Validity Examination of the Dissipative Quantum Model of Olfaction

Despite some inconclusive experimental evidences for the vibrational model of olfaction, the validity of the model has not been examined yet and therefore it suffers from the lack of conclusive experimental support. Here, we generalize the model and propose a numerical analysis of the dissipative odorant-mediated inelastic electron tunneling mechanism of olfaction, to be used as a potential examination in experiments. Our analysis gives several predictions on the model such as efficiency of elastic and inelastic tunneling of electrons through odorants, sensitivity thresholds in terms of temperature and pressure, isotopic effect on sensitivity, and the chiral recognition for discrimination between the similar and different scents. Our predictions should yield new knowledge to design new experimental protocols for testing the validity of the model.

Phase-Modulated Nonresonant Laser Pulses Can Selectively Convert Enantiomers in a Racemic Mixture

Deracemization occurs when a racemic molecular mixture is transformed into a mixture containing an excess of a single enantiomer. Recent advances in ultrafast laser technology hint at the possibility of using shaped pulses to generate deracemization via selective enantiomeric conversion; however, experimental implementation remains a challenge and has not yet been achieved. Here we suggest a simple, yet novel approach to laser-induced enantiomeric conversion based on dynamic Stark control. We demonstrate theoretically that current laser and optical technology can be used to generate a pair of phase-modulated, nonresonant, linearly polarized Gaussian laser pulses that can selectively deracemize a racemic mixture of 3D-oriented, 3,5-difluoro-3',5'-dibromobiphenyl (F₂H₃C₆-C₆H₃Br₂) molecules, the laser-induced dynamics of which are well studied experimentally. These results strongly suggest that designing a closed-loop coherent control scheme based on this methodology may lead to the first-ever achievement of enantiomeric conversion via coherent laser light in a laboratory setting.

Sisyphus Laser Cooling of a Polyatomic Molecule

We perform magnetically assisted Sisyphus laser cooling of the triatomic free radical strontium monohydroxide (SrOH). This is achieved with principal optical cycling in the rotationally closed P(N^{''}=1) branch of either the X[over ˜]^{2}Σ^{+}(000)↔A[over ˜]^{2}Π_{1/2}(000) or the X[over ˜]^{2}Σ^{+}(000)↔B[over ˜]^{2}Σ^{+}(000) vibronic transitions. Molecules lost into the excited vibrational states during the cooling process are repumped back through the B[over ˜](000) state for both the (100) level of the Sr-O stretching mode and the (02^{0}0) level of the bending mode. The transverse temperature of a SrOH molecular beam is reduced in one dimension by 2 orders of magnitude to ∼750  μK. This approach opens a path towards creating a variety of ultracold polyatomic molecules by means of direct laser cooling.

Chiral nanoparticles in singular light fields

The studying of how twisted light interacts with chiral matter on the nanoscale is paramount for tackling the challenging task of optomechanical separation of nanoparticle enantiomers, whose solution can revolutionize the entire pharmaceutical industry. Here we calculate optical forces and torques exerted on chiral nanoparticles by Laguerre-Gaussian beams carrying a topological charge. We show that regardless of the beam polarization, the nanoparticles are exposed to both chiral and achiral forces with nonzero reactive and dissipative components. Longitudinally polarized beams are found to produce chirality densities that can be 109 times higher than those of transversely polarized beams and that are comparable to the chirality densities of beams polarized circularly. Our results and analytical expressions prove useful in designing new strategies for mechanical separation of chiral nanoobjects with the help of highly focussed beams.

Comb-locked cavity ring-down saturation spectroscopy

We present a new method of comb-locked cavity ring-down spectroscopy for the Lamb-dip measurement of molecular ro-vibrational transitions. By locking both the probe laser frequency and a temperature-stabilized high-finesse cavity to an optical frequency comb, we realize saturation spectroscopy of molecules with kilohertz accuracy. The technique is demonstrated by recording the R(9) line in the υ = 3 - 0 overtone band of CO near 1567 nm. The Lamb-dip spectrum of such a weak line (transition rate 0.0075 s^-1) is obtained using an input laser power of only 3 mW, and the position is determined to be 191 360 212 770 kHz with an uncertainty of 7 kHz (δν/ν∼3.5×10^-11), which is currently limited by our rubidium clock.

Enantiomer-Specific State Transfer of Chiral Molecules

State-selective enantiomeric excess is realized using microwave-driven coherent population transfer. The method selectively promotes either R or S molecules to a higher rotational state by phase-controlled microwave pulses that drive electric-dipole allowed rotational transitions. We demonstrate the enantiomer-specific state transfer method using enantiopure samples of 1,2-propanediol. This method of state-specific enantiomeric enrichment can be applied to a large class of asymmetric, chiral molecules that can be vaporized and cooled to the point where rotationally resolved spectroscopy is possible, including molecules that rapidly racemize. The rapid chiral switching demonstrated here allows for new approaches in high-precision spectroscopic searches for parity violation in chiral molecules.

