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Published entries: 206
Matching entries: 206. Showing 151–175 of 206.
Paper · 2009
Semiclassical instability of dynamical warp drives
- Stefano Finazzi(Author)
- Stefano Liberati(Author)
- Carlos Barceló(Author)
Finazzi, Liberati and Barceló extend quantum corrections for warp drives from eternal bubbles at fixed speed to the more realistic case of a superluminal bubble created from initially flat spacetime. They map the causal structure of eternal and dynamical warp spacetimes and compute the renormalised stress-energy tensor of a quantum field in them. An observer at the centre of a superluminal bubble generically sees a thermal flux of Hawking particles, which becomes extremely high if the exotic matter comes from a quantum field obeying quantum inequalities. The stress-energy grows exponentially at the bubble's front wall, so these geometries are unstable to semiclassical backreaction.
Paper · 1997
Shearing the vacuum – quantum friction
- J B Pendry(Author)
J. B. Pendry asks whether two perfectly smooth surfaces at absolute zero, defined only by their dielectric functions and separated by a gap, feel friction when sheared past each other. The aim is the simplest possible system, stripped of every complication, to see how friction arises at all. Quantum fluctuations produce friction between such surfaces even at absolute zero. For materials with resistivity around 1 mΩ in close proximity, the friction is comparable to everyday frictional forces. It depends only on the surfaces' electromagnetic reflection coefficients and falls off as a power law with separation, so it can dominate at large gaps, like the van der Waals force.
Paper · 2009
Signal photon flux and background noise in a coupling electromagnetic detecting system for high-frequency gravitational waves
- Fangyu Li(Author)
- Nan Yang(Author)
- Zhenyun Fang(Author)
- Robert M. L. Baker(Author)
- Gary V. Stephenson(Author)
- Hao Wen(Author)
Li, Yang, Fang, Baker, Stephenson and Wen study a detector for high-frequency gravitational waves that couples a Gaussian microwave beam, a static magnetic field and fractal membranes or equivalent microwave lenses. Unlike the pure inverse Gertsenshtein effect, this scheme from Chinese and US groups combines synchro-resonance with the inverse Gertsenshtein effect. The measurable signal is the transverse first-order perturbative photon flux, not the second-order or longitudinal flux. The fluxes have different signal-to-noise ratios at different receiving surfaces. For typical laboratory conditions and wave amplitudes of 10^-26 to 10^-30 at 5 GHz with about 1 Hz bandwidth, the signal needs roughly 10^3 to 10^5 seconds of accumulation.
Paper · 2015
Simulation of the hydrogen ground state in stochastic electrodynamics
- Theo M Nieuwenhuizen(Author)
- Matthew T P Liska(Author)
Theo Nieuwenhuizen and Matthew Liska study stochastic electrodynamics, a classical theory in which the vacuum holds random fields with the zero-point energy of half ħω in every mode. The theory explains many harmonic oscillator phenomena, while firm results for nonlinear systems are still missing. They study the hydrogen ground state by numerically solving the Abraham-Lorentz equation in the dipole approximation, with the random field as a sum of Gaussian frequency components, computed with OpenCL. The approach extends Cole and Zou's 2003 work to the full three-dimensional problem and longer simulation times. Compared with a conjectured ground-state phase space density, short runs trend towards confirmation, but in every model tried the atom ionises at longer times.
Paper · 2016
Solar wind test of the de Broglie-Proca massive photon with Cluster multi-spacecraft data
- Alessandro Retinò(Author)
- Alessandro D.A.M. Spallicci(Author)
- Andris Vaivads(Author)
Retinò, Spallicci and Vaivads test whether the photon truly has zero mass, since nearly everything known about the universe arrives by photons. They use data from the four Cluster spacecraft in the solar wind at 1 AU. They look for departures from Ampère's law, computing the magnetic field's curl from four-point measurements and the current from ion and electron velocities, which a single spacecraft could never do. The upper bound on the photon mass lies between 1.4 × 10^-49 and 3.4 × 10^-51 kg. These limits rest on fewer assumptions than earlier estimates, and this is the only solar wind test to treat experimental errors in detail.
