KIP-Veröffentlichungen

We use a self-assembled two-dimensional Coulomb crystal of  70 ions in the presence of an external transverse eld to engineer a quantum simulator of the Dicke Hamiltonian. This Hamiltonian has spin and bosonic degrees of freedom which are encoded by two hyperne states in each ion and the center of mass motional mode of the crystal, respectively. The Dicke model features a quantum critical point separating two distinct phases: the superradiant (ferromagnetic) and normal (paramagnetic) phases. We experimentally explore protocols that aim to adiabatically prepare the superradiant ground state, a spin-boson cat state with macroscopic phonon occupation, which is well-suited for enhanced metrology and quantum information processing. We start in the normal phase, with all spins aligned along a large transverse eld and ramp down the eld across the critical point following various protocols. We measure the spin observables, both experimentally and in our simulations to characterize the state of the system at the end of the ramp. We nd that under current operating conditions an optimally designed ramp is not sucient to achieve signicant - delity with the superradiant ground state. However, our theoretical investigation shows that slight modications of experimental parameters, together with modest reductions in decoherence rates and thermal noise can increase the cat-state delity to  75% for N  20 spins. Our results open a path for the use of large ensembles of trapped ions as powerful quantum sensors and quantum computers.