Studying the fundamental physics of many-particle quantum systems, as well as the practical implementation of engineered quantum systems such as quantum computers and simulators, both require the ability to accurately characterise the underlying quantum states and processes.
However, even for quantum systems of very moderate sizes of only a few qubits, the required resources (time, number of measurements etc.) of standard methods to characterise quantum processors, such as quantum state and process tomography, grow exponentially so that these methods become practically inefficient.
The CETO collaboration, which involves besides our theory team the experimental ion-trap group at Innsbruck (Austria) and theory groups at Sydney (Australia), Waterloo (Canada) and Madrid (Spain), aims developing and implementing new tools to characterise and validate physical and logical gate operations. Here, we are developing techniques for the efficient detection, characterization and quantification of quantum correlations [1], as well as of noise and imperfections, such as spatial and temporal noise correlations [2] or leakage or loss of qubits. Complementary, we are interested in understanding and finding new ways to mitigate the impact of such imperfections [3], e.g. on quantum information and error correction protocols [4]. For instance, we recently developed a new, rigorous method to quantify the amount of correlations in the dynamics of quantum systems [5].
[1] Estimating localizable entanglement from witnesses
D. Amaro, M. Müller, A. K. Pal
New Journal of Physics 20, 063017 (2018)
[2] Experimental quantification of spatial correlations in quantum dynamics
L. Postler, A. Rivas, P. Schindler, A. Erhard, R. Stricker, D. Nigg, T. Monz, R. Blatt, M. Müller
Quantum 2, 90 (2018)
[3] Iterative Phase Optimisation of Elementary Quantum Error Correcting Codes
M. Müller, A. Rivas, E. A. Martínez, D. Nigg, P. Schindler, T. Monz, R. Blatt, M. A. Martin-Delgado
Physical Review X 6, 031030 (2016)
[4] Twins Percolation for Qubit Losses in Topological Color Codes
D. Vodola, D. Amaro, M.A. Martin-Delgado, M. Müller
Phys. Rev. Lett. 121, 060501 (2018)
[5] Quantifying spatial correlations in general quantum dynamics
A. Rivas, M. Müller
New Journal of Physics 17, 062001 (2015)