Congratulations to New ICFO PhD graduate

Dr. Jan Huwer received his Physics Diploma (Diplom-Physiker) from the Albert-Ludwigs University of Freiburg, Germany, before joining the Quantum Photonics group, led by former ICFOnian Prof. Jürgen Eschner (now at Universität des Saarlandes UdS, Germany). His work at ICFO (and later at UdS) centered on implementing experimental methods which pave the way for quantum-network studies with trapped ions and entangled photon pairs. Dr. Huwer’s thesis, entitled ‘Experimental tools for quantum networking operations with single photons and single ions’’ was co-supervised by former ICFOnian Prof. Jürgen Eschner at the UdS and by ICREA Prof. at ICFO Antonio Acín.

ABSTRACT:

One promising approach for future quantum networks is the combination of strings of trapped ions as quantum-information processors with entangled photon pairs produced by spontaneous parametric down conversion (SPDC) to establish quantum communication links between distant processing units.

This work reports on experiments using a hybrid quantum-optics set-up, comprising two separate linear ion traps and a resonant SPDC photon-pair source. It demonstrates the controlled interaction of single entangled photon pairs with a single trapped 40Ca+ ion. Preparing the ion as a polarization selective absorber in the main polarization bases allows for the reconstruction of the biphoton quantum state, manifesting the photon entanglement in the absorption process.

Beyond that, the thesis documents the implementation of additional experimental tools enabling quantum state transfer experiments from photons to single ions. A dedicated narrow bandwidth laser system is set up, laser sequences are developed for state discrimination and state rotations of ion qubits, and for the creation and characterization of coherent superposition states, of particular importance for state-transfer schemes.

Finally, detection efficiencies of single Raman photons emitted by an ion are characterized with a well-controlled single-photon source, and absorption probabilities of single photons are determined with a calibrated laser beam, providing precise values to assess efficiencies for different transfer scenarios.


THESIS COMMITTEE:

Giovanna Morigi, Universität des Saarlandes, Saarbrücken, Germany
Jonathan Home, ETH Zürich, Switzerland
Daniel Segal, Imperial College London, United Kingdom
Frank Koppens, ICFO, Spain
Jürgen Eschner, Universität des Saarlandes, Saarbrücken, Germany