556 research outputs found
Formation of Aluminum-Doped Zinc Oxide Nanocrystals via the Benzylamine Route at Low Reaction Kinetics
The influence of essential process parameters on the adjustability of specific process and particulate properties of aluminum‐doped zinc oxide (AZO) nanocrystals during synthesis via the benzylamine route at low reaction kinetics is demonstrated by enabling time‐resolved access of the selected measurement technique. It is shown that the validity of the pseudo‐first‐order process kinetics could be extended to the minimum operable reaction kinetics. On the other hand, the impacts of the process temperature and the initial precursor concentration on both the process kinetics and the particle morphology are discussed. The obtained data provide a versatile tool for precise process control by adjusting defined application‐specific particle properties of AZO during synthesis
Microwave photon-mediated interactions between semiconductor qubits
The realization of a coherent interface between distant charge or spin qubits
in semiconductor quantum dots is an open challenge for quantum information
processing. Here we demonstrate both resonant and non-resonant photon-mediated
coherent interactions between double quantum dot charge qubits separated by
several tens of micrometers. We present clear spectroscopic evidence of the
collective enhancement of the resonant coupling of two qubits. With both qubits
detuned from the resonator we observe exchange coupling between the qubits
mediated by virtual photons. In both instances pronounced bright and dark
states governed by the symmetry of the qubit-field interaction are found. Our
observations are in excellent quantitative agreement with master-equation
simulations. The extracted two-qubit coupling strengths significantly exceed
the linewidths of the combined resonator-qubit system. This indicates that this
approach is viable for creating photon-mediated two-qubit gates in quantum dot
based systems.Comment: 14 pages, 10 figures and 6 table
Development of a growth model for aluminum-doped zinc oxide nanocrystal synthesis via the benzylamine route
A DFT study of Ruthenium fcc nano-dots: size-dependent induced magnetic moments
Many areas of electronics, engineering and manufacturing rely on ferromagnetic materials, including iron, nickel and cobalt. Very few other materials have an innate magnetic moment rather than induced magnetic properties, which are more common. However, in a previous study of ruthenium nanoparticles, the smallest nano-dots showed significant magnetic moments. Furthermore, ruthenium nanoparticles with a face-centred cubic (fcc) packing structure exhibit high catalytic activity towards several reactions and such catalysts are of special interest for the electrocatalytic production of hydrogen. Previous calculations have shown that the energy per atom resembles that of the bulk energy per atom when the surface-to-bulk ratio < 1, but in its smallest form, nano-dots exhibit a range of other properties. Therefore, in this study, we have carried out calculations based on the density functional theory (DFT) with long-range dispersion corrections DFT-D3 and DFT-D3-(BJ) to systematically investigate the magnetic moments of two different morphologies and various sizes of Ru nano-dots in the fcc phase. To confirm the results obtained by the plane-wave DFT methodologies, additional atom-centred DFT calculations were carried out on the smallest nano-dots to establish accurate spin-splitting energetics. Surprisingly, we found that in most cases, the high spin electronic structures had the most favourable energies and were hence the most stable
Competitive Adsorption of H2O and SO2 on Catalytic Platinum Surfaces: a Density Functional Theory Study
Platinum has been widely used as the catalyst of choice for the production of hydrogen in the hybrid sulphur (HyS) cycle. In this cycle, water (H2O) and sulphur dioxide (SO2) react to form sulphuric acid and hydrogen. However, the surface reactivity of platinum towards H2O and SO2 is not yet fully understood, especially considering the competitive adsorption that may occur on the surface. In this study, we have carried out density functional theory calculations with long-range dispersion corrections [DFT-D3-(BJ)] to investigate the competitive effect of both H2O and SO2 on the Pt (001), (011) and (111) surfaces. Comparing the adsorption of a single H2O molecule on the various Pt surfaces, it was found that the lowest adsorption energy (Eads = –1.758 eV) was obtained for the dissociative adsorption of H2O on the (001) surface, followed by the molecular adsorption on the (011) surface (Eads = –0.699 eV) and (111) surface (Eads = –0.464 eV). For the molecular SO2 adsorption, the trend was similar, with the lowest adsorption energy (Eads = –2.471 eV) obtained on the (001) surface, followed by the (011) surface (Eads = –2.390 eV) and (111) surface (Eads = –1.852 eV). During competitive adsorption by H2O and SO2, the SO2 molecule will therefore preferentially adsorb onto the Pt surface. If the concentration of SO2 increases, self-reaction between two neighbouring SO2 molecules may occur, leading to the formation of sulphur monoxide (SO) and -trioxide (SO3) on the surface, which could lead to sulphur poisoning of the Pt catalytic surfac
In-situ Tuning of the Electric Dipole Strength of a Double Dot Charge Qubit: Charge Noise Protection and Ultra Strong Coupling
Semiconductor quantum dots, where electrons or holes are isolated via
electrostatic potentials generated by surface gates, are promising building
blocks for semiconductor-based quantum technology. Here, we investigate double
quantum dot (DQD) charge qubits in GaAs, capacitively coupled to high-impedance
SQUID array and Josephson junction array resonators. We tune the strength of
the electric dipole interaction between the qubit and the resonator in-situ
using surface gates. We characterize the qubit-resonator coupling strength,
qubit decoherence, and detuning noise affecting the charge qubit for different
electrostatic DQD configurations. We find that all quantities can be tuned
systematically over more than one order of magnitude, resulting in reproducible
decoherence rates MHz in the limit of high interdot
capacitance. Conversely, by reducing the interdot capacitance, we can increase
the DQD electric dipole strength, and therefore its coupling to the resonator.
