Quantum Simulations: Localization-delocalization transition in the dynamics of many-body systems

GONZALO A. ALVAREZ; ANALIA ZWICK; AGUSTIN DALLALBA; FABRICIO LOZANO

Conferencia; XXIII Latin American Symposium on Solid State Physics; 2018

Observing  and  controlling  quantum  systems  like photons,  electrons  or  nuclei  can  be  used  for  storing and manipulating information in emerging technologies. These quantum technologies include a new kind of computers, the so-called quantum computers, which will  be  qualitatively  faster  than  the  most  powerful computers  currently  available.  These  new  types  of computers  allow  the  simulation  of  complex  systems consisting  of  many  components,  like  biological  systems or other quantum systems. An outstanding challenge that needs to be overcome for developing these technologies is that one needs to control many interacting quantum systems. Quantum effects are extremely sensitive to external perturbations, which cause their quantum features to disappear extremely rapidly, and this problem grows quickly with increasing system size. I will report that the controlled creation of quantum states can show a novel type of phase transition on the coherent dynamic behavior of the quantum system . Using nuclear magnetic resonance (NMR) on a solid-state system of spins at room-temperature, we suddenly turn on (quench) an interaction between the nuclear spins that starts to correlate them. As a result, the collective system is driven into a quantum superposition. As time evolves, the number of correlated  spins  increases  and  consequently  the  extent  of the coherent quantum state grows in space. We discovered that depending of the strength of a controlled external  perturbation,  the  spreading  in  the  space  of the quantum correlations undergoes a transition from a delocalized ?diffusion?to a localized one. These results  show  that  in  order  to  controllably  create  large quantum states, one needs to reduce the strength of any perturbation below a given threshold. Only below this threshold is the observed quantum system free to expand in space.