ATOM-LASER MAKES MEASUREMENT OF GRAVITY

LY12724A

- Compared to a thermal light source, such as a light bulb, the optical laser revolutionised the precision of optical measurements, which utilise the interference of light waves in devices known as interferometers. In the same way, atom-interferometers, which use matter waves, should benefit from the use of an atom-laser; the direct analogy of an optical laser. This paper presents the first direct comparison of a thermal and laser-like atom sources used in an atom-interferometer that measures gravity. Everyday, many people take advantage of the optical laser’s measurement precision, for example, by using a DVD player. Perhaps less obvious is the permeation of atom-interferometers into society. Atomic clocks are examples of atom-interferometers, again affecting many people daily via their use of GPS, which requires exquisite precision in the measurement of time. More recently, atom-interferometers have been used for precision inertial measurements, such as measuring gravitational acceleration. Indeed, the most precise gravity sensors include atom-interferometers, and the measurement of gravity has applications ranging from fundamental tests of physical theories, through to Earth sciences, mineral exploration, and navigation. This work represents an important step forward in the development of the next generation precision inertial sensors.

Watching Flames Spread in Microgravity

LU12255EJ

- Waves of chemical reaction spreading through a heterogeneous media are found throughout biology, chemistry, and physics. Most theories to understand how these waves spread assume that individual particles can be neglected and their effect is smoothed over the media. Our paper shows that for some systems, this assumption fails and an unusual regime of wave propagation can occur which we call the “discrete regime.” Examples of familiar systems that might exhibit this behavior include clouds of combustible dust in air, forest fires, or flames propagating through a rocket propellant. In the discrete regime, even if the particles burn infinitely fast, the reactive wave (or flame) is still limited by the time it takes the heat released by one particle to spread to the neighboring particles. Therefore, the overall process becomes statistical, being influenced by the randomized position of the particles in three-dimensional space. In addition to theoretical and computer-based solutions, we experimentally observed this discrete regime by igniting flames in suspensions of iron particles in air, where the nitrogen had been replaced by xenon in order to decrease the heat conductivity of the gas. The slow propagation speed of the flames (3 to 5 cm/s) made them sensitive to being disrupted by gravity and necessitated conducting the experiments in a reduced-gravity (freefall) environment onboard an airplane flying along a parabolic trajectory.

Metamaterial-based model of warp drive

LY11889BJ

- Electromagnetic metamaterials are capable of emulating many exotic space-time geometries, such as black holes, rotating cosmic strings, and the big bang singularity. Here we present a metamaterial-based model of the Alcubierre warp drive, and study its limitations due to available range of metamaterial parameters. It appears that the material parameter range introduces strong limitations on the achievable “warp speed”, so that ordinary magnetoelectric materials cannot be used. On the other hand, newly developed “perfect” bi-anisotropic non-reciprocal magnetoelectric metamaterials should be capable of emulating the physics of warp drive gradually accelerating up to 1/4 the speed of light.

The figure here shows an example of a metamaterial geometry, which
explicitly violates spatial and time reversal symmetries in ways that make warp drive simulation possible.

Has the black hole at our Galaxy's center been feeding lately?

LD13673

- The recent discovery of huge `bubbles' emitting gamma-rays high above
and on either side of the galactic plane has puzzled the astrophysical
community and challenged long held beliefs: Has the supermassive black
hole at the centre of the Milky Way been shooting out jets of plasma?
Just how are high-energy particles being produced so far away from all
the stars in the Galaxy? We present a model that can explain these
mysterious structures and will allow us to answer such questions in the
near future.

The Milky Way is generally perceived as a flat thin disk of stars
visible by its faint glow in the night sky. Recently, this view has been
challenged by data from the Fermi-LAT satellite experiment. High-energy
particles must be radiating in huge bubble-like structures extending far
above and below the stellar disk which are shining in gamma-rays. This
is all the more surprising as the massive black hole at the centre of
our Galaxy is believed to be quiescent, in contrast to active galaxies
where we can see jets of plasma being shot out as the central black hole
swallows up stars and gas. We show that such activity may have occurred
in our own Galaxy just a few million years ago and that high energy
electrons can be accelerated by the resulting plasma turbulence and
produce high-energy gamma-rays. Our model explains the appearance of the
bubbles and the spectrum of their emission and makes detailed
predictions for future observations which can test the model further. It
appears that our Galaxy may not be such a quiet place as we had imagined
all this time.

Spin Transistors at Practical Temperatures

LE13564

- A European team of researchers has discovered that new electronic states in the so-called topological insulator Bismuth Selenide could prove the key to room temperature operation of a radically new type of computing technology. The ubiquitous transistor, on which almost all electronics is based, relies on the ability to tune the electrical conductivity of a semiconductor by applying a small external voltage to move charge around. For decades, researchers have been aspiring to create a faster and more energy efficient transistor by utilizing a different fundamental property of the electron - its tiny magnetic moment known as
its spin. This goal has proved remarkably elusive as the so-called Rashba effect, on which this spin-transistor is based, is miniscule. Consequently, to feel a large enough effect, electrons must travel long distances without being kicked off their path. This is only possible if the whole device is kept at a temperature below −270°C - hardly a practical requirement for everyday use. Now, in a paper to be published in Physical Review Letters, it has been shown that Bismuth Selenide can support an electrostatically tuneable Rashba effect which is over one hundred times larger than in any other known semiconductor and persists well above room temperature. This sets the stage for building a spin-transistor to work at realistic temperatures, and may well provide the first practical applications of the newly-famed topological insulators.