By employing a Josephson junction array resonator with an impedance of
k and a resonance frequency of GHz, we observe
a coupling strength of MHz, demonstrating the possibility to
achieve the ultrastrong coupling regime (USC) for electrons hosted in a
semiconductor DQD. These results are essential for further increasing the
coherence of quantum dot based qubits and investigating USC physics in
semiconducting QDs.Comment: 24 pages, 13 figure
Behavior of S, SO, and SO3 on Pt (001), (011), and (111) surfaces: a DFT study
In the hybrid sulfur (HyS) cycle, the reaction between SO2 and H2O is manipulated to produce hydrogen with water and sulfuric acid as by-products. However, sulfur poisoning of the catalyst has been widely reported to occur in this cycle, which is due to strong chemisorption of sulfur on the metal surface. The catalysts may deactivate as a result of these impurities present in the reactants or incorporated in the catalyst during its preparation and operation of the HyS cycle. Here, we report a density functional theory investigation of the interaction between S, SO, and SO3 with the Pt (001), (011), and (111) surfaces. First, we have investigated the adsorption of single gas phase molecules on the three Pt surfaces. During adsorption, the 4F hollow sites on the (001) and (011) surfaces and the fcc hollow site on the (111) surface were preferred. S adsorption followed the trend of (001)4F > (011)4F > (111)fcc, while SO adsorption showed (001)4F > (011)bridge/4F > (111)fcc and SO3 adsorption was most stable in a S,O,O bound configuration on the (001)4F > (011)4F > (111)fcc sites. The surface coverage was increased on all the surfaces until a monolayer was obtained. The highest surface coverage for S shows the trend (001)S = (111)S > (011)S, and for SO it is (001)SO > (011)SO > (111)SO, similar to SO3 where we found (001)SO3 > (011)SO3 > (111)SO3. These trends indicate that the (001) surface is more susceptible to S species poisoning. It is also evident that both the (001) and (111) surfaces were reactive toward S, leading to the formation of S2. The high coverage of SO3 showed the formation of SO2 and SO4, especially on the (011) surface. The thermodynamics indicated that an increased temperature of up to 2000 K resulted in Pt surfaces fully covered with elemental S. The SO coverage showed θ ≥ 1.00 on both the (001) and (011) surfaces and θ = 0.78 for the (111) surface in the experimental region where the HyS cycle is operated. Lower coverages of SO3 were observed due to the size of the molecule
Competitive adsorption of H2O and SO2 on catalytic platinum surfaces: a density functional theory study
Platinum has been widely used as the catalyst of choice for the production of hydrogen in the hybrid sulphur (HyS) cycle. In this cycle, water (H2O) and sulphur dioxide (SO2) react to form sulphuric acid and hydrogen. However, the surface reactivity of platinum towards H2O and SO2 is not yet fully understood, especially considering the competitive adsorption that may occur on the surface. In this study, we have carried out density functional theory calculations with long-range dispersion corrections [DFT-D3-(BJ)] to investigate the competitive effect of both H2O and SO2 on the Pt (001), (011) and (111) surfaces. Comparing the adsorption of a single H2O molecule on the various Pt surfaces, it was found that the lowest adsorption energy (Eads = –1.758 eV) was obtained for the dissociative adsorption of H2O on the (001) surface, followed by the molecular adsorption on the (011) surface (Eads = –0.699 eV) and (111) surface (Eads = –0.464 eV). For the molecular SO2 adsorption, the trend was similar, with the lowest adsorption energy (Eads=–2.471 eV) obtained on the (001) surface, followed by the (011) surface (Eads=–2.390 eV) and (111) surface (Eads=–1.852 eV). During competitive adsorption by H2O and SO2, the SO2 molecule will therefore preferentially adsorb onto the Pt surface. If the concentration of SO2 increases, self-reaction between two neighbouring SO2 molecules may occur, leading to the formation of sulphur monoxide (SO) and -trioxide (SO3) on the surface, which could lead to sulphur poisoning of the Pt catalytic surface
Photon-mediated long range coupling of two Andreev level qubits
In a superconducting weak link, the supercurrent is carried by Andreev bound
states (ABSs) formed by the phase-coherent reflection of electrons and their
time-reversed partners. A single, highly transmissive ABS can serve as an
ideal, compact two-level system, due to a potentially large energy difference
to the next ABS. While the coherent manipulation of such Andreev levels qubits
(ALQs) has been demonstrated, a long-range coupling between two ALQs, necessary
for advanced qubit architectures, has not been achieved, yet. Here, we
demonstrate a coherent remote coupling between two ALQs, mediated by a
microwave photon in a novel superconducting microwave cavity coupler. The
latter hosts two modes with different coupling rates to an external port. This
allows us to perform fast readout of each qubit using the strongly coupled
mode, while the weakly coupled mode is utilized to mediate the coupling between
the qubits. When both qubits are tuned into resonance with the latter mode, we
find excitation spectra with avoided-crossings, in very good agreement with the
Tavis-Cummings model. Based on this model, we identify highly entangled
two-qubit states for which the entanglement is mediated over a distance of six
millimeters. This work establishes ALQs as compact and scalable solid-state
qubits.Comment: 13 pages, 7 figure
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