Quantum Physics research is conducted in the Quantum Measurement and Manipulation Group (QMMG) at Aarhus University with a theoretical and an experimental division. It's in the QMMG that the potential of producing and manipulating ultracold atoms is explored for a number of main goals.
On the 14th of January Mads Kock Pedersen successfully defended his master's thesis "Human and measurement-based quantum optimization and game-based education". The external examiner was Niels O. Andersen from the Niels Bohr Institute. (01/2015)
State preparation in high-dimensional Hilbert-spaces does not require control over a system Hamiltonian or over applicable measurement operators: We show how to prepare a desired state or subspace, given a static projection operator onto the desired target that is applied repeatedly at optimised moments in time. Benchmarks against other schemes, performed on random Hamiltonians and on Bose-Hubbard systems, establish the competitiveness of the method. (11/2014)
Published in Physical Review A, as editors suggestion!
We propose a scheme for the detection of quantum phase transitions in the one-dimensional (1D) Bose-Hubbard (BH) and 1D Extended Bose-Hubbard (EBH) models, using the nondemolition measurement technique of quantum polarization spectroscopy. We use collective measurements of the effective total angular momentum of a particular spatial mode to characterize the Mott insulator to superfluid phase transition in the BH model and the transition to a density wave state in the EBH model.We extend the application of collective measurements to the ground states at various deformations of a superlattice potential. (10/14)
The quantum speed limit sets the minimum time required to transfer a quantum system completely into a given target state. At shorter times the higher operation speed has to be paid with a loss of fidelity. Here we quantify the trade-off between the fidelity and the duration in a system driven by a time-varying control and interpret the result in Hilbert space geometry. Formulating a necessary convergence criterion for Optimal Control (OC) algorithms allows us to implement an algorithm which minimizes the process duration while obtaining a predefined fidelity. http://arxiv.org/abs/1405.6079 (05/2014)
Our recent paper has been selected to appear on the PRA website as part of their Kaleidoscope feature. This means that it will feature on their front page for around a month. It appears in cycles so catch it if you can!
We propose an architecture which allows for the merger of a selected qubit pair in a long-periodicity superlattice structure consisting of two optical lattices with close-lying periodicity. We numerically optimize the gate time and fidelity, including the effects on neighboring atoms and in the presence of experimental sources of error. Furthermore, the superlattice architecture induces a differential hyperfine shift, allowing for single-qubit gates. The fastest possible single-qubit gate times, given a maximal tolerable rotation error on the remaining atoms at various values of the lattice wavelengths, are identified. (03/2014)