Letters in 2009

A technique that produces significant alignment of molecules in a beam should aid a wide range of experiments geared towards understanding and controlling molecular processes in the gas phase.

The spin state of electrons trapped in a quantum dot only lasts a few microseconds. Before this information is lost, it is useful to controllably rotate the spin as many times as possible. Laser pulses can now rotate electron spins in an ensemble of quantum dots in just a few picoseconds.

The additivity conjecture of quantum information theory implies that entanglement cannot, even in principle, help to funnel more classical information through a quantum-communication channel. A counterexample shows that this conjecture is false.

High-speed spectroscopy confirms predictions of the emission of terahertz radiation when a laser-induced acoustic wave passes across the interface between two piezoelectric materials.

Magnetic monopoles have for a long time eluded detection by experiment. Theory now identifies a signature of monopole dynamics that is measurable experimentally, and that has already been seen in magnetic relaxation measurements in a spin-ice material.

Although the bunching of photons emitted from an incoherent source is well known, this has only ever been measured down to a temporal resolution of nanoseconds. This has now been improved by many orders of magnitude to the level of femtoseconds, with the elegantly simple use of a GaAs two-photon detector.

Proteins seek out binding sites on DNA through diffusion and also by sliding along the strand. Although ‘roadblocks’—other bound proteins on the DNA strand—slow things down, it seems that looping of the DNA aids the search process.

The observation of a trimer resonance in an ultracold mixture of caesium atoms and dimers confirms one of the key predictions of three-body physics in the limit of resonant two-body interactions, with possible implications for understanding few-body states in nuclear matter.

Quantum superpositions of coherent light waves offer several advantages for quantum-information processing compared to single photons. A novel scheme for generating these so-called Schrödinger-cat states circumvents problems arising from their fragility, which has been a key obstacle towards applications.

Frequency-specific components that passively control the flow in a channel in an analogous manner to that of the resistors, capacitors and diodes of an electronic circuit could eliminate the need to exert active control in microfluidic circuits with bulky external pumps.

The observation of oscillations in the conductance characteristics of narrow graphene p–n-junctions confirms their ability to collimate ballistic carriers. Moreover, the phase of these oscillations at low magnetic field suggests the occurrence of the perfect transmission of carriers normal to the junction as a direct result of the Klein effect.

A variant on Fourier-transform scanning tunnelling spectroscopy enables spatial variations in the Fermi surface of bismuth-based cuprate superconductors to be probed. This technique reveals that these variations take place over nanometre distances.

Two experiments observe the so-called ‘Mollow triplet’ in the emission spectrum of a quantum dot—originating from resonantly driving a dot transition—and demonstrate the potential of these systems to act as single-photon sources and as a readout modality for electron-spin states.

Two experiments observe the so-called Mollow triplet in the emission spectrum of a quantum dot—originating from resonantly driving a dot transition—and demonstrate the potential of these systems to act as single-photon sources, and as a readout modality for electron-spin states.

Sensitive measurements of fluctuations in the current through carbon-nanotube-based quantum dots provide insight into the many-body physics of such systems.

Although spin fluctuations are believed to have an important role in the mechanism responsible for high-temperature superconductivity, it has been unclear whether the strength of their coupling with fermionic quasiparticles is sufficiently strong. Systematic analysis of angle-resolved photoemission and neutron spectra suggests it is.

Two intriguing shapes that appear in Bose–Einstein condensates are vortex rings and solitons. Experiments now suggest that there can be periodic oscillations between these qualitatively different structures.

When two single Rydberg atoms—those with electrons in highly excited states—interact, one can be used to control the quantum state of the other. Two independent experiments demonstrate such ‘Rydberg blockade’, an effect that might make long-range quantum gates between neutral atoms possible.

When two single Rydberg atoms—those having electrons in highly excited states—interact, one can be used to control the quantum state of the other. Two independent experiments now demonstrate a ‘Rydberg blockade’, an effect that might make long-range quantum gates between neutral atoms possible.