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

GONZALO A. ALVAREZ; A. DALLALBA, F. LOZANO, A. ZWICK

Simposio; 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 technolo- gies. 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 sys- tems or other quantum systems. An outstanding cha- llenge that needs to be overcome for developing these technologies is that one needs to control many interac- ting 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 si- ze. I will report that the controlled creation of quan- tum states can show a novel type of phase transition on the coherent dynamic behavior of the quantum sys- tem [1]. 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 [2,3]. As a result, the collective system is driven into a quantum superposition. As time evolves, the number of corre- lated spins increases and consequently the extent of the coherent quantum state grows in space. We disco- vered 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 re- sults 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.[1] G. A. Alvarez, D. Suter, and R. Kaiser. Science 349, 846 (2015).[2] G. A. Alvarez and D. Suter, Phys. Rev. Lett. 104, 230403 (2010); Phys. Rev. A 84, 012320 (2011).[3] G. A. Alvarez, R. Kaiser, and D. Suter, Ann. Phys. (Berlin) 525, 833 (2013).