arXiv subjects

N. F. Johnson

Publications and source records attributed to N. F. Johnson.

At least 19 recordsLinked to original sources

arXiv2025

Twisted light drives chiral excitations of interacting electrons in nanostructures with magnetic field

Twisted light (TL), a special kind of light carrying orbital angular momentum, provides a powerful tool for driving symmetry resolved transitions in quantum confined nanostructures. We study a realistic model where a TL pulse excites two interacting electrons in a nanostructure under a perpendicular magnetic field. To include image charge effects in layered systems, we use an effective electron electron potential of the form 1/r^n. For n = 2, the system exhibits an underlying su(1,1) dynamical symmetry, enabling analytical solutions and a clear interpretation of selection rules, parity changes, and angular momentum resolved absorption. We show that the bare Coulomb 1/r interaction produces similar spectra, indicating that twisted light driven excitations are robust against the precise interaction form. The excitation spectrum reveals strong chiral properties: TL pulses, unlike conventional dipolar fields, directly access interaction-driven transitions otherwise symmetry-forbidden. In particular, TL breaks the generalized Kohn theorem, exposing internal excitations through multi quanta orbital processes. More broadly, our results establish TL as a sensitive probe of correlations, symmetry, and magneto-optical dynamics in strongly interacting quantum systems, uncovering features that remain invisible to standard infrared absorption.

cond-mat.mes-hall↗

arXiv2023

Cavity-induced switching between Bell-state textures in a quantum dot

Nanoscale quantum dots in microwave cavities can be used as a laboratory for exploring electron-electron interactions and their spin in the presence of quantized light and a magnetic field. We show how a simple theoretical model of this interplay at resonance predicts complex but measurable effects. New polariton states emerge that combine spin, relative modes, and radiation. These states have intricate spin-space correlations and undergo polariton transitions controlled by the microwave cavity field. We uncover novel topological effects involving highly correlated spin and charge density that display singlet-triplet and inhomogeneous Bell-state distributions. Signatures of these transitions are imprinted in the photon distribution, which will allow for optical read-out protocols in future experiments and nanoscale quantum technologies.

cond-mat.mes-hall↗

arXiv2021

Ladder of Loschmidt anomalies in the deep strong-coupling regime of a qubit-oscillator system

We uncover a remarkably regular array of singularity-like structures within the deep strong-coupling limit of qubit-oscillator (e.g. light-matter) systems described by the quantum Rabi model, as a function of time and coupling strength. These non-analytic anomalies in the Loschmidt amplitude (echoes) suggest the existence of new forms of dynamical phase transition within this deep strong-coupling regime. The key feature whereby the initial state collapses into orthogonal states at select values of the interaction strength and select times, may be used to enhance - or attack - quantum information processing or computation schemes that rely on removing - or retaining - a given quantum state.

cond-mat.mes-hall↗

arXiv2021

Losing the battle over best-science guidance early in a crisis: Covid-19 and beyond

Ensuring widespread public exposure to best-science guidance is crucial in a crisis, e.g. Covid-19, climate change. Mapping the emitter-receiver dynamics of Covid-19 guidance among 87 million Facebook users, we uncover a multi-sided battle over exposure that gets lost well before the pandemic's official announcement. By the time Covid-19 vaccines emerge, the mainstream majority -- including many parenting communities -- have moved even closer to more extreme communities. The hidden heterogeneity explains why Facebook's own promotion of best-science guidance also missed key audience segments. A simple mathematical model reproduces these exposure dynamics at the system level. Our findings can be used to tailor guidance at scale while accounting for individual diversity, and to predict tipping point behavior and system-level responses to interventions.

physics.soc-ph↗

arXiv2021

Mainstreaming of conspiracy theories and misinformation

Parents - particularly moms - increasingly consult social media for support when taking decisions about their young children, and likely also when advising other family members such as elderly relatives. Minimizing malignant online influences is therefore crucial to securing their assent for policies ranging from vaccinations, masks and social distancing against the pandemic, to household best practices against climate change, to acceptance of future 5G towers nearby. Here we show how a strengthening of bonds across online communities during the pandemic, has led to non-Covid-19 conspiracy theories (e.g. fluoride, chemtrails, 5G) attaining heightened access to mainstream parent communities. Alternative health communities act as the critical conduits between conspiracy theorists and parents, and make the narratives more palatable to the latter. We demonstrate experimentally that these inter-community bonds can perpetually generate new misinformation, irrespective of any changes in factual information. Our findings show explicitly why Facebook's current policies have failed to stop the mainstreaming of non-Covid-19 and Covid-19 conspiracy theories and misinformation, and why targeting the largest communities will not work. A simple yet exactly solvable and empirically grounded mathematical model, shows how modest tailoring of mainstream communities' couplings could prevent them from tipping against establishment guidance. Our conclusions should also apply to other social media platforms and topics.

