1,704 research outputs found
Cooling mechanical resonators to quantum ground state from room temperature
Ground-state cooling of mesoscopic mechanical resonators is a fundamental
requirement for test of quantum theory and for implementation of quantum
information. We analyze the cavity optomechanical cooling limits in the
intermediate coupling regime, where the light-enhanced optomechanical coupling
strength is comparable with the cavity decay rate. It is found that in this
regime the cooling breaks through the limits in both the strong and weak
coupling regimes. The lowest cooling limit is derived analytically at the
optimal conditions of cavity decay rate and coupling strength. In essence,
cooling to the quantum ground state requires , with being the mechanical quality factor and
being the thermal phonon number. Remarkably, ground-state
cooling is achievable starting from room temperature, when mechanical
-frequency product , and both of the
cavity decay rate and the coupling strength exceed the thermal decoherence
rate. Our study provides a general framework for optimizing the backaction
cooling of mesoscopic mechanical resonators
Electrical Detection of Ferroelectric-like Metals through Nonlinear Hall Effect
Ferroelectric-like metals are a relatively rare class of materials that have
ferroelectric-like distortion and metallic conductivity. LiOsO is the first
demonstrated and the most investigated ferroelectric-like metal. The presence
of free carriers makes them difficult to be studied by traditional
ferroelectric techniques. In this paper, using the symmetry analysis and
first-principles calculations, we demonstrate that the ferroelectric-like
transition of LiOsO can be probed by a kind of electrical transport method
based on nonlinear Hall effect. The Berry curvature dipole exists in the
ferroelectric-like phase, and it can lead to a measurable nonlinear Hall
conductance with a conventional experimental setup. However, the symmetry of
the paraelectric-like phase LiOsO vanishes the Berry curvature dipole. The
Berry curvature dipole shows a strong dependence on the polar displacement,
which might be helpful for the detection of polar order. The nonlinear Hall
effect provides an effective method for the detection of phase transition in
the study of the ferroelectric-like metals and promotes them to be applied in
the ferroelectric-like electronic devices
Electrical detection of ferroelectriclike metals through the nonlinear Hall effect
Ferroelectriclike metals are a relatively rare class of materials that have ferroelectriclike distortion and metallic conductivity. LiOsO3 is the first demonstrated and the most investigated ferroelectriclike metal. The presence of free carriers makes them difficult to be studied by traditional ferroelectric techniques. In this paper, using symmetry analysis and first-principles calculations, we demonstrate that the ferroelectriclike transition of LiOsO3 can be probed by a kind of electrical transport method based on nonlinear Hall effect. The Berry curvature dipole exists in the ferroelectriclike phase and it can lead to a measurable nonlinear Hall conductance with a conventional experimental setup. However, the symmetry of the paraelectriclike phase LiOsO3 vanishes the Berry curvature dipole. The Berry curvature dipole shows a strong dependence on the polar displacement, which might be helpful for the detection of polar order. The nonlinear Hall effect provides an effective method for the detection of phase transition in the study of the ferroelectriclike metals and promotes them to be applied in ferroelectriclike electronic devices
Simultaneous Structural Identification of Natural Products in Fractions of Crude Extract of the Rare Endangered Plant Anoectochilus roxburghii Using 1H NMR/RRLC-MS Parallel Dynamic Spectroscopy
Nuclear magnetic resonance/liquid chromatography-mass spectroscopy parallel dynamic spectroscopy (NMR/LC-MS PDS) is a method aimed at the simultaneous structural identification of natural products in complex mixtures. In this study, the method is illustrated with respect to 1H NMR and rapid resolution liquid chromatography-mass spectroscopy (RRLC-MS) data, acquired from the crude extract of Anoectochilus roxburghii, which was separated into a series of fractions with the concentration of constituent dynamic variation using reversed-phase preparative chromatography. Through fraction ranges and intensity changing profiles in 1H NMR/RRLC–MS PDS spectrum, 1H NMR and the extracted ion chromatogram (XIC) signals deriving from the same individual constituent, were correlated due to the signal amplitude co-variation resulting from the concentration variation of constituents in a series of incompletely separated fractions. 1H NMR/RRLC-MS PDS was then successfully used to identify three types of natural products, including eight flavonoids, four organic acids and p-hydroxybenzaldehyde, five of which have not previously been reported in Anoectochilus roxburghii. In addition, two groups of co-eluted compounds were successfully identified. The results prove that this approach should be of benefit in the unequivocal structural determination of a variety of classes of compounds from extremely complex mixtures, such as herbs and biological samples, which will lead to improved efficiency in the identification of new potential lead compounds
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