A degenerate Fermi gas of polar molecules

Abstract

It has long been expected that quantum degenerate gases of molecules would open access to a wide range of phenomena in molecular and quantum sciences. However, the very complexity that makes ultracold molecules so enticing has made reaching degeneracy an outstanding experimental challenge over the past decade. We now report the production of a Fermi degenerate gas of ultracold polar molecules of potassium-rubidium (KRb). Through coherent adiabatic association in a deeply degenerate mixture of a rubidium Bose-Einstein condensate and a potassium Fermi gas, we produce molecules at temperatures below 0.3 times the Fermi temperature. We explore the properties of this reactive gas and demonstrate how degeneracy suppresses chemical reactions, making a long-lived degenerate gas of polar molecules a reality.Ultracold polar molecules have received attention as ideal candidates to realize a plethora of proposals in molecular and many-body physics. These include the development of chemistry in the quantum regime [1], the emulation of strongly interacting lattice spin models [2-6], the production of topological phases in optical lattices [7-10], the exploration of fundamental symmetries [11][12][13][14][15], and the study of quantum information science [16][17][18]. While magnetic atoms also exhibit long-ranged dipolar interactions and can be used to carry out these proposals [19,20], polar molecules offer more tunable, stronger interactions and additional degrees of freedom. A low-entropy, quantum degenerate sample is a prerequisite for many of these explorations.The intrinsic complexity of molecules relative to atoms, owing to the additional rotational and vibrational degrees of freedom, has made their cooling to ultralow temperatures one of the most significant experimental challenges in molecular physics [21]. While the direct laser cooling of certain diatomic molecules has progressed enormously in recent times so that magneto-optic [22][23][24][25] and pure optical [26] trapping have been demonstrated, phase space density in these systems remains many orders of magnitude away from degeneracy. To date, by far the coldest diatomic molecules have been made by cooling atoms to a few hundred nanokelvin (10 −9 K) and coherently associating the ultracold atoms into deeply bound molecules using a Fano-Feshbach resonance [27] fol-lowed by stimulated Raman adiabatic passage (STI-RAP) [28].

Chiral and counter-propagating Majorana fermions in a p-wave superconductor

“…One way to induce the desired p x -wave pairing is to couple the fermionic atoms with a Bose gas [48,49] or the p-orbital degrees of freedom [50,51]. Another approach is based on degenerate dipolar Fermi gases [52,53] where p x -wave pairing is natural by tilting the dipole towards the x-axis. The challenge then is to create spin-orbit coupling, as achieved recently for dysprosium [54], and integrate it with optical lattice.…”

Encoding a qubit in a molecule

“…Laser cooling and trapping techniques have recently enabled several seminal advances for diatomic polar molecules, namely: the creation of low-entropy arrays in an optical lattice [39,40], trapping and imaging in tweezer arrays [7,9] and magnetic traps [41,42], and even the first quantum degenerate gas of polar molecules [43]. Coherence times of ∼ 100 ms to ∼ 1 second in angular momentum states of diatomic polar molecules have already been observed in several experiments [44][45][46].…”

“…Momentum kicks We have now described how to correct the position shift − → X R in Eq. (43). Next, we need to understand how to contend with a momentum kick…”

Loading and cooling in an optical trap via hyperfine dark states

“…Sub-Doppler cooling schemes involving dark states (DSs) [9] have emerged as a powerful alternative; they are known as gray molasses. Very recently they have been pivotal in obtaining an alloptical BEC in microgravity [10] and a degenerate Fermi gas of polar molecules [11]. The DSs are coherent superpositions of internal and external (momentum) states that are decoupled from the optical field; their creation does not require cycling F → F = F + 1 transitions, but can rely on any transitions of the F → F ≤ F form.To prevent the expansion of the cold atom cloud during cooling, it is tempting to combine DS sub-Doppler cooling with spatial confinement in a far-off-resonance optical dipole trap (FORT).…”