Quantum catastrophes
le vendredi 5 mai 2017 à 11h00

Séminaire théorie

Personne à contacter : Robert Whitney ()

Lieu : Amphithéâtre, maison des Magistères

Résumé : Catastrophe theory provides a unified description of a broad range of singularities and defects in fields. A key idea is that of scale: at large scales the singularity appears truly singular but at smaller scales it is smoothed, e.g. by wave interference. In 2004 Michael Berry and Mark Dennis suggested that waves might themselves display singularities which are only smoothed by the fundamental discreteness of quantum field excitations (e.g. photons). In this talk I will give examples of such “quantum catastrophes” appearing in the dynamics of cold atom systems following a quench. Quantum catastrophes resemble classical wave catastrophes at large quantum numbers, but the quantization of excitations leads to an intrinsic granularity. This alters the morphology of the classic catastrophes, particularly the network of dislocations that underlie them. I will emphasize that, owing to the structural stability of catastrophes and their scaling properties, quantum catastrophes represent a universal aspect of dynamics in quantum fields.

Christophe Mora (Laboratoire Pierre Aigrain, Ecole Normale Supérieure)

Photons and electrons in quantum circuits
le vendredi 12 mai 2017 à 11h00

Colloque CPTGA

Personne à contacter :

Lieu : Amphithéâtre, maison des Magistères

Résumé : Current progresses in implementing quantum electronic devices open exciting perspectives for investigating unexplored regimes of quantum optics with microwave light. Playing with linear or non-linear, dissipative or dissipationless elements, quantum circuits involve the transport of electrons but can also be engineered to manipulate the state of the surrounding electromagnetic field. The electron-photon crosstalk is potentially enhanced by two means, either by significantly increasing the effective fine structure constant characterizing matter-light interaction, or by building superconducting high-finesse resonators in which photons remain coherently trapped for very long times.
Equipped with these tools and taking advantage of the offered strong non-linearities in quantum circuits, many experiments have designed protocols to create and probe non-classical states of microwave photons, such as Fock states, squeezed states or even cat states. Producing these typical non-classical states is known to be a key step towards quantum communication with scalable solid-state devices.
After a general introduction to the field of quantum circuits, we will discuss the fact that dissipation due to electron transport is not necessarily detrimental to the realization of coherent non-classical states such as squeezed vacuum. A tunnel junction will be shown to be able to generate a squeezed steady state in a microwave cavity when excited parametrically by a classical AC voltage source. Photon-assisted tunneling of electrons is accompanied by the emission of pairs of photons in the cavity, thereby engineering a driven squeezed state. The mechanism leading to squeezing differs from parametric amplifiers as it is steered by dissipation in the spirit of the reservoir engineering techniques used in quantum optics. We will finally mention ways to improve significantly the squeezing properties of radiation.
References
[1] U. C. Mendes and C. Mora, Cavity squeezing by a quantum conductor, New J. Phys. 17, 113014 (2015)
[2] U. C. Mendes and C. Mora, Electron-photon interaction in a quantum point contact coupled to a microwave resonator, Phys. Rev. B 93, 235450 (2016)
[3] C. Mora, C. Altimiras, P. Joyez, F. Portier, Quantum Properties of the radiation emitted by a conductor in the Coulomb Blockade Regime, Phys. Rev. B 95, 125311 (2017)