Kharkiv Quantum Seminar: 2024 May 07, 16:00 (EEST)

Engineering quantum coherence and control in diluted spin systems

Irinel Chiorescu

 (Department of Physics, Florida State University and the National High Magnetic Field Laboratory, Tallahassee, FL, USA)

Recently we have demonstrated experimentally the implementation of a novel and universal method to increase the decoherence time of spins qubits [1] in systems with different anisotropies / symmetries / spin-orbit coupling and type of element. The method is based on Floquet engineering of spin qubits quasi-energies by adding a second microwave drive with a frequency commensurate to that of the main Rabi drive. Qualitatively, the increase in coherence time can be linked to dynamical sweet spots (level repulsion) in quasi-energy spectra. Quantitatively, we add insight using numerical simulations [2] aiming to clarify the actual physical processes that take place in the bath surrounding the qubit. We are also exploring the potential use of spin systems as quantum memories [3] and to that effect, we have performed spectroscopic and pulsed studies of S=7/2 Gd ions placed on a coplanar stripline superconducting resonator. In the weak coupling limit, continuous-wave spectroscopy of the cavity resonance perturbation allows us to detect the forbidden electro-nuclear transition of the 155,157Gd isotopes by applying a static field almost perpendicular to crystal c-axis [4]. By increasing the coupling of the spin ensemble to the resonator we observe spin-cavity dressed states with a large mode splitting of ~150 MHz. Numerical simulations based on Dicke model shows a strong hybridization of the first excited level in the presence of a photon and the second excited level with no photon as well as a strong perturbation of the spin ground state generated by photons.