Demonstration of a symmetry-protected fermion pair qubit

Quantum simulation of large scale fermionic systems with ultracold atoms has shown great success in recent years. In situ manipulation and readout have been achieved using optical tweezers and quantum gas microscopes, removing the last roadblocks to performing digitized quantum computation on such platforms. Here we propose and demonstrate a novel way of storing and manipulating quantum information using a pair of fermionic neutral atoms in an optical lattice as the quantum register. The fermion pair forms a spin singlet in a quasi-harmonic trap, and the qubit is formed by a set of symmetry-protected two-particle motional states. The two pair states of the qubit are separated by a gap equal to the atomic recoil energy, providing robust protection from laser intensity noise. Coupling between the states is provided by tunable atomic interactions, controlled via the magnetic field. We observe seconds long coherence times, with gate speeds tunable over orders of magnitude by converting one of the pair states into a tightly bound Feshbach molecule. Individual readout of each qubit is achieved in parallel using fluorescence imaging under a quantum gas microscope. These results open the door towards digital quantum computation based on physical fermions, combining the paradigms of quantum simulation and quantum computation.