Prof. Dr. Christian Roos, Realizing and investigating quantum-many body systems of trapped ions

Realizing and investigating quantum-many body systems of trapped ions

Trapped ions illuminated with laser light constitute an engineered quantum system that enables the realization of spin-lattice models with long-range interactions that are mediated by the collective ion motion. While linear ion strings of up to 50 ions have been used for this purpose for a long time, experiments with two-dimensional ion crystals held in radiofrequency traps started only recently.

I will present experiments demonstrating control over planar ion crystals with more than 100 ions [1]. After cooling all transverse motional modes of the crystal close to the ground state, long-range transverse field Ising models can be realized by Raman interactions that off-resonantly couple the Zeeman ground states of singly-charged calcium ions to crystal’s motional modes. We demonstrate the creation of spin-squeezed states of up to 91 ions using an approach previously realized with long ion chains [2], characterize the spin-spin interactions and demonstrate single-qubit control over all ions in the crystal as well as entangling two-qubit gates.

An important question is to what degree the Hamiltonian one believes to generate is indeed realized in the experiment. To answer this question, we have carried out Hamiltonian and Liouvillian learning of our system, a procedure that opens a path to bounded-error quantum simulation.

[1] D. Kiesenhofer, H. Hainzer et al, PRX Quantum 4, 020317 (2023)

[2] J. Franke et al., Nature 621, 740 (2023)