The quantum free electron laser

The quantum regime of the free-electron laser (FEL) interaction, where the recoil associated with photon emission plays a significant role, is discussed. The role of quantum effects and their relation to electron beam coherence are considered. An outline derivation of a 1D quantum high-gain FEL model and some of its predictions for the behaviour of a quantum FEL in the linear and non-linear regimes are presented. The effect of slippage and, consequently, the quantum regime of self-amplified spontaneous emission are discussed. Suggestions on how to realise a quantum FEL are presented and some recent related work is summarized

Collective dynamics out of thermodynamic equilibrium

Thorough numerical studies reveal that spatially extended dissipative systems with long-range interactions may give rise to a large-scale dynamics. This phenomenon, which generalizes mean-field chaos, can be interpreted as a form of subtle pattern formation, where a chaotic microscopic dynamics coexists with a macroscopic irregular behavior, sustained by the spontaneous emergence of long-wavelength "hydrodynamic" modes. This regime can emerge only if the coupling is sufficiently long ranged, otherwise normal space-time chaos is observed. In Stuart-Landau oscillators a further regime is found, where the amplitude of the hydrodynamic modes exhibits an anomalous intermediate scaling between that of collective and standard space-time chaos

When Two Worlds Collide: Mātauranga Māori, Science and Health of the Toreparu Wetland

Much of our understanding of wetland health and function comes from scientific-based monitoring and methodologies. However, there is a wealth of knowledge to be gained from Māori-value based assessment methods for monitoring wetlands in New Zealand. I used the Wetland Cultural Health Index (WCHI) and a variety of scientific wetland survey methods to examine how these two approaches complement each other. For this research, I worked with the people from Mōtakotako marae at the Toreparu wetland (Waikato), developing a set of site specific cultural indicators. Comparative analysis revealed a range of similarities and differences between the WCHI indices and scientific parameters. We found that as Wetland Cultural Health Measure (WCHM) scores increased, there was also an increase in dissolved oxygen concentration, SQMCI-sb values, and total nitrogen concentrations. Cultural indices provided an overall indication of site health. It was apparent, however, that scores of contributing indicators could vary markedly at any one site. As such, high scores for some indicators (e.g., vegetation values) may obscure low values for other variables (e.g., water quality), providing an index that depicts site health as being of average condition. Capacity and resourcing issues were also highlighted as being an issue for Māori to be able to successfully carry out wetland monitoring, but also for staff in councils and other research and environmental governing bodies to build and maintain relationships with tangata whenua. Other challenges around site access provided a unique opportunity to develop and trial new WCHI assessment techniques. The use of video assessment to carry out WCHI monitoring was of varying success. Indicators that could be scored by visual assessment were useful, but indicators that relied on sound or felt sensation were difficult to assess. The use of mauri (life force) as an indicator had benefits when applied to the whole catchment, but the volunteer participants challenged its validity when used at the smaller site scale. Volunteers found assigning a numerical value to mauri very difficult, and felt that reducing mauri to a single number may diminish the significance of this holistic and metaphysical concept. Mauri has been used successfully as a measure of environmental health but it is important to communicate and understand what mauri is and why it is measured. Overall, the WCHI provided a wealth of information that could not be captured through scientific sampling, such as the presence of dye source, loss of bird/fish species and baseline information on the past condition of the Toreparu before the surrounding land was converted for agricultural use. This confirms that our understanding of wetland health is enhanced through the inclusion of cultural values. As the New Zealand government and Māori move towards a future of collaborative research and management of freshwater ecosystems, there is a need for greater understanding around cultural values and priorities. By using both scientific and Māori-value based wetland monitoring methods, Māori can articulate a range of values, goals and priorities to help inform environmental decision makers and empower iwi and hapū to have a meaningful and sustainable role in the management of wetlands. There needs to be a foundation of mutual understanding and relationships built between environmental governing bodies and Māori for the future success of collaborative research and management of New Zealand's wetlands

