School of Physical and Chemical Sciences Seminar Series

A single-atom spin-orbit system for computing applications


Dimitrie Culcer


School of Physics, University of New South Wales, Australia

Time & Place

Thu, 26 Oct 2017 11:00:00 NZDT in Room 531, Rutherford Building

All are welcome


Solid state systems in which spins are localised are ideal candidates for scalable, long-lived quantum computing architectures. An additional advantage of spin-orbit coupled systems is the possibility of all-electrical spin manipulation, obviating the necessity of localising magnetic fields, which in practice is difficult. I will demonstrate that quantum information can be encoded in a qubit based on the effective heavy hole states of a boron atom near a Si interface. I will present analytical, numerical and experimental results proving that this qubit can be reliably initialised, rotated and entangled by electrical means alone by harnessing the strong spin-orbit interaction of the atom near an interface. Initialisation can be accomplished straightforwardly if the qubit states are well separated by a constant, uniform magnetic field. Single qubit rotations rely on the Rashba spin-orbit interaction, which is enabled by inversion symmetry breaking at the interface. The cubic symmetry of the Si lattice allows terms linear in the electric field, which make the Rashba interaction particularly strong. Entanglement can be accomplished by coupling to a superconducting resonator. By performing a detailed analysis of the sensitivity of the qubit to both random telegraph and 1/f noise, we demonstrate that the proposed architecture can have the long coherence times necessary for quantum computation.


I study systems with strong spin-orbit interactions, such as topological insulators and electrons and holes in semiconductor nanostructures. My interests also include graphene, whose Hamiltonian resembles that of spin-orbit coupled systems, with the real spin replaced by a lattice pseudospin degree of freedom.

In these systems I am interested primarily in nonequilibrium phenomena such as charge and spin transport, and spin relaxation and dephasing. Of particular interest to me is the interplay of spin-orbit coupling with strong interactions and disorder, as well as with external electric and magnetic fields. Topics I have focused on lately include screening and Friedel oscillations, magnetic instabilities, the Kondo effect, and disorder effects such as weak localisation.

My second area of research is concerned with quantum dots, specifically using confined spins and pseudospins for quantum computing. I am interested in qubit architectures, entanglement schemes, as well as transport, relaxation and dephasing of spins and pseudospins in quantum dots. Dephasing is especially important in quantum computing, since it is equivalent to a loss of information, and can hamper single-qubit operations as well as entanglement. It can come from noise, phonons, as well as other mechanisms that we do not understand.