Paper · 2002
Spatially Averaged Quantum Inequalities Do Not Exist in Four-Dimensional Spacetime
- L. H. Ford(Author)
- Adam D. Helfer(Author)
- Thomas A. Roman(Author)
L. H. Ford, Adam Helfer and Thomas Roman start from the fact that quantum fields can produce local negative energy densities after renormalisation. This is possible because renormalisation involves an infinite subtraction, even though the classical energy density looks positive definite. For a massless free scalar field they construct states that superpose the vacuum with multi-mode two-particle states. These states can place an arbitrarily large amount of negative energy in a given region of space at a fixed time. Each state in the sequence used is of Hadamard form, so the energy density can be made as negative as desired with physically acceptable states. This gives an explicit counterexample: no spatially averaged quantum inequality exists in four-dimensional spacetime.
Paper · 2015
Spin-dependent two-color Kapitza-Dirac effects
- S. McGregor(Author)
- W. C.-W. Huang(Author)
- B. A. Shadwick(Author)
- H. Batelaan(Author)
McGregor, Huang, Shadwick and Batelaan analyse how electron spin behaves as electrons pass through a laser field. With pulsed electron sources synchronised to pulsed lasers becoming available, it is timely to study the weaker coupling of electron spin to laser light. They present an experimentally realisable two-colour Kapitza-Dirac scenario in which spin-dependent effects of the laser-electron interaction dominate. Both the laser strength and electron speed stay non-relativistic. This extends spin control of electrons by light, previously predicted for X-ray lasers and relativistic electrons, into the non-relativistic, visible-light domain. The effect could provide or analyse ultrafast spin-polarised electron pulses for ultrafast electron diffraction and microscopy.
Paper · 2026
Stimulated Emission of Gravitational Waves via Dissimilar Superconducting Josephson Junctions
- Gary V. Stephenson(Author)
Gary Stephenson proposes an experiment to show that stimulated emission of gravitational waves is achievable in the laboratory. He builds on Halpern and Laurent in 1964, Ford in 1982 and Fontana's 2012 high-temperature superconductor gaser. Ford showed that with enough quantum radiators the difference between semiclassical and quantum emission should be measurable. Josephson junctions joining an s-wave to a d-wave superconductor can force spin-2 transitions that trigger gravitational wave emission. He outlines phased-array gravitational wave emitters built from such junctions, and the next step is to build and test the hardware.
Paper · 2020
Stochastic Electrodynamics: Renormalized Noise in the Hydrogen Ground-State Problem
- Theo M. Nieuwenhuizen(Author)
Theo Nieuwenhuizen treats the hydrogen ground state as the touchstone for stochastic electrodynamics. This classical theory aims to explain quantum phenomena through a physical stochastic field that fills the universe and acts on charged particles, and earlier work reproduced the shape of the quantum ground state from it. His earlier work showed, numerically and theoretically, that the model hydrogen atom self-ionises after a characteristic time. For the harmonic oscillator he had renormalised the stochastic force to suppress high-frequency tails, so that physical resonances dominate every frequency integral. Here he applies several such noise renormalisation schemes to hydrogen: some behave well, while others create low-frequency pathologies. None of them removed the self-ionisation.
Paper · 2026
Subcycle tomography of quantum light
- Geehyun Yang(Author)
- Matthias Kizmann(Author)
- Alfred Leitenstorfer(Author)
- Andrey S. Moskalenko(Author)
This work asks what quantum light looks like at its most fundamental timescale, a single oscillation cycle of a mode. The authors show theoretically that local quantum measurements can reconstruct and visualise a quantum field below one cycle, even when its temporal mode structure is unknown in advance. They describe generating and performing tomography on ultrabroadband squeezed states and on photon-subtracted states derived from them, including single-photon states. Building phase-space distributions from subcycle-resolved tomography, they track how these states evolve in phase space and push temporal resolution to its physical limit. The results lay a cornerstone for time-domain quantum optics.
