Miniaturizing transmon qubits using van der Waals materials

Quantum computers can potentially achieve an exponential speedup versus classical computers on certain computational tasks, recently demonstrated in systems of superconducting qubits. However, the capacitor electrodes that comprise these qubits must be large in order to avoid lossy dielectrics. This tactic hinders scaling by increasing parasitic coupling among circuit components, degrading individual qubit addressability, and limiting the spatial density of qubits. Here, we take advantage of the unique properties of van der Waals (vdW) materials to reduce the qubit area by $>1000$ times while preserving the required capacitance without increasing substantial loss. Our qubits combine conventional aluminum-based Josephson junctions with parallel-plate capacitors composed of crystalline layers of superconducting niobium diselenide and insulating hexagonal-boron nitride. We measure a vdW transmon $T_1$ relaxation time of 1.06 $\mu$s, which demonstrates a path to achieve high-qubit-density quantum processors with long coherence times, and the broad utility of layered heterostructures in low-loss, high-coherence quantum devices.

Several case studies on electric field distributions for two human bodies inside the car at 3.5 GHz–5G frequency band

The study investigates basically, the electric field distribution in a semi-closed region. Specifically, the present work focuses on the electromagnetic wave diffraction at 3.5 GHz in the vicinity of a car where two humans are located inside. The car is modeled as the perfect electric conducting object whereas the human bodies are assumed to be homogeneous lossy dielectrics. To obtain field distributions for different sceneries, the Method of Auxiliary Sources (MAS) is employed. To achieve this goal, the auxiliary sources due to each obstacle are distributed over the corresponding surface element. In the present study, two main different scenarios are considered. One or two cellphones as the source of electromagnetic waves are considered. These cellphones are operating at the proposed 5G frequency band in the European Zone. In this frequency range, the resonances are observed at 3.5 GHz which is in the range of a planned 5G communication frequency band. The present study aims to obtain quantitative and qualitative results for a better understanding of 5G healthy issues. Therefore, as a frontier study, the specific absorption rate (SAR) values are examined for the first time to answer some important questions related to 5G. For such a scenario, MAS is a very efficient, fast, and trustworthy approach to obtain field distribution at semi-closed regions.

Thin Coatings of Cerium Oxide Nanoparticles with Anti-Reflective Properties

Cerium oxide, in addition to its catalytic properties, is also known for its optical properties such as ultraviolet (UV) radiation filtering and a relatively high refractive index ( n > 2 ), which makes it an excellent candidate for multifunctional coatings. Here, we focus on the optical properties of thin deposits (≲2 μ m) of densely packed C e O 2 nanoparticles, which we assemble using two evaporation-based techniques: convective self-assembly (CSA, a type of very slow blade-coating) to fabricate large-scale coatings of controllable thickness—from tens of nanometres to a few micrometers—and microfluidic pervaporation which permits us to add some micro-structure to the coatings. Spectroscopic ellipsometry yields the refractive index of the resulting nano-porous coatings, which behave as lossy dielectrics in the UV-visible regime and loss-less dielectrics in the visible to infra-red (IR) regime; in this regime, the fairly high refractive index (≈1.8) permits us to evidence thickness-tunable anti-reflection on highly refractive substrates, such as silicon, and concomitant enhanced transmissions which we checked in the mid-IR region.