Session B1: AMO and Nonlinear Dynamics

Linewidth Broadening of Coupled Quantum Dot Pairs

We report on linewidth analysis of optical transitions in InAs/GaAs coupled quantum dots (CQDs) as a function of temperature and tunnel coupling strength. A significant line broadening, up to 25 times that of the typical lifetime-limited linewidth of single-dot excitons is observed. This broadening occurs at tunnel resonances where the coherent tunnel coupling between spatially direct and indirect exciton states is considerable. With increasing temperature, the linewidth shows a characteristic temperature broadening. The linewidth as a function of tunnel coupling strength track the theoretical prediction of linewidth broadening due to the phonon assisted transitions, and is indirectly proportional to the energy splitting of the two exciton branches. These results highlight the linewidth broadening mechanisms and fundamental aspects between the interaction of these systems to that of the local environment.   

Protocols for dynamically probing topological edge states and dimerization with fermionic atoms in optical potentials

Behavior of topological states has been observed in ultra-cold atomic systems. However, imposing a confining harmonic potential distorts the energy spectrum and prevents the detection of topological boundary states. We propose protocols to resolve the detection of edge-states arising in a dimerized lattice using ultra-cold fermions. Atoms confined in ring lattice, whose boundary conditions are transformed from periodic to open using an off resonant laser sheet, generate topological boundary states. A particle injected onto the edge site of a dimerized structure in a topological configuration can sustain a finite density as the system evolves in time. Alternatively, depleting an initially filled lattice away from the boundary reveals prominent occupied edge states. Signatures of dimerization in the presence of onsite interactions can be found using certain correlations as the boundary conditions transform from periodic to open. These correlations reveal a memory effect of the initial state which can distinguish topological structures or different insulating phases.   

Bond-selected Single Molecule Photochemistry

Chemical reactions typically involve the dynamic reorganization of a large number of atoms and molecules. One persistent goal in the scientific community is to be able to visualize and manipulate individual molecules in a reaction and track their nuclear motions in real time. The combination of a femtosecond (fs) laser with the scanning tunneling microscope (STM) would enable the study of laser photochemistry to attain simultaneous spatial and temporal resolutions. Here, we demonstrate the laser photochemistry at single molecule level with a femtosecond laser STM, and ultimately probe the coherence molecular dynamics with joint fs-Å sensitivity.   

Level repulsion of two coupled 3D microwave cavities for quantum electrodynamics

Three-dimensional microwave cavities demonstrate excellent frequency selectivity and, as such, are known largely for their use in RF filters. However, this selectivity can be utilized to generate two or more narrowband signals whose frequency separation is controllable. Here, we investigate level repulsion in two quarter-wave stub microwave cavities while varying coupling parameters that dictate minimum separation of the signals in the avoided crossing. We observe a minimum separation of 20 MHz and maximum separation of 400 MHz at room temperature for antennas that are inserted approximately 2.5 mm and 4.8 mm into each cavity, respectively. We do not observe level repulsion below antenna length of 2.5 mm but we expect this will change upon re-testing at cryogenic temperatures and, therefore, higher quality factors. Three-dimensional SRF (Superconducting Radio Frequency) cavities with these capabilities have potential applications in quantum information science, precision displacement metrology, and quantum electrodynamics.   

Characterization and exploration of self pulsing behaviour in Holmium-doped fluoride fibers

Mid-infrared lasers have a multitude of applications, which are typified by medical, military and sensing applications. Fiber lasers provide an advantage due to their high beam quality and high surface to volume ratio, which allows for efficient cooling; they are comparatively speaking low maintenance high power CW lasers in operation. The mid-infrared field has been largely dominated by thulium doped lasers, which have been characterised as high power CW lasers that can be readily operated in Q-switched and mode locked regimes. These lasers have been limited to approximately 2.1 $\mu $m however the definition of mid-infrared has sometimes been referred to as being 3 $\mu $m or longer wavelengths. By exploring the Holmium-only doped fiber laser, the better understanding of mid-infrared lasers is gained. A system of self-pulsing in the kHz region was observed in a \textasciitilde 4 metre and \textasciitilde 3.5 metre Ho$^{\mathrm{3+}}$-doped laser, in addition to round trip MHz self-pulsing operation in both. The operation of the laser in both the spatial, temporal and spectral domains was examined. \newline The laser was also characterised in terms of power and pump efficiency.   