Paper · 1998
Superluminal travel requires negative energies
- Ken D. Olum(Author)
Ken Olum takes up whether the spacetime metric can be manipulated to allow very rapid travel between distant points, as in the Alcubierre and Krasnikov examples. Defining faster-than-light travel is subtle, and he shows a metric that seems to allow it but is just flat space. He defines superluminal travel as a path that reaches a destination surface earlier than any neighbouring path. With that definition and the generic condition, he proves superluminal travel requires violating the weak energy condition, that is, negative energy density. Known examples already needed negative energy densities, and this result shows the requirement is general rather than a feature of particular designs.
Paper · 2017
Superradiant Topological Peierls Insulator inside an Optical Cavity
- Farokh Mivehvar(Author)
- Helmut Ritsch(Author)
- Francesco Piazza(Author)
Farokh Mivehvar, Helmut Ritsch and Francesco Piazza study a spinless ultracold Fermi gas trapped along an optical resonator and lit from the side by a laser near a cavity mode. Above a threshold pump intensity the gas breaks a Z2 symmetry into a periodic pattern that collectively scatters laser photons into the cavity. With blue detuning the emerging superradiant lattice has two possible dimerisations, and one of them gives topologically nontrivial bands with a nonzero Zak phase. When the Fermi momentum is near half the cavity wavenumber, a Peierls-like instability creates a topological insulator with a gap at the Fermi surface and a pair of edge states.
Paper · 2019
Sustained Neutron Production from a Sheared-Flow Stabilized Z Pinch
- Y. Zhang(Author)
- U. Shumlak(Author)
- B. A. Nelson(Author)
- R. P. Golingo(Author)
- T. R. Weber(Author)
- A. D. Stepanov(Author)
- E. L. Claveau(Author)
- E. G. Forbes(Author)
- Z. T. Draper(Author)
- J. M. Mitrani(Author)
- H. S. McLean(Author)
- K. K. Tummel(Author)
- D. P. Higginson(Author)
- C. M. Cooper(Author)
Zhang, Shumlak and colleagues report the first sustained, quasi-steady neutron production from the Fusion Z-pinch Experiment, FuZE, running on 20% deuterium and 80% hydrogen by volume. The device uses sheared-flow stabilisation, which keeps the pinch plasma long-lived. Neutron emission lasting about 5 µs appears reproducibly at pinch currents near 200 kA, within a quiet plasma period of about 16 µs. Average yield is (1.25 ± 0.45) × 10^5 neutrons per pulse and scales with the square of the deuterium concentration. Integrated diagnostics measure 1 to 2 keV temperatures, densities near 10^17 cm^-3 and a 0.3 cm pinch radius alongside the neutrons.
Paper · 2024
Symmetries and selection rules: optimising axion haloscopes for gravitational wave searches
- Valerie Domcke(Author)
- Camilo Garcia-Cely(Author)
- Sung Mook Lee(Author)
- Nicholas L. Rodd(Author)
Domcke, Garcia-Cely, Lee and Rodd start from a shared signature: inside electromagnetic fields, both axions and gravitational waves induce oscillating magnetic fields. They demonstrate that the size of that response is set largely by the symmetries of the instrument. For low-mass axion haloscopes they derive selection rules giving each detector geometry's sensitivity to axions and gravitational waves, and showing how to shape the experiment to maximise both signals. For a toroidal magnet the best axion and gravitational-wave sensitivities cannot coincide, but changing the pickup loop geometry, or adding several loops, recovers sensitivity to both. The formalism forecasts the best gravitational-wave sensitivity from 100 kHz to 100 MHz for ABRACADABRA, BASE, ADMX SLIC, SHAFT, WISPLC and DMRadio.