physics.soc-ph↗

arXiv2020

Not sure? Handling hesitancy of COVID-19 vaccines

From the moment the first COVID-19 vaccines are rolled out, there will need to be a large fraction of the global population ready in line. It is therefore crucial to start managing the growing global hesitancy to any such COVID-19 vaccine. The current approach of trying to convince the "no"s cannot work quickly enough, nor can the current policy of trying to find, remove and/or rebut all the individual pieces of COVID and vaccine misinformation. Instead, we show how this can be done in a simpler way by moving away from chasing misinformation content and focusing instead on managing the "yes--no--not-sure" hesitancy ecosystem.

physics.soc-ph↗

arXiv2020

Covid-19 infodemic reveals new tipping point epidemiology and a revised $R$ formula

Many governments have managed to control their COVID-19 outbreak with a simple message: keep the effective '$R$ number' $R<1$ to prevent widespread contagion and flatten the curve. This raises the question whether a similar policy could control dangerous online 'infodemics' of information, misinformation and disinformation. Here we show, using multi-platform data from the COVID-19 infodemic, that its online spreading instead encompasses a different dynamical regime where communities and users within and across independent platforms, sporadically form temporary active links on similar timescales to the viral spreading. This allows material that might have died out, to evolve and even mutate. This has enabled niche networks that were already successfully spreading hate and anti-vaccination material, to rapidly become global super-spreaders of narratives featuring fake COVID-19 treatments, anti-Asian sentiment and conspiracy theories. We derive new tools that incorporate these coupled social-viral dynamics, including an online $R$, to help prevent infodemic spreading at all scales: from spreading across platforms (e.g. Facebook, 4Chan) to spreading within a given subpopulation, or community, or topic. By accounting for similar social and viral timescales, the same mathematical theory also offers a quantitative description of other unconventional infection profiles such as rumors spreading in financial markets and colds spreading in schools.

physics.soc-ph↗

arXiv2020

Hidden order in online extremism and its disruption by nudging collective chemistry

We show that the eclectic "Boogaloo" extremist movement that is now rising to prominence in the U.S., has a hidden online mathematical order that is identical to ISIS during its early development, despite their stark ideological, geographical and cultural differences. The evolution of each across scales follows a single shockwave equation that accounts for individual heterogeneity in online interactions. This equation predicts how to disrupt the onset and 'flatten the curve' of such online extremism by nudging its collective chemistry.

physics.soc-ph↗

arXiv2020

Hate multiverse spreads malicious COVID-19 content online beyond individual platform control

We show that malicious COVID-19 content, including hate speech, disinformation, and misinformation, exploits the multiverse of online hate to spread quickly beyond the control of any individual social media platform. Machine learning topic analysis shows quantitatively how online hate communities are weaponizing COVID-19, with topics evolving rapidly and content becoming increasingly coherent. Our mathematical analysis provides a generalized form of the public health R0 predicting the tipping point for multiverse-wide viral spreading, which suggests new policy options to mitigate the global spread of malicious COVID-19 content without relying on future coordination between all online platforms.

physics.soc-ph↗

arXiv2019

Health Wars and Beyond: The Rapidly Expanding and Efficient Network Insurgency Interlinking Local and Global Online Crowds of Distrust

We present preliminary results on the online war surrounding distrust of expertise in medical science -- specifically, the issue of vaccinations. While distrust and misinformation in politics can damage democratic elections, in the medical context it may also endanger lives through missed vaccinations and DIY cancer cures. We find that this online health war has evolved into a highly efficient network insurgency with direct inter-crowd links across countries, continents and cultures. The online anti-vax crowds (referred to as Red) now appear better positioned to groom new recruits (Green) than those supporting established expertise (Blue). We also present preliminary results from a mathematically-grounded, crowd-based analysis of the war's evolution, which offers an explanation for how Red seems to be turning the tide on Blue.

physics.soc-ph↗

arXiv2018

Social media cluster dynamics create resilient global hate highways

Online social media allows individuals to cluster around common interests - including hate. We show that tight-knit social clusters interlink to form resilient 'global hate highways' that bridge independent social network platforms, countries, languages and ideologies, and can quickly self-repair and rewire. We provide a mathematical theory that reveals a hidden resilience in the global axis of hate; explains a likely ineffectiveness of current control methods; and offers improvements. Our results reveal new science for networks-of-networks driven by bipartite dynamics, and should apply more broadly to illicit networks.

physics.soc-ph↗

arXiv2018

Social media affects the timing, location, and severity of school shootings

Over the past two decades, school shootings within the United States have repeatedly devastated communities and shaken public opinion. Many of these attacks appear to be `lone wolf' ones driven by specific individual motivations, and the identification of precursor signals and hence actionable policy measures would thus seem highly unlikely. Here, we take a system-wide view and investigate the timing of school attacks and the dynamical feedback with social media. We identify a trend divergence in which college attacks have continued to accelerate over the last 25 years while those carried out on K-12 schools have slowed down. We establish the copycat effect in school shootings and uncover a statistical association between social media chatter and the probability of an attack in the following days. While hinting at causality, this relationship may also help mitigate the frequency and intensity of future attacks.

