Magic conditions for multiple rotational states of bialkali molecules in optical lattices

We investigate magic-wavelength trapping of ultracold bialkali molecules in the vicinity of weak optical transitions from the vibrational ground state of the X 1 Σ + potential to low-lying rovibrational states of the b 3 Π 0 potential, focusing our discussion on the 87 Rb 133 Cs molecule in a magnetic field of B = 181 G. We show that a frequency window exists between two nearest-neighbor vibrational poles in the dynamic polarizability where the trapping potential is “near magic” for multiple rotational states simultaneously. We show that the addition of a modest DC electric field of E = 0.13 kV/cm leads to an exact magic-wavelength trap for the lowest three rotational states at a angular-frequency detuning of Δ v ′ = 0 = 2 π × 218.22 GHz from the X 1 Σ + ( v = 0 , J = 0 ) → b 3 Π 0 ( v ′ = 0 , J = 1 ) transition. We derive a set of analytical criteria that must be fulfilled to ensure the existence of such magic frequency windows and present an analytic expression for the position of the frequency window in terms of a set of experimentally measurable parameters. These results should inform future experiments requiring long coherence times on multiple rotational transitions in ultracold polar molecules

A motorized rotation mount for the switching of an optical beam path in under 20 ms using polarization control

We present a simple motorized rotation mount for a half-wave plate that can be used to rapidly change the polarization of light. We use the device to switch a high power laser beam between different optical dipole traps in an ultracold atom experiment. The device uses a stepper motor with a hollow shaft, which allows a beam to propagate along the axis of the motor shaft, minimizing inertia and mechanical complexity. A simple machined adapter is used to mount the wave plate. We characterize the performance of the device, focusing on its capability to switch a beam between the output ports of a polarizing beam splitter cube. We demonstrate a switching time of 15.9(3) ms, limited by the torque of the motor. The mount has a reaction time of 0.52(3) ms and a rotational resolution of 0.45(4)°. The rotation is highly reproducible, with the stepper motor not missing a step in 2000 repeated tests over 11 h

Modulation Transfer Spectroscopy of the D1 Transition of Potassium: Theory and Experiment

We report on a study of modulation transfer spectroscopy of the $4\textrm{S}_{1/2}\rightarrow 4\textrm{P}_{1/2}$ ($D_{1}$) transition of naturally abundant potassium in a room-temperature vapour cell. This transition is critical for laser cooling and optical pumping of potassium and our study is therefore motivated by the need for robust laser frequency stabilisation. Despite the absence of a closed transition, the small ground-state hyperfine splitting in potassium results in strong crossover features in the $D_{1}$ modulation transfer spectrum. To emphasise this we compare the $D_{1}$ and $D_{2}$ spectra of potassium with those of rubidium. Further, we compare our experimental results with a detailed theoretical simulation, examining different pump-probe polarization configurations to identify the optimal signals for laser frequency stabilisation. We find good agreement between the experiment and the theory, especially for the $\textrm{lin} \parallel \textrm{lin}$ polarization configuration

Enhanced Quantum Control of Individual Ultracold Molecules Using Optical Tweezer Arrays

Control over the quantum states of individual molecules is crucial in the quest to harness their rich internal structure and dipolar interactions for applications in quantum science. In this paper, we develop a toolbox of techniques for the control and readout of individually trapped polar molecules in an array of optical tweezers. Starting with arrays of up to eight Rb and eight Cs atoms, we assemble arrays of RbCs molecules in their rovibrational and hyperfine ground state with an overall efficiency of 48(2)%. We demonstrate global microwave control of multiple rotational states of the molecules and use an auxiliary tweezer array to implement site-resolved addressing and state control. We show how the rotational stateof the molecule can be mapped onto the position of Rb atoms and use this capability to readout multiple rotational states in a single experimental run. Further, using a scheme for the midsequence detection of molecule formation errors, we perform rearrangement of assembled molecules to prepare small defect-free arrays. Finally, we discuss a feasible route to scaling to larger arrays of molecules

Entangling two distinguishable quantum bright solitons via collisions

The generation of mesoscopic Bell states via collisions of distinguishable bright solitons has been suggested in Phys. Rev. Lett. 111, 100406 (2013). Here, we extend our former proposal to two hyperfine states of 85Rb instead of two different atomic species, thus simplifying possible experimental realisations. A calculation of the s-wave scattering lengths for the hyperfine states (f,mf) = (2, +2) and (3, +2) identifies parameter regimes suitable for the creation of Bell states with an advantageously broad Feshbach resonance. We show the generation of Bell states using the truncated Wigner method for the soliton's centre of mass and demonstrate the validity of this approach by a comparison to a mathematically rigorous effective potential treatment of the quantum many-particle problem

Absolute absorption on the potassium D lines: theory and experiment

We present a detailed study of the absolute Doppler-broadened absorption of a probe beam scanned across the potassium D lines in a thermal vapour. Spectra using a weak probe were measured on the 4S $\to$ 4P transition and compared to the theoretical model of the electric susceptibility detailed by Zentile et al (2015 Comput. Phys. Commun. 189 162–74) in the code named ElecSus. Comparisons were also made on the 4S $\to$ 5P transition with an adapted version of ElecSus. This is the first experimental test of ElecSus on an atom with a ground state hyperfine splitting smaller than that of the Doppler width. An excellent agreement was found between ElecSus and experimental measurements at a variety of temperatures with rms errors $\sim {10}^{-3}$. We have also demonstrated the use of ElecSus as an atomic vapour thermometry tool, and present a possible new measurement technique of transition decay rates which we predict to have a precision of ~$3\;\mathrm{kHz}$