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Soutenance de Nathanaël Cottet

Energy and Information in Fluorescence with Superconducting Circuits
When Nov 20, 2018
from 02:00 to 04:00
Where Salle des thèses
Contact Name Nathanaël Cottet
Attendees Nathanaël Cottet
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This experimental thesis explores energetic and informational aspects of the fluorescence emitted by superconducting circuits. A quantum bit interacting with a resonant drive exchanges quanta of energy during absorption and emission cycles. Using low-noise amplification and linear detection of microwave light, we have developed a measurement setup to record the energy and complex amplitude of the fluorescence field and realized three experiments based on the record of fluorescence.

First, we have realized and demonstrated a transfer of energy between two resonant drives. Owing to the properties of stimulated emission, the direction and magnitude of energy transfer can be controlled by the phase of a quantum superposition of qubit states. Second, we have used the information contained in fluorescence to implement a new readout scheme for superconducting circuits without the help of any ancillary quantum system. The circuit, directly coupled to the environment, encodes quantum information in a well-protected subspace and is read using the fluorescence of a strongly coupled transition.

Finally, we have explored the interplay between information and energy in the quantum regime by realizing an autonomous Maxwell's demon. The demon is a cavity measuring the system, a superconducting qubit. Work is extracted in the form of a stimulated photon emitted by the qubit and is directly measured using our fluorescence measurement setup. It is linked with the variations of the system's internal energy. Using independent measurements, the transfer of information from the system to the demon is quantified. In particular, we demonstrated the quantum signatures of the demon when the system is initialized in a quantum superposition.