No abstract

A single bichromatic field near-resonant to a qubit transition is typically used for σx or σy Mølmer-Sørensen type interactions in trapped ion systems. Using this field configuration, we present a novel scheme to synthesize a σz spin-dependent force instead; this basis change merely requires adjusting the beat-note frequency of the bichromatic field. We implement this scheme with a laser near-resonant to a quadrupole transition in 88 Sr + . We characterise its robustness to optical phase and qubit frequency offsets and demonstrate its versatility by entangling optical, metastable, and ground state qubits.Trapped ion systems are used for quantum computation [1-3], quantum simulation [4], metrology, and sensing [5,6]. These applications typically require coupling of the internal spin states of the ions to their shared motion via a spindependent force (SDF) [7]. These SDFs can arise from the intensity gradient of applied lasers, or from magnetic field gradients [3,[8][9][10][11]. The basis of the SDF, the specific Pauli spin-operator that it corresponds to, depends on its particular physical implementation. For example, time-varying ac Stark shifts can be used to implement σz -type interactions [12][13][14], while a bichromatic field near-resonant to the qubit transition can be used to implement σx or σy Mølmer-Sørensen (MS) type interactions [15][16][17][18][19]. The basis of the SDF determines the fields required, the applicability of the interaction to different qubit types, and its sensitivity to errors.