CQT Colloquium by Timothy C. Ralph, Centre for Quantum Computation & Communication Technology, The University of Queensland

Title: Quantum Entanglement: Gaussian and Macroscopic
Date/Time: 18-Oct, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15

Abstract: In the first half of this talk I will discuss the quantification of entanglement in Gaussian systems and how this relates to channel simulation and error correction. We conclude that entanglement of formation is a more faithful measure of entanglement in Gaussian systems than negativity, both qualitatively and quantitatively, and illustrate this with examples. In the second half of this talk I will discuss the macroscopicity problem in quantum mechanics. If quantum theory is universal we would expect to be able to observe quantum effects such as superpositions on a macroscopic scale. The current inability to observe such effects is commonly attributed to decoherence, leading to a so-called “macro-scale” beyond which physical systems can be analysed without any reference to the quantum formalism. We challenge this view by showing that, with the assistance of a second system, a macroscopic system can be proved to be entangled even after arbitrary decoherence. We show this by introducing a modified Wigner’s friend gedankenexperiment where the observer is not assumed to preserve quantum coherence.

CQT Talk by Guillermo Romero, The University of Santiago, Chile

Title: Nucleation of superfluid-light domains in a quenched dynamics
Date/Time: 17-Oct, 11:00AM
Venue: CQT Level 3 Seminar Room, S15-03-15

Abstract: Strong correlation effects emerge from light-matter interactions in coupled resonator arrays, such as the Mott-insulator to superfluid phase transition of atom-photon excitations. We demonstrate that the quenched dynamics of a finite-sized complex array of coupled resonators induces a first-order like phase transition. The latter is accompanied by domain nucleation that can be used to manipulate the photonic transport properties of the simulated superfluid phase; this in turn leads to an empirical scaling law. This universal behavior emerges from the light-matter interaction and the topology of the array. The validity of our results over a wide range of complex architectures might lead to a promising device for use in scaled quantum simulations.

CQT Colloquium by Mikhail Baranov, Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences

Title: Subwavelength optical barriers for cold atoms: creation and potential application
Date/Time: 22-Nov, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15

Abstract: The generation of subwavelength optical barriers on the scale of tens of nanometers, as conservative optical potentials for cold atoms, is discussed both theoretically and experimentally. In the proposed scheme they originate from nonadiabatic corrections to Born-Oppenheimer potentials for position-dependent “dark states” in atomic Λ configurations. The subwavelength optical barriers represent a “Kronig-Penney” potential, and I discuss the corresponding band structure including the effects of spontaneous emission and atom loss due to “bright” channels. Inclusion of an interparticle dipole-dipole interaction leads to formation of “domain wall molecules” and to unconventional Hubbard models with modulated in space interparticle interactions. As a brief discussion of potential applications, the subwavelength barrier can be used as a “splitter” to create a double-wire (or double-layer) with subwavelength spacing and, therefore, with substantially increased couplings as compared to ordinary optical lattices. As another application, specially designed subwavelength atomic internal-state spatial structures can be used for building an atomic scanning microscope with subwavelength resolution.

CQT Talk by Kishor Barti, CQT

Title: Machine Learning Bell Nonlocality
Date/Time: 19-Oct, 03:00AM
Venue: CQT Level 3 Seminar Room, S15-03-15

Abstract: In this talk, I will present a summary of papers, which are at the interface of Bell nonlocality and machine learning. In particular, I will discuss following papers:

1. Machine learning non-local correlations, and

2. Transforming Bell's Inequalities into state classifiers with machine learning.