Nov 6th: Dr. Tim Schröder (MIT)

Dr. Tim Schröder, Quantum Photonics Laboratory, MIT

“Spin qubits in diamond nanocavities”

ROOM 26-214
THURSDAY, NOVEMBER 06, 2014
12:00 PM – 13:00 PM

Short abstract: We demonstrate the deterministic creation of nitrogen-vacancy spin qubits (NV) at the mode maximum of diamond photonic crystal cavities, enhancement of the zero-phonon-line spontaneous emission rate greater than 60, and NV spin phase coherence times exceeding 200µs. These NV-cavity systems represent a step towards efficient solid-state based spin-photon interfaces for the implementation of quantum networks.

Detailed abstract: Diamond based quantum spin systems like the negatively charged nitrogen-vacancy center (NV) represent a promising platform for precision measurements and quantum information applications. Most of these applications rely on the long electron spin coherence time of the NV ground state of up to 600 ms in bulk. Solid-state cavity systems, on the other hand, have attracted much interest for enhancing light-matter interaction on the nano-scale. Cavity-enhanced light matter interaction can enable the speed up of established quantum protocols and the implementation of novel concepts for quantum networks. A first important step towards more complex systems is the Purcell induced spontaneous emission rate enhancement of an NV inside a cavity. First realizations of cavity-coupled NVs have been reported recently. In these realizations, NVs were randomly distributed with respect to the cavity mode thereby prohibiting a high NV – cavity-mode overlap, hence limiting the spontaneous emission rate enhancement, while spin coherence times were below 1 us.

Here, we present the realization of such systems with improved optical and spin properties. We fabricated photonic crystal cavities (PCC) in high-purity single-crystal diamond by oxygen reactive ion etching using silicon (Si) membranes as etch masks. The Si masks were produced from silicon-on-insulator wafers by standard nanolithography methods. Our fabrication process results in diamond PhCs with low surface roughness and uniform, vertical sidewalls. For single fabrication runs, we find high yield (up to 94 %) of cavities with a mean quality (Q) factor of up to 6,200 and a maximum Q of 9, 900 ± 200. To couple single NVs with high probability to the mode maxima of such cavities, we demonstrate their spatially deterministic creation inside the cavity region. 15N implantation through circular apertures and subsequent annealing result on average in about 1.1 (0.2) NVs per cavity. We show strong Purcell enhancement of the NV’s zero phonon line spontaneous emission rat and demonstrate electron spin coherence times of more than 200 microseconds of cavity coupled NVs paving the way to advanced quantum network implementations.

“The iQuISE program represents a bold step forward to coalesce and cohere the education and research training that will produce a new generation of quantum information researchers for our nation.”

—Claude R. Canizares, Bruno Rossi Professor of Physics, Vice President for Research, and Associate Provost