A relaxationless demonstration of the Quantum Zeno Paradox on an individual atom

The driven evolution of the spin of an individual atomic ion on the ground-state hyperfine resonance is impeded by the observation of the ion in one of the pertaining eigenstates. Detection of resonantly scattered light identifies the ion in its upper ``bright'' state. The lower ``dark'' ion state is free of relaxation and correlated with the detector by a null signal. Null events represent the straightforward demonstration of the quantum Zeno paradox. Also, high probability of survival was demonstrated when the ion, driven by a fractionated $\pi$ pulse, was probed {\em and monitored} during the intermissions of the drive, such that the ion's evolution is completely documented.Comment: 7 page

Quantum Coherence in a Single Ion due to strong Excitation of a metastable Transition

We consider pump-probe spectroscopy of a single ion with a highly metastable (probe) clock transition which is monitored by using the quantum jump technique. For a weak clock laser we obtain the well known Autler-Townes splitting. For stronger powers of the clock laser we demonstrate the transition to a new regime. The two regimes are distinguished by the transition of two complex eigenvalues to purely imaginary ones which can be very different in magnitude. The transition is controlled by the power of the clock laser. For pump on resonance we present simple analytical expressions for various linewidths and line positions.Comment: 6 figures. accepted for publication in PR

Lumino-réfrigération

In a paper of 1950, Alfred Kastler proposed cooling of vapours by resonant light via optical pumping of the orientational levels of angular momentum, and successive collisions. Optical pumping of the degrees of freedom of the translational momentum is also feasible. This phenomenon has been demonstrated with ions, even with a single ion, in an electrodynamic or electromagnetic trap. Optical cooling by Raman-like two-photon transitions seems to be capable of generating ultra-low temperature levels

ULTRA-SENSITIVE INTRACAVITY SPECTROSCOPY WITH MULTIMODE LASERS

Intracavity laser spectroscopy is characterized by extreme sensitivity of the emission spectrum to narrow spectral perturbations such as absorption, gain or light injection. Intracavity absorption spectra obey a modified Lambert-Beer law, where the length of the absorption cell is substituted by 1 = c.t, where c is the velocity of light, and t is the duration of the laser pulse. The time resolution of intracavity measurements is limited only by the sensitivity required for the detection of the extinction k, such that i ≥ 1/kc. With the minimum detectable absorption being 10-5 cm-1, e.g., the resolvable time is on the order of a microsecond. The ultimate sensitivity of intracavity spectroscopy with a cw laser is limited by one of two competing factors : spontaneous emission, and non-linear mode interaction, such as stimulated Brillouin scattering. Depending on laser parameters, minimum detectable extinction is in the range 10-7-10-12 cm-1. Non-linear mode interaction can also give rise to distortion of the line shapes observed with intracavity spectroscopy. High sensitivity along with time resolution opens a wide field of practical application for intracavity spectroscopy such as pollution detection, detection of forbidden and non-linear transitions, combustion and plasma diagnostics, and the study of kinetics of molecules and radicals

INTRACAVITY SPECTROSCOPY WITH MODULATED MULTIMODE LASERS

Successful application of intracavity spectroscopy is based on its high sensitivity and linearity. Unfortunately a number of experiments revealed recently nonlinearities of intracavity measurements appearing as complex asymmetric line shapes, sometimes with spectral condensation on one or both wings of an absorption line. We found that this spectral condensation is a result of phase lccking of mode groups near the absorption line. Mode locking originates from the interaction of the laser light with a strong inhomogeneously broadened absorber