October 2013
Abstracts of the QSIT Lunch Seminar, Oct 3, 2013
Manipulation of the nuclear spin ensemble in a quantum dot with chirped magnetic resonance pulses
Mathieu Munsch, Nano-Photonics Group, University of Basel
The nuclear spins in nano-structured semiconductors play a central role in quantum applications. They represent a useful resource for generating local magnetic fields and carrying out quantum control but are also a major source of dephasing for both quantum dot based electron spin qubits and single photon sources. Controlling the nuclear spins is therefore essential.
Nuclear magnetic resonance (NMR) on QDs is challenging because of 1. strong inhomogeneities, which lead to complex spectra 2. nano-scale size which makes NMR signal hard to detect.
I will show how we circumvent these difficulties with sequences of highly chirped NMR pulses (adiabatic sweeps) and report indications of a quantum coherence extending over seconds for the nuclear spin ensemble (via Stückelberg interferometry measurement).
Experimental realization of non-abelian geometric gates with a superconducting three-level system
Abdufarrukh Abdumalikov, Quantum Device Lab, ETH Zurich
Geometric gates hold promise to provide the building blocks for robust quantum computation. In our experiments, we use a superconducting three-level system (transmon) to realize non-adiabatic non-abelian geometric gates. As computational basis we choose the ground and second excited states, while the first excited state acts as an ancilla state. The gates are realized by applying two resonant drives between the transmon levels. During the geometric gate ration of the amplitudes of the two drive tone is kept constant. Different gates are obtained for different ratio of the drive tones. We implement a Hadamard, a NOT and a phase gates with the fidelities of 95%, 98%, and 97% as determined by full process tomography and maximum likelihood methods. We explicitly show the non-abelian nature of gates by applying two non-commuting gates in alternating order. The demonstrated holonomic gates are not exclusive to superconducting quantum devices, but can also be applied to other three level systems with similar energy level structure.