ИСТИНА

Quantum entanglement between spins is considered as a key resource for future quantum technologies. For a system of spins, we can speak of entanglement, when the many-spin state cannot be represented as a product of single-spin states. Antiferromagnetic (AF) spin chains were proposed to use for quantum entanglement between remote qubits and for information transfer between them. In very recent experiment the possibility to tune entanglement in AF chains of magnetic adatoms on a Cu2N/Cu(001) surface was demonstrated. It would be of paramount importance to create entanglement among adatoms on surfaces at large inter-atomic separation. Combining ab initio and quantum spin Hamiltonian studies, we have investigated quantum entanglement and spin dynamics in spin chains on insulating substrates for experimentally realized conditions. The time-dependent Schrödinger equation is solved together with the damping term. First, we show that AF chains can be used for a fast spin switching and entanglement generation by locally applied magnetic pulses Bz(t). As an example, we present our results for Co chains. Our simulations predict that mutual information increases rapidly during a propagation of entanglement through the spin chain. The relaxation time significantly differs for the chains with even and odd numbers of spins. Our studies show that AF spin chains due to entanglement properties can serve as quantum mediators for long-distance entanglement (LDE) between magnetic adatoms. Sensing of remote spins based on LDE is demonstrated. We perform the spin dynamics calculations for two probe spins SA and SB supported on a Cu2N/Cu(001) surface and remotely separated via AF coupling with the quantum mediator composed by single AF Fe dimer. For simulation of spin sensing we kept SB spin fixed to the state with quantum number SFe=2, whereas SA was changed in the range of the spin quantum numbers S{1/2;1;3/2;2}. The obtained results reveal that the expectation value of SB spin (<SFez>) depends on the SA spin for both dynamical and static regimes, despite the large separation between them (dAB>20Å). Thus, one can treat SB spin as the spin sensor, which exhibits a non-local time-dependent sensing of the remote SA spin.