Ultracold Dipolar Gas of FermionicNa23K40Molecules in Their Absolute Ground State

Abstract

We report on the creation of an ultracold dipolar gas of fermionic 23 Na 40 K molecules in their absolute rovibrational and hyperfine ground state. Starting from weakly bound Feshbach molecules, we demonstrate hyperfine resolved two-photon transfer into the singlet X 1 Σ þ jv ¼ 0; J ¼ 0i ground state, coherently bridging a binding energy difference of 0.65 eV via stimulated rapid adiabatic passage. The spin-polarized, nearly quantum degenerate molecular gas displays a lifetime longer than 2.5 s, highlighting NaK's stability against two-body chemical reactions. A homogeneous electric field is applied to induce a dipole moment of up to 0.8 D. With these advances, the exploration of many-body physics with strongly dipolar Fermi gases of 23 Na 40 K molecules is within experimental reach. DOI: 10.1103/PhysRevLett.114.205302 PACS numbers: 67.85.−d, 03.75.Ss, 33.20.−t, 37.10.Mn Quantum gases of dipolar molecules promise to become a platform for precision measurements, quantum information processing, high-speed quantum simulation, and the creation of novel many-body systems [1][2][3]. The long-range, anisotropic nature of electric dipolar interactions between molecules is expected to yield novel types of order, such as topological superfluidity with fermionic molecules [4][5][6], interlayer pairing between two-dimensional systems [7,8], and the formation of dipolar quantum crystals [9]. The necessary prerequisite is the full control over the molecules' translational, electronic, vibrational, rotational, and nuclear spin degrees of freedom [10]. In pioneering work on 40 K 87 Rb and nondipolar 133 Cs 2 , weakly bound molecules were associated from ultracold atoms via Feshbach resonances and were subsequently coherently transferred into the absolute rovibrational ground state via a two-photon stimulated rapid adiabatic passage (STIRAP) [11][12][13][14][15]. Hyperfine control of the KRb molecules was demonstrated using microwave radiation [16]. Ground state KRb molecules are chemically unstable against two-body collisions, as the reaction KRb þ KRb → K 2 þ Rb 2 is energetically allowed. This enabled studies of quantum-state controlled chemical reactions [17,18], but it also led to loss and heating of the trapped molecules. Loading of KRb molecules into optical lattice potentials efficiently suppressed the reactions and enhanced the lifetime of molecular samples [19][20][21].For the study of collisionally dense molecular gases in the quantum regime, molecules that are stable against two-body collisions are of great interest. Possible choices among the alkali-metal dimers were summarized in Ref. [ 2 =ð4πϵ 0 ℏ 2 Þ (m NaK denotes the molecular mass) reaches 0.6 μm, comparable to the interparticle spacing of 1.6 μm for the realized peak densities of n 0 ¼ 2.5 × 10 11 cm −3 . The corresponding dipolar interaction energy E d ¼ d 2 n 0 =ð4πϵ 0 Þ approaches 5% of the local Fermi energy and should therefore dominate the many-body physics of the gas.Our starting point is a gas of about 7 × 10 3 Feshbach molecules of 23 Na 40 K, tr...

New frontiers for quantum gases of polar molecules

“…This approach has been extremely successful in creating ultracold, dense samples of ground-state molecules, including fermionic KRb [36], bosonic Cs 2 [37], bosonic RbCs [38,39], fermionic NaK [40], and bosonic NaRb [41]. Our recent work finally demonstrated the production of a quantum degenerate molecular gas in an optical lattice [42].…”

“…In bulk gases of bosonic magnetic atoms, the competition between contact and dipolar interactions has led to the observation of droplets, which are stabilized by quantum fluctuations [99,100]. For fermionic molecules, the dipolar interactions can contribute an energy comparable to the Fermi energy [40], and can give rise to topological superfluid phases [15,16] and superfluid pairing between layers of an optical lattice [17]. The field of ultracold polar molecules shows no signs of slowing down, and there should be many fruitful experiments in the next few years.…”

Hyperfine structure of alkali-metal diatomic molecules

“…The polar molecules produced so far include 40 K 87 Rb [1], 87 Rb 133 Cs [2,3], 23 Na 40 K [4], and 23 Na 87 Rb [5]. Such molecules have many potential applications, ranging from quantum-statecontrolled chemistry [6][7][8][9] to quantum simulation [10,11] and quantum information [12,13].…”

Correlations and enlarged superconducting phase of t−J⊥ chains of ultracold molecules on optical lattices

“…At the interface between atomic, molecular, optical, and condensed-matter physics, systems of ultracold polar molecules [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] have caused a great deal of excitement and opened a path for the quantum simulation [21][22][23][24][25][26][27][28][29] of quantum magnetism [30][31][32][33][34][35][36][37][38] and superconductivity [39,40] on optical lattices [41,42]. Intrinsic to these systems are the long-range dipolar-type interactions, which, in contrast to the long-range Coulomb interaction in condensed-matter systems, are not affected by screening.…”