Optically active quantum-dot molecules

Chiral molecules made of coupled achiral semiconductor nanocrystals, also known as quantum dots, show great promise for photonic applications owing to their prospective uses as configurable building blocks for optically active structures, materials, and devices. Here we present a simple model of optically active quantum-dot molecules, in which each of the quantum dots is assigned a dipole moment associated with the fundamental interband transition between the size-quantized states of its confined charge carriers. This model is used to analytically calculate the rotatory strengths of optical transitions occurring upon the excitation of chiral dimers, trimers, and tetramers of general configurations. The rotatory strengths of such quantum-dot molecules are found to exceed the typical rotatory strengths of chiral molecules by five to six orders of magnitude. We also study how the optical activity of quantum-dot molecules shows up in their circular dichroism spectra when the energy gap between the molecular states is much smaller than the states' lifetime, and maximize the strengths of the circular dichroism peaks by optimizing orientations of the quantum dots in the molecules. Our analytical results provide clear design guidelines for quantum-dot molecules and can prove useful in engineering optically active quantum-dot supercrystals and photonic devices.

Antisymmetric Couplings Enable Direct Observation of Chirality in Nuclear Magnetic Resonance Spectroscopy

Here we demonstrate that a term in the nuclear spin Hamiltonian, the antisymmetric J-coupling, is fundamentally connected to molecular chirality. We propose and simulate a nuclear magnetic resonance (NMR) experiment to observe this interaction and differentiate between enantiomers without adding any additional chiral agent to the sample. The antisymmetric J-coupling may be observed in the presence of molecular orientation by an external electric field. The opposite parity of the antisymmetric coupling tensor and the molecular electric dipole moment yields a sign change of the observed coupling between enantiomers. We show how this sign change influences the phase of the NMR spectrum and may be used to discriminate between enantiomers.

Characterising molecules for fundamental physics: an accurate spectroscopic model of methyltrioxorhenium derived from new infrared and millimetre-wave measurements

Precise spectroscopic analysis of polyatomic molecules enables many striking advances in physical chemistry and fundamental physics. We use several new high-resolution spectroscopic devices to improve our understanding of the rotational and rovibrational structure of methyltrioxorhenium (MTO), the achiral parent of a family of large oxorhenium compounds that are ideal candidate species for a planned measurement of parity violation in chiral molecules. Using millimetre-wave and infrared spectroscopy in a pulsed supersonic jet, a cryogenic buffer gas cell, and room temperature absorption cells, we probe the ground state and the Re[double bond, length as m-dash]O antisymmetric and symmetric stretching excited states of both CH₃¹⁸⁷ReO₃ and CH₃¹⁸⁵ReO₃ isotopologues in the gas phase with unprecedented precision. By extending the rotational spectra to the 150-300 GHz range, we characterize the ground state rotational and hyperfine structure up to J = 43 and K = 41, resulting in refinements to the rotational, quartic and hyperfine parameters, and the determination of sextic parameters and a centrifugal distortion correction to the quadrupolar hyperfine constant. We obtain rovibrational data for temperatures between 6 and 300 K in the 970-1015 cm^-1 range, at resolutions down to 8 MHz and accuracies of 30 MHz. We use these data to determine more precise excited-state rotational, Coriolis and quartic parameters, as well as the ground-state centrifugal distortion parameter D_K of the ¹⁸⁷Re isotopologue. We also account for hyperfine structure in the rovibrational transitions and hence determine the upper state rhenium atom quadrupole coupling constant eQq'.

High-resolution FTIR spectroscopy of trisulfane HSSSH: a candidate for detecting parity violation in chiral molecules

We present the first analysis of high resolution infrared spectra for trisulfane, a candidate to measure molecular parity violation.

Synthetic routes for a variety of halogenated (chiral) acetic acids from diethyl malonate

We focus on a synthetic route to synthesise chiral halogenated acetic acids with F, Cl, Br, and H/D isotopic substitution at the α-C-atom starting from diethyl malonate.

Mixing of quantum states: A new route to creating optical activity

The ability to induce optical activity in nanoparticles and dynamically control its strength is of great practical importance due to potential applications in various areas, including biochemistry, toxicology, and pharmaceutical science. Here we propose a new method of creating optical activity in originally achiral quantum nanostructures based on the mixing of their energy states of different parities. The mixing can be achieved by selective excitation of specific states or via perturbing all the states in a controllable fashion. We analyze the general features of the so produced optical activity and elucidate the conditions required to realize the total dissymmetry of optical response. The proposed approach is applicable to a broad variety of real systems that can be used to advance chiroptical devices and methods.

