Coherent control of spin and orbital wavepackets of donors in silicon using mid-infrared and terahertz light

• Main Author: Chick, Steven
• Other Authors: Murdin, Ben ; Clowes, Steven
• Published: University of Surrey 2017
• Subjects: 530.12
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.703537

Quantum computation holds the promise of efficient solutions to currently formidable problems. A prospective technology is that of computing using quantum states, which may dramatically speed up or otherwise reduce the complexity for the solution of some hard problems. Of the many different schemes proposed, shallow substitutional donors in Silicon hold great attractiveness for the detailed study of the medium, high industrial capacity, and ubiquity of raw materials. We develop control over the quantum orbital and spin states of bound electrons using the THz ultrafast laser FELIX. Manipulation of orbital states is studied using interferometric methods to produce Ramsey fringes, read out using optical and electrical methods. Contactless electrical measurement of free charge carriers is implemented, and the details of its advantages and limitations are explored. Both types of readout are used to demonstrate a coherent 3-level orbital manipulation, otherwise known as a quantum beat. The work constitutes a nontrivial control over the spatial distribution of the wavefunction of the atom which may enable error correcting surface code implementations. Spin dynamics are then explored in the presence of FELIX using donor-bound exciton techniques, which allow a sensitive and fast control over the electron spin states. The implementation is used to probe whether orbital excitation has a strong effect upon the spin states of the donor electrons, and it is shown that any modification of the spin is negligible. Experimental measurements of optically gated spin-exchange coupling are enabled by this methodology, and a roadmap to future implementation is discussed in the context of the present work. Overall, the work advances the state of spin and orbital control of neutral donor states for the purposes of optically gated quantum computing. Combined spin and orbital manipulations are now possible in the system, which will allow a more advanced implementation of quantum computation using orbital states than was previously possible.