Graphene ink bags UK photography prize

An image of swirling graphene ink in alcohol has won the Engineering and Physical Sciences Research Council's 2017 Science Photography Competition. Taken by James Macleod, a technician at the University of Cambridge's Graphene Centre, the image shows powdered graphite in alcohol that can be used to produce a conductive ink for printing electrical circuits onto paper. "We are working to create conductive inks for printing flexible electronics and are currently focused on optimising our recipe for use in different printing methods and for printing onto different surfaces," says Macleod. "This was the first time we had used alcohol to create our ink and I was struck by how mesmerising it looked while mixing." The competition, which is now in its fourth year, received more than 100 entries and was open to researchers who currently receive grants from the UK funding council.

NASA mission reshapes understanding of plasma waves

NASA has observed unexpected, small-scale complexities in kinetic Alfvén waves (KAWs). KAWs were predicted more than 50 years ago as the means of transferring energy through plasmas. As a KAW propagates, electrons travelling at a certain speed get trapped in weak spots of the wave's magnetic field. Either side of such points, the magnetic field is stronger so the electrons are contained, creating pockets of higher electron density. Meanwhile faster and slower electrons pass energy back and forth with the wave. Using NASA's Magnetospheric Multiscale mission (MMS), scientists have been able to observe the waves at the relatively small scales where the energy transfer happens. The mission contains four spacecraft in a compact pyramid formation, near Earth. As they are just 6 km apart – the closest arrangement achieved to date – they fit between two KAW peaks. The 3D arrangement allows scientists to measure details such as wave direction and speed. "We're seeing a more detailed picture of Alfvén waves than anyone's been able to get before," says team member Dan Gershmam of NASA's Goddard Space Flight Center in the US. Although predicted over half a century ago, the new results, published in Nature Communications, are the most comprehensive measurements to date and showed a higher rate of trapping than expected. The researchers hope the findings may have benefits for nuclear-fusion technology and help to improve energy efficiency.

Two-photon blockade seen in single-atom system

An atomic system that produces bunches of two or fewer photons has been unveiled by physicists in Germany. Based on a two-photon blockade, the system could be useful for creating quantum-optical devices that use multiple photons. A single-photon blockade occurs when an atomic system absorbs one photon and in doing so becomes unable to absorb further light. Unlike most other light sources, such systems emit photons one-by-one in a steady stream – making them potentially very useful for quantum-optics experiments. Physicists would like to extend this concept to create light sources that emit at most two photons at a time by creating an atomic system that exhibits two-photon blockade. Now, Gerhard Rempe and colleagues at the Max Planck Institute for Quantum Optics in Garching have created such a system. It comprises a single rubidium-87 atom that is strongly coupled to an optical cavity. The atom is trapped in the cavity using laser light, which is also used to put the atom into a quantum state that makes it a strong single-photon blockade. When the cavity and atom are strongly coupled, light emitted from the system exhibits strong three-photon "antibunching" – which means that three photons emitted from the system are more equally spaced in time than photons in a conventional laser beam. At the same time, pairs of photons exhibit bunching – which means that they are less equally spaced than photons in a laser beam. Writing in Physical Review Letters, Rempe and colleagues say that these two observations are evidence that a two-photon blockade has been achieved. The team also points out that it should be possible to create a three-photon blockade in their system, and also say that the system could be adapted to produce bunches of photons with a specific number of photons.

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