Synchrotron-Based Highest Resolution Terahertz Spectroscopy of the ν24 Band System of 1,2-Dithiine (C4H4S2): A Candidate for Measuring the Parity Violating Energy Difference between Enantiomers of Chiral Molecules

The chiral C₂ symmetric molecule 1,2-dithiine (1,2-dithia-3,5-hexadiene, C₄H₄S₂) has been identified as a possible candidate for measuring the parity violating energy difference between enantiomers. We report here the observation and analysis of the low-frequency fundamental ν₂₄ using highest resolution synchrotron-based interferometric Fourier transform infrared (FTIR) spectroscopy in the terahertz range with a band center of ν₀ = 6.95375559 THz (ν̃₀ = 231.952319 (10) cm^-1) and two related hot bands, the (ν₁₃ + ν₂₄) ← ν₁₃ band at ν₀ = 6.97256882 THz (ν̃₀ = 232.579861 (33) cm^-1) and the 2ν₂₄ ← ν₂₄ band at ν₀ = 7.01400434 THz (ν̃₀ = 233.962001 (14) cm^-1). This success in the difficult analyses of the THz spectrum of a complex chiral molecule of importance for fundamental tests on molecular parity violation is enabled by the ideal setup of an FTIR experiment of currently unique resolution with the very stable and bright synchrotron radiation at the Swiss Light Source (SLS).

Detecting Chirality in Molecules by Linearly Polarized Laser Fields

A new scheme for enantiomer differentiation of chiral molecules using a pair of linearly polarized intense ultrashort laser pulses with skewed mutual polarization is presented. The technique relies on the fact that the off-diagonal anisotropic contributions to the electric polarizability tensor for two enantiomers have different signs. Exploiting this property, we are able to excite a coherent unidirectional rotation of two enantiomers with a π phase difference in the molecular electric dipole moment. The approach is robust and suitable for relatively high temperatures of molecular samples, making it applicable for selective chiral analysis of mixtures, and to chiral molecules with low barriers between enantiomers. As an illustration, we present nanosecond laser-driven dynamics of a tetratomic nonrigid chiral molecule with short-lived chirality. The ultrafast time scale of the proposed technique is well suited to study parity violation in molecular systems in short-lived chiral states.

Chiral Analysis Using Broadband Rotational Spectroscopy

broadband microwave spectroscopy is a proven tool to precisely determine molecular properties of gas-phase molecules. Recent developments make it applicable to investigate chiral molecules. Enantiomers can be differentiated, and the enantiomeric excess and, indirectly, the absolute configuration can be determined in a molecule-selective manner. The resonant character and high resolution of rotational spectroscopy provide a unique mixture compatibility. Future directions, such as extending the technique to chemical analysis, are discussed.

High resolution GHz and THz (FTIR) spectroscopy and theory of parity violation and tunneling for 1,2-dithiine (C4H4S2) as a candidate for measuring the parity violating energy difference between enantiomers of chiral molecules

Our results show that this molecule is a suitable candidate for a possible first determination of the parity violating energy difference Δ_pvE between enantiomers.

Dissipative vibrational model for chiral recognition in olfaction

We examine the olfactory discrimination of left- and right-handed enantiomers of chiral odorants based on the odorant-mediated electron transport from a donor to an acceptor of the olfactory receptors embodied in a biological environment. The chiral odorant is effectively described by an asymmetric double-well potential whose minima are associated to the left- and right-handed enantiomers. The introduced asymmetry is considered an overall measure of chiral interactions. The biological environment is conveniently modeled as a bath of harmonic oscillators. The resulting spin-boson model is adapted by a polaron transformation to derive the corresponding Born-Markov master equation with which we obtain the elastic and inelastic electron tunneling rates. We show that the inelastic tunneling through left- and right-handed enantiomers occurs with different rates. The discrimination mechanism depends on the ratio of tunneling frequency to localization frequency.

Stochastic and empirical models of the absolute asymmetric synthesis by the Soai-autocatalysis

Absolute asymmetric synthesis (AAS) is the preparation of pure (or excess of one) enantiomer of a chiral compound from achiral precursor(s) by a chemical reaction, without enantiopure chiral additive and/or without applied asymmetric physical field. Only one well-characterized example of AAS is known today: the Soai-autocatalysis. In an attempt at clarification of the mechanism of this particular reaction we have undertaken empirical and stochastic analysis of several parallel AAS experiments. Our results show that the initial steps of the reaction might be controlled by simple normal distribution ("coin tossing") formalism. Advanced stages of the reaction, however, appear to be of a more complicated nature. Symmetric beta distribution formalism could not be brought into correspondence with the experimental observations. A bimodal beta distribution algorithm provided suitable agreement with the experimental data. The parameters of this bimodal beta function were determined by a Pólya-urn experiment (simulated by computer). Interestingly, parameters of the resulting bimodal beta function give a golden section ratio. These results show, that in this highly interesting autocatalysis two or even perhaps three catalytic cycles are cooperating. An attempt at constructing a "designed" Soai-type reaction system has also been made.

