The present diploma work is motivated by an experiment (recently performed at NEC
laboratories) on the so called "superconducting laser". It is a single-qubit laser inside
a superconducting resonator driven through a Josephson quasi-particle cycle. An introduction
to the properties of the \superconducting laser" requires then an introduction
to the large body of work which has been performed in the last years in the eld of
superconducting nano-circuits.
In the introduction, we present a general description of the topic and the motivations
to study it further. We also introduce the physics of Josephson junctions and brie
y
explain their use in quantum information and computation. We present a specic architecture
for a quantum computer and explain how this all is connected to our work.
Small superconducting circuits have been recognized to be very important as possible
implementations of a quantum computer. Therefore part of the thesis is devoted to a
description of the relation between quantum information and the physics of superconducting
nano-circuits.
Chapter 2 is devoted to a more quantitative description of the concepts used later
in the thesis to analyse the superconducting JQP laser. We start with a brief introduction
to superconductivity and present the equation of the Josephson eect, analysing
the most striking behaviors of Josephson junctions. We then analyse the importance
of quantum information and quantum computation, explaining which are their main
tasks. To conclude the chapter, we explain how to use Josephson junctions to build
superconducting qubits.
With Chapter 3 we enter the main body of the thesis. Here we explain in detail the
experimental setup and we describe which theoretical approaches has been used until
now to explain the results.
In the following chapter we generalize the master equation governing the dynamics
of the superconducting laser. We overcome the hypothesis of two separate subsystems,
atom and photons, when calculating the interaction of the laser with the environment.
We then derive equations that explain the behavior of the laser under external pumping
and in interaction with the environment. This interaction can cause decoherence and
relaxation, and thus alters signicantly the output of the laser. We present the results
in the Markovian and time independent regime, under the rotating wave approximation
(RWA).
The results obtained with this approach, along with the numerical analysis derived
from the equations we found in the previous chapter, are presented in Chapter 5. We see
that our results are compatible with the known small coupling results, already studied
in the literature, and discuss the behavior in the new strong coupling regime.
We conclude the work with a summary of the results and some hints at possible
future studies
