Complete quantum control of exciton qubits bound to isoelectronic centres.

In recent years, impressive demonstrations related to quantum information processing have been realized. The scalability of quantum interactions between arbitrary qubits within an array remains however a significant hurdle to the practical realization of a quantum computer. Among the proposed ideas to achieve fully scalable quantum processing, the use of photons is appealing because they can mediate long-range quantum interactions and could serve as buses to build quantum networks. Quantum dots or nitrogen-vacancy centres in diamond can be coupled to light, but the former system lacks optical homogeneity while the latter suffers from a low dipole moment, rendering their large-scale interconnection challenging. Here, through the complete quantum control of exciton qubits, we demonstrate that nitrogen isoelectronic centres in GaAs combine both the uniformity and predictability of atomic defects and the dipole moment of semiconductor quantum dots. This establishes isoelectronic centres as a promising platform for quantum information processing.

Non-contact in vivo diffuse optical imaging using a time-gated scanning system.

We report on the design and first in vivo tests of a novel non-contact scanning imaging system for time-domain near-infrared spectroscopy. Our system is based on a null source-detector separation approach and utilizes polarization-selective detection and a fast-gated single-photon avalanche diode to record late photons only. The in-vivo tests included the recording of hemodynamics during arm occlusion and two brain activation tasks. Localized and non-localized changes in oxy- and deoxyhemoglobin concentration were detected for motor and cognitive tasks, respectively. The tests demonstrate the feasibility of non-contact imaging of absorption changes in deeper tissues.

Delayed spongiform leukoencephalopathy after heroin abuse.

Here we report the clinical and pathological findings in a 30-year-old drug addict in whom an intravenous injection of heroin led to reversible coma with respiratory depression and heart failure. On regaining consciousness, the patient was found to have rhabdomyolysis with renal failure requiring dialysis and peripheral neuropathy. Three weeks later his neurological condition suddenly deteriorated and delayed encephalopathy developed, leading to death 20 days later. The neuropathological study of the brain disclosed pale, spongy myelin with diffuse reactive astrogliosis and microglial proliferation, without hypoxic necrotic lesions. The cerebral and cerebellar cortices were unchanged. The absence of typical hypoxic lesions and the presence of spongiosis with massive astrocytosis distinguished this case from the previously reported cases of delayed leukoencephalopathy following severe hypoxia. An immunocytochemical study designed to exclude an underlying alteration of the metabolic oxidative pathway detected normal expression of the respiratory chain complexes IV, III and V. Despite the absence of an oxidative chain alteration in our patient, we cannot exclude the possibility that an individual predisposition played a pathogenetic role in this delayed leukoencephalopathy.