Quantum spin dynamics

Abstract:

Er3N@C80 exhibits sharp optical emission lines in the near-infrared attributed to fluorescence from the Er³⁺ ion. Here we demonstrate that high magnetic fields cause this spectrum to split, corresponding to transitions from the lowest field-split Kramers doublet of the ⁴I13/2 manifold to the four lowest field-split levels of the ⁴I15/2 manifold. The internal structure of these fullerenes can be spatially aligned with a preferred orientation under high magnetic field; the effect of alignment is to reduce the broadening associated with the isotropic spatial averaging characteristic of powder or frozen-solution spectra. Using a tunable 1.5 μm laser, we directly observe non-cage-mediated optical interactions with the Er³ ion. This spectroscopic method provides the opportunity to map the energy level structure of the incarcerated ion and to coherently control its quantum state. These qualities suggest that rare-earth endohedral fullerenes have characteristics that could be employed as a readout pathway for fullerene-based quantum information processing. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.

Abstract:

Nuclear spins have been proposed for the embodiment of quantum information and yielded the most complex demonstrations of quantum algorithms to date. However, the weak thermal polarisation of nuclear spins in experimentally accessible conditions has presented a barrier to further scaling. Here, we discuss the benefits of a coupled electron spin to the nuclear spin qubit and demonstrate the ideas using the ¹⁴N nuclear spin in the N@C 60 molecule. In addition to providing a resource for nuclear spin polarisation and detection, the electron spin can be exploited to perform ultrafast nuclear spin phase gates, which can in turn be used to dynamically bang-bang decouple the nuclear spin from unwanted interactions. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.