patent · 2024
System and Method for Generating Forces Using Asymmetrical Electrostatic Pressure (continuation)
- Andrew Neil Aurigema(Author)
- Charles Raymond Buhler, IV(Author)
Aurigema and Buhler’s continuation application proposes generating net force through asymmetric electrostatic pressure on shaped surfaces. For a multiblade test article, the inventors report approximately 237 micronewtons at +25 kilovolts and 421 micronewtons after enlarging the opposing electrode area from 8 to 15 square inches, a factor of 1.77. The plotted raw-force resolution is 0.1 millinewton. They describe grounded transparent enclosures and device reversal as controls addressing ion wind and attraction to surrounding surfaces. The application also proposes a volumetric force associated with divergent electric fields in dielectric materials; those mechanism claims and suggested spacecraft propulsion uses extend beyond the specifically reported test measurements and apparatus configurations.
Paper · 2014
Temperature Dependence of Excess Power in Two-laser Experiments
- Peter L. Hagelstein(Author)
- Dennis Letts(Author)
Peter Hagelstein and Dennis Letts analyse the Letts two-laser experiment, where excess heat depends on temperature and is mostly zero without a magnetic field. Earlier Fleischmann-Pons work and other groups had also seen excess power rise with temperature. A new experiment by the authors confirms higher excess power at higher temperature. They add this temperature dependence to their earlier empirical model of the two-laser experiment. They explain it through helium-4 that blocks active sites when excess power is high, and whose removal at higher temperature frees those sites again.
Paper · 2007
Tests of new physics from precise measurements of the Casimir pressure between two gold-coated plates
- R. S. Decca(Author)
- D. López(Author)
- E. Fischbach(Author)
- G. L. Klimchitskaya(Author)
- D. E. Krause(Author)
- V. M. Mostepanenko(Author)
Decca, López, Fischbach, Klimchitskaya, Krause and Mostepanenko use the Casimir effect, a direct manifestation of the quantum vacuum, to test for new physics. The effect reaches from particle physics, gravitation and cosmology to condensed matter and nanotechnology, and it constrains physics beyond the standard model. A micromechanical torsion oscillator measures the Casimir pressure between two gold-coated plates. They sharply reduce random errors and, for the first time, compare with theory using measured electronic parameters of gold coatings made under the same conditions. The data conclusively exclude predictions of large thermal effects below 1 µm. They also tighten limits on Yukawa-type corrections to Newtonian gravity over ranges from 29.5 nm to 86 nm.
Paper · 1999
The 'friction' of vacuum, and other fluctuation-induced forces
- Mehran Kardar(Author)
- Ramin Golestanian(Author)
Kardar and Golestanian review forces born of fluctuations, starting from the static Casimir attraction between two conducting plates caused by quantum fluctuations of the electromagnetic field between them. Thermal fluctuations in correlated fluids such as superfluids, liquid crystals and electrolytes are likewise changed by boundaries, producing forces that shape wetting and layering. A path integral formalism handles boundaries of any shape and opens the dynamic Casimir effect of moving boundaries. The electromagnetic vacuum then acts like a complex fluid that alters how objects move through it. A plate's effective mass depends on its shape and becomes anisotropic, and its motion is damped by photon emission.
Paper · 2012
The Alcubierre Warp Drive: On the Matter of Matter
- Brendan McMonigal(Author)
- Geraint F. Lewis(Author)
- Philip O’Byrne(Author)
McMonigal, Lewis and O'Byrne study the Alcubierre warp drive, which moves a ship at any global velocity by deforming spacetime in a bubble around it. They trace how light and massive particles, with starting speeds anywhere from −c to c, interact with bubbles moving below and above light speed at constant and changing velocity. Particles moving the same way as the ship gain extremely high energy and become time locked, experiencing very little proper time inside the bubble. An accelerating bubble boosts particles moving toward its front and slows those moving toward its rear, while matter at rest with the bubble is unaffected. The size of the boost scales with the bubble's acceleration.
