Single donor qubits in 28Si: New benchmarks for solid state qubits

22 08/2014

Friday, 22 Aug. 2014, 11:00 - 12:00

Presenter: Juha Muhonen; CQC2T, University of New South Wales, Sidney, Australia
Host: M. Aspelmeyer
Where: Schrödingerroom, 4th floor, Boltzmanngasse 5, 1090 Wien

Quantum information processing would greatly benefit from a physical implementation that combines long quantum coherence with proven manufacturability. Using silicon - the material that underpins modern information technology - as the platform for quantum bits could allow leveraging the huge industrial fabrication resources. Spin-based quantum bits in silicon have been realized with quantum dots and phosphorus atoms but the quantum coherence has been limited by the fluctuating magnetic fields arising from the natural abundance of 29-Si nuclear spins. We have now demonstrated new benchmarks for coherence time (>30 seconds) and control fidelity (>99.98 %) of a single quantum bit in solid state, using the spin of an individual phosphorous dopant atom in isotopically purified 28-Si. Bulk ensembles of spins in 28-Si are known to exhibit exceptionally long coherence, but it was often suspected that this would be disrupted by the noise and disorder in a functional nanostructure - such as our device - which is required to readout a single spin. Conversely, through a detailed noise spectroscopy analysis we show that device-intrinsic phenomena, such as charge and spin noise from oxides and interfaces, seem not play the limiting role. Our results confirm that donors in silicon are a very promising platform for the future of quantum information.