Events at Physics |
Events on Monday, March 23rd, 2009
- R. G. Herb Condensed Matter Seminar
- Circuit QED<sup>2</sup>: Two amplifiers, two resonators, and two photons
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Matteo Mariantoni, Walther-Meissner-Institut and Technical University
- Abstract: In order to better understand the fundamental properties of quantum electrodynamics (QED), studying the zero-point fluctuations of microwave radiation represents an important task. In the first part of this talk, I present a full experimental characterization of the microwave vacuum fluctuations via the Planck distribution of noise at very low temperatures. I show a detailed study of the cross-over from thermal noise to vacuum quantum noise and quantify the vacuum fluctuations level for a narrow frequency band centered around 6 GHz. I also demonstrate the change of the vacuum fluctuations level with the carrier frequency. In addition, I present a new type of heterodyne detection particularly suitable for circuit QED systems. It is based on a microwave beam splitter and cross-correlation measurements and allows for a reconstruction of the entire covariance matrix of the vacuum fluctuations. Finally, I show that such a cross-correlation setup can be used for detecting entanglement in a two-resonator circuit QED system.
In the second part of the talk, I report on the observation of key signatures of a two-photon driven Jaynes-Cummings model, which unveils the upconversion dynamics of a superconducting flux qubit coupled to an on-chip resonator. The experimental results show a clear evidence for the coexistence of one- and two-photon driven level anticrossings of the qubit-resonator system. This results from the symmetry breaking of the system Hamiltonian, when parity becomes a not well-defined property. This experiment provides deep insight into the interplay of multiphoton processes and symmetries in a qubit-resonator system. - Host: Robert McDermott