Molecules containing heavy and octupole deformed radioactive nuclei are predicted to provide enhanced sensitivity to investigate the violation of fundamental symmetries and to search for physics beyond the Standard Model of particle physics. However, experimental measurements of such radioactive systems are scarce. Octupole deformed nuclei are very rare in nature or do not occur naturally. Thus, their study requires to overcome major experimental challenges. This contribution will discuss the recent achievements in laser spectroscopy of radioactive molecules at CRIS, ISOLDE-CERN. Spectroscopy measurements of short-lived radium fluoride molecules (RaF), and their impact in fundamental physics research will be discussed.

The parity and time-reversal symmetry violating electric dipole moments (EDMs) of diamagnetic atoms have the potential to probe physics beyond TeV scale. EDMs of atomic systems arise from the nuclear Schiff moment (NSM), S, and the tensor-pseudotensor (T-PT) electron-nucleus (e-N) interaction that is characterized by its coupling coefficient, C_T. A combination of high-precision experiment and relativistic many-body theory gives upper limits on these two quantities. Such limits aid in extracting bounds on EDMs of neutron, d_n, and proton, d_p, chromo-EDMs, and the quantum chromodynamics parameter, |―θ|. Previous calculations on these quantities using relativistic coupled-cluster (RCC) theory differ by about 40 percent, as compared to the results obtained from other variants of relativistic many-body methods Y. Singh and B. K. Sahoo, Phys. Rev. A 92, 022502 (2015). In this work, we employ the recently developed relativistic normal coupled-cluster theory B. K. Sahoo and B. P. Das Phys. Rev. Lett. 120, 203001 (2018). which alleviates the deficiencies of RCC method, to obtain the EDM of ²²⁵Ra, and combine it with the latest measurement to obtain limits on S and C_T. Further, taking into account the enhancement to EDM due to octuple moment of ²²⁵Ra, these limits are revised to 〈σ_N 〉|C_T| < 1.06 ×10⁻⁷ and S < 2.19 ×10⁻¹⁰ |e| fm³, with 〈σ_N 〉 being the nuclear Pauli spinor. The accuracy of our results is corroborated by the dipole polarizability, which is obtained as 257(8) e a₀³. Our EDM results, in combination with measurement, are about 8% and 28% improvements over the limits that were reported using the relativistic coupled-cluster theory for the NSM and T-PT e-N coupling coefficient, respectively. Further combining with the nuclear calculations, we infer the following limits: d_n < 1.15 ×10⁻²³ |e| cm, d_p < 1.1 ×10⁻²² |e| cm, |―θ| < 2.46 ×10⁻¹⁰, and the combined up- and down- quark chromo-EDMs |d̃_u − d̃_d| < 1.36 ×10⁻²⁶ |e|cm. Though these bounds are not competitive at present with the current-best limits acquired from ¹⁹⁹Hg atom, they can be bettered when the measurement of EDM in ²²⁵Ra improves by four orders. Y. Singh and B. K. Sahoo, Phys. Rev. A 92, 022502 (2015).. B. K. Sahoo and B. P. Das Phys. Rev. Lett. 120, 203001 (2018).,

Diatomic heavy polar molecules as well as molecular ions have proved to be very good candidates for table-top experimental searches for electric dipole moment of electron (eEDM). These experiments in combination with relativistic many-body calculations set an upper bound to the eEDM, thus probing physics beyond the Standard-Model (SM) of elementary particles. Theoretically, we can check the suitability of a molecular candidate for eEDM experiments by calculating the effective electric field (E_eff), permanent dipole moment (μ), and polarizing electric field (E_pol), as these are among the major factors that determine the experimental sensitivity of the molecule. The production of radioactive elements like lawrencium opens up the possibility of performing eEDM experiments with molecules having radioactive atoms. In this abstract, we focus on lawrencium flouride ion and its potential for probing new physics beyond the SM via the eEDM. To ensure the stability of the molecule, we obtained the equilibrium bond length of LrF⁺ from the minima of the potential energy curve (PEC), and we also showed how the PEC depends on the choice of basis sets. As E_eff is entirely relativistic in origin, relativistic calculations are required to obtain it. We report the values of E_eff and μ of LrF+ calculated at Dirac-Fock level, using quadruple-zeta basis. Our calculated Dirac-Fock level value E_eff of LrF⁺ is 213.6 GV/cm, which is two times larger than that of HgF V. S. Prasannaa, A. C. Vutha, M. Abe, and B. P. Das,Phys. Rev. Lett.114, 183001 (2015). and approximately nine times larger than that of the ionic candidate HfF⁺ W Cairncross et al, Phys. Rev. Lett. 119, 153001 (2017). thus suggesting larger experimental sensitivity. Inclusion of correlation effects to the properties by performing calculations using the relativistic coupled-cluster (RCC) method is underway. We propose a molecular ion trap procedure to confine the molecules for performing eEDM experiment with LrF⁺ ion, as trap experiments would give larger coherence time compared to beam experiments, thus improving experimental sensitivity.

