arXiv subjects

Quansheng Zhang

Publications and source records attributed to Quansheng Zhang.

10 recordsLinked to original sources

arXiv2021

Collective Effects of Organic Molecules based on Holstein-Tavis-Cummings Model

We study the collective effects of an ensemble of organic molecules confined in an optical cavity based on Holstein-Tavis-Cummings model. By using the quantum Langevin approach and adiabatically eliminating the degree of freedom of the vibrational motion, we analytically obtain the expression of the cavity transmission spectrum to analyze the features of polaritonic states. As an application, we show that the dependence for the frequency shift of the lower polaritonic state on the number of molecules can be used in the detection of the ultra-cold molecules. We also numerically analyze the fluorescence spectrum. The variation of the spectral profile with various numbers of molecules gives signatures for the modification of molecular conformation.

quant-ph↗

arXiv2021

Improved laser-distillation method for complete enantio-conversion of chiral mixtures

Laser-assisted enantio-conversion is an ambitious issue related to chiral molecules in the atomic, molecular, and optical physics. The theoretical laser-distillation method had been proposed to realize enantio-conversion based on a four-level double-$Δ$ model of two degenerated chiral ground states and two achiral excited states. Here, we re-investigate and improve the laser-distillation method so that a chiral mixture can be converted to an enantiopure sample of the desired chirality, i.e., complete enantio-conversion, which has not been discussed in the previous theoretical works of the laser-distillation method. Since the undesired chirality may be inefficient or even cause serious side effects in pharmacology, our work plays as an important improvement to the original theoretical works of the laser-assisted enantio-conversion.

physics.chem-ph↗

arXiv2020

Evading thermal population influence in enantiomeric-specific state transfer based on a cyclic three-level system via ro-vibrational transitions

Optical methods of enantiomeric-specific state transfer had been proposed theoretically based on a cyclic three-level system of chiral molecule. According to these theoretical methods, recently the breakthrough progress has been reported in experiments [S. Eibenberger et al., Phys. Rev. Lett. 118, 123002 (2017); C. Pérez et al., Angew. Chem. Int. Ed. 56, 12512 (2017)] for cold gaseous chiral molecules but with low state-specific enantiomeric enrichment. One of the limiting factors is the influence of the thermal population in the selected three purely rotational states in experiment. Here, we theoretically propose an improved optical method of enantiomeric-specific state transfer to effectively evade such an adverse impact of thermal population by introducing ro-vibrational transitions for the cyclic three-level system of chiral molecules. Then, at the typical temperature in experiments approximately only the lowest state in the chosen three-level system is thermally occupied and the optical method of enantiomeric-specific state transfer works well. Comparing with the case of purely rotational transitions where all the three states are thermally occupied, this modification will remarkably increase the obtained state-specific enantiomeric enrichment with enantiomeric excess approximately 100%.

quant-ph↗

arXiv2020

Enantio-discrimination via light deflection effect

We propose a theoretical method for enantio-discrimination based on the light deflection effect in four-level models of chiral molecules. This four-level model consists of a cyclic three-level subsystem coupled by three strong driving fields and an auxiliary level connected to the cyclic three-level subsystem by a weak probe field. It is shown that the induced refractive index for the weak probe field is chirality-dependent. Thus it will lead to chirality-dependent light deflection when the intensities of two of the three strong driving fields are spatially inhomogeneous. As a result, the deflection angle of the weak probe light can be utilized to detect the chirality of pure enantiomers and enantiomeric excess of chiral mixture. Therefore, our method may act as a tool for enantio-discrimination.

physics.optics↗

arXiv2020

Fast enantioconversion of chiral mixtures based on a four-level double-$Δ$ model

Based on the four-level double-$Δ$ model composed of two degenerated (left- and right-handed) chiral ground states and two achiral excited states, we propose a purely optical method for enantio-conversion of chiral mixture. By choosing appropriate parameters, the original four-level model will be simplified to two effective two-level sub-systems with each of them involving one chiral ground state. Then, with the help of well-designed optical operations, the initial unwanted and wanted chiral ground states are converted, respectively, to the wanted chiral ground state and an auxiliary chiral excited state with the wanted chirality, i.e., achieving the enantioconversion of the chiral mixture. Comparing with the original work of enantioconversion based on the four-level double-$Δ$ model with the requirement of the time-consuming relaxation step and repeated operations, our method can be three orders of magnitude faster since we use only purely optical operations. Thus, it offers a promising candidate for fast enantioconversion when the total operation time is limited due to the racemization and/or experimental conditions.

physics.optics↗

arXiv2019

Effective two-level models for highly efficient inner-state enantio-separation based on cyclic three-level systems of chiral molecules

