12 research outputs found
Quantum statistical measurements of an atom laser beam
We describe a scheme, operating in a manner analogous to a reversed Raman
output coupler, for measuring the phase-sensitive quadrature statistics of an
atom laser beam. This scheme allows for the transferral of the atomic field
statistics to an optical field, for which the quantum statistics may then be
measured using the well-developed technology of optical homodyne measurement.Comment: 4 pages, 2 fugure
A multi-mode model of a non-classical atom laser produced by outcoupling from a Bose-Einstein condensate with squeezed light
We examine the properties of an atom laser produced by outcoupling from a
Bose-Einstein condensate with squeezed light. We introduce a method which
allows us to model the full multimode dynamics of the squeezed optical field
and the outcoupled atoms. We show that for experimentally reasonable parameters
that the quantum statistics of the optical field are almost completely
transferred to the outcoupled atoms, and investigate the robustness to the
coupling strength and the two-photon detuning.Comment: 6 pages, 4 figures. Accepted to Laser physics letter
The stability of a continuously pumped atom laser
In this thesis we theoretically model a continuously pumped atom laser using the mean-field description. We find that it is unstable below a critical scattering length. Above the critical scattering length, the atom laser reaches a steady state, the stability of which increases with pumping. Below this limit the atom laser does not reach a steady state. We show that this instability results from the competition between gain and loss for the excited states of the lasing mode, and show how the nonlinearities stabilise the system. The requirement for a minimum scattering length will determine a fundamental limit for the linewidth of an atom laser beam. We propose a method of stabilising the system below the critical scattering length and investigate its effectiveness
Stability of continuously pumped atom lasers
A multimode model of a continuously pumped atom laser is shown to be unstable below a critical value of the scattering length. Above the critical scattering length, the atom laser reaches a steady state, the stability of which increases with pumping. Below this limit the laser does not reach a steady state. This instability results from the competition between gain and loss for the excited states of the lasing mode. It will determine a fundamental limit for the linewidth of an atom laser beam
Control of an atom laser using feedback
A generalised method of using feedback to control Bose-Einstein condensates
is introduced. The condensates are modelled by the Gross-Pitaevskii equation,
so only semiclassical fluctations can be suppressed, and back-action from the
measurement is ignored. We show that for any available control, a feedback
scheme can be found to reduce the energy while the appropriate moment is still
dynamic. We demonstrate these schemes by considering a condensate trapped in a
harmonic potential that can be modulated in strength and position. The
formalism of our feedback scheme also allows the inclusion of certain types of
non-linear controls. If the non-linear interaction between the atoms can be
controlled via a Feshbach resonance, we show that the feedback process can
operate with a much higher efficiency.Comment: 6 pages, 7 figure
Mode Selectivity and Stability of Continuously Pumped Atom Lasers
A semiclassical, multimode model of a continuously pumped atom laser is presented. For a spatially independent coupling process it is found that the system is unstable below a critical scattering length. As large atomic interactions will increase the phase diffusion of the lasing mode, it is desirable to obtain a stable atom laser with low nonlinearity. It is shown that spatially dependent pumping stabilizes the atom laser to a finite number of modes, and can induce single-mode operation
Non-destructive, dynamic detectors for Bose-Einstein condensates
We propose and analyze a series of non-destructive, dynamic detectors for
Bose-Einstein condensates based on photo-detectors operating at the shot noise
limit. These detectors are compatible with real time feedback to the
condensate. The signal to noise ratio of different detection schemes are
compared subject to the constraint of minimal heating due to photon absorption
and spontaneous emission. This constraint leads to different optimal operating
points for interference-based schemes. We find the somewhat counter-intuitive
result that without the presence of a cavity, interferometry causes as much
destruction as absorption for optically thin clouds. For optically thick
clouds, cavity-free interferometry is superior to absorption, but it still
cannot be made arbitrarily non-destructive . We propose a cavity-based
measurement of atomic density which can in principle be made arbitrarily
non-destructive for a given signal to noise ratio
Stationary quantum statistics of a non-Markovian atom laser
We present a steady state analysis of a quantum-mechanical model of an atom
laser. A single-mode atomic trap coupled to a continuum of external modes is
driven by a saturable pumping mechanism. In the dilute flux regime, where
atom-atom interactions are negligible in the output, we have been able to solve
this model without making the Born-Markov approximation. The more exact
treatment has a different effective damping rate and occupation of the lasing
mode, as well as a shifted frequency and linewidth of the output. We examine
gravitational damping numerically, finding linewidths and frequency shifts for
a range of pumping rates. We treat mean field damping analytically, finding a
memory function for the Thomas-Fermi regime. The occupation and linewidth are
found to have a nonlinear scaling behavior which has implications for the
stability of atom lasers.Comment: 12 pages, 2 figures, submitted to PR