Kilobot as a single autonomous agent for testing collective motion

Over the last few decades, research on the topic of collective dynamics of active systems has spanned many disciplines such as physics, mathematics, computer science, biology and robotic engineering. One of the main reasons for the broad interest in this subject derives from its natural origins in the form of flocks, swarms, and crowds. In general, these natural systems are composed of single, autonomous organisms that communicate only locally, but form extended collective mobile groups capable of collective decision-making and displaying highly nontrivial dynamics over a wide range of length and time scales. This sort of decentralized, leaderless decision-making and collective action has inspired efforts especially in the area of robotic drones. In this work, we will show the application of Kilobot as a single autonomous agent to execute the swarming or collective transport algorithms. Kilobot is a small, low-cost robot, which has a limited communication range with the surrounding neighbors. These robots can work in a group of a thousand and they all execute the same program simultaneously, where a specific program is sent to them through the infra-red communication channel.   

Exploring Hidden Quantum Markov Models

Does quantum information offer advantage in the prediction and simulation of classical stochastic processes? In this work I explore many examples of hidden quantum Markov models (HQMM), which are a quantum generalization of classical Markov chains. In particular, I discuss how a particular subset of HQMMs can be easily parametrized and generated. By studying their properties we can observe some non-intuitive features displayed by the improvement in memory requirements when going from classical to quantum models.   

Introducing E-tec: Ensemble-based Topological Entropy Calculation

Topological entropy is a measurement of orbit complexity in a dynamical system that can be estimated in 2D by embedding an initial material curve $L_0$ in the fluid and estimating its growth under the evolution of the flow. This growth is given by \begin{equation} L(t) ~ = ~ |L_0|~e^{ht}, \end{equation} where $L(t)$ is the length of the curve as a function of $t$ and $h$ is the topological entropy. In order to develop a method for computing Eq. (1) that will efficiently scale up in both system size and modeling time, one must be clever about extracting the maximum information from the limited trajectories available. The relative motion of trajectories through phase space encodes global information that is not contained in any individual trajectory. That is, extra information is "hiding" in an ensemble of classical trajectories, which is not exploited in a trajectory-by-trajectory approach. Using tools from computational geometry, we introduce a new algorithm designed to take advantage of such additional information that requires only potentially sparse sets of particle trajectories as input and no reliance on any detailed knowledge of the velocity field: the $\textbf{E}$nsemble-Based $\textbf{T}$opological $\textbf{E}$ntropy $\textbf{C}$alculation, or E-tec.   

Intrinsic Transfer Entropy

Quantifying information flow within a system is paramount to understanding its behavior. One common, though flawed, method of doing this is via the \emph{transfer entropy}. The transfer entropy is a particular form of conditional mutual information, which captures both \emph{intrinsic dependence} between variables as well as \emph{conditional dependence}. Here, we propose a new method of quantifying information flow, the \emph{intrinsic transfer entropy}. Rather than utilizing the conditional mutual information, intrinsic transfer entropy uses the \emph{intrinsic mutual information} from information-theoretic cryptography. This provides for the first time a concrete method of separately quantifying intrinsic information flow from conditional information flow. We apply this measure to a variety of systems to demonstrate its usefulness.   

Untangling Superfluid Vortices

Previous work has shown that simple knotted vortices will untie in both viscous fluids and superfluids. Does the same behavior hold for complexly tangled vortices, irrespective or shape and topology? By simulating large numbers of vortex configurations in the Gross-Pitaevskii equation, I will show that the spontaneous unknotting of vortices is a universal feature of undriven fluids. I will also discuss the connection to conservation of helicity and topological features of the unknotting process.