Atoms in the vapor phase can show extreme coherence (up to hours), and are used in important technologies including atomic clocks and ultra-sensitive magnetometers. Here we study their quantum mechanical properties, and their use in advanced sensors.

A spinor Bose-Einstein condesate is a new phase of matter that shows both magnetic and superfluid behaviour. We use rubidium-87 and non-destructive probing to study the quantum properties of this exotic material.

We trap individual 87Rb atoms in a wavelength-scale optical trap in a Maltese-Cross geometry consisting of 4 high numerical aperture lenses (Fig. (a)). It allows multiple optical accesses for efficient light-matter interactions and large collection efficiencies in free space. Single-atoms are obtained via light-assisted collisions from a magneto-optical trap (MOT). The emitted resonance fluorescence is characterized by a telegraph signal from which the second-order correlation function can be measured (Fig. (c)) showing the expected anti-bunching for a single quantum emitter.

We also generate atom-resonant narrowband photon-pairs by cavity-enhanced spontaneous parametric down-conversion (Fig. (e)). Both idler and signal photon frequencies can be tuned independently on the D1-line of 87Rb.

The ongoing projects are:

• Quantifying the absorption of single-photon power levels by a single-atom using quantum jump photodetections (d).
• 3D thermometry of a single-atom using a single-photon sensitive camera (b).
• Study of unconventional quantum correlations of a single-atom in a pump-probe scheme.
• Atom-induced phase shift in an atomic vapor cell using autoheterodyne characterization of photon pairs.

The aim of that project is to explore light-matter interactions at its most fundamental level.

Current members: Laura Zarraoa, Tomáš Lamich, Yanan Li, Romain Veyron.

We generate atom-resonant, narrow-bandwidth quantum states of light, for example polarization squeezed states and entangled photon pairs that are resonant to atomic resonance lines. We then interact these states with atomic ensembles. This allows us to study the interaction of atoms and light at the most fundamental, fully-quantum mechanical level. For example, we study how non-classical light can be used to make more sensitive atomic instruments, and how atoms can be used as optical elements to shape quantum properties of photons.