Andrew Manning

Direct measurement of long-range third-order coherence in Bose-Einstein condensates.

Correlation of arrival times of metastable helium atoms is consistent with long-range coherence to higher orders. A major advance in understanding the behavior of light was to describe the coherence of a light source by using correlation functions that define the spatio-temporal relationship between pairs and larger groups of photons. Correlations are also a fundamental property of matter. We performed simultaneous measurement of the second- and third-order correlation functions for atoms. Atom bunching in the arrival time for pairs and triplets of thermal atoms just above the Bose-Einstein condensation (BEC) temperature was observed. At lower temperatures, we demonstrated conclusively the long-range coherence of the BEC for correlation functions to third order, which supports the prediction that like coherent light, a BEC possesses long-range coherence to all orders.

Ideal n -body correlations with massive particles

Quantum coherence has been extensively investigated in quantum optics, but less is known about its properties in massive particles. The higher-order many-body correlation functions have now been measured in an atom optics experiment, validating Wick’s theorem.

Observation of atomic speckle and Hanbury Brown–Twiss correlations in guided matter waves

Speckle patterns produced by multiple independent light sources are a manifestation of the coherence of the light field. Second-order correlations exhibited in phenomena such as photon bunching, termed the Hanbury Brown-Twiss effect, are a measure of quantum coherence. Here we observe for the first time atomic speckle produced by atoms transmitted through an optical waveguide, and link this to second-order correlations of the atomic arrival times. We show that multimode matter-wave guiding, which is directly analogous to multimode light guiding in optical fibres, produces a speckled transverse intensity pattern and atom bunching, whereas single-mode guiding of atoms that are output-coupled from a Bose-Einstein condensate yields a smooth intensity profile and a second-order correlation value of unity. Both first- and second-order coherence are important for applications requiring a fully coherent atomic source, such as squeezed-atom interferometry.

Characterizing Atom Sources with Quantum Coherence

Exciting work is being done in quantum information theory and the detection of low light levels.

Observation of the first excited transverse mode in guided matter waves

In direct analogy to the textbook example of light guided in a few-mode fiber (FMF), we report the observation of the first excited mode of an optically guided atomic beam. We selectively excite the atomic analog of the LP₀₁ optical mode by controlling the energy distribution of ultracold atoms loaded into the guide, resulting in a modal structure dominated by a 47(2)% population in the first excited transverse mode. The ability to guide lower-order modes has been essential to demonstrating optical effects such as multimode interferometry, slow light, and entanglement, and an atomic analog to a FMF may lead to similarly useful applications.

Third-order spatial correlations for ultracold atoms

We present here the first measurement of the third-order spatial correlation function for atoms, made possible by cooling a metastable helium cloud to create an ultracold thermal ensemble just above the Bose-Einstein condensation point. The resulting large correlation length well exceeds the spatial resolution limit of the single-atom detection system, and enables extension of our earlier temporal measurements to evaluate the third-order correlation function in the spatial plane of the detector. The enhancement of the spatial third-order correlation function above a value of unity demonstrates the presence of spatial three-atom bunching, as expected for an incoherent source.

Using Correlation Measurements to Probe Amplified Matter Waves and Bose-Einstein Condensate Formation

Using single atom detection offered by metastable helium atoms (He*), we are able to measure correlations between atoms. With this we have demonstrated second-order coherence of matter waves that emerge from amplified four-wave mixing (FWM). Our results provide the first second-order, or quantum test of coherence for amplified matter waves. Using the same detection scheme, we have investigated the onset of coherence during the formation of a Bose-Einstein condensate (BEC), attempting to reveal how the long-range order of a BEC is established. Our initial results support the existence of quasi-condensates.

Higher order correlations in ultracold quantum gases

One of the seminal advances in quantum optics was the understanding that a quantised description of ensembles of photons is best characterised by correlation functions. Correlations are also a fundamental property of matter waves, and the single wavefunction that describes a Bose-Einstein condensate (BEC) is in principle characterised by long range coherence to all orders (i.e. a universal correlation value of unity). Here we measure the higher order correlation properties of ultra-cold matter waves and use them to probe the coherence of the gas.

Atom bunching with ultracold metastable helium

We measure the second order correlation function for metastable helium atoms released from an ultracold trap source and observe bunching between thermal atoms. When correlations between Bose-Einstein condensed atoms are measured no bunching is observed.