Quantum systems engineering

Abstract:

We consider the dephasing of two internal states |0〉 and |1〉 of a trapped impurity atom, a so-called atomic quantum dot (AQD), where only state 1〉 couples to a Bose-Einstein condensate (BEC). A direct relation between the dephasing of the internal states of the AQD and the temporal phase fluctuations of the BEC is established. Based on this relation we suggest a scheme to probe BEC phase fluctuations non-destructively via dephasing measurements of the AQD. In particular, the scheme allows to trace the dependence of the phase fluctuations on the trapping geometry of the BEC. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Abstract:

We show how to efficiently exploit decoherence free subspaces (DFSs), which are immune to collective noise, for realizing quantum repeaters with long-lived quantum memories. Our setup consists of an assembly of simple modules and we show how to implement them in systems of cold, neutral atoms in arrays of dipole traps. We develop methods for realizing robust gate operations on qubits encoded in a DFS using collisional interactions between the atoms. We also give a detailed analysis of the performance and stability of all required gate operations and emphasize that all modules can be realized with current or near future experimental technology. © 2006 The American Physical Society.

Abstract:

We investigate the feasibility of simulating different model Hamiltonians used in high-temperature superconductivity. We briefly discuss the most common models and then focus on the simulation of the so-called t-J-U Hamiltonian using ultra-cold atoms in optical lattices. For this purpose, previous simulation schemes to realize the spin interaction term J are extended. We especially overcome the condition of a filling factor of exactly one, which otherwise would restrict the phase of the simulated system to a Mott-insulator. Using ultra-cold atoms in optical lattices allows simulation of the discussed models for a very wide range of parameters. The time needed to simulate the Hamiltonian is estimated and the accuracy of the simulation process is numerically investigated for small systems. © 2006 The American Physical Society.

Abstract:

Studying the unitary time evolution of strongly correlated quantum systems is one of the most challenging theoretical and experimental problems in physics. For an important class of one-dimensional (11)) systems dynamical simulations have become possible since the advent of the time-evolving block decimation (TEBD) algorithm. We study the computational properties of TEBD using the Bose-Hubbard model (BHM) as a test-bed. We demonstrate its efficiency and verify its accuracy through comparisons with an exactly solvable small system and via the convergence of one- and two-particle observables in a larger system.