Ultracold <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mrow><mml:mi>Li</mml:mi><mml:mi>Cr</mml:mi></mml:mrow></mml:math>: A New Pathway to Quantum Gases of Paramagnetic Polar Molecules

Abstract

Quantum gases of doubly polar molecules represent appealing frameworks for a variety of cross-disciplinary applications, encompassing quantum simulation and computation, controlled quantum chemistry, and precision measurements. Through a joint experimental and theoretical study, here we explore a novel class of ultracold paramagnetic polar molecules combining lithium alkali and chromium transition metal elements. Focusing on the specific bosonic isotopologue <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><a:msup><a:mi/><a:mn>6</a:mn></a:msup><a:msup><a:mi>Li</a:mi><a:mn>53</a:mn></a:msup><a:mi>Cr</a:mi></a:math>, leveraging on the Fermi statistics of the parent atomic mixture and on suitable Feshbach resonances recently discovered, we produce up to <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><d:mn>50</d:mn><d:mo>×</d:mo><d:msup><d:mn>10</d:mn><d:mn>3</d:mn></d:msup></d:math> ultracold <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><g:mrow><g:mi>Li</g:mi><g:mi>Cr</g:mi></g:mrow></g:math> molecules at peak phase-space densities exceeding 0.1, prepared within the least bound rotationless level of the <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><j:mrow><j:mi>Li</j:mi><j:mi>Cr</j:mi></j:mrow></j:math> electronic ground state <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><m:mi>X</m:mi><m:msup><m:mspace width="0.1em"/><m:mn>6</m:mn></m:msup><m:msup><m:mi mathvariant="normal">Σ</m:mi><m:mo>+</m:mo></m:msup></m:math>. By also developing new probing methods, we thoroughly characterize the molecular gas, demonstrating the paramagnetic nature of <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><r:mrow><r:mi>Li</r:mi><r:mi>Cr</r:mi></r:mrow></r:math> dimers and the precise control of their quantum state. We investigate their stability against inelastic processes and identify a parameter region where pure <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><u:mrow><u:mi>Li</u:mi><u:mi>Cr</u:mi></u:mrow></u:math> samples exhibit lifetimes exceeding 0.2 s. Parallel to this, we employ state-of-the-art quantum chemical calculations to accurately predict the properties of <x:math xmlns:x="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><x:mrow><x:mi>Li</x:mi><x:mi>Cr</x:mi></x:mrow></x:math> ground and excited electronic states. This model, able to reproduce the experimental <ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><ab:mi>Li</ab:mi></ab:math>-<db:math xmlns:db="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><db:mi>Cr</db:mi></db:math> high-spin, scattering length, allows us to identify both efficient paths to coherently transfer weakly bound <gb:math xmlns:gb="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><gb:mrow><gb:mi>Li</gb:mi><gb:mi>Cr</gb:mi></gb:mrow></gb:math> dimers to their absolute ground state, and suitable transitions for their subsequent optical manipulation. Our studies establish <jb:math xmlns:jb="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><jb:mi>Li</jb:mi></jb:math>-<mb:math xmlns:mb="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mb:mi>Cr</mb:mi></mb:math> as a prime candidate to realize ultracold gases of doubly polar molecules with significant electric (3.3 D) and magnetic (<pb:math xmlns:pb="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><pb:mn>5</pb:mn><pb:msub><pb:mi>μ</pb:mi><pb:mi>B</pb:mi></pb:msub></pb:math>) dipole moments. Published by the American Physical Society 2024