The ability to assemble weakly interacting subsystems is a prerequisite for implementing quantum information processing and generating controlled entanglement. In recent years, molecular nanomagnets have been proposed as suitable candidates for qubit encoding and manipulation. In particular, antiferromagnetic Cr7Ni rings behave as effective spin-1/2 systems at low temperature and show long decoherence times. Here, we show that these rings can be chemically linked to each other and that the coupling between their spins can be tuned by choosing the linker. We also present calculations that demonstrate how realistic microwave pulse sequences could be used to generate maximally entangled states in such molecules.

The substitution of one metal ion in a Cr-based molecular ring with dominant antiferromagnetic couplings allows the engineering of its level structure and ground-state degeneracy. Here we characterize a Cr7Ni molecular ring by means of low-temperature specific-heat and torque-magnetometry measurements, thus determining the microscopic parameters of the corresponding spin Hamiltonian. The energy spectrum and the suppression of the leakage-inducing S mixing render the Cr7Ni molecule a suitable candidate for the qubit implementation, as further substantiated by our quantum-gate simulations.

An unusually large magnetocaloric effect for the temperature region below 10 K is found for the Fe14 molecular nanomagnet. This is to large extent caused by its extremely large spin S ground-state combined with an excess of entropy arising from the presence of low-lying excited S states. We also show that the highly symmetric Fe14 cluster core, resulting in small cluster magnetic anisotropy, enables the occurrence of long-range antiferromagnetic order below T_N=1.87 K.Comment: 4 pages, 3 figures, accepted for publication in Applied Physics Letter

We characterize supramolecular magnetic structures, consisting of two weakly coupled antiferromagnetic rings, by low-temperature specific heat, susceptibility, magnetization and electron paramagnetic resonance measurements. Intra- and inter-ring interactions are modeled through a microscopic spin-Hamiltonian approach that reproduces all the experimental data quantitatively and legitimates the use of an effective two-qubit picture. Spin entanglement between the rings is experimentally demonstrated through magnetic susceptibility below 50 mK and theoretically quantified by the concurrence.

Coplanar microwave resonators made of 330 nm-thick superconducting YBa2Cu3O7 have been\ud realized and characterized in a wide temperature (T, 2–100 K) and magnetic field (B, 0–7 T) range.\ud The quality factor (QL) exceeds 104 below 55K and it slightly decreases for increasing fields,\ud remaining 90% of QLðB ¼ 0Þ for B¼7 T and T¼2K. These features allow the coherent coupling\ud of resonant photons with a spin ensemble at finite temperature and magnetic field. To demonstrate\ud this, collective strong coupling was achieved by using di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium\ud organic radical placed at the magnetic antinode of the fundamental mode: the in-plane magnetic\ud field is used to tune the spin frequency gap splitting across the single-mode cavity resonance\ud at 7.75 GHz, where clear anticrossings are observed with a splitting as large as 82 MHz at\ud T¼2K. The spin-cavity collective coupling rate is shown to scale as the square root of the number\ud of active spins in the ensemble