Temporal multiplexing provides an efficient and scalable approach to realize a quantum random walk with photons that can exhibit topological properties. But two-dimensional time-multiplexed ...topological quantum walks studied so far have relied on generalizations of the Su-Shreiffer-Heeger model with no synthetic gauge field. In this work, we demonstrate a two-dimensional topological quantum random walk where the nontrivial topology is due to the presence of a synthetic gauge field. We show that the synthetic gauge field leads to the appearance of multiple band gaps and, consequently, a spatial confinement of the quantum walk distribution. Moreover, we demonstrate topological edge states at an interface between domains with opposite synthetic fields. Our results expand the range of Hamiltonians that can be simulated using photonic quantum walks.
Synchronization is of central importance in power distribution, telecommunication, neuronal and biological networks. Many networks are observed to produce patterns of synchronized clusters, but it ...has been difficult to predict these clusters or understand the conditions under which they form. Here we present a new framework and develop techniques for the analysis of network dynamics that shows the connection between network symmetries and cluster formation. The connection between symmetries and cluster synchronization is experimentally confirmed in the context of real networks with heterogeneities and noise using an electro-optic network. We experimentally observe and theoretically predict a surprising phenomenon in which some clusters lose synchrony without disturbing the others. Our analysis shows that such behaviour will occur in a wide variety of networks and node dynamics. The results could guide the design of new power grid systems or lead to new understanding of the dynamical behaviour of networks ranging from neural to social.
Humans have long dreamed of traveling to space. In response to the recent increase in commercial space flight, this paper evaluates environmental impacts of human space travel, both past and present, ...to shed light on the large environmental footprint of such activities. This environmental impact also has a moral component, since most of the global population will never be able to participate in such activities, yet still must bear the cost. Ironically, instead of a space future acting as a relief valve on Earth's resources, few activities exact a heavier burden on our planet's resources than the space pursuit, for the number of people it serves.
This analysis utilized the structure of life cycle assessment. Data on launch vehicles mass and propellant type and mass was taken from public sources. Combustion emission results were calculated using combustion analysis software. These data were then combined with data from life cycle inventory databases and impact assessment methods to evaluate midpoint impact indicators.
The hourly impact from sustaining humans in space over 1500 kg CO2-eq per hour. To put this into context, this is 2000 times greater than the emission rate of the average person on the globe, which we term global citizen equivalents (GCE). This global warming impact is also 650 times greater than the average person in the U.S.
In terms of familiar activities, this is equivalent to continuously supplying at least 4 MW of electricity from the U.S. grid; simultaneously driving over sixty diesel buses; or occupying twenty seats on a Boeing 747 that never lands. Clearly such impacts raise questions not only to the sustainability of such activities, but also to the moral and ethical implications where such travel is limited to only the very wealthiest, but the costs are borne by all with few benefits to show from the endeavour.
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•First investigation of environmental impacts of the whole period of human space travel•Estimates global warming impacts in units of global citizen equivalents (GCE)•Hourly global warming impact from sustaining humans in space is around 1500–3500 kg CO2-eq per hour.•Space travelers are found to have global warming impacts of 2000–4600 GCE per hour.•Disparities in access to space travel entail moral issues related to these large impacts.
One of the major difficulties in the development of optoelectronic THz modulators is finding an active material that allows for large modulation depth. Graphene is a promising candidate because in ...the terahertz regime it behaves as a Drude metal with conductivity that can be electrostatically tuned through the application of a gate voltage. However, the maximum absorption incurred when a terahertz signal passes through a monolayer of graphene is still only on the order of 10–20%, even for the highest practically achievable carrier concentrations. We demonstrate here a THz modulator that overcomes this fundamental limitation by incorporating a graphene sheet on the surface of a passive silicon dielectric waveguide, in which the evanescent field penetrates the graphene sheet. By applying a gate voltage to the graphene sheet, a modulation depth of up to 50% was achieved. The performance of the modulator is confirmed through electromagnetic simulations, which give further insights into the spatial structure of the guided mode and polarization dependence of the modulation. We show both theoretically and experimentally that the modulation depth can be increased to over 90% by integrating the graphene sheet at the center of the waveguide.
2D THz Optoelectronics Mittendorff, Martin; Winnerl, Stephan; Murphy, Thomas E.
Advanced optical materials,
02/2021, Volume:
9, Issue:
3
Journal Article
The terahertz (THz) region of the electromagnetic spectrum spans the gap between optics and electronics and has historically suffered from a paucity of optoelectronic devices, in large part because ...of inadequate optical materials that function in this spectral range. 2D materials, including graphene and a growing family of related van der Waals materials, have been shown to exhibit unusual optical and electrical properties that can enable diverse new applications in the THz regime. In this review, some of the unusual properties of 2D materials that make them promising for THz applications are explained, the recent work in the field of 2D THz optoelectronics is summarized, and the challenges and opportunities that await this promising new field are outlined.
