Volume 7 Issue 2, February 2011

The nonlinear optical process of high-order harmonic generation is usually seen in atomic gases. Now, the process has been observed in a bulk crystalline solid, with important implications for ultrafast coherent short-wavelength sources and perhaps attosecond science.

Intuition suggests that the occurrence of large quantum fluctuations should prevent a material from forming a glass, yet theory and simulations that explicitly incorporate such fluctuations suggest the opposite could be true.

A study of the autoresonant behaviour of a superconducting pendulum reveals that quantum fluctuations determine only the initial oscillator motion and not its subsequent dynamics. This could be important in the development of more efficient methods for reading solid-state qubits.

Emulating condensed-matter physics with ground-state atoms trapped in optical lattices has come a long way. But excite the atoms into higher orbital states, and a whole new world of exotic states appears.

Semiconductor quantum dots have good prospects as a platform for implementing a quantum information processor. A demonstration that in such nanostructures quantum information can survive for fractions of a millisecond only adds to this promise.

A study of autoresonant behaviour in a superconducting quantum pendulum reveals that fluctuations, both quantum and classical, only determine the initial oscillator motion, not its subsequent dynamics.

Electron spins in semiconductor structures are quantum bits with good prospects, but the information stored in the spin states tends to degrade quickly owing to interactions with nuclei in the host material. A study of GaAs quantum dots now provides a fuller understanding of this memory loss and how it can be suppressed. Quantum-memory times exceeding 200 μs are demonstrated, two orders of magnitude longer than previously reported for this system.

Ultrafast spectroscopy reveals the many-body effects behind the metallization of a one-dimensional Mott insulator. Unlike in ultracold gases, these femtosecond excitation studies of quantum dynamics occur at room temperature.

A neutron-scattering study provides quantitative evidence for magnetically mediated superconductivity close to a quantum critical point in the heavy fermion superconductor CeCu₂Si₂.

If vortex cores within a superconductor can trap electrostatic charge, the cores will experience a repulsive Coulomb interaction. Evidence from NMR measurements indeed suggests that above some threshold magnetic field, the Abrikosov vortex lattice becomes unstable.

Bound pairs consisting of a vortex and an antivortex are expected to dominate the low-temperature physics in a variety of two-dimensional systems. The observation of such bound pairs, however, remains elusive. A study now establishes non-equilibrium condensates of exciton-polaritons as a platform for exploring the physics of vortex–antivortex pairs.

Intuition suggests that the occurrence of large quantum fluctuations should prevent a material from forming a glass by enabling its atoms to rearrange into a lower-energy ordered state. But new simulations suggest the opposite could be true, with fluctuations sometimes enhancing glass formation.

High-order harmonic generation is a nonlinear optical process that enables the creation of light pulses at frequencies much higher than that from a seed laser. The host medium for this interaction is typically a gas. Now, the process has been observed in a bulk crystalline solid with important implications for attosecond science.

A potentially critical limiting factor in the use of free-electron lasers to determine the structure of organic molecules is the damage the procedure may cause. A model based on coherence theory and quantum electrodynamics suggests that it should be possible to reconstruct a molecule’s structure from the X-ray data obtained as it undergoes damage.

Atoms trapped in optical lattices have been used successfully to study many-body phenomena. But the shape that bosonic ground-state wavefunctions can take is limited, compromising the usefulness of this approach. Such limitations, however, do not apply to excited states of bosons. An atomic superfluid that has now been realized in such a higher-energy band promises to provide insight into a wider range of many-body effects.

Detecting and counting individual microwave photons is important for processing quantum information, but it is made challenging by an absence of detectors that are sensitive enough to radiation at this wavelength. Correlations between microwave photons have now been measured using a series of amplifiers and digital analysis.

Networks of atom–cavity systems necessarily require that single atoms sit near dielectric interfaces. Real-time monitoring of caesium atoms just 100 nm from the surface of a micro-toroid resonator now demonstrates that the Casimir effect plays an important role in these systems.

Quantum cascade lasers can operate at terahertz frequencies because they use intraband, rather than interband, transitions in semiconductor nanostructures. However, they seemed to have reached a ceiling in terms of maximum operating temperature. This trend has now been broken with the introduction of a new scheme for charge injection.

Single-molecule techniques and femtosecond pulse shaping are now combined to investigate quantum coherence in biomolecules. The creation and manipulation of such coherence enables a basic single-qubit operation with terrylene diimide at room temperature.

A study of a non-liquid glass former reveals a correlation length that decreases as the transition temperature is approached from above, which is the opposite of what is expected. It suggests that ‘strong’ and ‘fragile’ liquids exist on opposite sides of an order–disorder phase transition.