We describe a microwave photon counter based on the current-biased Josephson junction. The junction is tuned to absorb single microwave photons from the incident field, after which it tunnels into a classically observable voltage state. Using two such detectors, we have performed a microwave version of the Hanbury Brown-Twiss experiment at 4 GHz and demonstrated a clear signature of photon bunching for a thermal source. The design is readily scalable to tens of parallelized junctions, a configuration that would allow number-resolved counting of microwave photons.
We calculate the room-temperature thermoelectric properties of highly doped ultrathin silicon nanowires (SiNW) of square cross section (3 × 3 to 8 × 8 nm 2 ) by solving the Boltzmann transport equations for electrons and phonons on an equal footing, using the ensemble Monte Carlo technique for each. We account for the two-dimensional confinement of both electrons and phonons and all the relevant scattering mechanisms, and present data for the dependence of electrical conductivity, the electronic and phononic thermal conductivities, the electronic and phonon-drag Seebeck coefficients, as well as the thermoelectric figure of merit (ZT ) on the SiNW rms roughness and thickness. ZT in ultrascaled SiNWs does not increase as drastically with decreasing wire cross section as suggested by earlier studies. The reason is surface roughness, which (beneficially) degrades thermal conductivity, but also (adversely) degrades electrical conductivity and offsets the Seebeck coefficient enhancement that comes from confinement. Overall, room-temperature ZT of ultrathin SiNWs varies slowly with thickness, having a soft maximum of about 0.4 at the nanowire thickness of 4 nm.
Silicon-based metal-oxide-semiconductor quantum dots are prominent candidates
for high-fidelity, manufacturable qubits. Due to silicon's band structure,
additional low-energy states persist in these devices, presenting both
challenges and opportunities. Although the physics governing these valley
states has been the subject of intense study, quantitative agreement between
experiment and theory remains elusive. Here, we present data from a new
experiment probing the valley states of quantum dot devices and develop a
theory that is in quantitative agreement with both the new experiment and a
recently reported one. Through sampling millions of realistic cases of
interface roughness, our method provides evidence that, despite radically
different processing, the valley physics between the two samples is essentially
the same. This work provides the first evidence that valley splitting can be
deterministically predicted and controlled in metal oxide semiconductor quantum
dots, a critical requirement for such systems to realize a reliable qubit
platform.Comment: 7 pages, 4 figure
We simulate phonon transport in suspended graphene nanoribbons (GNRs) with real-space edges and experimentally-relevant widths and lengths (from submicron to hundreds of microns). The full-dispersion phonon Monte Carlo (PMC) simulation technique, which we describe in detail, involves a stochastic solution to the phonon Boltzmann transport equation with the relevant scattering mechanisms (edge, three-phonon, isotope, and grain boundary scattering) while accounting for the dispersion of all three acoustic phonon branches, calculated from the fourth-nearest-neighbor dynamical matrix. We accurately reproduce the results of several experimental measurements on pure and isotopically modified samples [S.
Thermal conductivity of silicon bulk and nanowires: Effects of isotopic composition, phonon confinement, and surface roughness J. Appl. Phys. 107, 083503 (2010); 10.1063/1.3340973Electron transport in silicon nanowires: The role of acoustic phonon confinement and surface roughness scattering J. Appl. Phys.
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