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Quantum dots are a promising host for spin-based qubits. Whereas nuclear-field fluctuations adversely affect electron-spin coherence, the smaller hyperfine interaction between holes and nuclei makes holes a promising alternative. A sensitive measurement of the hyperfine constant of the holes in different quantum-dot material systems now demonstrates how this interaction can be tuned and perhaps further reduced.
The elusive effects of quantum gravity could be betrayed by subtle deviations from standard quantum mechanics. An experiment using the gravitational wave bar detector AURIGA explores the limits of quantum gravity-induced modifications in the ground state of a mechanical oscillator cooled to the sub-millikelvin regime.
Topological insulators are now shown to be protected not only by time-reversal symmetry, but also by crystal lattice symmetry. By accounting for the crystalline symmetries, additional topological insulators can be predicted.
A time-dependent study of the effective temperature of carriers in impurity-free graphene now indicates that a disorder-assisted mechanism is responsible for cooling hot electrons. Observation of this so-called supercollision contradicts the idea that electron–phonon interactions dominate cooling.
Charge transport is usually limited by collisions between the carriers, impurities and/or phonons. Collisions involving three bodies are generally much rarer. A study now reveals, however, that such supercollisions can play an important role in the properties of graphene.
Many-particle entangled states and entanglement between continuous properties are valuable resources for quantum information, but are notoriously difficult to generate. An experiment now entangles the energy and emission times of three photons, creating generalized Einstein–Podolsky–Rosen correlations.
The electronic properties of graphene are spatially controlled from metallic to semiconducting by patterning steps into the underlying silicon carbide substrate. This bottom-up approach could be the basis for integrated graphene electronics.
Photonic crystals efficiently control wave propagation on a wavelength scale, but this means they can become very large when long wavelengths are involved. Metamaterials made of resonant unit cells can confine and guide waves even at scales far below their wavelength.
Different experimental probes have found different bosonic modes in the iron-based superconductors. A scanning tunnelling spectroscopy study of two separate superconductors now links the tunnelling mode with the ‘neutron resonance’, both of which vanish when superconductivity disappears.
Liquid water inclusions in quartz can withstand negative pressures in excess of −100 MPa. Other techniques report much lower thresholds—suggesting that water in inclusions is stabilized by impurity effects. Experiments on a single inclusion in quartz now provide evidence consistent with a homogeneous mechanism for cavitation.
In the highly degenerate spin-ice ground state, flipped spins give rise to magnetic charges, or monopoles, which form a measurable current in a magnetic field. The low-temperature relaxation dynamics of spin-ice materials now reveal that defects can impede monopole flow—creating a magnetic analogue of electrical resistance.
An increase in diffusion beyond the ballistic-transport regime is now demonstrated. This so-called hyper-transport is observed in an optical experiment, but it might also be evident in other systems with time-varying disorder.
Topological entanglement entropy provides a robust measure for detecting the long-range entanglement that characterizes quantum ground states displaying topological order. A new method for calculating this entropy isolates minimally entangled states from the ground states of a topological phase—offering a reliable test for identifying topological spin liquids.
Long-distance quantum communication is limited by optical absorption and scattering. A noiseless amplifier for photonic qubits coherently encoded across two optical modes is now demonstrated, which could combat this negative effect. The method enabled a fivefold increase in the transmission fidelity of the polarization state of a single photon.
New data, backed up by simulations, support the existence of Majorana fermions in the one-dimensional topological superconductor that is induced by placing an aluminium superconductor close to an indium-arsenide nanowire.
Non-local quantum correlations between distant particles cannot be explained by signals propagating slower than the speed of light. It is now shown that they cannot be explained by hidden influences propagating faster than the speed of light either, because that would permit faster-than-light communication.
Fast particles propagating through a classical medium give rise to shock waves. Calculations now uncover the surprising behaviour of particles in one-dimensional quantum fluids: a fast particle will never come to a full stop, and a supersonic particle will propagate through the medium undergoing long-lived oscillations.
Enhanced control of the nuclear spin orientation of rare isotopes has now been demonstrated. This technique is considerably more efficient than traditional methods and significantly broadens the domain of accessible nuclei, promising insights in nuclear physics and applications in material science.
X-ray diffraction experiments reveal that spatial charge ordering occurs in the pseudogap state of YBa2Cu3O6.67. Moreover, this charge ordered state competes with high-temperature superconductivity, and their relative strengths can be tuned using a magnetic field.
