Transport in Floquet-Bloch bands

We report Floquet band engineering of long-range transport and direct imaging of Floquet-Bloch bands in an amplitude-modulated optical lattice. In one variety of Floquet-Bloch band we observe tunable rapid long-range high-fidelity transport of a Bose condensate across thousands of lattice sites. Quenching into an opposite-parity Floquet-hybridized band allows Wannier-Stark localization to be controllably turned on and off using modulation. A central result of this work is the use of transport dynamics to demonstrate direct imaging of a Floquet-Bloch band structure. These results demonstrate that transport in dynamical Floquet-Bloch bands can be mapped to transport in quasi-static effective bands, opening a path to cold atom quantum emulation of ultrafast multi-band electronic dynamics.Comment: 5 pages, 4 figure

Experimental Realization of a Relativistic Harmonic Oscillator

We report the experimental study of a harmonic oscillator in the relativistic regime. The oscillator is composed of Bose-condensed lithium atoms in the third band of an optical lattice, which have an energy-momentum relation nearly identical to that of a massive relativistic particle, with an effective mass reduced below the bare value and a greatly reduced effective speed of light. Imaging the shape of oscillator trajectories at velocities up to 98% of the effective speed of light reveals a crossover from sinusoidal to nearly photon-like propagation. The existence of a maximum velocity causes the measured period of oscillations to increase with energy; our measurements reveal beyond-leading-order contributions to this relativistic anharmonicity. We observe an intrinsic relativistic dephasing of oscillator ensembles, and a monopole oscillation with exactly the opposite phase of that predicted for non-relativistic harmonic motion. All observed dynamics are in quantitative agreement with longstanding but hitherto-untested relativistic predictions.Comment: 10 pages; 4 figure

MODELLING AGRO·FORESTRY SYSTEMS FOR IMPROVED ECONOMIC PERFORMANCE: A COMPARATIVE ECONOMIC ANALYSIS

Despite promising ecological features of various agro-Iorestry systems, adoption or thesesystems by farmers is not always encouraging. This is not surprising. as fanners areoperating in a highly competitive commercial environment. where priority is given toeconomic goals rather than environmental goals. One solution is to develop AF modelswith species combinations that generate economic returns comparable to competingenterprises. simultaneously with environmental benefits.The main objective of the current study is to investigate species combinations withimproved economic performance. Here two AF practices in Sri Lanka, namely, coconutinter cropping and avenue cropping based on Gliricidia were considered. lnformationgathered both from primary and secondary sources were used in the study. A number ofpotential crops were categorized according to their income generating and resourceutilisation patterns. Among them, there are perennials, semi perennials as well as seasonalcrops. Two AF models were developed using Linear Programming technique. Modelsproposed jak, banana, pepper and coffee as the inter cropping combination which gives thehighest economic performance under coconut based systems. In case of avenue croppingwith Gliricidia, number of legumes and cereals along with banana was selected as theoptimum combination. The economic performance of the developed models were assessedby cost-benefit analysis and their implications on a selected set of economic parametershave been discussed.The whole exercise shows that, species combination of a system is an important aspectwhich determines the economic performance of the system. It further suggests that speciescombination can be manipulated to generate models with desired economic characteristics.Therefore, challenge ahead is to design models with species combinations that find ahalance between economic and environmental objectives.

Observation and uses of position-space Bloch oscillations in an ultracold gas

We report the direct observation and characterization of position-space Bloch oscillations using an ultracold gas in a tilted optical lattice. While Bloch oscillations in momentum space are a common feature of optical lattice experiments, the real-space center-of-mass dynamics are typically too small to resolve. Tuning into the regime of rapid tunneling and weak force, we observe real-space Bloch oscillation amplitudes of hundreds of lattice sites, in both ground and excited bands. We demonstrate two unique capabilities enabled by tracking of Bloch dynamics in position space: measurement of the full position-momentum phase-space evolution during a Bloch cycle, and direct imaging of the lattice band structure. These techniques, along with the ability to exert long-distance coherent control of quantum gases without modulation, may open up new possibilities for quantum control and metrology.Comment: 5 pages, 6 figure

Quantifying and Controlling Prethermal Nonergodicity in Interacting Floquet Matter

The use of periodic driving for synthesizing many-body quantum states depends crucially on the existence of a prethermal regime, which exhibits drive-tunable properties while forestalling the effects of heating. This dependence motivates the search for direct experimental probes of the underlying localized nonergodic nature of the wave function in this metastable regime. We report experiments on a many-body Floquet system consisting of atoms in an optical lattice subjected to ultrastrong sign-changing amplitude modulation. Using a double-quench protocol, we measure an inverse participation ratio quantifying the degree of prethermal localization as a function of tunable drive parameters and interactions. We obtain a complete prethermal map of the drive-dependent properties of Floquet matter spanning four square decades of parameter space. Following the full time evolution, we observe sequential formation of two prethermal plateaux, interaction-driven ergodicity, and strongly frequency-dependent dynamics of long-time thermalization. The quantitative characterization of the prethermal Floquet matter realized in these experiments, along with the demonstration of control of its properties by variation of drive parameters and interactions, opens a new frontier for probing far-from-equilibrium quantum statistical mechanics and new possibilities for dynamical quantum engineering