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Footnotes:

V. S. Prasannaa, A. C. Vutha, M. Abe, and B. P. Das,Phys. Rev. Lett.114, 183001 (2015)., W Cairncross et al, Phys. Rev. Lett. 119, 153001 (2017).,

We introduce a comb-referenced optical spectrometer operating in the long-wavelength (LW) part of the mid-infrared (MIR) region. It is based on an innovative laser source based on difference frequency generation between two MIR lasers, namely a cw DFB-QCL and a CO₂ laser, which produces widely tunable light from 12.1 to 14.8 μm with optical power up to 110 μW and MHz-level linewidth. We exploit it to give the first evidence of bending modes metrology in this region, with the assessment of several CO₂-based frequency benchmarks with uncertainties down to 30 kHz, and the accurate study of the ν₁₁ band of benzene, which is a significant testbed for the resolution of the spectrometer. These results foster optical metrology in a region not explored so far and pave the way for accurate rotationally-resolved studies of the energy structure of large molecules, such as aromatic hydrocarbons.

We introduce Multi-spectrum Rotational States Thermometry (MRST) as a new optical method for primary thermometry that relies on the global fitting of multiple molecular absorption lines of the same band at different pressures. This allows leveraging the temperature-dependence of the Doppler width and also of the distribution of line intensities across the ro-vibrational band, provided a sufficiently accurate line-strength model is available. We give a preliminary demonstration of the method with a comb-locked frequency-swept cavity-ring-down spectrometer operated on the 3ν₁+ν₃ band of CO₂ located around 1577 nm, which stands out among other spectroscopic samples for the availability of several line intensity models of both experimental and theoretical origin. The spectra signal-to-noise ratio represents the main limitation to a combined uncertainty to 510 ppm, but the comparative analysis between different line-strength models shows promise to reduce the error budget to 33 ppm. As compared to Doppler-broadening-thermometry, an advantage of the approach is the reduced impact of a wrong modelling of the absorption line-shapes. In a reversed approach, MRST can be applied on a gas of known temperature to set an upper limit to the accuracy of a given line intensity model.

Continuous-wave optical parametric oscillators (CW-OPOs) can offer broad tuning with high resolution and high power in the mid-IR and have many important potential applications in precision spectroscopy. The widely tunable cw-OPO system (TOPO) developed by TOPTICA Photonics is capable of covering the wavelength range of 1.45-4.0 μm (with a degenerate gap between 2.07-2.19 μm) without optics or nonlinear optical crystal exchanges. A computer-controlled automation system has been developed to achieve broad (up to 300 GHz) mode-hop-free (MHF) tuning range of the idler wavelengths and high output power ( > 1 W). Its narrow linewidth is demonstrated in direct measurements and in sub-Doppler absorption spectroscopy of atmospheric molecules. Furthermore, a much-improved frequency accuracy has been achieved by referencing the OPO to a frequency comb and creating a phase-coherent bridge between the NIR and MIR spectral ranges. Frequency noise from both the OPO cavity and the seed laser are eliminated by (i) beating the OPO signal output against the fundamental of the frequency comb and (ii) beating the seed laser against a 1064 nm comb extension.

Cooling atoms to the ultracold regime has allowed for studies of physics, ranging from many-body physics of quantum degenerate gases, quantum computing, precision measurements and tests of fundamental symmetries. Extending these experiments to polar molecules has the prospect of enhancing the sensitivity of such tests and of enabling novel studies, such as cold controlled chemistry. However, applying traditional laser cooling techniques to molecules is rendered difficult due their additional degrees of freedom which result in a limited photon scattering budget. Here we study aluminum monochloride (AlCl) as a promising candidate for laser cooling and trapping. The cooling transition at 261 nm (A¹ Π− X¹ Σ⁺) has an estimated Franck-Condon factor of 0.9988 which allows for scattering  800 photons with a single laser before the molecule enters an excited vibrational state. We use a frequency-tripled (SHG + SFG) Titanium-Sapphire laser. We generate AlCl via laser ablation of AlCl₃ in a cryogenic helium buffer gas beam source and we will discuss initial spectroscopy on AlCl necessary for future laser cooling and trapping.