Aarhus Universitets segl

Research: qM&M Theory

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.



Congratulations to Mads

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)

Many-body state engineering using measurements and fixed unitary dynamics

Published in New Journal of Physics

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)

Characterization of Bose-Hubbard models with quantum nondemolition measurements

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)

Time limited optimal dynamics beyond the Quantum Speed Limit

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)

Recent article selected for the front page of the PRA website

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!

One- and two-qubit quantum gates using superimposed optical-lattice potentials

Published in PRA

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)