Project Details
Projekt
Decoherence and Relaxation in Quantum Spin Clusters
Subject Area
Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
Term
since 2018
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 355031190
The major goal is to elucidate internal decoherence in few-body spin systems under unitary time-evolution. Here decoherence refers to the behavior of asubsystem.Group Schnack: We are interested in caseswhere internal decoherence is reduced similar to schemes whererelaxation and thermalization are prevented by phenomena such asmany-body localization. We plan to further investigatethe role of conservation laws, the possibility to reducedecoherence in systems of toroidal moments and the influence ofparticular external drives to refocus decohering spin systems.We also want to extend the range of investigated systems frompure spin systems to spin-phonon systems.Group Michielsen: Since quantum manipulationis no longer a future dream, but at our hands today, we propose as an application to simulatethe calculation of the ground-state energy of the Hubbard modelwith a quantum annealer. In order to take account of decoheringenvironmental spins we will study the Hubbard model embeddedinto a bath of spins by time-evolving the combined systemaccording to the time-dependent Schroedinger equation.The two Ph.D. students will interact strongly both on numericalmethods as well as on physical concepts. Goal A: Driven dynamics to improve coherence:We want to investigate the question how periodic or aperiodic stimuli/driving of system and/or bathreduces decoherence of the system. This concerns in particularthe simulation of the free-induction decay of multi-spin systemsas well as their study in the presence of Hahn echos and generalUhrig pulse sequences.Goal B: Decoherence and relaxation of toroidal moments:Like clock transitions,superpositions of states with pronounced toroidal moments may bemore robust against magnetic disturbances by other spins orfluctuating magnetic fields. Goal C: Decoherence in spin-phonon systems:We can now investigate combined systems of spins and phonons, an extension that offers veryrealistic descriptions for magnetically diluted compounds. Itwould allow to study so-called internal friction at avoidedlevel crossings induced by the phonon subsystem.Goal D: Reformulation of the Hubbard model for quantum annealing:Using the Jordan-Wigner transformation, the one-dimensionalHubbard model can be formulated as a 2N-qubit modeldefined on a two-leg ladder where the qubits on the first(second) leg of the ladder correspond to the spin-up (spin-down)fermions. We plan to study the ground state energy of the18x1 and 3x6 Hubbard model, corresponding to a36-qubit model, for various fillings by simulating the ideal analog quantumannealing process by using the Massively Parallel Quantum SpinDynamics Simulator.Goal E: Investigation of the Hubbard model:We propose to study theeffect of the environmental temperature and disorder on idealquantum annealing. We therefore simulate the quantumannealer coupled to a heat bath by solving the time-dependentSchroedinger equation of the whole system.
DFG Programme
Research Units
Subproject of
FOR 2692:
Fundamental Aspects of Statistical Mechanics and the Emergence of Thermodynamics in Non-Equilibrium Systems
Co-Investigator
Professor Dr. Robin Steinigeweg
