Quantum Atom Optics

Permanent staff: Marc Cheneau, Denis Boiron, Christoph Westbrook

Postdocs: Maxime Perrier, Alexandre Dareau

PhD. Students: Ziyad Amodjee

We have been using condensates of metastable helium atoms (in the 2³S₁ state often referred to as He*) to revisit several well known situations in quantum optics. Perhaps the most important feature of He* is its 20 eV internal energy. This energy causes electron emission upon contact with a surface enables the use electron multipliers and micro-channel plates (MCP) to electronically detect the atoms. The MCP detector together with a delay line anode allows us to reconstruct the three dimensional momentum vectors of single atoms. With this information we can reconstruct momentum distributions and the correlations of the atom clouds released from a trap.

We have used a variant of the Hong Ou Mandel setup described below to realize a two-particle interferometer with four input and four output ports as shown in the figure. The source generates atom pairs in a superposition of different momentum states:

|ψ) ~ |p,-p) + |p',-p').

When such a state is injected into the atom interferometer, the probability of detecting an atom at each output port is 1/4, independent of any interferometer phase. The correlations between the different output ports however do vary as a function of the relative phase of the two closed circuits (red and blue in the figure). We have demonstrated this effect in our apparatus. An improved version of this experiment can lead to the violation of a Bell inequality involving the motional degrees of freedom of freely falling massive particles.

The Hong Ou Mandel (HOM) effect is a remarkable illustration of 2 particle interference. Two identical particles arrive at the input ports of a beam splitter. If they are perfectly overlapped, they never exit in opposite output ports. The effect is well known for photons. We have recently performed the analogous experiment for atoms.