Atomic coherence and novel laser systems

Chang Zeng-Guang, Jiancheng Liu, Yan Ke-zhu +1 more

In this paper we study the dependence of steady-state gain of a closed V-type atomic system and a closed Λ-type atomic system of lasing without inversion on the detuning of the coherence lasers under the condition that the corresponding parameters of the two atomic systems are equal. By the way of numerical simulation and comparison, we find that the curves of probe-laser gain of the two atomic systems versus the detuning of probe-laser have similar shapes but their values are different, which are related to the characteristics of atomic coherence and population distribution of the two atomic systems directly. In addition, we find that the driving laser deturning and the additional atomic coherence caused by spontaneously generated coherence can exert a great influence upon the probe-laser gain.

Dipankar Bhattacharyya, Jyotirmoy Guha

K. Khanbekyan, G. Bevilacqua, Alen Khanbekyan +3 more

We consider an atomic dual Λ-system under two-laser-field excitation to investigate the possibility of indirect coherent transfer of population between atomic ground states through an excited state. The atomic system, namely atomic vapor in a buffered cell, is excited by a frequency modulated pump laser and probed by a low-power cw laser. The study can be helpful to understand the mechanisms of collisional coherent transfer of population and other related phenomena and applications.

Luigi A. Lugiato, Franco Prati, Massimo Brambilla

Howard M. Wiseman, John A. Vaccaro

A laser, be it an optical laser or an atom laser, is an open quantum system that produces a coherent beam of bosons (photons or atoms, respectively). Far above threshold, the stationary state ${\ensuremath{\rho}}_{\mathrm{ss}}$ of the laser mode is a mixture of coherent-field states with random phase, or, equivalently, a Poissonian mixture of number states. This paper answers the question: can descriptions such as these, of ${\ensuremath{\rho}}_{\mathrm{ss}}$ as a stationary ensemble of pure states, be physically realized? Here physical realization is as defined previously by us [H. M. Wiseman and J. A. Vaccaro, Phys. Lett. A 250, 241 (1998)]: an ensemble of pure states for a particular system can be physically realized if, without changing the dynamics of the system, an experimenter can (in principle) know at any time that the system is in one of the pure-state members of the ensemble. Such knowledge can be obtained by monitoring the baths to which the system is coupled, provided that coupling is describable by a Markovian master equation. Using a family of master equations for the (atom) laser, we solve for the physically realizable (PR) ensembles. We find that for any finite self-energy $\ensuremath{\chi}$ of the bosons in the laser mode, the coherent-state ensemble is not PR; the closest one can come to it is an ensemble of squeezed states. This is particularly relevant for atom lasers, where the self-energy arising from elastic collisions is expected to be large. By contrast, the number-state ensemble is always PR. As the self-energy $\ensuremath{\chi}$ increases, the states in the PR ensemble closest to the coherent-state ensemble become increasingly squeezed. Nevertheless, there are values of $\ensuremath{\chi}$ for which states with well-defined coherent amplitudes are PR, even though the atom laser is not coherent (in the sense of having a Bose-degenerate output). We discuss the physical significance of this anomaly in terms of conditional coherence (and hence conditional Bose degeneracy).

Howard M. Wiseman, John A. Vaccaro