Fast Charge Sensing of Si/SiGe Quantum Dots via a High-Frequency Accumulation Gate.

Quantum dot arrays are a versatile platform for the implementation of spin qubits, as high-bandwidth sensor dots can be integrated with single-, double-, and triple-dot qubits yielding fast and high-fidelity qubit readout. However, for undoped silicon devices, reflectometry off sensor ohmics suffers from the finite resistivity of the two-dimensional electron gas (2DEG), and alternative readout methods are limited to measuring qubit capacitance, rather than qubit charge. By coupling a surface-mount resonant circuit to the plunger gate of a high-impedance sensor, we realized a fast charge sensing technique that is compatible with resistive 2DEGs. We demonstrate this by acquiring at high speed charge stability diagrams of double- and triple-dot arrays in Si/SiGe heterostructures as well as pulsed-gate single-shot charge and spin readout with integration times as low as 2.4 µs.

Single-electron operations in a foundry-fabricated array of quantum dots.

Silicon quantum dots are attractive for the implementation of large spin-based quantum processors in part due to prospects of industrial foundry fabrication. However, the large effective mass associated with electrons in silicon traditionally limits single-electron operations to devices fabricated in customized academic clean rooms. Here, we demonstrate single-electron occupations in all four quantum dots of a 2 x 2 split-gate silicon device fabricated entirely by 300-mm-wafer foundry processes. By applying gate-voltage pulses while performing high-frequency reflectometry off one gate electrode, we perform single-electron operations within the array that demonstrate single-shot detection of electron tunneling and an overall adjustability of tunneling times by a global top gate electrode. Lastly, we use the two-dimensional aspect of the quantum dot array to exchange two electrons by spatial permutation, which may find applications in permutation-based quantum algorithms.

Combined mechanical and pharmacologic thrombolysis for portal vein thrombosis in liver-graft recipients and in candidates for liver transplantation.

Portal vein thrombosis (PVT) is an uncommon cause for presinusoidal portal hypertension and can occur even in liver-graft recipients. Interventional radiology by percutaneous approach may represent a valid and less invasive alternative to surgical treatment. We describe three cases of PVT (2 liver-transplant patients and a cirrhotic patient candidate for liver transplantation) treated by combined mechanical and pharmacologic thrombolysis. The Arrow-Trerotola device was used along with the infusion of urokinase by way of a percutaneous-transhepatic approach. In all cases, a recanalization of the portal system was obtained and maintained during the follow-up. The best result was achieved when mechanical thrombectomy was performed before urokinase infusion. The combined locoregional treatment with mechanical thrombectomy and pharmacologic thrombolysis appears to be a promising approach for PVT because of its rapid and durable effect and its ability to reduce the dose of urokinase required to achieve recanalization.