Physics

Experiments with cold ion-atom mixtures have recently opened the way for the production and application of ultracold molecular ions. Here, in a comparative study, we theoretically investigate ground and several excited electronic states and prospects for the formation of molecular ions composed of a calcium ion and an alkali-metal atom: CaAlk + (Alk=Li, Na, K, Rb, Cs). We use a quantum chemistry approach based on non-empirical pseudopotential, operatorial core-valence correlation, large Gaussian basis sets, and full configuration interaction method for valence electrons. Adiabatic potential energy curves, spectroscopic constants, and transition and permanent electric dipole moments are determined and analyzed for the ground and excited electronic states. We examine the prospects for ion-neutral reactive processes and the production of molecular ions via spontaneous radiative association and laser-induced photoassociation. After that, spontaneous and stimulated blackbody radiation transition rates are calculated and used to obtain radiative lifetimes of vibrational states of the ground and first-excited electronic states. The present results pave the way for the formation and spectroscopy of calcium--alkali-metal-atom molecular ions in modern experiments with cold ion-atom mixtures.

Ultracold polar and magnetic 23 Na 6 Li molecules in the rovibrational ground state of the lowest triplet a 3 Σ + electronic state have been recently produced. Here, we calculate the electronic and rovibrational structure of these 14-electron molecules with spectroscopic accuracy ( <0.5 cm −1 ) using state-of-the-art ab initio methods of quantum chemistry. We employ the hierarchy of the coupled-cluster wave functions and Gaussian basis sets extrapolated to the complete basis set limit. We show that the inclusion of higher-level excitations, core-electron correlation, relativistic, QED, and adiabatic corrections is necessary to reproduce accurately scattering and spectroscopic properties of alkali-metal systems. We obtain the well depth, D e =229.9(5) cm −1 , the dissociation energy, D 0 =208.2(5) cm −1 , and the scattering length, a s =− 84 +25 −41 bohr, in good agreement with recent experimental measurements. We predict the permanent electric dipole moment in the rovibrational ground state, d 0 = 0.167(1) debye. These values are obtained without any adjustment to experimental data, showing that quantum chemistry methods are capable of predicting scattering properties of many-electron systems, provided relatively weak interaction and small reduced mass of the system.

The optical lattice clock NICT-Sr1 regularly reports calibration measurements of the international timescale TAI. By comparing measurement results to the reports of eight Primary Frequency Standards, we find the absolute frequency of the 87 Sr clock transition to be f(Sr)= 429228004229873.082(76) , with a fractional uncertainty of less than 1.8x10 −16 approaching the systematic limits of the best realization of SI second. Our result is consistent with other recent measurements and further supported by the loop closure over the absolute frequencies of 87 Sr , 171 Yb and direct optical measurements of their ratio.

We present a detailed spectroscopic investigation of a thermal 87 Rb atomic vapour in a magnetic field of 1.5~T in the Voigt geometry. We fit experimental spectra for all Stokes parameters with our theoretical model \textit{ElecSus} and find very good quantitative agreement, with RMS errors of ∼1.5 \% in all cases. We extract the magnetic field strength and the angle between the polarisation of the light and the magnetic field from the atomic signal, and we measure the birefringence effects of the cell windows on the optical rotation signals. This allows us to carry out precise measurements at a high field strength and arbitrary geometries, allowing further development of possible areas of application for atomic magnetometers.

We demonstrate a new technique for the accurate measurement of diffusion coefficients for alkali vapor in an inert buffer gas. The measurement was performed by establishing a spatially periodic density grating in isotopically pure 87 Rb vapor and observing the decaying coherent emission from the grating due to the diffusive motion of the vapor through N 2 buffer gas. We obtain a diffusion coefficient of 0.245±0.002 cm 2 /s at 50$\degree$C and 564~Torr. Scaling to atmospheric pressure, we obtain D 0 =0.1819±0.0024 cm 2 /s . To the best of our knowledge, this represents the most accurate determination of the Rb--N 2 diffusion coefficient to date. Our measurements can be extended to different buffer gases and alkali vapors used for magnetometry and can be used to constrain theoretical diffusion models for these systems.

