Volume 9 Issue 1, January 2013

Preparations for the construction of an international linear collider have reached another milestone — but is the way ahead clear?

A technique for detecting the presence of a photon without destroying the quantum message it carries could ultimately lead to a loophole-free test of quantum non-locality.

Liquid water expands when heated — or cooled — away from a particular temperature that increases when the fluid is stretched. Experiments on water under extreme tension now enable tracking of this distinctive behaviour well into the negative-pressure domain.

The idea of monopoles in spin ice has enjoyed much success in the intermediate temperature regime. Low-temperature measurements now point to the importance of surfaces and impurities in monopole dynamics, in providing extrinsic resistance for monopole currents.

Could biological systems have evolved to find the optimal quantum solutions to the problems thrown at them by nature? This Review presents an overview of the possible quantum effects seen in photosynthesis, avian magnetoreception and several other biological systems.

Many-particle entangled states and entanglement between continuous properties are valuable resources for quantum information, but are notoriously difficult to generate. An experiment now entangles the energy and emission times of three photons, creating generalized Einstein–Podolsky–Rosen correlations.

Long-distance quantum communication is limited by optical absorption and scattering. A noiseless amplifier for photonic qubits coherently encoded across two optical modes is now demonstrated, which could combat this negative effect. The method enabled a fivefold increase in the transmission fidelity of the polarization state of a single photon.

Entanglement is an important resource in quantum-enhanced technologies, but it is difficult to generate, especially in solid-state systems. An experiment now demonstrates the entanglement of two nuclear spins via a parity measurement of the electron spin in a nitrogen-vacancy centre in diamond.

In the highly degenerate spin-ice ground state, flipped spins give rise to magnetic charges, or monopoles, which form a measurable current in a magnetic field. The low-temperature relaxation dynamics of spin-ice materials now reveal that defects can impede monopole flow—creating a magnetic analogue of electrical resistance.

Liquid water inclusions in quartz can withstand negative pressures in excess of −100 MPa. Other techniques report much lower thresholds—suggesting that water in inclusions is stabilized by impurity effects. Experiments on a single inclusion in quartz now provide evidence consistent with a homogeneous mechanism for cavitation.

Different experimental probes have found different bosonic modes in the iron-based superconductors. A scanning tunnelling spectroscopy study of two separate superconductors now links the tunnelling mode with the ‘neutron resonance’, both of which vanish when superconductivity disappears.

The electronic properties of graphene are spatially controlled from metallic to semiconducting by patterning steps into the underlying silicon carbide substrate. This bottom-up approach could be the basis for integrated graphene electronics.

Photonic crystals efficiently control wave propagation on a wavelength scale, but this means they can become very large when long wavelengths are involved. Metamaterials made of resonant unit cells can confine and guide waves even at scales far below their wavelength.