Paper · 2006
The Casimir effect within scattering theory
- Astrid Lambrecht(Author)
- Paulo A Maia Neto(Author)
- Serge Reynaud(Author)
Astrid Lambrecht, Paulo Maia Neto and Serge Reynaud review the theory of the Casimir effect built on scattering techniques. The formalism is now largely mastered, so the accuracy of theory-experiment comparisons depends on how precisely experimental conditions are described. Imperfect knowledge of real mirrors' optical properties leaves uncertainty in reflection effects and keeps the temperature dependence of the force between dissipative mirrors under debate. Real mirrors are not perfectly specular, and a more general formalism with non-specular reflection, mixing wavevectors and polarisations, handles this. It has been used for roughness corrections and the lateral force between corrugated surfaces, where the proximity force approximation proves inaccurate.
Paper · 2004
The Casimir effect: recent controversies and progress
- Kimball A Milton(Author)
Kimball Milton reviews the Casimir effect, the family of phenomena implied by quantum vacuum fluctuations, with emphasis on results from the preceding four years. He rederives the force between parallel plates as the strong-coupling limit of delta-function potential planes and clarifies the role of surface divergences. For real materials he derives the Lifshitz formula from geometrical optics and rederives the Casimir-Polder forces. He gives close attention to the debate over temperature corrections to the force between real metal surfaces, and to improvements in the proximity force approximation and the state of experiments. New results on Casimir self-stress appear alongside summaries of Casimir effects for solitons and of the dynamical Casimir effect.
Paper · 2026
The classical linear oscillator in classical electrodynamics with classical zero-point radiation
- Timothy H Boyer(Author)
Timothy Boyer shows that a classical charged linear oscillator in classical electromagnetic zero-point radiation has a stable ground state and resonant excited states analogous to the quantum oscillator's. Because zero-point radiation is Lorentz invariant, any system reaching equilibrium in it must be at least approximately Lorentz invariant, and few potentials qualify. Finite wave speed means the charge must feel the full field at its actual position, not just the dipole approximation. In the resonant excited states, dipole radiation is balanced by energy absorbed from zero-point radiation at odd multiples of the oscillator frequency. The Bohr frequency condition appears naturally, giving a classical electromagnetic basis for the old quantum picture of electrons in classical orbits.
Paper · 2013
The Generalized Second Law implies a Quantum Singularity Theorem
- Aron C Wall(Author)
Aron Wall uses the generalised second law of thermodynamics to prove a quantum singularity theorem, extending the idea of a trapped surface to quantum situations. Like Penrose's theorem, it implies null geodesic incompleteness inside black holes and in the past of spatially infinite Friedmann-Robertson-Walker cosmologies. If space is finite, the past can hold only finitely many entropy-producing processes unless the arrow of time reverses. In asymptotically flat spacetime the law also forbids traversable wormholes, negative masses, faster-than-light travel between asymptotic regions and closed timelike curves. Because the semiclassical approximation is used only at low curvature, the results may hold in full quantum gravity.
Paper · 2024
The Nature of Cold Fusion (Cold Fusion Made Simple)
- Edmund Storms(Author)
Edmund Storms explains cold fusion through a new reading of the observed behaviour that links the behaviours to one another and to the mechanism behind them. His model is built on how the process behaves, with observation as the teacher, rather than on why it works. The nuclear-active environment is most likely a gap or crack of critical size, larger than the spacing of hydrogen atoms but too small for H2 molecules to form. Many past successes, from long electrolysis to codeposition, can be explained by creating this same condition. The mechanism is meant to make the nuclear process start more reliably, and the paper proposes ways to test the model.
Paper · 2014
The Pd + D co-deposition: process, product, performance
- Stanislaw Szpak(Author)
Stanislaw Szpak describes in detail how palladium electrodes are made by palladium and deuterium co-deposition. Proposed in May 1989, the method electrodeposits palladium and deuterium ions together onto a substrate that does not absorb deuterium, removing the long charging time of massive electrodes. It was also meant to study the processes that start nuclear activity in the polarised palladium and heavy water system. Szpak responds to Letts and Hagelstein, who modified his protocol for 100% reproducible excess heat, noting his group had shown deuterium loading above 100%. He concludes that co-deposition gives effective cathodes and insight into the conditions behind nuclear events inside the palladium lattice.