Contributed talk

Rational design of boron-doped graphene nanofragments for quantum computation
Roberto A. Boto, and David Casanova

Donostia International Physics Center DIPC, 20018, Donostia-San Sebastian, Spain

Graphene nanofragments are promising candidates to design materials for quantum computation due to the easy tunability of their optical and magnetic properties through modifications in their chemical structure. The physical properties of graphene nanofragments have been extensively studied, but the connection between their chemical structure and the dynamics of the electronic spin states which determine their magnetic properties is not yet fully understood. In this work, we address the effect of the chemical structure on the magnetic properties and on the relaxation time of the triplet ground state spin density for some selected boron-doped graphene nanofragments (inset of Fig. 1a).[1] We use the Redfield theory to connect the relaxation time with the magnetic properties that determine the Zeeman splitting, zero-field splitting and the hyperfine interactions of the triplet ground state of the selected graphene nanofragments. To illustrate this connection, we show in Figure 1a the evolution of the parameter g-shift (Δg^Iso), which determines the Zeeman splitting, with the distance between the boron atoms for the selected nanofragments. The parameter gIso drives the relaxation process of the spin state of the nanofragment in the presence of an external magnetic field (Figure 1b). We observe that the relaxation time shows little dependence on the distance between the atoms of boron, but changes rapidly with the strength of the external magnetic field. We obtain relaxation times that range from seconds to microseconds, regardless of the size of the nanofragments. Thus, being able to determine which factors control the relaxation times is crucial to design novel materials for quantum computation.

Figure 1: Simulated g-shift and relaxation times for the selected boron-doped graphene nanofragments. Panel a. Evolution of g-shift (Δg^Iso) with the distance between the boron atoms for the selected boron-doped graphene nanofragments. In the inset, an atomistic model of the minimum energy structure of a selected nanofragment. Panel b. Evolution of the relaxation times T1 and T2 with the distance between the boron atoms for magnetic fields (B₀) on increasing strength.

[1] N. Friedrich, P. Brandimante, et al. Phys. Rev. Lett. 125, 146801 (2020)