physics.soc-ph↗

arXiv2018

Pulsed Generation of Quantum Coherences and Non-classicality in Light-Matter Systems

We show that a pulsed stimulus can be used to generate many-body quantum coherences in light-matter systems of general size. Specifically, we calculate the exact real-time evolution of a driven, generic out-of-equilibrium system comprising an arbitrary number N qubits coupled to a global boson field. A novel form of dynamically-driven quantum coherence emerges for general N and without having to access the empirically challenging strong-coupling regime. Its properties depend on the speed of the changes in the stimulus. Non-classicalities arise within each subsystem that have eluded previous analyses. Our findings show robustness to losses and noise, and have potential functional implications at the systems level for a variety of nanosystems, including collections of N atoms, molecules, spins, or superconducting qubits in cavities -- and possibly even vibration-enhanced light harvesting processes in macromolecules.

quant-ph↗

arXiv2017

Population polarization dynamics and next-generation social media algorithms

We present a many-body theory that explains and reproduces recent observations of population polarization dynamics, is supported by controlled human experiments, and addresses the controversy surrounding the Internet's impact. It predicts that whether and how a population becomes polarized is dictated by the nature of the underlying competition, rather than the validity of the information that individuals receive or their online bubbles. Building on this framework, we show that next-generation social media algorithms aimed at pulling people together, will instead likely lead to an explosive percolation process that generates new pockets of extremes.

physics.soc-ph↗

arXiv2017

Dynamics of Entanglement and the Schmidt Gap in a Driven Light-Matter System

The ability to modify light-matter coupling in time (e.g. using external pulses) opens up the exciting possibility of generating and probing new aspects of quantum correlations in many-body light-matter systems. Here we study the impact of such a pulsed coupling on the light-matter entanglement in the Dicke model as well as the respective subsystem quantum dynamics. Our dynamical many-body analysis exploits the natural partition between the radiation and matter degrees of freedom, allowing us to explore time-dependent intra-subsystem quantum correlations by means of squeezing parameters, and the inter-subsystem Schmidt gap for different pulse duration (i.e. ramping velocity) regimes -- from the near adiabatic to the sudden quench limits. Our results reveal that both types of quantities indicate the emergence of the superradiant phase when crossing the quantum critical point. In addition, at the end of the pulse light and matter remain entangled even though they become uncoupled, which could be exploited to generate entangled states in non-interacting systems.

quant-ph↗

arXiv2017

New Online Ecology of Adversarial Aggregates: ISIS and beyond

Support for extremist entities - whether from the far right, or far left - often manages to survive globally online despite significant external pressure, and may ultimately inspire violent acts by individuals having no obvious prior history of extremism. Examining longitudinal records of extremist online activity, we uncovered an ecology evolving on a daily timescale that drives online support, and we provide a mathematical theory that describes it. The ecology features self-organized aggregates (online groups such as on Facebook or another social media analog) that proliferate preceding the onset of recent real-world campaigns, and adopt novel adaptive mechanisms to enhance their survival. One of the predictions is that development of large, potentially potent online groups can be thwarted by targeting smaller ones.

physics.soc-ph↗

arXiv2017

Universality and correlations in individuals wandering through an online extremist space

The 'out of the blue' nature of recent terror attacks and the diversity of apparent motives, highlight the importance of understanding the online trajectories that individuals follow prior to developing high levels of extremist support. Here we show that the physics of stochastic walks, with and without temporal correlation, provides a unifying description of these online trajectories. Our unique dataset comprising all users of a global social media site, reveals universal characteristics in individuals' online lifetimes. Our accompanying theory generates analytical and numerical solutions that describe the characteristics shown by individuals that go on to develop high levels of extremist support, and those that do not. The existence of these temporal and also many-body correlations suggests that existing physics machinery can be used to quantify and perhaps mitigate the risk of future events.

physics.soc-ph↗

arXiv2017

Dynamical patterns in individual trajectories toward extremism

Society faces a fundamental global problem of understanding which individuals are currently developing strong support for some extremist entity such as ISIS (Islamic State) -- even if they never end up doing anything in the real world. The importance of online connectivity in developing intent has been confirmed by recent case-studies of already convicted terrorists. Here we identify dynamical patterns in the online trajectories that individuals take toward developing a high level of extremist support -- specifically, for ISIS. Strong memory effects emerge among individuals whose transition is fastest, and hence may become 'out of the blue' threats in the real world. A generalization of diagrammatic expansion theory helps quantify these characteristics, including the impact of changes in geographical location, and can facilitate prediction of future risks. By quantifying the trajectories that individuals follow on their journey toward expressing high levels of pro-ISIS support -- irrespective of whether they then carry out a real-world attack or not -- our findings can help move safety debates beyond reliance on static watch-list identifiers such as ethnic background or immigration status, and/or post-fact interviews with already-convicted individuals. Given the broad commonality of social media platforms, our results likely apply quite generally: for example, even on Telegram where (like Twitter) there is no built-in group feature as in our study, individuals tend to collectively build and pass through so-called super-group accounts.

physics.soc-ph↗