28,707 research outputs found
Pumping Current in a Quantum Dot by an Oscillating Magnetic Field
We investigate spin and charge current through a quantum dot pumped by a
time-varying magnetic field. Using the density matrix method, quantum rate
equations for the electronic occupation numbers in the quantum dot are obtained
and solved in the stationary state limit for a wide set of setup parameters.
Both charge and spin current are expressed explicitly in terms of several
relevant parameters and analyzed in detail. The results suggest a way of
optimizing experimental setup parameters to obtain an maximal spin current
without the charge current flow.Comment: to appear in the proceedings of the international conference on
frontiers in nonlinear and complex systems as a special issue in the
International Journal of Modern Physics B, vol. 21
Floquet engineering of long-range p-wave superconductivity: Beyond the high-frequency limit
It has been shown that long-range {\it p}-wave superconductivity in a Kitaev
chain can be engineered via an ac field with a high frequency [Benito et al.,
Phys. Rev. B 90, 205127 (2014)]. For its experimental realization, however,
theoretical understanding of Floquet engineering with a broader range of
driving frequencies becomes important. In this work, focusing on the ac-driven
tunneling interactions of a Kitaev chain, we investigate effects from the
leading correction to the high-frequency limit on the emergent {\it p}-wave
superconductivity. Importantly, we find new engineered long-range {\it p}-wave
pairing interactions that can significantly alter the ones in the
high-frequency limit at long interaction ranges. We also find that the leading
correction additionally generates nearest-neighbor {\it p}-wave pairing
interactions with a renormalized pairing energy, long-range tunneling
interactions, and in particular multiple pairs of Floquet Majorana edge states
that are destroyed in the high- frequency limit.Comment: 13 pages, 8 figure
Probing weak dipole-dipole interaction using phase-modulated non-linear spectroscopy
Phase-modulated non-linear spectroscopy with higher harmonic demodulation has
recently been suggested to provide information on many-body excitations. In the
present work we theoretically investigate the application of this method to
infer the interaction strength between two particles that interact via weak
dipole-dipole interaction. To this end we use full numerical solution of the
Schr\"odinger equation with time-dependent pulses. For interpretation purpose
we also derive analytical expressions in perturbation theory. We find one can
detect dipole-dipole interaction via peak intensities (in contrast to
line-shifts which typically are used in conventional spectroscopy). We provide
a detailed study on the dependence of these intensities on the parameters of
the laser pulse and the dipole-dipole interaction strength. Interestingly, we
find that there is a phase between the first and second harmonic demodulated
signal, whose value depends on the sign of the dipole-dipole interaction.Comment: 12 pages, 8 figures, Supporting information provided with the source
file
Collective quantum phase slips in multiple nanowire junctions
Realization of robust coherent quantum phase slips represents a significant
experimental challenge. Here we propose a new design consisting of multiple
nanowire junctions to realize a phase-slip flux qubit. It admits good
tunability provided by gate voltages applied on superconducting islands
separating nanowire junctions. In addition, the gates and junctions can be
identical or distinct to each other leading to symmetric and asymmetric setups.
We find that the asymmetry can improve the performance of the proposed device,
compared with the symmetric case. In particular, it can enhance the effective
rate of collective quantum phase slips. Furthermore, we demonstrate how to
couple two such devices via a mutual inductance. This is potentially useful for
quantum gate operations. Our investigation on how symmetry in multiple nanowire
junctions affects the device performance should be useful for the application
of phase-slip flux qubits in quantum information processing and quantum
metrology.Comment: 12 pages, 6 figure
A readily accessible multifunctional probe: simultaneous recognition of the cation ZN²⁺ and the anion F⁻ via distinguishable wavelengths
The probe 1 was readily prepared via condensation of 8-formyl-7-hydroxy-coumarin and carbonic dihydrazide in a one-step procedure. Probe 1 exhibited high sensitivity and selectivity towards Zn²⁺ and F⁻ through a “turn-on” fluorescence response and/or ratiometric colorimetric response with low detection limits of the order of 10-8 M. The complex behaviour was fully investigated by spectral titration, isothermal titration calorimetry, 1H NMR spectroscopic titration and mass spectrometry. Interestingly, probe 1 not only recognizes the cation Zn²⁺ and the anion F⁻, but can also distinguish between these two ions via the max wavelength in their UV-vis spectra (360 nm for 1-Zn²⁺ versus 400 nm for 1-F⁻ complex) or their fluorescent spectra (λₑₓ / λₑm = 360 nm/ 454 nm for 1-Zn²⁺ versus λₑₓ / λₑm = 400 nm/ 475 nm for 1-F⁻ complex) due to their differing red-shifts. Additionally, probe 1 has been further explored in the detection of Zn²⁺ in living cells
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