Although quantum at its fundamental level, nature appears classical on a macroscopic scale. Since the collective degrees of freedom of large objects have multiple pathways for the spread of entanglement with the surrounding environment, they rapidly decohere. The ambition of harnessing nature’s ultimate computing power is at odds with this fundamental phenomenon. Therefore, quantum error correction (QEC) will be indispensable. This cooperative phenomenon, which requires participation of multiple quantum and classical components, creates a special type of dissipation that removes entropy brought into the system by the errors, thereby protecting the stored logical quantum state. Previous experimental attempts to engineer such a process faced an excessive generation of errors that overwhelmed the error correcting capability of the process itself. The question of whether it is practically possible to utilize QEC for extending quantum coherence thus remains open. We answer this question affirmatively and definitively. Our main result is the demonstration of a fully stabilized and error-corrected logical qubit whose quantum coherence is significantly longer than that of all the imperfect quantum components involved in the QEC process, beating the best of them with a coherence gain of G=2.27. In this thesis defense, starting with a brief introduction to the principles of QEC, I will explain the ideas behind this experiment, and how it fits into a broader effort of the quantum information community.
Thesis Advisor: Michel Devoret (michel.devoret@yale.edu)