laboratoire pierre aigrain
électronique et photonique quantiques
 
laboratoire pierre aigrain
 

June 26, 2015 - 2pm - Salle Dussane (45 rue d’Ulm)

Philippe Campagne-Ibarcq
Measurement bakaction and feedback in superconducting circuits


The public thesis defense of Philippe Camapgne-Ibacq will take place on June 26, 2015 at 2pm in Salle Dussane (45 rue d’Ulm). He realized his PhD work under the supervision of Benjamin Huard and Michel Devoret. The committee is made of Leo DiCarlo (TU Delft), Steven Girvin (Yale University), John Martinis (Google, UC Santa Barbara), Jean-Michel Raimond (LKB) and Denis Vion (CEA Saclay).

Abstract:

In quantum physics, a measurement corresponds to the interaction of a system with an observer, who is part of the environment. In general, this measurement disturbs the system state in a an effect known as the quantum back action. This perturbation is stochastic and cannot be predicted a priori. However, if the observer efficiently extracts the information from the measurement, he can know about the back action a posteriori, and thus keep track of the system evolution.

As flexible quantum machines, whose collective behavior follows the laws of quantum physics, superconducting circuits are promising systems to investigate this subject. A particular superconducting qubit, the 3D transmon, which follows a recently developed architecture, has been shown to reach coherence times over 100 microseconds. Combined with the development of near quantum limited parametric amplifiers, also based on superconducting circuits, it is possible to coherently control, measure and react on the 3D transmon before it loses its coherence.

In this thesis, we describe several experiments performing such tasks on a 3D transmon. In particular, the fluorescence signal is used to unravel quantum jumps during relaxation. When averaged conditionnally to a final projective measurement outcome, the signal displays weak values out of range for unconditionnal average. It is also use to implement continuous analog feedback in order to stabilize an arbitrary state of the qubit. A high fidelity non demolition measurement in a single shot is also demonstrated and is used to implement stroboscopic digital feedback, which also stabilizes an arbitrary state.