Synchronization of Bloch oscillations by a ring cavity

We consider Bloch oscillations of ultracold atoms stored in a one-dimensional vertical optical lattice and simultaneously interacting with a unidirectionally pumped optical ring cavity whose vertical arm is collinear with the optical lattice. We find that the feedback provided by the cavity field on the atomic motion synchronizes Bloch oscillations via a mode-locking mechanism, steering the atoms to the lowest Bloch band. It also stabilizes Bloch oscillations against noise, and even suppresses dephasing due to atom-atom interactions. Furthermore, it generates periodic bursts of light emitted into the counter-propagating cavity mode, providing a non-destructive monitor of the atomic dynamics. All these features may be crucial for future improvements of the design of atomic gravimeters based on recording Bloch oscillations.Comment: 14 pages, 7 figure

A design for a civic center, dedicated to the memory of those who have devoted their lives to exploration

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1913.Accompanying drawings held by MIT Museum.by Gordon Howard Robb.B.S

Avoided Crossing and sub-Fourier-sensitivity in Driven Quantum Systems

The response of a linear system to an external perturbation is governed by the Fourier limit, with the inverse of the interaction time constituting a lower limit for the system bandwidth. This does not hold for nonlinear systems, which can thus exhibit sub-Fourier-behavior. The present Letter identifies a mechanism for sub-Fourier-sensitivity in driven quantum systems, which relies on avoided crossing between Floquet states. Features up to three orders of magnitude finer than the Fourier limit are presented.Ministerio de Economía y Competitividad of Spain, Grant No. FIS2016-80244-

Long-range interactions in a quantum gas mediated by diffracted light

A BEC interacting with an optical field via a feedback mirror can be a realisation of the quantum Hamiltonian Mean Field (HMF) model, a paradigmatic model of long-range interactions in quantum systems. We demonstrate that the self-structuring instability displayed by an initially uniform BEC can evolve as predicted by the quantum HMF model, displaying quasiperiodic "chevron" dynamics for strong driving. For weakly driven self-structuring, the BEC and optical field behave as a two-state quantum system, regularly oscillating between a spatially uniform state and a spatially periodic state. It also predicts the width of stable optomechanical droplets and the dependence of droplet width on optical pump intensity. The results presented suggest that optical diffraction-mediated interactions between atoms in a BEC may be a route to experimental realisation of quantum HMF dynamics and a useful analogue for studying quantum systems involving long-range interactions

Generating multiparticle entangled states by self-organization of driven ultracold atoms

We describe a mechanism for guiding the dynamical evolution of ultracold atomic motional degrees of freedom towards multiparticle entangled Dicke-squeezed states, via nonlinear self-organization under external driving. Two examples of many-body models are investigated. In the first model the external drive is a temporally oscillating magnetic field, leading to self-organization by interatomic scattering. In the second model the drive is a pump laser, leading to transverse self-organization by photon-atom scattering in a ring cavity. We numerically demonstrate the generation of multiparticle entangled states of atomic motion and discuss prospective experimental realizations of the models. For the cavity case, the calculations with adiabatically eliminated photon sidebands show significant momentum entanglement generation to occur even in the ``bad cavity" regime. The results highlight the potential for using self-organization of atomic motion in quantum technological applications

Graphene plasmonics : ultra-tunable graphene light source

Free-electron-based light sources have long attracted interest due to their continuous tunability that has been demonstrated to extend across the electromagnetic spectrum from millimetre waves and microwaves through the infrared and visible to ultraviolet and X-ray regions. However this intrinsic tunability, particularly at short wavelengths, usually involves sources that are large and costly. The prospect of a compact, continuously tunable light source with the capability to generate short-wavelength ultraviolet and even X-ray light is an exciting one for many scientific, medical and engineering applications

Optomechanical self-structuring in cold atomic gases

The rapidly developing field of optomechanics aims at the combined control of optical and mechanical (solid-state or atomic) modes. In particular, laser cooled atoms have been used to exploit optomechanical coupling for self-organization in a variety of schemes where the accessible length scales are constrained by a combination of pump modes and those associated to a second imposed axis, typically a cavity axis. Here, we consider a system with many spatial degrees of freedom around a single distinguished axis, in which two symmetries - rotations and translations in the plane orthogonal to the pump axis - are spontaneously broken. We observe the simultaneous spatial structuring of the density of a cold atomic cloud and an optical pump beam. The resulting patterns have hexagonal symmetry. The experiment demonstrates the manipulation of matter by opto-mechanical self-assembly with adjustable length scales and can be potentially extended to quantum degenerate gases.Comment: 20 pages, 6 figure