Photoionisation detection of single 87Rb-atoms using channel electron multipliers

Fast and efficient detection of single atoms is a universal
requirement concerning modern experiments in atom physics, quantum
optics, and precision spectroscopy. In particular for future
quantum information and quantum communication technologies, the
efficient readout of qubit states encoded in single atoms or ions
is an elementary prerequisite. The rapid development in the eld of
quantum optics and atom optics in the recent years has enabled to
prepare individual atoms as quantum memories or arrays of single
atoms as qubit registers. With such systems, the implementation of
quantum computation or quantum communication protocols seems
feasible. This thesis describes a novel detection scheme which
enables fast and efficient state analysis of single neutral atoms.
The detection scheme is based on photoionisation and consists of
two parts: the hyperfine-state selective photoionisation of single
atoms and the registration of the generated photoion-electron pairs
via two channel electron multipliers (CEMs). In this work, both
parts were investigated in two separate experiments. For the first
step, a photoionisation probability of p_ion = 0.991 within an
ionisation time of t_ion = 386 ns is achieved for a single
87Rb-atom in an optical dipole trap. For the second part, a compact
detection system for the ionisation fragments was developed
consisting of two opposing CEM detectors. Measurements show that
single neutral atoms can be detected via their ionisation fragments
with a detection efficiency of eta_atom = 0.991 within a detection
time of t_det = 415.5 ns. In a future combined setup, this will
allow the state-selective readout of optically trapped, single
neutral 87Rb-atoms via photoionisation detection with an estimated
detection efficiency eta = 0.982 and a detection time of t_tot =
802 ns. Although initially developed for single 87Rb-atoms, the
concept of photoionisation detection is in principle generally
applicable to any atomic or molecular species. As efficient readout
unit for single atoms or even ions, it might represent a
considerable alternative to conventional detection methods due to
the high optical access and the large sensitive volume of the CEM
detection system. Additionally, its spatial selectivity makes it
particularly suited for the readout of single atomic qubit sites in
arrays of neutral atoms as required in future applications such as
the quantum-repeater or quantum computation with neutral atoms. The
obtained high detection efficiency eta and fast detection time
t_tot of the new detection method fullfill the demanding detector
requirements for a future loophole-free test of Bell's inequality
under strict Einstein locality conditions using two optically
trapped, entangled 87Rb-atoms at remote locations. In such a
configuration, the locality and the detection loophole can be
simultaneously closed in one experiment.