Engineering Atomic and Molecular Interactions with Radio Frequency Electric Fields  

We have demonstrated promising applications for radio frequency electric fields in trapped ion quantum sensing and computation.

Quantum-Enhanced Correlation Spectroscopy:

Correlation spectroscopy utilizes a phase-sensitive measurement to record correlations between measurements to obtain frequency resolution beyond the sensor's T₂ limit (Science 356, 832-837). We utilize motional Raman transitions (Nat. Phys. 21, 380–385) for wideband, phase-sensitive sensing of radio frequency electric fields via a trapped atomic ion. By combining this technique with correlation spectroscopy and quantum-enhancement with Fock states (Nat Commun 10, 2929), we can measure small GHz radio frequency signals with nanohertz resolution.

Quantum-Enhanced Mass Spectroscopy:

Mass spectroscopy is used to determine the charge-to-mass ratio of charged elements in precision measurements and chemistry applications. The secular frequency of a dual-species trapped ionic chain depends on the mass ratio of the species (Phys. Rev. A 61, 032310). We co-trap a dark molecular ion with ⁴⁰Ca⁺ and create a Schrödinger cat state via spin-motion entanglement for quantum-enhanced sensing (Nature Photonics 7, 630–633) of the secular frequency below the standard quantum limit. Measurements at the Hz level appear possible, allowing precise determination of the mass ratio to the ppm level with an interrogation time smaller than classically achievable

Electric Field Gradient Gates for Quantum Computation:

Molecular ions possess a rich internal structure for promise as a quantum information platform. Many molecular species contain low-lying opposite-parity states with electric-dipole transitions in the radio frequency or microwave regime. Application of radio frequency voltages to the electrodes of an ion trap implements a universal laser-free gate set for molecules containing these electric-dipole transitions (Phys Rev A 104, 042605). By configuring the field geometry, we can generate single-qubit rotations and entanglement between molecular ions. In our experiment we have co-trapped H³⁵Cl⁺ with ⁴⁰Ca⁺ to demonstrate this technique.