Atom detection and counting in ultracold gases using photoionisation and ion detection

Tom Campey (2009). Atom detection and counting in ultracold gases using photoionisation and ion detection PhD Thesis, School of Physical Sciences, The University of Queensland.

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Author Tom Campey
Thesis Title Atom detection and counting in ultracold gases using photoionisation and ion detection
School, Centre or Institute School of Physical Sciences
Institution The University of Queensland
Publication date 2009-01
Thesis type PhD Thesis
Supervisor Dr Halina Rubinsztein-Dunlop
Dr Chris Vale
Total pages 290
Total colour pages 46
Total black and white pages 244
Subjects 240000 Physical Sciences
Formatted abstract
In recent years there has been increasing interest in quantum atom optics, in which the discrete
nature of atoms plays an important role. As such, the ability to resolve atoms at the single
atom level has become important.
This thesis investigates detecting atoms using photoionisation and ion detection. This
method is applicable to all atoms in common use in atom optics experiments, enables their
detection with high e±ciency, allows atom counting with sub-Poissonian resolution (¾N < pN)
and is applicable for large atom numbers (up to » 105). Two approaches towards atom detection
via photoionisation and ion detection are examined, di®ering in the rate of photoionisation. Fast
photoionisation of individual atoms can be used for detecting a series of single atoms, such as
might be produced with an atom laser. Slow ionisation is required for counting large numbers
of atoms contained in a single region, due to the necessity of being able to resolve the individual
ions with the ion detector. The application of these methods to 87Rb is examined, although
they can be adapted to other atoms.
The scheme for quickly detecting single atoms uses STImulated Raman Adiabatic Passage
(STIRAP) to excite 87Rb atoms to the 5D5=2 level followed by ionisation from this level using
a Nd:YAG laser pulse. Simulations and experiments were carried out and used to predict that
excitation to the 5D5=2 level can be achieved with close to 100% e±ciency, and to show the
experimental parameters required. The photoionisation cross-section of 87Rb in the 5D5=2 state
using 1064 nm light was measured in order to predict the photoionisation e±ciency that may
be achieved, which was found to approach 100%.
The scheme for atom counting uses 2£778 nm photon excitation to raise atoms to the
5D5=2 state followed by ionisation from this state using a cw Nd:YAG laser. The statistics
of atom counting are examined and used to ¯nd the counting accuracy as a function of the
detection e±ciency and its uncertainty. For a precisely calibrated detector, sub-Poissonian
counting is possible for detection e±ciencies greater than 50%. The e®ect of losses and the use
of the scheme for measuring number squeezing are examined. Achieving low count uncertainties
requires measuring the ion detection e±ciency to high accuracy. A method for doing this is
proposed and analysed, and experiments were carried out to measure the ion detection e±ciency
of an ion detector in a mock experimental setup. A detailed scheme is proposed and analysed for measuring number di®erence squeezing in
a RF induced double well potential using atom counting via photoionisation and ion detection.
Simulations of the double well potential were performed to show how even splitting can be
achieved and the degree of squeezing expected to occur. A design for an experimental setup is
described and analysed in detail, in order to show the accuracy with which number di®erence
squeezing can be measured.
Keyword atom optics, BEC, atom counting, number squeezing, photoionisation, ion detection
Additional Notes 63, 67-75, 79-86, 88-89, 97, 101, 104, 106, 108, 128, 132-133, 135-136, 143-146, 148-149, 152-153, 160-163, 174-175, 177-178

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Created: Mon, 12 Jan 2009, 05:44:38 EST by Mr Tom Campey on behalf of Library - Information Access Service