Experiments with a transmon artificial atom - state manipulation and detection of magnetic fields

Abstract

The field of quantum computation and simulation has its origins in the early 1980s, when the limitations of the existing paradigm of classical computing machines became apparent. The continuous miniaturization of circuit elements and the increase in their number per unit area will ultimately lead to practical difficulties and to the manifestation of quantum phenomena. This foresight triggered the research work for the invention of new principles of computation. The physical laws of our world are fundamentally quantum mechanical; that is why quantum systems have started to be considered as platforms for possible more powerful computing systems and simulators. Superconducting quantum circuits offer one of the most convenient and promising architectures in this field of research. They are macroscopic and, as a result, provide a better controllability. At the same time they can be produced with customary electronics fabrication methods and they are easily integrable with nowadays electronics.

This dissertation contains experimental studies of fully coplanar superconducting quantum circuits comprising a transmon type artificial atom coupled to a quarter-wavelength waveguide resonator. This circuit represents the simplest simulator of light-matter interaction and acts as a testbed for the gate operations needed to control the quantum state in the field of quantum computation. The stimulated Raman adiabatic passage and the shortcut to its adiabaticity were experimentally studied as methods for the efficient population transfer between the ground and the second excited state of the transmon. The possibility of using a hybrid adiabatic-nonadiabatic pulse sequences for preparing an arbitrary quantum three-level state was shown theoretically. The operation of gates based on geometric phases was implemented on the same type of superconducting structure. Finally, the structure was used as a magnetic flux sensor. The magnetic flux resolution of this sensor is enhanced by the use of two properly modified phase estimation algorithms and it is potentially limited only by the Heisenberg uncertainty principle. The superiority of the realized sensor over the standard classical measurement done on the same sample is clearly demonstrated. This experiment indicates the utility of superconducting quantum circuits for the tasks of quantum metrology.