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Quantum Atom Optics

Quantum Atom Optics

Permanent staff: Marc Cheneau, Denis Boiron, Christoph Westbrook

Postdocs: Alexandre Dareau

PhD. Students: Ziyad Amodjee, Quentin Marolleau

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.

Two-Particle Four-Mode Interferometer for Atoms, Dussarrat et al., Phys. Rev. Lett. 119, 1732 (2017), arXiv:1707.01279.

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.

Atomic Hong Ou Mandel effect, R. Lopes et al., Nature 520, 66 (2015)

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.

Results

 

Intensity fluctuations of superradiance

Second-order coherence of superradiance from a Bose-Einstein condensate, R. Lopes et al., Phys. Rev. A 90, 013615 (2014)

Fluorescence in standard (left) and supperadiance (right) cases
A BEC has sufficient optical thickness to act as a gain medium. When an elongated BEC is excited by a laser beam, the gain causes the spontaneous emission to be preferentially directed in the elongated direction, in so called endfire modes. Since it involves considerable gain and is highly directional, this emission resembles laser emission. We have measured the intensity (2nd order) correlation function of this emission and found that its statistical properties resemble those of a thermal source rather than those of a laser. We do this by observing the recoil of each atom undergoing a superradiant scattering process. Our detector allows us to construct the 2-atom correlation function and thereby infer the correlation function of the emitted light.

 

 

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