Λ\Lambda-Enhanced Imaging of Molecules in an Optical Trap

We report non-destructive imaging of optically trapped calcium monofluoride (CaF) molecules using in-situ $\Lambda$-enhanced gray molasses cooling. $200$ times more fluorescence is obtained compared to destructive on-resonance imaging, and the trapped molecules remain at a temperature of $20\,\mu\text{K}$. The achieved number of scattered photons makes possible non-destructive single-shot detection of single molecules with high fidelity.Comment: 6 pages, 4 figure

An Optical Tweezer Array of Ultracold Molecules

Arrays of single ultracold molecules promise to be a powerful platform for many applications ranging from quantum simulation to precision measurement. Here we report on the creation of an optical tweezer array of single ultracold CaF molecules. By utilizing light-induced collisions during the laser cooling process, we trap single molecules. The high densities attained inside the tweezer traps have also enabled us to observe in the absence of light molecule-molecule collisions of laser cooled molecules for the first time

Spin-Orbit Coupling and Spin Textures in Optical Superlattices

We proposed and demonstrated a new approach for realizing spin orbit coupling with ultracold atoms. We use orbital levels in a double well potential as pseudospin states. Two-photon Raman transitions between left and right wells induce spin-orbit coupling. This scheme does not require near resonant light, features adjustable interactions by shaping the double well potential, and does not depend on special properties of the atoms. A pseudospinor Bose-Einstein condensate spontaneously acquires an antiferromagnetic pseudospin texture which breaks the lattice symmetry similar to a supersolid

Observation of Collisions between Two Ultracold Ground-State CaF Molecules

We measure inelastic collisions between ultracold CaF molecules by combining two optical tweezers, each containing a single molecule. We observe collisions between $^2\Sigma$ CaF molecules in the absolute ground state $|X,v=0, N=0,F=0\rangle$, and in excited hyperfine and rotational states. In the absolute ground state, we find a two-body loss rate of $7(4) \times 10^{-11} \text{cm}^{3}/\text{s}$, which is below, but close to the predicted universal loss rate.Comment: 5 pages, 4 figure

Observation of Microwave Shielding of Ultracold Molecules

Harnessing the potential wide-ranging quantum science applications of molecules will require control of their interactions. Here, we use microwave radiation to directly engineer and tune the interaction potentials between ultracold calcium monofluoride (CaF) molecules. By merging two optical tweezers, each containing a single molecule, we probe collisions in three dimensions. The correct combination of microwave frequency and power creates an effective repulsive shield, which suppresses the inelastic loss rate by a factor of six, in agreement with theoretical calculations. The demonstrated microwave shielding shows a general route to the creation of long-lived, dense samples of ultracold molecules and evaporative cooling

Laser Cooling of Optically Trapped Molecules

Calcium monofluoride (CaF) molecules are loaded into an optical dipole trap (ODT) and subsequently laser cooled within the trap. Starting with magneto-optical trapping, we sub-Doppler cool CaF and then load $150(30)$ CaF molecules into an ODT. Enhanced loading by a factor of five is obtained when sub-Doppler cooling light and trapping light are on simultaneously. For trapped molecules, we directly observe efficient sub-Doppler cooling to a temperature of $60(5)$ $\mu\text{K}$. The trapped molecular density of $8(2)\times10^7$ cm$^{-3}$ is an order of magnitude greater than in the initial sub-Doppler cooled sample. The trap lifetime of 750(40) ms is dominated by background gas collisions.Comment: 5 pages, 5 figure

Spin-orbit coupled Bose-Einstein condensates with observation of a stripe phase

Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2017.Cataloged from PDF version of thesis.Includes bibliographical references.In this work we build a new spin-orbit coupling experiment to observe the supersolidlike stripe phase. The phase diagram of a 1-dimensional spin-orbit coupled Bose- Einstein condensate shows several interesting phases including the stripe phase. We find the stripe phase particularly interesting because the condensate develops a density modulation in free space while remaining superfluid, which are the signature of supersolidity. In order to observe the stripe phase, we develop a novel spin-j basis which uses the orbital bands of an optical superlattice. Our choice of pseudo-spin basis allows the condensate components to remain miscible at high enough spin-orbit coupling strengths to observe the stripe phase. The superlattice constitutes a chain of spins which develop an antiferromagnetic spin texture and a density modulation at twice the lattice spacing. Breaking the discrete translational symmetry of the lattice while maintaining superfluidity indicates the formation of a lattice supersolid which we detected with Bragg scattering. Finally, the density modulation of the stripe phase is measured with a Bragg reflected beam and a camera setup to resolve the angular spread of the beam. An angle resolved, coherent Bragg beam is direct evidence of the stripe phase density modulation in free space. The formation of a free space density modulation in a superfluid Bose-Einstein condensate breaks the continuous spatial translation symmetry of space; fulfilling the definition of supersolidity. My primary contributions to the work include: controlling the superlattice, designing and building the Bragg detection scheme, some data collection and analysis.by Sean Burchesky.S.B

Observation of microwave shielding of ultracold molecules

Shielding ultracold molecules Ultracold molecules hold promise for a wide range of exciting applications. However, such applications are currently hampered by the limited number of ultracold molecular ensembles that can be created and by their short lifetimes. Anderegg et al . used a microwave dressing field to tune the collisional properties of calcium monofluoride molecules trapped in optical tweezers. This approach allowed a sixfold suppression of inelastic trap-loss collisions. This scheme paves the way for the creation of a variety of long-lived ultracold molecular ensembles. —YS </jats:p

Rotational Coherence Times of Polar Molecules in Optical Tweezers

Qubit coherence times are critical to the performance of any robust quantum computing platform. For quantum information processing using arrays of polar molecules, a key performance parameter is the molecular rotational coherence time. We report a 93(7) ms coherence time for rotational state qubits of laser cooled CaF molecules in optical tweezer traps, over an order of magnitude longer than previous systems. Inhomogeneous broadening due to the differential polarizability between the qubit states is suppressed by tuning the tweezer polarization and applied magnetic field to a "magic" angle. The coherence time is limited by the residual differential polarizability, implying improvement with further cooling. A single spin-echo pulse is able to extend the coherence time to nearly half a second. The measured coherence times demonstrate the potential of polar molecules as high fidelity qubits