Special Seminar

Spin Qubits in Silicon – Advantages of Dressed States

Tuesday, 22 August 2017 12:00PM PDT
Special Seminar
Dr. Arne Laucht
University of New South Wales - Sydney
Spin Qubits in Silicon – Advantages of Dressed States
Aug 22, 2017 at 12PM


Précis- A single electron spin in silicon is dressed by a microwave field to create a new qubit with tangible advantages for quantum computation and nanoscale research.
Coherent dressing of a quantum two-level system has been demonstrated on a variety of systems, including atoms [1], self-assembled quantum dots [2], and superconducting quantum bits [3]. It is used to gain access to a new quantum system with improved properties - a different and tuneable level splitting, faster and easier control, and longer coherence times. Here, we present coherent dressing of a single electron spin bound to a 31P donor in isotopically purified silicon. The electron spin already constitutes a two level quantum system with extremely long coherence times of T2CPMG=0.5 s [4] and excellent control fidelities of 99.95 % [5], figures of merit that are on a par with the best solid-state quantum bits realized.
In our work we investigate the properties of the dressed, donor-bound electron spin in silicon, and probe its potential for the use as quantum bit in scalable architectures. Here, the two dressed spin-polariton levels constitute the quantum bit. We observe a Mollow triplet [1] in the excitation spectrum (see Fig. 1), and demonstrate full two-axis control of the driven qubit in the dressed frame with a number of different control methods. We present coherent control with an oscillating magnetic field, an oscillating electric field [6], by frequency modulating the driving field, or by a simple detuning pulse. We measure coherence times of T2r* = 2.4 ms and T2rHahn = 9 ms, one order of magnitude longer than those of the undressed qubit [7]. Furthermore, we demonstrate that the dressed spin can be driven at Rabi frequencies as high as its transition frequency, making it a model system for the breakdown of the rotating wave approximation [8].
This research was funded by the Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology (project number CE110001027) and the US Army Research Office (W911NF-13-1-0024). We acknowledge support from the Australian National Fabrication Facility, and from the laboratory of Prof. Robert Elliman at the Australian National University for the ion implantation facilities. The work at Keio has been supported in part by FIRST, the Core-to-Core Program by JSPS, and the Grant-in-Aid for Scientific Research and Project for Developing Innovation Systems by MEXT.

A. Laucht et al. 

1. B. R. Mollow. Phys. Rev. 188, 1969 (1969). ‘Power Spectrum of Light Scattered by Two-Level Systems’.
2. X. Xu et al. Science 317, 929 (2007). ‘Coherent optical spectroscopy of a strongly driven quantum dot’.
3. M. Baur et al. Phys. Rev. Lett. 102, 243602 (2009). ‘Measurement of Autler-Townes and Mollow transitions in a strongly driven superconducting qubit’.
4. J. T. Muhonen, et al. Nature Nanotechnology 9, 986 (2014). ‘Storing quantum information for 30 seconds in a nanoelectronic device’.
5. J. T. Muhonen, et al. J. Phys.: Condens. Matter 27, 154205 (2015). ‘Quantifying the quantum gate fidelity of single-atom spin qubits in silicon by randomized benchmarking’.
6. A. Laucht, et al. Science Advances 1, 1500022 (2015). ’Electrically controlling single-spin qubits in a continuous microwave field’.
7. A. Laucht, et al. Nature Nanotechnology 12, 61 (2017). ‘A Dressed Spin Qubit in Silicon’.
8. A. Laucht, et al. Phys. Rev. B 94, 161302(R) (2016). ‘Breaking the rotating wave approximation for a strongly-driven, dressed, single electron spin’.