Volume 8 Issue 6, June 2012

Do quantum states offer a faithful representation of reality or merely encode the partial knowledge of the experimenter? A new theorem illustrates how the latter can lead to a contradiction with quantum mechanics.

Modern optics enables precision control over the laser field entering a nonlinear optical crystal. This has made it possible to realize a classical analogue of Bose–Einstein condensation, and it could provide a means of exerting microscopic control over the macroscopic state of complex systems.

Quantum non-locality can improve the quality of sources of randomness.

The quantum spin Hall effect is predicted to be the result of two oppositely polarized spin currents travelling in opposite directions around the edges of a topological insulator. But only now has the spin polarization of these currents been confirmed.

Bell’s equations enable scientists to test the fundamental implications of quantum physics. A central tenet of this idea is that the choice of measurement is truly random. Researchers now show that some Bell experiments can even increase randomness in cases where choice is not entirely free. The concept could increase the usefulness of weakly random sources for more thorough tests of quantum mechanics.

An interferometric implementation of Young’s double-slit experiment is used to probe quantum correlations that are manifest in the distribution of local spin fluctuations in a two-component degenerate Fermi gas.

Despite their name, the bulk electrical conductivity of most topological insulators is relatively high, masking many of the important characteristics of its protected, surface conducting states. Counter-doping reduces the bulk conductivity of Bi₂Se₃ significantly, allowing these surface states and their properties to be clearly identified.

The proximity effect enables the injection of Cooper pairs from a superconductor into a normal metal, but they usually do not travel far into the metal. A study of the propagation of Cooper pairs from irregularly shaped superconducting islands on a metal film finds that they can travel further than expected for certain island geometries.

Bose–Einstein condensation is usually considered to be an inherently quantum mechanical phenomenon. An observation of the condensation in a classical system of light waves in a nonlinear crystal demonstrates that it is a general wave-mechanical phenomenon.

A no-go theorem on the reality of the quantum state is demonstrated. If the quantum state merely represents information about the physical state of a system, then predictions that contradict those of quantum theory are obtained.

In 2000, Asher Peres put forward the paradoxical idea that entanglement could be produced after the entangled particles have been measured, even if they no longer exist. Researchers now experimentally demonstrate this idea using four photons.

The quantum spin Hall state is predicted to consist of two oppositely polarized spin currents travelling in opposite directions around the edges of a topological insulator. Non-local measurements of the transport in HgTe quantum wells confirm the polarized nature of these edge states.

Ferromagnetic resonance excitations offer a means to coherently manipulate the spin dynamics of spintronic devices and systems. A demonstration of the ability to control these excitations with electric fields alone could drastically reduce the power consumption of these devices.

Small clusters of magnetic atoms can behave in very different ways to those same atoms in bulk. Arranging iron atoms one by one into complex but well-defined patterns on a copper surface enables the construction of nanoscale magnetic structures with tailored characteristics.