A slow, continuous beam of cold benzonitrile

A cold, continuous, high flux beam of benzonitrile has been created via buffer gas cooling.

Probing chirality fluctuations in molecules by nonlinear optical spectroscopy

Symmetry breaking caused by geometric fluctuations can enable processes that are otherwise forbidden. An example is a perylene bisimide dyad whose dipole moments are perpendicular to each other. Förster-type energy transfer is thus forbidden at the equilibrium geometry since the dipolar coupling vanishes. Yet, fluctuations of the geometric arrangement have been shown to induce finite energy transfer that depends on the dipole variance, rather than the mean. We demonstrate an analogous effect associated with chirality symmetry breaking. In its equilibrium geometry, this dimer is non-chiral. The linear chiral response which depends on the average geometry thus vanishes. However, we show that certain 2D chiral optical signals are finite due to geometric fluctuations. Furthermore, the correlation time of these fluctuations can be experimentally revealed by the waiting time dependence of the 2D signal.

High-resolution spectroscopy of the chiral metal complex [CpRe(CH₃)(CO)(NO)]: a potential candidate for probing parity violation

Heavy-metal containing chiral compounds have been suggested as promising candidates for studying parity-violation effects. We report herein the broadband rotational spectroscopy study of the chiral complex [CpRe(CH3)(CO)(NO)] in the gas phase. The spectra obtained are very rich due to the two rhenium isotopologues ((185)Re and (187)Re), hyperfine structure arising from the rhenium and nitrogen nuclei, and the asymmetry of the chiral complex. Since rhenium is located very close to the molecular center of mass, the rotational constants for the two rhenium isotopologues are very similar. However they can be differentiated by their characteristic nuclear quadrupole hyperfine splitting patterns. Comparison with calculated nuclear quadrupole coupling constants shows that all-electron relativistic basis sets are necessary for a correct description of the rhenium atom in this type of complex. The present study is an important step towards future precision studies on chiral molecules.

Origin of anomalous electronic circular dichroism spectrum of RuPt2(tppz)2Cl2(PF6)4 in acetonitrile

We report a theoretical study of the structures, energetics, and electronic spectra of the Pt(II)/Ru(II) mixed-metal complex RuPt2(tppz)2Cl2(PF6)4 (tppz = 2,3,5,6-tetra(2-pyridyl)pyrazine) in acetonitrile. The hybrid B3LYP density functional theory and its TDDFT methods were used with a complete basis set (CBS) extrapolation scheme and a conductor polarizable continuum model (C-PCM) for solvation effects. Results showed that the trinuclear complex has four types of stable conformers and/or enantiomers. They are separated by high barriers owing to the repulsive H/H geometrical constraints in tppz. A strong entropy effect was found for the dissociation of RuPt2(tppz)2Cl2(PF6)n in acetonitrile. The UV-visible and emission spectra of the complex were also simulated. They are in good agreement with experiments. In this work we have largely focused on exploring the origin of anomalous electronic circular dichroism (ECD) spectra of the RuPt2(tppz)2Cl2(PF6)4 complex in acetonitrile. As a result, a new mechanism has been proposed together with a clear illustration by using a physical model.

Strong enhancement of parity violation effects in chiral uranium compounds

A new generation of molecular candidates for parity violation measurements. The chiral UNXYZ compounds are predicted to exhibit strong parity violating effects which are up to an order of magnitude larger than for any of the previously suggested candidates.

Are collapse models testable with quantum oscillating systems? The case of neutrinos, kaons, chiral molecules

Collapse models provide a theoretical framework for understanding how classical world emerges from quantum mechanics. Their dynamics preserves (practically) quantum linearity for microscopic systems, while it becomes strongly nonlinear when moving towards macroscopic scale. The conventional approach to test collapse models is to create spatial superpositions of mesoscopic systems and then examine the loss of interference, while environmental noises are engineered carefully. Here we investigate a different approach: We study systems that naturally oscillate-creating quantum superpositions-and thus represent a natural case-study for testing quantum linearity: neutrinos, neutral mesons, and chiral molecules. We will show how spontaneous collapses affect their oscillatory behavior, and will compare them with environmental decoherence effects. We will show that, contrary to what previously predicted, collapse models cannot be tested with neutrinos. The effect is stronger for neutral mesons, but still beyond experimental reach. Instead, chiral molecules can offer promising candidates for testing collapse models.