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Defects in Josephson junctions are considered a nuisance when it comes to using superconducting circuits as building blocks for a quantum-information processor. But if the interaction between the circuit and defects is accurately controlled—as has been demonstrated now—the imperfections might be useful, serving as memory elements.
Like their classical counterparts, quantum computers can, in theory, cope with imperfections—provided that these are small enough. The regime of fault-tolerant quantum computing has now been reached for a system based on trapped ions, in which a gate operation for entangling qubits has been implemented with a fidelity exceeding 99%.
Superfluid 3He is a quantum condensate in which the He atoms are paired in an unconventional way. Yet despite extensive research on the collective modes of superfluid 3He, one mode has remained undiscovered, until now.
Spins in a two-dimensional triangular lattice are geometrically frustrated and cannot form an ordered ground state. Instead, a spin-liquid state is expected, and now thermodynamic measurements suggest that a spin liquid exists down to the lowest temperatures.
Four electrons in a semiconductor quantum dot exhibit similar correlation effects to those found in a molecule. Excitations of these electrons can be probed by inelastic light scattering, which reveals a decoupling of their rigid rotational motion from their spin excitations.
The analysis of the interference fringes generated by initially independent one-dimensional Bose condensates reveals contributions of both quantum noise and thermal noise, advancing our fundamental understanding of quantum states in interacting many-body systems.
A proposal describes how to detect topologically ordered states of ultracold matter in an optical lattice, and shows how these exotic states, which strongly correlated quantum systems can exhibit, could be harnessed for practical applications, such as robust quantum computation.
Valuable insight into the influence of scattering from impurities on the peculiar electronic properties of graphene are gained by a systematic study of how its conductivity changes with increasing concentration of potassium ions deposited on its surface.
Laser-driven resolved sideband cooling of the resonant vibrational mode of a toroidal microcavity represents another step towards reaching the quantum ground state.
A magnetic vortex trapped by a notch in a nanowire is no larger than 10 nm, but both the direction and polarity of the vortex can now be measured without applying a magnetic field. In this set-up, the vortex is therefore both stable and switchable for use in possible device applications.
Nonlinear optics traditionally involves macroscopic atomic ensembles or solid-state crystals. The observation of a nonlinear two-photon resonance in a system consisting of one single atom trapped inside an optical cavity demonstrates nonlinear optics at the level of individual quanta.
Unprecedented control over the superposition of electronic states of a ‘quantum coral’, by changing the position of a single atom within it, provides a powerful tool for studying the quantum behaviour of matter.
Grains, foams and colloids can behave as liquids or solids. Their flow is difficult to predict, often jamming. Such systems are far from equilibrium but there may now be a thermodynamic framework for granular media.
