AF molecular rings for quantum computation.
Molecular magnets have been recently proposed as possible building blocks for a solid-state quantum computer. In order to substantiate and develop such a proposal, one needs to identify those molecules that are best suited for the qubit encoding and manipulation. Here, we focus on a heterometallic molecular ring, namely Cr7Ni, where the Substitution of one Cr3+(S = 3/2) with Ni2+(S = 1) provides an extra spin to the otherwise compensated molecule. We show that its ground state consists in an S = 1/2 doublet, energetically well separated (Delta(0)/k(B) similar to 13 K at zero magnetic field) from the first excited multiplet. This relatively large value of Delta(0), together with the reduced mixing of the subspaces corresponding to different values of the total spin S, enables a safe encoding of the vertical bar 0 > and vertical bar 1 > states with the ground-state doublet, and allows to coherently rotate the effective S = 1/2 spin, while keeping the population loss to the excited states negligible. A further, intriguing challenge is represented by the implementation of the conditional dynamics (two-qubit gates). We present here preliminary characterization of molecular “Cr7Ni-dimers”, i.e., derivatives in which two Cr7Ni rings are linked with each other by means of delocalized aromatic amines. The resulting intercluster couplings are estimated to be <= 1 K and are expected to be permanent, i.e., not tuneable during gating, as required by the standard approach to quantum computation. We discuss a computational scheme that allows in principle to overcome this limitation. The most relevant decoherence mechanisms for Cr7Ni and possible ways to reduce their effects are discussed as well. (c) 2005 Elsevier Ltd. All rights reserved.