Transport and charge sensing measurements on few electron quantum dots and going to ultra low electron temperatures

Setting up a new low temperature, low noise, and high sensitivity measurement
laboratory suitable for electron spin relaxation time
measurements, fabricating appropriate quantum dot samples and implementing the first experimental steps towards this goal was
the primary task of this thesis.\\
For this purpose we installed a new high power dilution refrigerator on a
vibration table including
appropriate
commercially available as well as adequate home made measurement electronics
fulfilling our demands. The system contains a two axis vector magnet reaching
fields up to 8 T and we
designed a sample holder enabling us to orientate samples in all possible x-
and y-
field directions.\\
New self made miniature cryogenic microwave filters combine the advantage of
powder filters with higher conductive silver epoxy and a special coil winding
technique that reduces parasitic capacitive coupling between windings. Together
with excellent heat sinking while mounted directly to the mixing chamber plate
of the refrigerator, they enable us
to decrease the electron temperature in samples down to ultra low values of
18 mK, providing very good conditions for investigating new physics in a
variety of fields with the ability to resolve very small
energy scales.\\
In terms of electron spin relaxation time measurements, we commenced the
fabrication of laterally gated semiconductor quantum dot devices. Transport
measurements show that our samples are very stable over large time scales and
measurement ranges and show high tunability to all relevant regimes. We can
completely empty the quantum dots of electrons and our design enables us to use
them as single as well as double quantum dots, suitable for investigations
regarding one or two qubit operations when talking in terms of quantum
computing.\\
With charge sensing techniques we could measure electron tunneling in real-time,
being able to tune the tunneling rates down to about 1 Hz, thus being
adequate for measuring long electron spin relaxation times in the range of seconds. In magnetic
field measurements we could resolve the Zeeman splitting between spin-up and
spin-down electrons, another important
ingredient for spin relaxation time studies.\\
Furthermore we observed second order transport mechanisms as inelastic
cotunneling processes and we associate some of our measurements with cotunneling
assisted sequential tunneling (CAST). These measurements provide a basis for following
interesting studies of transport mechanisms.