10,376 research outputs found
A Coherent Spin-Photon Interface in Silicon
Electron spins in silicon quantum dots are attractive systems for quantum
computing due to their long coherence times and the promise of rapid scaling
using semiconductor fabrication techniques. While nearest neighbor exchange
coupling of two spins has been demonstrated, the interaction of spins via
microwave frequency photons could enable long distance spin-spin coupling and
"all-to-all" qubit connectivity. Here we demonstrate strong-coupling between a
single spin in silicon and a microwave frequency photon with spin-photon
coupling rates g_s/(2\pi) > 10 MHz. The mechanism enabling coherent spin-photon
interactions is based on spin-charge hybridization in the presence of a
magnetic field gradient. In addition to spin-photon coupling, we demonstrate
coherent control of a single spin in the device and quantum non-demolition spin
state readout using cavity photons. These results open a direct path toward
entangling single spins using microwave frequency photons
Investigation of Mobility Limiting Mechanisms in Undoped Si/SiGe Heterostructures
We perform detailed magnetotransport studies on two-dimensional electron
gases (2DEGs) formed in undoped Si/SiGe heterostructures in order to identify
the electron mobility limiting mechanisms in this increasingly important
materials system. By analyzing data from 26 wafers with different
heterostructure growth profiles we observe a strong correlation between the
background oxygen concentration in the Si quantum well and the maximum
mobility. The highest quality wafer supports a 2DEG with a mobility of 160,000
cm^2/Vs at a density 2.17 x 10^11/cm^2 and exhibits a metal-to-insulator
transition at a critical density 0.46 x 10^11/cm^2. We extract a valley
splitting of approximately 150 microeV at a magnetic field of 1.8 T. These
results provide evidence that undoped Si/SiGe heterostructures are suitable for
the fabrication of few-electron quantum dots.Comment: Related papers at http://pettagroup.princeton.ed
Binary Reactive Adsorbate on a Random Catalytic Substrate
We study the equilibrium properties of a model for a binary mixture of
catalytically-reactive monomers adsorbed on a two-dimensional substrate
decorated by randomly placed catalytic bonds. The interacting and
monomer species undergo continuous exchanges with particle reservoirs and react
() as soon as a pair of unlike particles appears on sites
connected by a catalytic bond.
For the case of annealed disorder in the placement of the catalytic bonds
this model can be mapped onto a classical spin model with spin values , with effective couplings dependent on the temperature and on the mean
density of catalytic bonds. This allows us to exploit the mean-field theory
developed for the latter to determine the phase diagram as a function of in
the (symmetric) case in which the chemical potentials of the particle
reservoirs, as well as the and interactions are equal.Comment: 12 pages, 4 figure
In situ synchrotron x-ray study of ultrasound cavitation and its effect on solidification microstructures
Considerable progress has been made in studying the mechanism and effectiveness of using ultrasound waves to manipulate the solidification microstructures of metallic alloys. However, uncertainties remain in both the underlying physics of how microstructures evolve under ultrasonic waves, and the best technological approach to control the final microstructures and properties. We used the ultrafast synchrotron X-ray phase contrast imaging facility housed at the Advanced Photon Source, Argonne National Laboratory, US to study in situ the highly transient and dynamic interactions between the liquid metal and ultrasonic waves/bubbles. The dynamics of ultrasonic bubbles in liquid metal and their interactions with the solidifying phases in a transparent alloy were captured in situ. The experiments were complemented by the simulations of the acoustic pressure field, the pulsing of the bubbles, and the associated forces acting onto the solidifying dendrites. The study provides more quantitative understanding on how ultrasonic waves/bubbles influence the growth of dendritic grains and promote the grain multiplication effect for grain refinement
Fermi resonance-algebraic model for molecular vibrational spectra
A Fermi resonance-algebraic model is proposed for molecular vibrations, where
a U(2) algebra is used for describing the vibrations of each bond, and Fermi
resonances between stretching and bending modes are taken into account. The
model for a bent molecule XY_2 and a molecule XY_3 is successfully applied to
fit the recently observed vibrational spectrum of the water molecule and arsine
(AsH_3), respectively, and results are compared with those of other models.
Calculations show that algebraic approaches can be used as an effective method
for describing molecular vibrations with small standard deviations
A Microcalorimetric Method for Studying the Biological Effects of Mg2+ Ion on Recombinant Escherichia coli
Power-time curves of growing recombinant Escherichia coli B1 cell suspensions, treated with different concentrations of Mg2+, were recorded by microcalorimeter. The extent of the stimulatory effect of Mg2+ on the growth of recombinant E. coli B1 was compared by reference to the changes in the values of the growth rate coefficient of bacteria (k), the time of reaching the maximum effect in the log phase (tD), the time of maintaining the maximum effect in the stationary period (tS), and the maximum thermal power during the entire bacterial growth (Pm) at different Mg2+ doses and the optimal Mg2+ dose was calculated. The experimental results revealed that when Mg2+ mass concentration reached γ = 2.2 mg mL-1, the stimulatory effect is the greatest. With more Mg2+ (γ > 2.2 mg mL-1) added, the promotive effect would decrease drastically
Decoupling without outsourcing? How China’s consumption-based CO2 emissions have plateaued
The shift of China’s economy since 2013, dubbed the “new normal”, has caused its production and consumption emissions to plateau, with the country seeming to embody the tantalizing promise of decoupling its economic growth from carbon emissions. By using multi-region input-output analysis, we find that China’s relative decoupling in the new normal is technology driven, evidenced by the narrowing gap between its technology-adjusted and non-adjusted consumption emissions. By applying structural decomposition analysis, we further explore the driving forces behind the slowdown in China’s imported emissions growth, finding that it is attributable to restructuring of import patterns resulting from changes in the structures of domestic demand. These changes could have been caused by China moving along the global value chain and rebalancing its industrial linkages toward trade in carbon-efficient goods to avoid transferring emissions-intensive production to other regions, indicating a shift to less emissions-intensive trade rather than pure outsourcing
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