104 research outputs found
Influences of Stone–Wales defects on the structure, stability and electronic properties of antimonene: A first principle study
AbstractDefects are inevitably present in materials, and their existence strongly affects the fundamental physical properties of 2D materials. Here, we performed first-principles calculations to study the structural and electronic properties of antimonene with Stone–Wales defects, highlighting the differences in the structure and electronic properties. Our calculations show that the presence of a SW defect in antimonene changes the geometrical symmetry. And the band gap decreases in electronic band structure with the decrease of the SW defect concentration. The formation energy and cohesive energy of a SW defect in antimonene are studied, showing the possibility of its existence and its good stability, respectively. The difference charge density near the SW defect is explored, by which the structural deformations of antimonene are explained. At last, we calculated the STM images for the SW defective antimonene to provide more information and characters for possible experimental observation. These results may provide meaningful references to the development and design of novel nanodevices based on new 2D materials
Landau-Zener-Stuckelberg-Majorana interference in a 3D transmon driven by a chirped microwave
By driving a 3D transmon with microwave fields, we generate an effective
avoided energy-level crossing. Then we chirp microwave frequency, which is
equivalent to driving the system through the avoided energy-level crossing by
sweeping the avoided crossing. A double-passage chirp produces
Landau-Zener-St\"uckelberg-Majorana interference that agree well with the
numerical results. Our method is fully applicable to other quantum systems that
contain no intrinsic avoided level crossing, providing an alternative approach
for quantum control and quantum simulation
Simulating the Kibble-Zurek mechanism of the Ising model with a superconducting qubit system
The Kibble-Zurek mechanism (KZM) predicts the density of topological defects
produced in the dynamical processes of phase transitions in systems ranging
from cosmology to condensed matter and quantum materials. The similarity
between KZM and the Landau-Zener transition (LZT), which is a standard tool to
describe the dynamics of some non-equilibrium physics in contemporary physics,
is being extensively exploited. Here we demonstrate the equivalence between KZM
in the Ising model and LZT in a superconducting qubit system. We develop a
time-resolved approach to study quantum dynamics of LZT with nano-second
resolution. By using this technique, we simulate the key features of KZM in the
Ising model with LZT, e.g., the boundary between the adiabatic and impulse
regions, the freeze-out phenomenon in the impulse region, especially, the
scaling law of the excited state population as the square root of the quenching
rate. Our results supply the experimental evidence of the close connection
between KZM and LZT, two textbook paradigms to study the dynamics of the
non-equilibrium phenomena.Comment: Title changed, authors added, and some experimental data update
Absorption spectra of superconducting qubits driven by bichromatic microwave fields
We report experimental observation of two distinct quantum interference patterns in the absorption spectra when a transmon superconducting qubit is subjected to a bichromatic microwave field with the same Rabi frequencies. Within the two-mode Floquet formalism with no dissipation processes, we propose a graph-theoretical representation to model the interaction Hamiltonian for each of these observations. This theoretical framework provides a clear visual representation of various underlying physical processes in a systematic way beyond rotating-wave approximation. The presented approach is valuable to gain insights into the behavior of multichromatic field driven quantum two-level systems, such as two-level atoms and superconducting qubits. Each of the observed interference patterns is represented by appropriate graph products on the proposed color-weighted graphs. The underlying mechanisms and the characteristic features of the observed fine structures are identified by the transitions between the graph vertices, which represent the doubly dressed states of the system. The good agreement between the numerical simulation and experimental data confirms the validity of the theoretical method. Such multiphoton interference may be used in manipulating the quantum states and/or generate nonclassical microwave photons
BiOBr nanoflakes with strong Kerr nonlinearity towards hybrid integrated photonic devices
© 2020 SPIE. As a new group of advanced 2D layered materials, bismuth oxyhalides, i.e., BiOX (X = Cl, Br, I), have recently become of great interest. In this work, we characterize the third-order optical nonlinearities of BiOBr, an important member of the BiOX family. The nonlinear absorption and Kerr nonlinearity of BiOBr nanoflakes at both 800 nm and 1550 nm are characterized via the Z-Scan technique. Experimental results show that BiOBr nanoflakes exhibit a large nonlinear absorption coefficient β ∼ 10-7 m/W as well as a large Kerr coefficient n2 ∼ 10-14 m2/W. We also note that the n2 of BiOBr reverses sign from negative to positive as the wavelength is changed from 800 nm to 1550 nm. We further characterize the thickness-dependent nonlinear optical properties of BiOBr nanoflakes, finding that the magnitudes of β and n2 increase with decreasing thickness of the BiOBr nanoflakes. Finally, we integrate BiOBr nanoflakes into silicon integrated waveguides and measure their insertion loss, with the extracted waveguide propagation loss showing good agreement with mode simulations based on ellipsometry measurements. These results confirm the strong potential of BiOBr as a promising nonlinear optical material for high-performance hybrid integrated photonic devices
BiOBr 2D materials for integrated nonlinear photonics devices
As a new group of advanced 2D layered materials, bismuth oxyhalides, i.e.,
BiOX (X = Cl, Br, I), have recently become of great interest. In this work, we
characterize the third-order optical nonlinearities of BiOBr, an important
member of the BiOX family. The nonlinear absorption and Kerr nonlinearity of
BiOBr nanoflakes at both 800 nm and 1550 nm are characterized via the Z-Scan
technique. Experimental results show that BiOBr nanoflakes exhibit a large
nonlinear absorption coefficient = \b{eta} = 10-7 m/W as well as a large Kerr
coefficient n2 = 10-14 m2/W. We also note that the n2 of BiOBr reverses sign
from negative to positive as the wavelength is changed from 800 nm to 1550 nm.
We further characterize the thickness-dependent nonlinear optical properties of
BiOBr nanoflakes, finding that the magnitudes of \b{eta} and n2 increase with
decreasing thickness of the BiOBr nanoflakes. Finally, we integrate BiOBr
nanoflakes into silicon integrated waveguides and measure their insertion loss,
with the extracted waveguide propagation loss showing good agreement with mode
simulations based on ellipsometry measurements. These results confirm the
strong potential of BiOBr as a promising nonlinear optical material for
high-performance hybrid integrated photonic devices.Comment: 10 pages, 4 figures, 113 references. arXiv admin note: substantial
text overlap with arXiv:1909.02183; text overlap with arXiv:2003.0409
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