Electron spins trapped in quantum dots have been proposed as basic building blocks of a future quantum processor. Although fast, 180-picosecond, two-quantum-bit (two-qubit) operations can be realized ...using nearest-neighbour exchange coupling, a scalable, spin-based quantum computing architecture will almost certainly require long-range qubit interactions. Circuit quantum electrodynamics (cQED) allows spatially separated superconducting qubits to interact via a superconducting microwave cavity that acts as a 'quantum bus', making possible two-qubit entanglement and the implementation of simple quantum algorithms. Here we combine the cQED architecture with spin qubits by coupling an indium arsenide nanowire double quantum dot to a superconducting cavity. The architecture allows us to achieve a charge-cavity coupling rate of about 30 megahertz, consistent with coupling rates obtained in gallium arsenide quantum dots. Furthermore, the strong spin-orbit interaction of indium arsenide allows us to drive spin rotations electrically with a local gate electrode, and the charge-cavity interaction provides a measurement of the resulting spin dynamics. Our results demonstrate how the cQED architecture can be used as a sensitive probe of single-spin physics and that a spin-cavity coupling rate of about one megahertz is feasible, presenting the possibility of long-range spin coupling via superconducting microwave cavities.
We demonstrate strong suppression of charge dispersion in a semiconductor-based transmon qubit across Josephson resonances associated with a quantum dot in the junction. On resonance, dispersion is ...drastically reduced compared to conventional transmons with corresponding Josephson and charging energies. We develop a model of qubit dispersion for a single-channel resonance, which is in quantitative agreement with experimental data.
Coherence of superconducting qubits can be improved by implementing designs that protect the parity of Cooper pairs on superconducting islands. Here, we introduce a parity-protected qubit based on ...voltage-controlled semiconductor nanowire Josephson junctions, taking advantage of the higher harmonic content in the energy-phase relation of few-channel junctions. A symmetric interferometer formed by two such junctions, gate-tuned into balance and frustrated by a half-quantum of applied flux, yields a cos ( 2φ ) Josephson element, reflecting coherent transport of pairs of Cooper pairs. We demonstrate that relaxation of the qubit can be suppressed tenfold by tuning into the protected regime.
By use of a Swedish Market basket study from 1999, in which foods were sampled from four regions, the dietary intake of persistent organic pollutants (POPs) was assessed. Based on earlier data, six ...food groups (fish, meat, dairy products, egg, fats/oils, and pastries; comprising 52 food items) were selected for POP analyses. Homogenates from these six groups were subjected to POP analyses and levels presented on dioxins (PCDD/PCDFs), dioxin-like PCBs, PCB-153, ∑PCBs, BDE-47, ∑PBDEs, DDE, ∑DDTs, HCB, ∑HCHs, and ∑chlordanes, after adjusting non-quantified levels to 1/2 LOQ. For all compounds, the fish homogenate contained the comparatively highest levels, on a fresh weight basis. Intake calculations based on the six food groups showed that ∑PCBs and ∑DDTs gave per capita intakes of 615 and 523
ng/day, respectively, that the estimated ∑PBDE intake was 51
ng/day and that of dioxins and dioxin-like PCBs was 96
pg WHO–TEQ/day. The estimated mean intakes were below (total-TEQ: 1.3
pg/kgbw/day) or well below (∑DDTs: 8.9
ng/kgbw/day) internationally agreed intake limits (total-TEQ: 2
pg/kgbw/day; ∑DDTs: 10 000
ng/kgbw/day). A number of uncertainty factors, including analytical limitations due to low POP levels in food, give reason for caution in the use of the presented intake data. However, the intake estimations of dioxins, ∑PCBs and ∑PBDEs are well in accordance to calculations of POP intakes in Sweden made by alternate methods.
State readout is a key requirement for a quantum computer. For semiconductor-based qubit devices it is usually accomplished using a separate mesoscopic electrometer. Here we demonstrate a simple ...detection scheme in which a radio frequency resonant circuit coupled to a semiconductor double quantum dot is used to probe its charge and spin states. These results demonstrate a new noninvasive technique for measuring charge and spin states in quantum dot systems without requiring a separate mesoscopic detector.
We investigate transmon qubits made from semiconductor nanowires with a fully surrounding superconducting shell. In the regime of reentrant superconductivity associated with the destructive ...Little-Parks effect, numerous coherent transitions are observed in the first reentrant lobe, where the shell carries 2π winding of superconducting phase, and are absent in the zeroth lobe. As junction density was increased by gate voltage, qubit coherence was suppressed then lost in the first lobe. These observations and numerical simulations highlight the role of winding-induced Andreev states in the junction.
The acute neural effects of progesterone are mediated by its neuroactive metabolites allopregnanolone and pregnanolone. These neurosteroids potentiate the inhibitory actions of gamma-aminobutyric ...acid (GABA). Progesterone is known to produce anxiolytic effects in animals, but recent animal studies suggest that pregnanolone increases anxiety after a period of low allopregnanolone concentration. This effect is potentially mediated by the amygdala and related to the negative mood symptoms in humans that are observed during increased allopregnanolone levels. Therefore, we investigated with functional magnetic resonance imaging (MRI) whether a single progesterone administration to healthy young women in their follicular phase modulates the amygdala response to salient, biologically relevant stimuli. The progesterone administration increased the plasma concentrations of progesterone and allopregnanolone to levels that are reached during the luteal phase and early pregnancy. The imaging results show that progesterone selectively increased amygdala reactivity. Furthermore, functional connectivity analyses indicate that progesterone modulated functional coupling of the amygdala with distant brain regions. These results reveal a neural mechanism by which progesterone may mediate adverse effects on anxiety and mood.
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