Unitary p-wave interactions between fermions in an optical lattice

Exchange-antisymmetric pair wavefunctions in fermionic systems can give rise to unconventional superconductors and superfluids 1 – 3 . The realization of these states in controllable quantum systems, such as ultracold gases, could enable new types of quantum simulations 4 – 8 , topological quantum gates 9 – 11 and exotic few-body states 12 – 15 . However, p -wave and other antisymmetric interactions are weak in naturally occurring systems 16 , 17 , and their enhancement via Feshbach resonances in ultracold systems has been limited by three-body loss 18 – 24 . Here we create isolated pairs of spin-polarized fermionic atoms in a multiorbital three-dimensional optical lattice. We spectroscopically measure elastic p -wave interaction energies of strongly interacting pairs of atoms near a magnetic Feshbach resonance. The interaction strengths are widely tunable by the magnetic field and confinement strength, and yet collapse onto a universal curve when rescaled by the harmonic energy and length scales of a single lattice site. The absence of three-body processes enables the observation of elastic unitary p -wave interactions, as well as coherent oscillations between free-atom and interacting-pair states. All observations are compared both to an exact solution using a p -wave pseudopotential and to numerical solutions using an ab initio interaction potential. The understanding and control of on-site p -wave interactions provides a necessary component for the assembly of multiorbital lattice models 25 , 26 and a starting point for investigations of how to protect such systems from three-body recombination in the presence of tunnelling, for instance using Pauli blocking and lattice engineering 27 , 28 . The authors measure elastic p -wave interaction energies in pairs of fermionic atoms occupying the lowest two orbitals of an optical lattice; isolation of individual pairs of atoms protects against three-body recombination, enabling a theoretical maximum of interaction energy to be achieved.