Atomically thin materials like graphene and related van der Waals materials have unusual optical, thermal, and electrical properties in the far‐infrared or terahertz spectral regime. This review article summarizes recent work in the burgeoning field of 2D THz optoelectronics, and explains some of the properties of 2D materials that make them especially useful in this regime.
Delayed dynamical systems: networks, chimeras and reservoir computing Hart, Joseph D; Larger, Laurent; Murphy, Thomas E ...
Philosophical transactions - Royal Society. Mathematical, Physical and engineering sciences/Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences,
09/2019, Volume:
377, Issue:
2153
Journal Article
Peer reviewed
Open access
We present a systematic approach to reveal the correspondence between time delay dynamics and networks of coupled oscillators. After early demonstrations of the usefulness of spatio-temporal ...representations of time-delay system dynamics, extensive research on optoelectronic feedback loops has revealed their immense potential for realizing complex system dynamics such as chimeras in rings of coupled oscillators and applications to reservoir computing. Delayed dynamical systems have been enriched in recent years through the application of digital signal processing techniques. Very recently, we have showed that one can significantly extend the capabilities and implement networks with arbitrary topologies through the use of field programmable gate arrays. This architecture allows the design of appropriate filters and multiple time delays, and greatly extends the possibilities for exploring synchronization patterns in arbitrary network topologies. This has enabled us to explore complex dynamics on networks with nodes that can be perfectly identical, introduce parameter heterogeneities and multiple time delays, as well as change network topologies to control the formation and evolution of patterns of synchrony. This article is part of the theme issue 'Nonlinear dynamics of delay systems'.
Cerebral laterality has been linked to accident proneness and time perception, but the possible role of time estimation abilities has received little attention. Accordingly, the present study focused ...on this under-explored question while also aiming to replicate past work examining the relationship between measures of laterality and injury proneness. Participants reported on the number of accidents they have had in their lifetime requiring medical care and the number of minor accidents they had in the past month as outcome variables. They also completed the Waterloo Handedness Questionnaire, a left bias visual task (Greyscales task), a right bias auditory verbal task (Fused Dichotic Words Task), and an objective measure of time perception. Extensive examination of statistical model fit showed that a model assuming a Poisson distribution provided the best fit for minor injuries and an additional negative binomial provided the best fit to the lifetime accidents. Results showed a negative relation between the degree of verbal laterality (absolute right bias) and injuries requiring medical care. Furthermore, the number of accidents requiring medical care was positively related to the precision of time estimation and the direction of verbal laterality on response time (raw right bias). Interpretations of these findings emphasize their implications for interhemispheric communication and motor control in the context of time estimation and auditory verbal laterality. These aspects seem to provide promising avenues for future research.
Networks of nonlocally coupled phase oscillators can support chimera states in which identical oscillators evolve into distinct groups that exhibit coexisting synchronous and incoherent behaviours ...despite homogeneous coupling. Similar nonlocal coupling topologies implemented in networks of chaotic iterated maps also yield dynamical states exhibiting coexisting spatial domains of coherence and incoherence. In these discrete-time systems, the phase is not a continuous variable, so these states are generalized chimeras with respect to a broader notion of incoherence. Chimeras continue to be the subject of intense theoretical investigation, but have yet to be realized experimentally. Here we show that these chimeras can be realized in experiments using a liquid-crystal spatial light modulator to achieve optical nonlinearity in a spatially extended iterated map system. We study the coherence incoherence transition that gives rise to these chimera states through experiment, theory and simulation. Our system is an experimental realization of a coupled-map lattice (CML), a class of systems that has received sustained theoretical interest for the past three decades. Although the dynamics and statistical physics of CML systems have been theoretically explored, very few (if any) experimental realizations exist. In our experiments, we create CML dynamics by using a liquid-crystal spatial light modulator (SLM) to control the polarization properties of an optical wavefront. We may electronically introduce any desired coupling topology including nearest neighbour, nonlocal, small world and scale free. In this work, we impose periodic boundary conditions for both one-dimensional (1D) and 2D nonlocally coupled maps. Thus, we have developed a powerful experimental technique to observe the parallel evolution of the dynamics of arrays of coupled maps numbering up to thousands or more depending on the goals of the experiment. PUBLICATION ABSTRACT
The property of self-imaging combined with the polarization birefringence of the angled multimode waveguide is used to design a silicon nitride (SiN) polarization splitter (PS) at λ ∼ 1550 nm. The ...demonstrated PS on a 450 nm thick SiN device layer (with 2.5 µm cladding oxide) has a footprint of 80 µm×13 µm and exhibits nearly wavelength independent performance over the C+L bands. Also, the device can be configured as a polarization combiner (PC) in reverse direction with similar bandwidth and performance. The measured crosstalk (CT) and insertion loss (IL) are respectively <−18 dB (<−20 dB) and ∼0.7 dB (∼0.8 dB) for TE (TM) polarization over the measurement wavelength range of 1525 nm ≤ λ ≤ 1625 nm. The measured device parameter variations suggest some tolerance to fabrication variations. Such a device is a good candidate for a photonics integrated chip (PIC) foundry-compatible, SiN PS.
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