The existence of the fundamental CP-violating interactions inside the nucleus leads to the existence of the nuclear Schiff moment. The Schiff moment potential corresponds to the electric field localized inside the nucleus and directed along its spin. This field can interact with electrons of an atom and induce the permanent electric dipole moment (EDM) of the whole system. The Schiff moment and corresponding electric field are enhanced in the nuclei with the octupole deformation leading to the enhanced atomic EDM. There is also a few-order enhancement of the T,P-violating effects in molecules due to the existence of energetically close levels of opposite parity. We study the Schiff moment enhancement in the class of diatomic molecules with octupole-deformed lanthanide and actinide nuclei: 227 AcF, 227 AcN, 227 AcO + , 229 ThO, 153 EuO + and 153 EuN. Projecting the existing experimental achievements to measure EDM in diamagnetic molecules with spherical nucleus ( 205 TlF) to the considered systems one can expect a very high sensitivity to the quantum chromodynamics parameter θ ¯ and other hadronic CP-violation parameters surpassing the current best limits by several orders of magnitude. It can have a dramatic impact on the modern understanding of the nature of CP-violating fundamental interactions.

Light-shifts are known to be an important limitation to the mid- and long-term fractional frequency stability of different types of atomic clocks. In this article, we demonstrate the experimental implementation of an advanced anti-light shift interrogation protocol onto a continuous-wave (CW) microcell atomic clock based on coherent population trapping (CPT). The method, inspired by the Auto-Balanced Ramsey (ABR) spectroscopy technique demonstrated in pulsed atomic clocks, consists in the extraction of atomic-based information from two successive light-shifted clock frequencies obtained at two different laser power values. Two error signals, computed from the linear combination of signals acquired along a symmetric sequence, are managed in a dual-loop configuration to generate a clock frequency free from light-shift. Using this method, the sensitivity of the clock frequency to both laser power and microwave power variations can be reduced by more than an order of magnitude compared to normal operation. In the present experiment, the consideration of the non-linear light-shift dependence allowed to enhance light-shift mitigation. The implemented technique allows a clear improvement of the clock Allan deviation for time scales higher than 1000 s. This method could be applied in various kinds of atomic clocks such as CPT-based atomic clocks, double-resonance Rb clocks, or cell-stabilized lasers.

Most ions lack the fast, cycling transitions that are necessary for direct laser cooling. In most cases, they can still be cooled sympathetically through their Coulomb interaction with a second, coolable ion species confined in the same potential. If the charge-to-mass ratios of the two ion types are too mismatched, the cooling of certain motional degrees of freedom becomes difficult. This limits both the achievable fidelity of quantum gates and the spectroscopic accuracy. Here we introduce a novel algorithmic cooling protocol for transferring phonons from poorly- to efficiently-cooled modes. We demonstrate it experimentally by simultaneously bringing two motional modes of a Be + -Ar 13+ mixed Coulomb crystal close to their zero-point energies, despite the weak coupling between the ions. We reach the lowest temperature reported for a highly charged ion, with a residual temperature of only T??00 μK in each of the two modes, corresponding to a residual mean motional phonon number of ?�n?�≲0.4 . Combined with the lowest observed electric field noise in a radiofrequency ion trap, these values enable an optical clock based on a highly charged ion with fractional systematic uncertainty below the 10 ??8 level. Our scheme is also applicable to (anti-)protons, molecular ions, macroscopic charged particles, and other highly charged ion species, enabling reliable preparation of their motional quantum ground states in traps.

Atomic comagnetometers, which measure the spin precession frequencies of overlapped species simultaneously, are widely applied to search for exotic spin-dependent interactions. Here we propose and implement an all-optical single-species Cs atomic comagnetometer based on the optical free induction decay (FID) signal of Cs atoms in hyperfine levels F g =3 & 4 within the same atomic ensemble. We experimentally show that systematic errors induced by magnetic field gradients and laser fields are highly suppressed in the comagnetometer, but those induced by asynchronous optical pumping and drift of residual magnetic field in the shield dominate the uncertainty of the comagnetometer. With this comagnetometer system, we set the constraint on the strength of spin-gravity coupling of the proton at a level of 10 −18 eV, comparable to the most stringent one. With further optimization in magnetic field stabilization and spin polarization, the systematic errors can be effectively suppressed, and signal-to-noise ratio (SNR) can be improved, promising to set more stringent constraints on spin-gravity interactions.

In this work we demonstrate a high sensitivity atomic gradiometer capable of operation in earth-field level environments. We apply a light-pulse sequence at four times the Larmor frequency to achieve gradiometer sensitivity <20 fT/cm/ Hz − − − √ at the finite field strength of 22 μ T. The experimental timing sequence can be tuned to the field magnitude of interest. Our one dimensional all-optical gradiometer performs a differential measurement between two regions of a single vapor cell on a 4 cm baseline. Our results pave the way for extensions to operation in higher dimensions, vector sensitivity, and more advanced gradiometers.