Optical Trapping Ion Crystals and Atoms

• Applicant: Professor Dr. Tobias Schätz
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 501849855

Developing the ability to control and measure the state and dynamics of complex many-body systems is a central goal in modern quantum physics. Prospects for applications, such as quantum sensing, -metrology and experimental quantum simulations are improving, in particular, due the development of atom- and ion-trapping. Extensive accuracy, as well as spatial and temporal resolution are required.Seminal work over decades has allowed to coherently control and couple the external (motional) and internal (electronic) degrees of freedom (DOF) of few-ions with unique fidelity. Lasers provide versatile trapping geometries for ensembles of atoms, e.g. by optical lattices and Bessel beams. Combining atoms and ions while exploiting their interaction has led to seminal proposals and progress in so-called hybrid traps. Here, ion(s) are trapped by conventional radio-frequency (rf) fields while immersed into ultra-cold atomic gases, confined by optical means. However, it has been revealed that the kinetic energy of the ion inevitably remains several orders of magnitude above the temperature of the atomic bath. The rf-fields impose fundamental constraints, since any displacement of ions from the centre of the trap leads to rf-driven motion, whether by the intended interaction with atoms or due to the ions’ position in higher dimensional Coulomb Crystals (CC).Yet, our group demonstrated ion trapping by optical means and sympathetic cooling of a single ion - in absence of any rf-field. While our approach is still unique, we now request a quantum leap in coherent control, enabled by deterministically handling the DOFs of the ion. Besides, we recently demonstrated controlling the ion-atom interaction by external fields, opening up Feshbach resonances for controlling atom-ion scattering for the first time. Considering more ions, optically shapeable potential landscapes, such as non-divergent Bessel-cylinders, might allow higher dimensional CCs to enter the quantum regime.As first showcases, we aim at benchmarking long-pending proposals, e.g. on the emergence of entanglement via quantum phase transitions. Here, CCs can evolve through structural criticality, when we reduce the radial confinement (linear chain (|•••⟩, for 3 ions) to zigzag conformation (|•°•⟩). Ideally, this leads to mesoscopic superpositions of the two degenerate conformations (|•°•⟩ + |°•°⟩), an entangled state. Preparing the ions in a coherent superposition of two electronic states features state-dependent optical potentials. Here an entangled state is predicted to bridge across criticality (|•••⟩ + (|•°•⟩ + |°•°⟩). Ultimately controlling pathways and recording quantum signatures, starting on the few-particle level, will allow for “scaling” Quantum by Quantum. Successfully combining the state-of-the-art tools of both fields might become a substantial advance for the deterministic control of complex quantum systems and magnified lattice structures, extendable in size and dimension.

• DFG Programme: Research Grants
• International Connection: Poland, Singapore
• Cooperation Partners: Professor Murray Barrett; Professor Dr. Michal Tomza