CQT Talk by Kihwan Kim, Tsinghua University
Title: High NOON State of Phonons in a Trapped Ion System.
Date/Time: 26 Aug, 10:30 AM
Venue: CQT level 3 Seminar Room, S15-03-15
Multi-party entangled state, in particular, NOON state has brought great interests because it allows the precision measurement to the ultimate limit as the number of particles increases. However, experimental preparation of the NOON state with sufficiently high number of particles N remains as a challenge. Here we develop a deterministic method to generate the NOON state of arbitrary phonon numbers and experimentally create the states up to $N$ = 9 phonons in two radial modes of a single trapped Yb171 ion. We clearly observe the fidelity of the NOON state over classical limit by measuring the contrast of the characteristic phase oscillations and the populations through the phonon projective measurement of two motional modes. We also observe the Heisenberg scaling of phase sensitivity in the NOON states through quantum Fisher information. Our scheme is generic and directly applicable to cavity QED or circuit QED systems and optomechanical systems.
Quantum Thermodynamic Series: Talk by Konstantin Dorfman, University of California
Title: Quantum Heat Engine Enhanced by Coherence: Is it possible to go beyond Chambadal-Novikov-Curzon-Ahlborn Limit?
Date/Time: 29 Aug, 12:30 PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Various quantum effects have been observed in the thermodynamic of small systems. For instance understanding the microscopic origin of the quantum coherence and its role in the energy and charge transfer processes along with thermodynamics characteristics of the small systems is a key problem in both thermodynamics and quantum mechanics.
We had investigated the possible role of quantum coherence and interference on steady state and transient behavior of the quantum heat engines (QHE), e.g lasers, photovoltaic cells, photosynthetic reaction centers, and nanoplasmonic devices. We showed that the maximum power of a QHE that converts incoherent thermal energy into coherent cavity photons could be enhanced by manipulating quantum coherences. We demonstrated that in both artificial (solar cells) and natural (photosynthesis) light harvesting coherence affects the same population–coherence coupling term which is induced by bath (e.g. phonons), does not require coherent light, and will therefore work for incoherent excitation under natural conditions of solar excitation.
We further investigate a novel model of the three-level laser QHE where lasing occurs between two closely spaced metastable states and the ground stated. Engine operates by transferring energy from hot bath to cold bath via nonequilibrium coherence assisted process. Coherence has two sources: first is due to quantum interference generated via hot bath and second is due to the lasing field coupled to both metastable states. The resulting efficiency at maximum power can be significantly improved due to interplay between these two coherence contributions.