Directional properties of polar paramagnetic molecules subject to congruent electric, magnetic and optical fields

We show that congruent electric, magnetic and non-resonant optical fields acting concurrently on a polar paramagnetic (and polarisable) molecule offer possibilities to both amplify and control the directionality of the ensuing molecular states that surpass those available in double-field combinations or in single fields alone. At the core of these triple-field effects is the lifting of the degeneracy of the projection quantum number $M$ by the magnetic field superimposed on the optical field and a subsequent coupling of the members of the "doubled" (for states with $M \neq 0$) tunneling doublets due to the optical field by even a weak electrostatic field.Comment: 25 pages, 25 figures. Submitted to New Journal of Physic

Pair-eigenstates and mutual alignment of coupled molecular rotors in a magnetic field

We examine the rotational states of a pair of polar $^2\Sigma$ molecules subject to a uniform magnetic field. The electric dipole-dipole interaction between the molecules creates entangled pair-eigenstates of two types. In one type, the Zeeman interaction between the inherently paramagnetic molecules and the magnetic field destroys the entanglement of the pair-eigenstates, whereas in the other type it does not. The pair-eigenstates exhibit numerous intersections, which become avoided for pair-eigenstates comprised of individual states that meet the selection rules $\Delta J_{i}=0,\pm 1$, $\Delta N_{i}=0,\pm 2$, and $\Delta M_{i}=0,\pm 1$ imposed by the electric dipole-dipole operator. Here $J_{i}$, $N_{i}$ and $M_{i}$ are the total, rotational and projection angular momentum quantum numbers of molecules $i=1,2$ in the absence of the electric dipole-dipole interaction. We evaluate the mutual alignment of the pair-eigenstates and find it to be independent of the magnetic field, except for states that undergo avoided crossings, in which case the alignment of the interacting states is interchanged at the magnetic field corresponding to the crossing point. We present an analytic model which provides ready estimates of the pairwise alignment cosine that characterises the mutual alignment of the coupled rotors.Comment: 29 Pages, 11 figures, submitted to PCC

Interpreting 750 GeV diphoton excess in SU(5) grand unified theory

The ATLAS and CMS experiments at the LHC have found significant excess in the diphoton invariant mass distribution near 750 GeV. We interpret this excess in a predictive nonsupersymmetric SU(5) grand unified framework with a singlet scalar and light adjoint fermions. The 750 GeV resonance is identified as a gauge singlet scalar. Both its production and decays are induced by 24 dimensional adjoint fermions predicted within SU(5). The adjoint fermions are assumed to be odd under $Z_2$ symmetry which forbids their direct coupling to the standard model fermions. We show that the observed diphoton excess can be explained with sub-TeV adjoint fermions and with perturbative Yukawa coupling. A narrow width scenario is more preferred while a simultaneous explanation of observed cross section and large total decay width requires some of the adjoint fermions lighter than 375 GeV. The model also provides a singlet fermion as a candidate of cold dark matter. The gauge coupling unification is achieved in the framework by introducing color sextet scalars while being consistent with the proton decay constraint.Comment: Discussion added, conclusion unchanged; Matches published version in Physics Letters

Vibronic And Spin Angular Momentum In Rotationally Resolved Spectra Of Jahn-teller Active Molecules

Effects due to vibronic and spin angular momentum have long been observed in rotationally resolved spectra of Jahn-Teller active molecules. The breakdown of the Born-Oppenheimer approximation in these molecules leads to complications in their vibronic spectra. The molecular picture is further complicated due to the coupling of spin angular momenta with rotational and vibronic angular momentum. Values of these coupling constants have been determined by many high resolution rotationally resolved spectroscopic experiments. However, the presence of a conical intersection in the adiabatic potential energy surfaces has made getting a reliable quantum chemistry calculation of these terms challenging. In this talk we present methods that have been developed to make first principles calculations of vibronic angular momenta and Coriolis coupling constants from quantum chemistry. Further methods have been developed to calculated spin related terms (spin-orbit quenching and spin rotation coupling), using ab initio methods and model vibronic hamiltonian. We report a comparision of calculations of these parameters with corresponding results determined from high resolution spectroscopy for molecules like methoxy radical and cyclopentadienyl radical

Prospects for Quantum Computing with an Array of Ultracold Polar Paramagnetic Molecules

Arrays of trapped ultracold molecules represent a promising platform for implementing a universal quantum computer. DeMille has detailed a prototype design based on Stark states of polar $^1\Sigma$ molecules as qubits. Herein, we consider an array of polar $^2\Sigma$ molecules which are, in addition, inherently paramagnetic and whose Hund's case (b) free-rotor states are Bell states. We show that by subjecting the array to combinations of concurrent homogeneous and inhomogeneous electric and magnetic fields, the entanglement of the array's Stark and Zeeman states can be tuned and the qubit sites addressed. Two schemes for implementing an optically controlled CNOT gate are proposed and their feasibility discussed in the face of the broadening of spectral lines due to dipole-dipole coupling and the inhomogeneity of the electric and magnetic fields.Comment: 23 Pages, 11 figures, Submitted to Journal of Chemical Physic

CALCULATING ROTATIONAL SIGNATURES FOR JAHN-TELLER DISTORTED MOLECULES

A Jahn-Teller active molecule demonstrates a characteristic signature in its rotationally resolved spectra due to the distortions from the symmetric configuration. In the past decades, this signature has been used to experimentally access and understand the dynamics around a conical intersection. In this talk we present a method to calculate this rotational signature starting with electronic structure calculations. We derive an Effective Rotational Hamiltonian (ERH) for Jahn-Teller active systems and determine the relationship between the experimentally observable rotational parameters and electronic structure theory. The methodology has been further extended to include molecules with significant spin-orbit interaction. We have calculated both $h_1$, which manifests from distortions in the plane perpendicular to the highest symmetry rotational axis of the molecule, and $h_2$, which manifests from out-of-plane distortions of the molecule. We present our findings for cyclopentadienyl (C$_5$H$_5$), methoxy (CH$_3$O) and nitrate (NO$_3$) radicals and compare them to experimental data available in the literature. These calculations not only help guide experiments but are also a great tool for benchmarking high-level quantum chemistry calculations

CALCULATION AND VISUALIZATION OF THE VIBRONIC EIGENFUNCTIONS OF JAHN-TELLER ACTIVE MOLECULES

Jahn Teller active molecules are a convenient tool for understanding various nonadiabatic effects due to a conical intersection in the potential energy surface (PES), whether its position is determined by symmetry or accidentally along a reaction path. Computing PES, including the nonadiabatic coupling parameters, helps us to interpret the vibronic spectra of these molecules. Vibronic eigenfunctions are calculable either by utilizing fit data obtained from these vibronic spectra or electronic structure methods. In this talk we discuss the application and efficacy of these eigenvectors for calculating rovibronic parameters that characterize eigenstates in Jahn-Teller active molecules. Methods have been developed to plot spin vibronic eigenfunctions for multimode calculations. These plots give us considerable insight and enhance our understanding by visualizing Jahn-Teller interactions, multimode effects, and potentially the dynamics around a conical intersection