Diamond Cavities Its Present Structure

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Family matters barely interact with the surrounding lattice. job. Importantly, the potentials have a Nature 479, 372–375 (2011) By creating an array of these defects, it desirable quality of ‘flatness’, have vacuum might be possible to encode an ensemble of expectation values that fall below the Neutron stars arise from the gravitational coupled quantum bits in their spins. Planck scale, and can be embedded, collapse of massive stars during One way of enhancing the coupling without too much fine-tuning, in a a supernova event. Most are thought between qubits of such an array is to embed version of the standard model that is to form via one of two mechanisms, them in an optical cavity — most obviously extended to include supersymmetry. each associated with a different type by forming a cavity out of diamond itself. Supersymmetry links integer-spin and of supernova: iron-core collapse or What’s needed is a narrow-resonance, high- half-integer-spin particles, such that every electron capture. However, attempts to quality cavity that avoids losses to phonon known particle of the standard model is distinguish the two groups by examining modes and other non-radiative channels, partnered by a ‘superparticle’. Evidence of the resulting neutron stars have not yet but this has proved difficult to achieve supersymmetry could be found at the Large been successful. in diamond. Hadron Collider. AW A magnetized neutron star in orbit Janine Riedrich-Möller and colleagues with a companion can, however, constitute have gone some way to overcoming Let it flow a powerful source of X-rays, and such the difficulties by using focused ion- Phys. Rev. Lett. (in the press) X-ray pulsars may hold the key to telling beam milling to create one- and two- apart the two types of neutron star — as dimensional photonic-crystal cavities Christian Knigge and colleagues now show. in suspended single-crystal diamond They have examined data for a large, membranes. They can then tune the well-characterized class of pulsar, and characteristics of the cavities to enhance the have identified a bimodality in the zero-phonon photoluminescent emission distributions of their spin and orbital of silicon–vacancy defects present in periods, and of their orbital eccentricities. the diamond. EG Shorter periods and lower eccentricity, they say, are likely to be associated with Putting it together supernovae that were initiated through Phys. Rev. D 84, 101301 (2011) electron capture by neon and magnesium nuclei in a lower-mass stellar core, rather Sometime after the Big Bang, the Universe than those created when a high-mass is thought to have undergone a period star’s degenerate iron core tips over the of exponential expansion, known as Chandrasekhar limit. AK inflation — and thus quantum fluctuations in the early Universe were amplified to seed Diamond cavities its present structure. Cosmological data Nature Nanotech. http://dx.doi.org/10.1038/ support inflation, but it’s proving harder nnano.2011.190 (2011) to reconcile with the well-developed and well-tested standard model of particle

The leading proposal for a solid-state physics. A particular problem is matching GONZALEZ © ISTOCKPHOTO.COM/ROXANA quantum computer that works at room the ‘inflaton’ — the hypothetical scalar field temperature relies on the electronic, spin that would drive inflation — to a scalar field It’s simple, really: the basic principle of and optical characteristics of discrete point that sits comfortably with particle physics writing with ink is the delivery of a liquid defects in diamond. Diamond is a good as we know it. from a reservoir to an absorbent surface, host for spin-based quantum computing Rouzbeh Allahverdi and colleagues and then the spreading of that liquid as the because it has very few nuclear spins of its have developed what they consider to be source moves across the porous substrate. own, and it is able to host defects — most a general prescription for constructing To study the hydrodynamics in more detail, notably nitrogen–vacancy centres — that the right kind of potentials for the however, Jungchul Kim and colleagues have used a ‘minimal pen’ made of a capillary tube, brought close to a highly hydrophilic Dots work together Phys. Rev. Lett. 107, 196802 (2011) micropillar array, which served as their model of paper. When a beam of light hits a thin metal film, some of it is absorbed and the rest is reflected. The basic hydrodynamics of the writing However, pierce the same film with a regular array of holes and, even if the hole size is process is governed by the capillary force smaller than the wavelength of the light, more light is transmitted than would be expected. that makes the ink flow and by the viscous Researchers have now shown that an effect similar to this so-called extraordinary optical force exerted by the substrate. Considering transmission might also be seen with electrons. the balance of the two forces, Kim et al. In the analogy put forward by L. S. Petrosyan and colleagues, the optical apertures have succeeded in reproducing both the are replaced by quantum dots — nanostructures that can support discrete and localized dynamics of the blot that is created before electron states by virtue of their small size. The researchers considered a device in which the pen starts moving, and the frontal shape this quantum-dot array is sandwiched between two electrical leads and calculated that the and final width of the line produced by device’s conductance per quantum dot in the array is significantly enhanced over the single- their simple pen. AT quantum-dot case. They attribute this to the fact that some of the quantum-dot electron states become delocalized because of coherent coupling to the leads. DG Written by Abigail Klopper, Ed Gerstner, David Gevaux, Alison Wright and Andreas Trabesinger.

922 NATURE PHYSICS | VOL 7 | DECEMBER 2011 | www.nature.com/naturephysics