We present an experimental study on the continuous atom laser. The experiments show that a high field seeking state atom laser with stable flux can be formed by increasing the strength of outcoupling before large density fluctuations appear. It is easy to obtain a long length or high speed output with this kind of atom laser.
If atom lasers are to transform many fields of physics, as well as find applications in industry, the most essential development needed is increased atom flux. In this thesis we report on the experimental observation of fundamental limits on the flux of continuous atom lasers. The flux produced by the commonly used radio frequency outcoupler, can not be arbitrarily increased by increasing the strength of the outcoupling. Above a critical Rabi frequency, the atom laser shows large classical density fluctuations, due to coupling between the multiple Zeeman states. In our system this critical Rabi frequency is about 1 kHz. Futhermore, at large coupling strengths (> 4 kHz for our experimetnal parameters), the continuous atom laser output completely switches off, as a result of the atoms remaining trapped in a bound state. In addition to the investigations of the radio frequency outcoupler, we have demonstrated the first continuous Raman outcoupled atom laser. Preliminary data indicates that the Raman outcoupler will be flux limited in a similar way to the radio frequency outcoupler.
We present experimental results demonstrating that the flux of a continuous atom laser beam cannot be arbitrarily increased by increasing the strength of output coupling. We find that the continuous atom laser has large density fluctuations when the Rabi frequency becomes greater than the radial trapping frequency, due to the output coupling populating all accessible Zeeman states. In addition, we find that a state-changing output coupler for a continuous atom laser switches off as the output-coupling strength, parametrized in general by the Rabi frequency, is increased above a critical value. The numerical solution of a one-dimensional five-state Gross-Pitaevskii model for the atom laser is in good qualitative agreement with the experiment.
By direct comparison between experiment and theory with no adjustable parameters, we show how the classical fluctuations on a multistate atom laser beam increase with increasing flux. The fluctuations are inherent to state changing out coupling, rf, Raman, or otherwise and are likely to be present in all atom lasers, pulsed or continuous, that employ such out coupling. If not removed or avoided, these classical fluctuations will prevent shot noise limited measurement employing atom lasers of this kind.
An ideal atom laser would produce an atomic beam with highly stable flux and energy. In practice, the stability is likely to be limited by technical noise and nonlinear dynamical effects. We investigate the dynamics of an atom laser using a comprehensive one-dimensional, mean-field numerical model. We fully model the output beam and experimentally important physics such as three-body recombination. We find that at high-pump rates, the latter plays a role in suppressing the high-frequency dynamics, which would otherwise limit the stability of the output beam.