NANOMAGIQC

Project Description

State Preparation

The prepared materials, clusters and nanoparticles, will be characterised by using both ac and dc magnetic techniques. The values of

• the total spin,
• the anisotropy barrier height,
• the tunneling rate, and
• quantum coherence splitting

will be determined by using these two techniques.

These measurements will determine

• the spin level structure in the two wells separated by the anisotropy barrier, as well as
• the range of values for both temperature and external magnetic fieldneeded to achieve the quantum superposition for the different spin levels in the two wells.

The state preparation (and indeed the operation of magnetic cluster qubits) must be realised at temperature significantly lower than the energy gap between the two lowest states |0> and |1>:

• The energy gap in case (1) (see Fig. 1), may be controlled by applying anexternal magnetic field perpendicular to the anisotropy axis of the molecular cluster.
• The typical gap in case (2) (see Fig. 2), is of the order of a few kelvin and depends on both the anisotropy barrier height and the net spin of the nanomagnet.

The operation of a magnetic cluster qubit must therefore be carried out in the temperature range from kelvins down to millikelvins.

A system of cases (1) and (2) qubits allowed to attain equilibrium at such a temperature is effectively prepared in the state |0000…>.

Clearly, the actual system state will be a thermal density operator, so there will besmall contributions with excited qubits (and much smaller corrections with the cluster spin(s) in states outside the truncated space which forms the effective qubit(s) Hilbert space). These corrections can be calculated from the system parameters and the temperature and will be damped by an appropriate Boltzmann factor.