Quantum spin dynamics

Abstract:

The magnetic properties of ErSc2 N @ C80, Er2 ScN @ C80 and Er3 N @ C80 metallofullerenes are characterized in the temperature range 2 to 300 K up to a magnetic field of 7 T. The magnetic susceptibility of these fullerenes follows the Curie-Weiss law. The fitting parameters to the Curie-Weiss law provide an effective magnetic moment μeff of Er3 + ion in each of the fullerenes. The magnetic moment decreases with the increase in number of Er3 + ions inside the cage. This is related to crystal-field effects, intramolecular interactions and the local quenching of the angular momentum of the ion within the fullerene cage. © 2008 Elsevier B.V. All rights reserved.

Abstract:

We present electrical transport and Raman measurements on individual single-wall carbon nanotubes filled with the paramagnetic metallofullerene Sc@ C82. We find nearly all devices to be metallic p -type conductors, which we tentatively attribute to bandstructure modification of the nanotubes by the encapsulated Sc@ C82 molecules. At low temperatures the peapod devices behave as quantum dots and transport is shown to be quantum coherent over distances of at least ∼100 nm. Kondo features are observed at the lowest measurement temperatures of 50 mK. Our results are of fundamental interest because of the long spin coherence times of the unpaired electrons on the Sc@ C82 molecules and the possibility this offers for studying one-dimensional spin chains in carbon nanotubes. © 2008 American Institute of Physics.

Abstract:

The transfer of information between different physical forms-for example processing entities and memory-is a central theme in communication and computation. This is crucial in quantum computation, where great effort must be taken to protect the integrity of a fragile quantum bit (qubit). However, transfer of quantum information is particularly challenging, as the process must remain coherent at all times to preserve the quantum nature of the information. Here we demonstrate the coherent transfer of a superposition state in an electron-spin 'processing' qubit to a nuclear-spin 'memory' qubit, using a combination of microwave and radio-frequency pulses applied to (31)P donors in an isotopically pure (28)Si crystal. The state is left in the nuclear spin on a timescale that is long compared with the electron decoherence time, and is then coherently transferred back to the electron spin, thus demonstrating the (31)P nuclear spin as a solid-state quantum memory. The overall store-readout fidelity is about 90 per cent, with the loss attributed to imperfect rotations, and can be improved through the use of composite pulses. The coherence lifetime of the quantum memory element at 5.5 K exceeds 1 s.