P. Zoller

Quantum nondemolition measurement of transverse atomic position in Kapitza-Dirac atomic beam scattering

It is demonstrated that one can measure the distribution of the transverse position of an atom crossing one or more optical cavities by monitoring the phase of the standing wave fields in the cavities. For the atom-field interaction the Kapitza-Dirac regime is assumed; it is shown that in this regime the method represents a quantum nondemolition measurement of the atomic position. On the other hand it can be applied to prepare narrow distributions of the transverse atomic position. In order to show this, a numerical simulation is performed, which illustrates the collapse of a broad initial Gaussian wavepacket, which can be coherent or incoherent, to a distribution with narrow peaks. Preparing the cavity fields in a squeezed state, one can greatly enhance the impact of the cavity field measurements on the atomic density matrix.

Quantum Noise Reduction in Raman Lasers

We demonstrate that the intensity fluctuations of a laser with a Raman gain medium, described by a large number of independent 3-level atoms, can drop well below the shot noise level. In the limit of a good cavity, where one can adiabatically eliminate the atoms, we find an optimum Mandel Q parameter of Q ≈ −1/2 over a large range of parameters, when the laser is operated well above threshold. This leads to a strong suppression of the low-frequency quantum fluctuations in the laser output. In addition we find that due to suppression of spontaneous emission into the lasing mode, the spectral linewidth of the emitted light can be reduced below the Schawlow-Townes limit by more than one order of magnitude.

Optical bistability from three-level atoms

A novel mechanism is proposed for optical bistability utilizing the population trapping which may occur in a coherent superposition of sublevels in a three-level system. The resulting bistability does not require atomic saturation and is insensitive to Doppler and laser bandwidth effects.

Cooling of a trapped ion coupled strongly to a quantized cavity mode

Abstract The interaction of a trapped two-level ion, confined in a harmonic potential, with a quantized cavity mode of the radiation field is studied theoretically. The ion is considered to be spatially localized on the scale of the optical wavelength (Lamb-Dicke limit), and the ion-cavity-mode coupling is assumed to be larger than or comparable to the spontaneous emission and cavity-mode loss rates. With broadband thermal light driving the cavity mode, we show that the cooling rates and final temperatures of the trapped-ion motion reflect the Jaynes-Cummings energy spectrum of the strongly-coupled ion-cavity system.

Localization of atoms in light fields: Optical molasses, adiabatic compression and squeezing

We present a theoretical study of the localization1 of atoms with an angular momentumJg=3 toJe=4 transition (e.g., chromium atoms) in quantized optical molasses created by two counterpropagating linearly polarized laser beams. We study the localization as a function of the potential depth, the angle between the polarizations and the interaction time with the molasses in the low-intensity limit, and discuss the possibility of adiabatic compression and squeezing of the atomic distribution.

Inhibition of Quantum Tunneling of an Atom due to the Continuous Observation of Light Scattering

We propose a scheme for observing the inhibition of quantum tunneling of an atom trapped in a double-well potential due to continuous observation of light scattering. A resonant laser beam is focused in one of the wells. Continuous measurement of the position of the atom is performed by observing the presence (or absence) of photons emitted by the atom. An interpretation in terms of a quantum Zeno effect is given.

Phase shifts and intensity dependence in frequency-modulation spectroscopy

We discuss experimental observations of an induced phase shift of the rf signal produced in frequency-modulated saturated-absorption measurements under the conditions of large probe-beam intensities. This phase shift can be understood in terms of the phase difference between the phase modulation of the optical driving field and the steady-state macroscopic polarization of the medium. We also present theoretically calculated spectra that are based on the optical Bloch equations and that are in excellent agreement with the experimental results.

Deflection of Atoms by Circularly Polarized Light Beams in Triple Laue Configuration

Abstract A new type of atomic interferometer is discussed, in which atoms with two ground-state Zeeman sub-levels m = ± 1, and an excited state with m = 0, pass through three laser interaction zones—each comprising two counter-propagating waves of opposite circular polarization with a large detuning from resonance. By means of Raman-type transitions between the two ground-state levels, which convey a recoil of two photon momenta, the atomic wave function is split up into two coherent spatially separated branches, and subsequently recombined. In this system, conservation of energy and momentum leads to a strong correlation between the external centre of mass motion and internal magnetic degrees of freedom. As a consequence, the paths within the interferometer are tagged by the internal quantum number m. As an example, we calculate the position and momentum distribution function of a helium atom on its way through the interferometer.

Laser-induced excitation of electronic rydberg wave packets

Abstract We give a qualitative review of theoretical ideas and experimental work on laser-induced excitation of atomic Rydberg wave packets. Studying the motion of Rydberg wave packets with the help of short or intense laser pulses provides a bridge between quantum mechanics and the classical concept of the trajectory of an electron and corresponds to the real-time observation of atomic dynamics.

Intensity dependent phase shifts in frequency modulation spectroscopy

We discuss experimental observations of an induced phase shift of the rf signal produced in FM saturated absorption measurements under the conditions of large probe beam intensities. This phase shift can be understood in terms of the phase difference between the phase modulation of the optical driving field and the steady state macroscopic polarization of the medium. This phase difference is relatively insensitive to detuning of the laser from the atomic resonance, such that essentially the same spectrum can be observed by changing the rf detection phase. We also present theoretically calculated spectra which are based on the optical Bloch equations, and which are in excellent agreement with the experimental results.