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Atomic, Mesoscopic and Optical Physics

AMOP Group

Studying at Cambridge

 

Current AMOP Seminars

Seminars

AMOP SEMINARS

Usually held on Mondays at 3.30pm in the Ryle seminar room 930

 

3.6.18 Dr. Tobias Donner

ETH Zurich, Switzerland 

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20.3.18 Prof. Sabrina Maniscalco  Tuesday, 10:00am, TCM Seminar room, Mott building, 2nd floor

University of Turku, Finland 

Quasiperiodic lattices as tunable quantum reservoirs: exploring the Markovian to non-Markovian crossover

Fermionic systems under the influence of quasiperiodic fields display different relaxation properties. In particular, employing bichromatic optical lattices and initial fermionic gases prepared in the so called charge density wave state, the crossover from ergodic to non-ergodic dynamics can be witnessed monitoring the density imbalance in the occupation of even and odd sites. 

We investigate such setup from an open quantum system theory perspective, designing a protocol in which an impurity atom is coupled to the fermionic cloud trapped in the bichromatic lattice. This interaction induces decoherence in the probe induced by the complex out-of equilibrium environment. We focus our attention on the time evolution of the impurity in such environment and study wether the probe dynamics can be classified as Markovian or non-Markovian. Specifically we see how the localised phase of the Aubry-Andre’ model displays evidence of strong memory effects.

 

19.3.18 Dr. Bernhard Urbaszek  Monday, 3:30pm, RYLE Seminar room

CNRS – Toulouse University, France 

Light-matter interaction in atomically thin semiconductors: darkness, brightness, spins and valleys

Transition metal dichalcogenides (TMDCs) such as MoS2 and WSe2 are layered materials that are semiconductors with a direct bandgap when thinned down to one monolayer. Despite an incredible number of results published in the field since 2010, many basic parameters such as the effective carrier mass are not experimentally determined – which leaves plenty of room for further exploration of these fascinating materials. Even samples exfoliated in ambient conditions with simple scotch-tape methods show remarkable properties for optoelectronics and spintronics: TMDC monolayers strongly interact with light in the visible region of the optical spectrum. The optically generated electrons and holes form excitons with high binding energy (several hundred meV) and high oscillator strength, resulting in optical absorption up to 20 % per monolayer. Interband optical selection rules are polarization selective (chiral). This allows addressing non-equivalent valleys in momentum space with polarized lasers for optical spin and valley index manipulation.
We access the optical and spin properties, studying valley dynamics for different exciton species and resident carriers, with unprecedented detail in TMDC monolayers sandwiched between ultrathin insulating layers of hexagonal boron nitride (hBN) in van der Waals heterostructures. The optical emission of these encapsulated monolayers is spectrally narrow (down to 1 nm FWHM) comparable to emission from III-V quantum well structures used in today’s optoelectronic devices and approaching the homogenous limit. This insight paves the way for integrating TMDCs in photonic devices and ferromagnetic- semiconductor heterostructures.

 

16.1.18 Dr. Philipp Preiss  **Tuesday, 3:30pm, RUTHERFORD Seminar room**

Heidelberg University, Germany 

Quantum Simulation of Mesoscopic Fermi Systems

Ultracold quantum gases in optical potentials have achieved spectacular progress in the experimental simulation of complex quantum systems. Complementary to many-body experiments, mesoscopic systems comprised of a small number of atoms offer the possibility to study entangled quantum states with an exceptional degree of versatility and control.
We have implemented a highly tunable platform to study such correlated few-fermion systems. Using reconfigurable optical microtraps, we prepare quantum states of 6Li atoms with a deterministic atom number and spin configuration and tune interactions via a magnetic Feshbach resonance. A novel readout scheme with single-particle sensitivity allows us to measure spin-resolved correlation functions in position and in momentum space.
Such correlators characterize few-body systems via the coherence and symmetry of the wavefunction. Focusing on the Fermi-Hubbard double-well, we observe high-contrast interference of indistinguishable fermions, the build-up of correlations due to interactions, and the emergence of entanglement between particles. Our techniques can be applied to larger systems to characterize many-body phases via their higher-order correlation functions.

 

16.10.17 Prof. Alain Aspect  

Institut d'Optique Graduate School Université Paris-Saclay 

Hanbury Brown-Twiss, Hong-Ou-Mandel, and other landmarks in quantum optics : from photons to atoms

The second quantum revolution is based on entanglement, discovered by Einstein and Schrödinger in 1935. Its extraordinary character has been experimentally demonstrated by landmark experiments in quantum optics.  

At Institut d'Optique, we are currently revisiting these landmarks using atoms instead of photons, and after the observation of the atomic HOM effect1, we are progressing towards a test of Bell's inequalities with pairs of momentum entangled atoms2.

1. Lopes, R., Imanaliev, A., Aspect, A., Cheneau, M., Boiron, D., & Westbrook, C. I. (2015). Atomic Hong-Ou-Mandel experiment. Nature, 520(7545), 66-68.

2. Pierre Dussarrat, Maxime Perrier, Almazbek Imanaliev, Raphael Lopes, Alain Aspect, Marc Cheneau, Denis Boiron, and Christoph I. Westbrook: A two-particle, four-mode interferometer for atoms, arXiv 1707. 01279, to appear in Phys. Rev. Lett..

 

30.10.17 Dr. Eva-Maria Graefe 

Mathematical Physics Group, Faculty of Natural Sciences, Imperial College London

Evolution of Gaussian wave packets in the presence of losses and gains

In recent years there has been growing interest in open quantum systems described by non-Hermitian Hamiltonians in various fields. Examples are scattering systems and the effective description of absorption and amplification. The classical counterparts of non-Hermitian quantum systems, however, remained illusive. In this talk I present results on the quantum evolution of Gaussian wave packets generated by a non-Hermitian Hamiltonian in the semiclassical limit of small hbar. This yields a generalisation of the Ehrenfest theorem for the dynamics of observable expectation values. The resulting equations of motion for dynamical variables are coupled to an equation of motion for the phase-space metric - a phenomenon having no analogue in Hermitian theories. The insight that can be gained by this classical description will be demonstrated for a number of example systems.

 

13.11.17 Internal Double Feature  

AMOP, Cavendish

Ultracold Bose soup: where few-body meets many-body physics

     Loss, correlation and energy dynamics of a Bose gas quenched to unitarity

Daniel Malz   (Nunnenkamp group)

     Nonreciprocity through reservoir engineering in cavity optomechanics

 

27.11.17 Prof. Eric Cornell  11

JILA, University of Colorado, Boulder, CO, USA

Ultracold Bose soup: where few-body meets many-body physics

Degenerate bose gases were first created in labs about twenty years ago. These gases now come in many varieties and their microscopic properties may be probed with a diverse range of experimental tools.  Degenerate bose liquid, on the other hand, is available in any element the customer wants, but only if that element is helium, and even a century after it was first realized, microscopic experimental probes are relatively limited.  Can we make our ultracold bose gases more liquid-like?  On the way, can we learn some interesting things at the interface between few- and many-body physics?

 

11.12.17 Internal Double Feature  

AMOP, Cavendish

Dorian Gangloff   (Atature group)

     Controlling mesoscopic nuclear spin ensembles

Ed Carter  (Schneider group)

     Quantum Walks in four dimensions

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