Coherent spectroscopy of a strongly driven triple quantum dot molecule

Based on a calculation model, we study the interference phenomena of serially coupled ∨-type and ∧-type triple quantum dots （CTQDs） driven simultaneously by a strong driving field and a weak probe field. Strongly depending on the configuration of the three-level CTQD, the probe absorption spectra, which are shown in the tunneling current, exhibit various quantum coherence properties. In the case where the two pairs of transitions of the CTQD have a small eigenfrequency difference △ω, the double-coupling effect of the driving field results in two Autler Townes doublets and one weak Mollow triplet in one spectrum. With the value of △ω increasing, only one Autler-Townes splitting remains due to the single-coupling of the field. We also find that the effect of spontaneous emission of phonons may lead to an obvious background current, which can be used to distinguish which transition is driven by the driving field in experiment. The interesting quantum property of a CTQD revealed in our results suggests its potential applications in quantum modulators and quantum logic devices.

Optical two-dimensional coherent spectroscopy of excitons in transition-metal dichalcogenides

Exciton physics in atomically thin transition-metal dichalcogenides(TMDCs)holds paramount importance for fundamental physics research and prospective applications.However,the experimental exploration of exciton physics,including excitonic coherence dynamics,exciton many-body interactions,and their optical properties,faces challenges stemming from factors such as spatial heterogeneity and intricate many-body effects.In this perspective,we elaborate upon how optical two-dimensional coherent spectroscopy(2DCS)emerges as an effective tool to tackle the challenges,and outline potential directions for gaining deeper insights into exciton physics in forthcoming experiments with the advancements in 2DCS techniques and new materials.

Study of capillary transit time distribution in coherent hemodynamics spectroscopy

A recently proposed analytical hemodynamie modell[s.Fantini,Neurolmage 85,202-221(2014)]is able to predict the changes of oxy,deoxy,and total hemoglobin concentrations(model outputs)given arbitrary changes in blood flow,blood volume,and rate of oygen consumption(model inputs).One asumption of this model is that the capillary compartment is characterized by a single blood transit time.In this work,we have extended the original model by considering a distribution of capillary transit times and we have compared the outputs of both models(original and extended)for the case of sinusoidal input signals at different frequencies,which realizes the new technique of coherent hemodynamics spectroscopy(CHS).For the calculations with the original model,we have used the mean value of the distribution of capillary transit times con-sidered in the extended model.We have found that,for distributions of capillary transit times having mean values around 1 s and a standard deviation less than about 45%of the mean value,the original and extended models yield the same CHS spectra(i.e.,model outputs versus fre-quency of ocillation)within typical experimental errors.For wider capillary transit time dis-tributions,the two models yield different CHS spectra.By assuming that Poiseuille's law is valid in the capillary compartment,we have related the distribution of capillary transit times to the distributions of capillary lengths and capillary speed of blood flow to calculate the average capillary and venous saturations.We have found that,for standard deviations of the capillanry transit time distrilbution that are less than about 80%of the mean value,the average capillary saturation is always larger than the venous saturation.By contrast,the average capillary satu-ration may be less than the venous saturation for wider distributions of the capillary transit times.

Structural deformation of nitro group of nitromethane molecule in liquid phase in an intense femtosecond laser field

The structural deformation of NO2 group induced by an intense femtosecond laser field of liquid nitromethane（NM）molecule is detected by time-and frequency-resolved coherent anti-Stokes Raman spectroscopy（CARS） technique with the intense pump laser. Here, we present the mechanism of molecular alignment and deformation. The CARS spectra and its FFT spectra of liquid NM show that the NO2 torsional mode couples with the CN symmetric stretching mode and that the NO2 group undergoes ultrafast structural deformation with a relaxation time of 195 fs. The frequency of the NO2 torsional mode in liquid NM（50.8±0.3 cm^-1） at room temperature is found. Our results prove the structural deformation of two groups in liquid NM molecule occur simultaneously in the intense laser field.