Project Details
Projekt
Long-range correlations in disordered spin systems with dipolar interactions
Applicants
Professor Dr. Daniel Braun; Dr. Andreas Günther
Subject Area
Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
Term
since 2022
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 465199066
Following the initial funding period, the project continues to study quantum correlations in disordered, long-range interacting spin systems, both in experiment and theory. Our main goal is to achieve ultra-long-range interactions and correlations mediated by a dipole-dipole interacting spin ensemble. Therefore, we employ quasi-one-dimensional ensembles of cold atoms coupled to highly excited Rydberg states. In the presence of strong electric fields, field adjustments on the sub-V/cm level permit precise tuning of the dipole-dipole interaction strength over a wide range. Tailored driving schemes then facilitate the formation of a quasi-1D Rydberg crystalline structure, with emergent Rydberg-Rydberg correlations strongly dependent on interaction strength and boundary conditions. Using our high-resolution ion microscope, based on a 1000-fold magnifying electrostatic lens system, we will measure the build-up of these correlations and characterise their dependence on system parameters, such as the initial ensemble density and the specific interaction type - van der Waals or dipole-dipole. With 100 ps temporal and 100 nm spatial resolution, the microscope surpasses conventional fluorescence-based detection schemes, making it ideally suited to study Rydberg–Rydberg correlations in disordered systems. Finally, we aim to directly observe conditional phase shifts between distant Rydberg atoms mediated by the correlated spin ensemble. On the theory side, we will develop numerical methods to study the build-up of correlations in Rydberg excitation crystals and adapt them to the experimental part. Conventional methods often struggle with disordered, long-range interacting systems: full quantum simulations are limited in scale, and semiclassical approaches like tree tensor networks have only recently addressed disorder in short-range interacting systems. Therefore, new methods for treating disorder in long-range interacting systems are in high demand, and our recently developed 'grabit' (gradient bit) approach is a promising candidate. It is a stochastic approach that represents pure quantum states as higher-order derivatives of classical probability distributions, making it well-suited to simulate the type of disordered spin systems studied in the experiment. Moreover, it handles entanglement growth efficiently and incorporates stochasticity from the outset, making disorder naturally accessible. During the second funding period, we aim to develop the 'grabit' formalism towards simulating the continuous-time dynamics of quantum systems and apply it to the disordered, long-range interacting spin systems studied in the experimental project part.
DFG Programme
Research Units
