energy levels. Although the atom has only one transition channel, the multilevel effects are possible because there are multichannel transitions between dressed states induced by the driving field. In particular, we show that the system can exhibit multiple electromagnetically induced transparency and can also produce a strong amplification at the central frequency which is not attributed to population inversion in both the atomic bare states and in the dressed atomic states. Moreover, we show that the absorption and dispersion of the probe field is sensitive to the initial relative phase of the components of the driving field. In addition, we show that the group velocity of the probe field can be controlled by changing the initial relative phases or frequencies of the driving fields and can also be varied from subluminal to superluminal.

Cavity-damping effects in the interaction of a three-level atom with a single-mode radiation field

Abstract The influence of cavity damping in the interaction of a three-level atom with a single-mode radiation field is investigated. Closed equations of motion are derived for arbitrary cavity damping. Numerical results show the appearance of quasistationary occupation probabilities of the atomic levels which is a consequence of the cavity damping.

Phase control of subharmonic resonances

We analyze the steady-state population inversion in a two-level atom driven by three laser fields of unequal frequencies. The dependence of the population inversion on initial relative phases between the driving lasers and cancellation of subharmonic resonances are predicted and explained in terms of quantum interference between dressed states of the system.

Ordered moments in the case of a one-mode radiation field with Gaussian Wigner functions

Abstract We compute the generating function for the moments of the creation and annihilation operators of a single mode radiation field described by a Gaussian Wigner distribution. It is shown that the moments of this field can be calculated by making use of Hermitian polynomials of two variables. Moreover, the moments of a generalized radiation field introduced recently by G.S. Agarwal [Phys. Rev. A 45 (1992) 1787] are computed as well.

Saturation of a two-level atom in polychromatic fields

The response of a two-level atom in a strong polychromatic field composed of a large number of equidistant frequency components is investigated. We calculate numerically, as well as analytically,:the stationary population inversion and show that the saturation of the atomic transition strongly depends on whether or not there is a central (resonant) frequency component in the driving field. We find that, in the presence of the central component, the atom can remain in the ground state even for a strong Rabi frequency of the driving field. In addition, we find that the inversion is sensitive to the relative phase between the frequency components. When the central component is suppressed, the atomic transition saturates with the Rabi frequency independent of the relative phase.

Two-atom spontaneous emission in a detuned damped cavity

By using a new technique developed recently exact closed equations of motion for expectation values for spontaneous emission from two two-level atoms in a detuned damped cavity are derived. These equations are solved numerically for different values of the cavity damping and detuning. It is pointed out that the spontaneous emission is inhibited if the cavity is detuned. Moreover, by comparing the result of the single-atom case with that of the two-atom case it is shown that the collective effects can be suppressed by changing the cavity damping and detuning.

Stationary lineshape of a two-level atom in a narrow-bandwidth squeezed vacuum

The stationary lineshape of a two-level atom driven by low-intensity narrow-bandwidth squeezed light is shown to exhibit significant differences in behaviour compared to the lineshape for broadband squeezed light. We find that for narrow-bandwidth squeezed light the lineshape is composed of two Lorentzians whose amplitudes depend on the squeezing correlations. Moreover, one of the Lorentzians has a negative weight which leads to narrowing of the line. These features are absent in the broadband case, where the stationary lineshape is the same as for a thermal field.