The ground and low-lying excited states and feasibility of laser cooling for GaH+ and InH+ cations

Direct laser cooling the NH molecule with the pseudo-closed loop triplet-triplet transition including intervening electronic states

Direct laser cooling molecule is useful way to obtain the accurate molecular spectroscopy. However, most of the reported direct laser cooling schemes are only involved the molecules with a singlet or doublet ground state because the one with a triplet ground state is more complex, especially when the first-excited state is not suitable for the pseudo-closed loop transition. Using NH as the prototype of the simplest heteronuclear molecule with a triplet ground state, we focus on constructing the direct laser cooling scheme with a pseudo-closed loop triplet-triplet transition including intervening electronic states. The potential energy curves and transition dipole moments are calculated for the X³Σ^-, a¹Δ, b¹Σ⁺, and A³Π states by using the multireference configuration interaction including spin-orbit coupling with the aug-cc-pV5Z basis sets. The rotational and vibrational energy levels of each electronic state are obtained by solving the Schrödinger equation of nuclear motion with the obtained potential energy curves. A two-color laser cooling scheme is established based on the ³Π₁ → X³Σ^- transition because the highly diagonal Franck-Condon factors make the transition suitable for constructing the pseudo-closed loop transition. The radiative lifetimes, the Doppler temperature, and the recoil temperature are calculated to access the cooling effect of the optical scheme. The results demonstrate that the ³Π₁ → X³Σ^- transition is much superior to the other transitions and the intervening a¹Δ and b¹Σ⁺ will not significantly impact the pseudo-closed loop transition of the laser cooling scheme. The accumulate FCF reach 0.99996 implies that about 25,000 scattering photons are available before leaking, which can cool the NH molecule to the Doppler temperature of 20.2 μK.

In search of molecular ions for optical cycling: a difficult road

Optical cycling, a continuous photon scattering off atoms or molecules, is the key tool in quantum information science.

Theoretical study on the low-lying excited electronic states and laser cooling feasibility of CuH molecule

To evaluate the feasibility of the laser cooling of CuH molecule, we investigate the electronic properties, the vibrational and rotational characteristics of the molecule based on the multi-reference configuration interaction method with all-electron basis sets. The potential energy curves (PECs) of X¹Σ⁺, A¹Σ⁺, B¹Σ⁺, a³Σ⁺, b³Σ⁺, e³Σ⁺, C¹П, D¹П, c³П and d³П states and the transition dipole moments between these states are calculated. The Schrödinger equation of nuclear movement is solved for each electronic state to obtain the rotational and vibration energy levels. The spectroscopic parameters are calculated based on the fitted analytical function from the PECs. The present results are in good agreement with the theoretical and experimental values available in the literature. The optical scheme of the laser cooling for CuH molecule is constructed with A¹Σ⁺ ↔ X¹Σ⁺ as the close-loop transition. Three lasers are necessary in each direction to maintain enough scattering photons because of the limited Franck-Condon factor of 0.78. The wavelengths of the pumping lasers are determined. The recoil temperature is 1.72 μk, which is the expected temperature to be reached through the method of the cooling below the doppler limit.

Optical Pumping of TeH+: Implications for the Search for Varying mp/me

Molecular overtone transitions provide optical frequency transitions sensitive to variation in the proton-to-electron mass ratio ( μ ≡ m p / m e ). However, robust molecular state preparation presents a challenge critical for achieving high precision. Here, we characterize infrared and optical-frequency broadband laser cooling schemes for TeH + , a species with multiple electronic transitions amenable to sustained laser control. Using rate equations to simulate laser cooling population dynamics, we estimate the fractional sensitivity to μ attainable using TeH + . We find that laser cooling of TeH + can lead to significant improvements on current μ variation limits.