Phonon-Induced Quantum Magnetic Deflagration in Mn12

A comprehensive set of experiments on the effect of high-frequency surface acoustic waves, SAWs, in the spin relaxation in Mn12-acetate is presented. We have studied the quantum magnetic deflagration induced by SAWs under various experimental conditions extending the data shown in a very recent paper [A. Hernandez-Minguez et. al., Phys. Rev. Lett. 95, 217205 (2005)]. We have focused our study on the dependence of both the ignition time and the propagation speed of the magnetic avalanches on the frequency, amplitude, and duration of the SAW pulses in experiments performed under different temperatures and external magnetic fields.Comment: 7 pages, 9 figure

Surface acoustic wave modulation of single photon emission from GaN/InGaN nanowire quantum dots

On-chip quantum information processing requires controllable quantum light sources that can be operated on-demand at high-speeds and with the possibility of in-situ control of the photon emission wavelength and its optical polarization properties. Here, we report on the dynamic control of the optical emission from core-shell GaN/InGaN nanowire (NW) heterostructures using radio frequency surface acoustic waves (SAWs). The SAWs are excited on the surface of a piezoelectric lithium niobate crystal equipped with a SAW delay line onto which the NWs were mechanically transferred. Luminescent quantum dot (QD)-like exciton localization centers induced by compositional fluctuations within the InGaN nanoshell were identified using stroboscopic micro-photoluminescence (micro-PL) spectroscopy. They exhibit narrow and almost fully linearly polarized emission lines in the micro-PL spectra and a pronounced anti-bunching signature of single photon emission in the photon correlation experiments. When the nanowire is perturbed by the propagating SAW, the embedded QD is periodically strained and its excitonic transitions are modulated by the acousto-mechanical coupling, giving rise to a spectral fine-tuning within a ~1.5 meV bandwidth at the acoustic frequency of ~330 MHz. This outcome can be further combined with spectral detection filtering for temporal control of the emitted photons. The effect of the SAW piezoelectric field on the QD charge population and on the optical polarization degree is also observed. The advantage of the acousto-optoelectric over other control schemes is that it allows in-situ manipulation of the optical emission properties over a wide frequency range (up to GHz frequencies).Comment: arXiv admin note: text overlap with arXiv:1902.0791

How cyclical do cyclically-adjusted balances remain? An EU study

Observed budget balances are an imperfect indicator of the fiscal policy stance, because fluctuations in economic activity induce automatic changes in the balance, hence the use of cyclically-adjusted balances (CAB). However, this paper shows that CABs (as measured through one of the two methods currently used by the Commission) tend to be systematically overestimated during downturns and underestimated during expansions. The dominant source of this distortion arises from the filtering of revenues deemed to be cyclical, possibly signalling a problem with the computation of elasticities. The effect of the items which are assumed not to move with the cycle is non significant, but this overall result conceals offseting effects: public investment turns to be significantly procyclical and interest payments and transfers to firms are countercyclical. Classification-JEL : H6, E6.. cyclically adjusted balances, fiscal policy, EU.