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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.
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.
A genetic-algorithm approach to analysing quantum oscillations in a high-temperature superconductor reveals that quasiparticles behave as nearly free spins—split into spin-up and spin-down populations, known as the Zeeman effect.
Birefringent particles manipulated with an optical torque wrench exhibit strongly nonlinear, ‘excitable’ behaviour similar to that governing the firing of neurons. This technique could be used to detect small perturbations in the local environment of such a particle.
Light-emitting quantum dots are usually assumed to behave as perfect point-source emitters. It is now found that this assumption breaks down when quantum dots are placed near structures that support nanoscale optical modes — information that could be useful in building better nanophotonic devices.
Optical control over electron spins embedded in semiconductor structures is an efficient way of manipulating quantum information. But a fully fledged quantum information processor will require control over two-spin states. This has now been demonstrated, including the implementation of ‘ultrafast’ two-qubit gate operations that take less than a nanosecond.
Topological insulators are bulk insulators beneath conducting surface states with very special properties. By doping these surface states with iron, the surface band structure can be explored and controlled.
A neutron-scattering study provides quantitative evidence for magnetically mediated superconductivity close to a quantum critical point in the heavy fermion superconductor CeCu2Si2.
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.
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.
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.
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.
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.
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.
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.
The pseudogap state in the cuprate superconductors shows signs of electronic pair formation above the superconducting temperature. Is it just a ‘precursor’ state or a separate (and competing) state? In fact, both interpretations seem to be correct.
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.
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.
Simply cooling down an artificial spin-ice does not necessarily lead to ground-state magnetic order. But as-grown artificial square ice reaches a thermodynamic ground state, with monopole dynamics possibly involved in the thermalization.