J. Hald

Entanglement transfer from light to atoms

Abstract We describe an approach to mapping of a quantum polarization state of free propagating light on a collective spin of an atomic ensemble. Recent experimental results on generation of a macroscopic spin squeezed ensemble of cold atoms via interaction with squeezed light are analysed in detail.

Mapping a quantum state of light onto atoms

We derive a theory for mapping a quantum state of nonclassical light onto a collective, excited atomic state via complete absorption of the light. We allow for an arbitrary polarization-squeezed state of light and an arbitrary spin of the atomic ground state. The present derivation thereby generalizes the results of Kuzmich et al. We compare the theory to the recently published experimental results on atomic spin squeezing.

Squeezing with for atomic physics and spectroscopy

Parametric downconversion in media has, so far, proved to be the most effective way of generating squeezed light. The development of frequency tunable sources of such non-classical light opens up novel possibilities in atomic physics and spectroscopy. A brief overview of the results in this area of quantum optics is given, and a new experiment aimed on subshot-noise measurement of atomic orientation is described. We report a preliminary 5 dB quantum noise reduction observed directly around the 917 nm Cs line. We introduce a figure of merit for the medium utilized for squeezed light generation in an optical parametric oscillator and evaluate some available nonlinear media from this perspective.

Quantum noise of cold atomic spins illuminated with non-classical light

Recent results and future perspectives in the field of interaction of cold atomic spins with non-classical light are reviewed. We describe how such light can be used for passive probing of the collective atomic spin and for generation of the non-classical correlations between the individual atomic spins.

Fundamental noise of an atomic spin measurement

The noise in spin measurements of an ensemble of cold trapped atoms is investigated by means of a polarization interferometer. Limiting noise sources of such a measurement are defined. Noise reduction via employment of non-classical states of light is discussed. The contribution of spin noise to the experimental uncertainty is analysed.

Spectroscopy on a modulated magneto-optical trap.

We demonstrate a new type of high-resolution two-photon frequency modulation (FM) spectroscopy with cold atoms in a magneto-optical trap. Instead of modulating the probe as in ordinary FM spectroscopy, we modulate the trap itself by FM of the trapping beams. We present theoretical as well as experimental results for both absorption and polarization rotation spectroscopy. Finally, we demonstrate two-photon FM spectroscopy, using the intrinsic phase noise of the trapping diode lasers.

From Entangled Photons to Entangled Atoms

Mapping quantum states of light on atoms opens up the possibilities for quantum information storage,teleportation of atoms, and quantum computing. We describe a novel approach to such mapping based on creation of pairwise atomic entanglement in a large macroscopic atomic ensemble. As opposed to the previously demonstrated methods involving strong coupling of a single two-level atom to a cavity field, our strategy utilizes a large sample of three- and more level atoms weakly interacting with a free propagating qua ntum field. Besides practical advantages offered by the new method (no high-Q cavities involved), it also allows for production of a large number of correlated atoms which can be spatially separated and trapped in magnetic or magneto-optical traps.

Spectroscopy with non-classical light and non-classical atoms

In the last few years a new field, atomic physics and spectroscopy with non-classical, squeezed light, has emerged. The frequency tunable sources of such light utilize tunable lasers and frequency doubling and/or parametric down conversion to create quantum correlations between frequency components of radiation [1–5]. The non-classical features of light result in manifestly non-classical features of spectral lines, namely in the rate of atomic processes, in the line shapes, and in the level of quantum noise in atomic spectroscopy. Moreover, the non-classical features of light can be transferred onto atoms leading to their manifestly non-classical behavior. We will briefly review some theoretical proposals and experimental results in this new area.