Based on cyclic three-level systems of chiral molecules, we propose two methods to realize highly efficient inner-state enantio-separations of a chiral mixture with the two enantiomers initially prepared in their ground states. Our methods work in the region where the evolutions of the two enantiomers can be described by their corresponding effective two-level models, simultaneously. The approximately $100\%$-efficiency inner-state enantio-separations can be realized when the probability occupying the ground state of one enantiomer becomes $0$ by experiencing half-integer periods of its corresponding on-resonance Rabi oscillation and in the meanwhile the other one still stays approximately in the ground state, under the conditions that the two enantiomers are governed by the effective on-resonance and large-detuning two-level models, respectively. Alternatively, the exactly $100\%$-efficiency inner-state enantio-separation can be obtained when the probabilities occupying the ground states of the two enantiomers simultaneously experience half-integer and integer periods of their corresponding on-resonance and detuned (instead of largely-detuned) Rabi oscillations with final $0$ and $1$ probabilities occupying the ground state, respectively.

physics.optics↗

arXiv2019

Static non-linear Schrödinger equations for the achiral-chiral transitions of polar chiral molecules

In the mean-field theory, the stabilization of polar chiral molecules is understood as a quantum phase transition where the mean-field ground state of molecules changes from the achiral eigenstate of the molecular Hamiltonian to one of the degenerated chiral states as the increase of the intermolecular interaction. Starting from the many-body Hamiltonian of the molecular gases with electric dipole-dipole interactions, we give the static non-linear Schrödinger equations without free parameters to explore the achiral-chiral transitions of polar chiral molecules. We find that the polar chiral molecules of different species can be classified into two categories: At the critical point for the achiral-chiral transition, the mean-field ground state changes continuously in one category, and changes discontinuously in the other category. We further give the mean-field phase diagram of the achiral-chiral transitions for both two categories.

physics.chem-ph↗

arXiv2019

MPC-Based Precision Cooling Strategy (PCS) for Efficient Thermal Management of Automotive Air Conditioning System

In this paper, we propose an MPC-based precision cooling strategy (PCS) for energy efficient thermal management of automotive air conditioning (A/C) system. The proposed PCS is able to provide precise tracking of the time-varying cooling power trajectory, which is assumed to match the passenger comfort requirements. In addition, by leveraging the emerging connected and automated vehicles (CAVs) technology, vehicle speed preview can be incorporated in our A/C thermal management strategy for further energy efficiency improvement. This proposed A/C thermal management strategy is developed and evaluated based on a physics-based A/C system model (ACSim) from Ford Motor Company for the vehicles with electrified powertrains. In a comparison with Ford benchmark case over SC03 cycle, for tracking the same cooling power trajectory, the proposed PCS provides 4.9% energy saving at the cost of a slight increase in the cabin temperature (less than 1$^oC$). It is also demonstrated that by coordinating with future vehicle speed and shifting the A/C power load, the A/C energy consumption can be further reduced.

eess.SY↗

arXiv2019

Determination of enantiomeric excess with chirality-dependent AC Stark effects in cyclic three-level models

Determination of enantiomeric excess is important and remains challenges. We theoretically propose a new spectroscopic method for this issue based on the chirality-dependent AC Stark effects in cyclic three-level models under the three-photon resonance condition. The enantiomeric excess of the chiral mixture is determined by comparing the amplitudes of the two chosen AC Stark peaks in the Fourier transform spectrum of the induced polarizations, which are (approximately) proportional to the molecule numbers of the two enantiomers, respectively. Comparing with current spectroscopic methods based on the interference between the electric- and (usually weak) magnetic-dipole transition moments and/or with the need for enantio-pure samples, our method only involves electric-dipole transitions and does not require the enantio-pure samples. Therefore, it will give strong chiral signals and can be applied to the determinations of enantiomeric excess for chiral molecules whose enantio-pure samples are still challenging to achieve.

physics.optics↗

arXiv2018

Real single-loop cyclic three-level configuration of chiral molecules

Single-loop cyclic three-level ($Δ$-type) configuration of chiral molecules was used for enantio-separation in many theoretical works. Considering the effect of molecular rotation, this simple single-loop configuration is generally replaced by a complicated multiple-loop configuration containing multiple degenerate magnetic sub-levels and the ability of the enantio-separation methods is suppressed. For chiral asymmetric top molecules, we propose a scheme to construct a real single-loop $Δ$-type configuration with no connections to other states by applying three microwave fields with appropriate polarization vectors and frequencies. With our scheme, the previous theoretical proposals for enantio-separation based on single-loop $Δ$-type configurations can be experimentally realized when the molecular rotation is considered.

quant-ph↗