Cold atom physics using ultra-thin optical fibres

We have developed an atom-guiding technique that loads $3\times 10^6$ cold rubidium atoms into hollow-core optical fibre, an order-of-magnitude larger than previously reported results. This achievement was guided by a physically realistic simulation that led to an experimental loading efficiency of $3\%$ , giving a peak optical depth of over $600$ . The loading efficiency was limited only by the geometric overlap of the atom cloud an an optical guide beam, and we have identified techniques that would allows us to exceed this limit. We also present a fast and minimally destructive probing technique that enables us to follow the dynamics of the cold atom cloud as it falls into the fibre - this strengthens the confidence in our detailed model, and enables adjustment of the experiment into an optimal state. We are able to observe the effect of light-assisted cold atom collisions as well as background gas collisions in the fibre. The combination of these observations and physical understanding from the simulation allows us to estimate the ultimate limits to loading cold atoms into hollow-core fibres.We have developed an atom-guiding technique that loads $3\times 10^6$ cold rubidium atoms into hollow-core optical fibre, an order-of-magnitude larger than previously reported results. This achievement was guided by a physically realistic simulation that led to an experimental loading efficiency of $3\%$, giving a peak optical depth of over $600$. The loading efficiency was limited only by the geometric overlap of the atom cloud an an optical guide beam, and we have identified techniques that would allows us to exceed this limit. We also present a fast and minimally destructive probing technique that enables us to follow the dynamics of the cold atom cloud as it falls into the fibre - this strengthens the confidence in our detailed model, and enables adjustment of the experiment into an optimal state. We are able to observe the effect of light-assisted cold atom collisions as well as background gas collisions in the fibre. The combination of these observations and physical understanding from the simulation allows us to estimate the ultimate limits to loading cold atoms into hollow-core fibres.

Feb 15, 20181 citation

Cold Atom Physics: Trapping Methods And Detection Schemes.

Thejesh Bandi

"The work presented in this thesis is concerned with the manipulation of laser- cooled rubidium atoms and the detection of small numbers of cold atoms using very sensitive light detectors. Laser-cooled atoms are atoms that have been slowed to very low velocities, corresponding to temperatures of the order of 100 //K, and they can be trapped in magnetic and/or optical traps. The advantage of using cold atoms for experiments in atomic and quantum physics stems from the fact that these atoms are effectively confined within a region of space and this provides longer interaction and observation times compared to atoms at room temperature. Hence, it is possible to explore and observe a number of effects that would otherwise be extremely challenging. The achievement of laser cooling and trapping of neutral atoms was a major breakthrough in the mid 80’s and has resulted in significant advances being made in modern spectroscopy, the realisation of Bose-Einstein condensation, atomic clocks, and quantum information technologies amongst others. In particular, the work focuses on two theoretical proposals for developing microtraps for cold rubidium atoms involving (i) ultrathin optical fibres and (ii) wavelength sized apertures in thin films. In addition, a number of experimental techniques are explored with emphasis on the detection of small numbers of atoms near ultrathin optical fibres using both avalanche photodiodes and single photon detectors. A study on the interactions between atoms and photons is crucial for a full understanding of quantum mechanical processes at the few atom scale and detection schemes sensitive to very low levels of fluorescence from the laser-cooled atoms are vital for attaining this goal. Finally, an experimental study on the design and fabrication of arrays of silica microdisks, that could be used for facilitating interactions between cold atoms and photons, is presented.""The work presented in this thesis is concerned with the manipulation of laser- cooled rubidium atoms and the detection of small numbers of cold atoms using very sensitive light detectors. Laser-cooled atoms are atoms that have been slowed to very low velocities, corresponding to temperatures of the order of 100 //K, and they can be trapped in magnetic and/or optical traps. The advantage of using cold atoms for experiments in atomic and quantum physics stems from the fact that these atoms are effectively confined within a region of space and this provides longer interaction and observation times compared to atoms at room temperature. Hence, it is possible to explore and observe a number of effects that would otherwise be extremely challenging. The achievement of laser cooling and trapping of neutral atoms was a major breakthrough in the mid 80’s and has resulted in significant advances being made in modern spectroscopy, the realisation of Bose-Einstein condensation, atomic clocks, and quantum information technologies amongst others. In particular, the work focuses on two theoretical proposals for developing microtraps for cold rubidium atoms involving (i) ultrathin optical fibres and (ii) wavelength sized apertures in thin films. In addition, a number of experimental techniques are explored with emphasis on the detection of small numbers of atoms near ultrathin optical fibres using both avalanche photodiodes and single photon detectors. A study on the interactions between atoms and photons is crucial for a full understanding of quantum mechanical processes at the few atom scale and detection schemes sensitive to very low levels of fluorescence from the laser-cooled atoms are vital for attaining this goal. Finally, an experimental study on the design and fabrication of arrays of silica microdisks, that could be used for facilitating interactions between cold atoms and photons, is presented."

SwordJan 1, 20080 citations

We have developed an atom-guiding technique that loads

3\times 10^6

cold rubidium atoms into hollow-core optical fibre, an order-of-magnitude larger than previously reported results. This achievement was guided by a physically realistic simulation that led to an experimental loading efficiency of

3\%

, giving a peak optical depth of over

600

. The loading efficiency was limited only by the geometric overlap of the atom cloud an an optical guide beam, and we have identified techniques that would allows us to exceed this limit. We also present a fast and minimally destructive probing technique that enables us to follow the dynamics of the cold atom cloud as it falls into the fibre - this strengthens the confidence in our detailed model, and enables adjustment of the experiment into an optimal state. We are able to observe the effect of light-assisted cold atom collisions as well as background gas collisions in the fibre. The combination of these observations and physical understanding from the simulation allows us to estimate the ultimate limits to loading cold atoms into hollow-core fibres.