We provide the first evidence for coherence and Rabi oscillations of spin-solitons pinned by the local breaking of translational symmetry in isotropic Heisenberg chains (simple antiferromagnetic-N{e}el or spin-Peierls).We show that these correlated s
pin systems made of hundreds of coupled spin bear an overall spin S=1/2 and can be manipulated as a single spin. This is clearly contrary to all known spin-qubits which are paramagnetic centres, highly diluted to prevent decoherence. These results offer an alternative approach for spin-qubits paving the way for the implementation of a new type of quantum computer.
Contrary to the well known spin qubits, rare-earth qubits are characterized by a strong influence of crystal field due to large spin-orbit coupling. At low temperature and in the presence of resonance microwaves, it is the magnetic moment of the crys
tal-field ground-state which nutates (for several $mu$s) and the Rabi frequency $Omega_R$ is anisotropic. Here, we present a study of the variations of $Omega_R(vec{H}_{0})$ with the magnitude and direction of the static magnetic field $vec{H_{0}}$ for the odd $^{167}$Er isotope in a single crystal CaWO$_4$:Er$^{3+}$. The hyperfine interactions split the $Omega_R(vec{H}_{0})$ curve into eight different curves which are fitted numerically and described analytically. These spin-orbit qubits should allow detailed studies of decoherence mechanisms which become relevant at high temperature and open new ways for qubit addressing using properly oriented magnetic fields.
