Accurate control and addressability of quantum devices will come with the
promise of improvement in a wide variety of theoretical and applied fields, such as
chemistry, condensed matter physics, theoretical computer science, foundational
physics, communications, metrology and others.
Decoherence of quantum states and the loss of quantum systems have adverse effects and deter a satisfactory usage of quantum devices. This is the main problem
to be overcome, which is the goal of quantum fault tolerance. In this thesis
we present a series of works that contribute to some of the fields mentioned above,
in the direction of fighting decoherence and loss.
These works fall in two categories: on one hand, we looked at computer architectures
which can be used to combat errors, using techniques of quantum error
correcting codes. In a first project we found decoherence and loss probability
thresholds below which quantum computing is provably possible. We assumed a
very particular error model tailored specially to quantum dots as single photon
sources and linear optics. Subsequently we looked at the problem of loss, both
of heralded and unheralded, and devised some ways to fight it. The framework
under which this work was done was used to develop theory which is currently
being tested in a quantum optics experimental group and will be reported in an
article later this year.
On the other hand, we studied how the error probability can be reduced at
the physical level, thanks exclusively to the properties of the system in which
information is stored, as opposed to making use of quantum codes. We looked
at a particular superconducting circuit, which is potentially very well protected
against some types of decoherence. In particular, we observed that the interaction
with the environment become weaker for certain values of the circuit external
parameters
