Kharkiv Quantum Seminar

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.

[1] S. Bertaina, H. Vezin, H. De Raedt, and I. Chiorescu, Experimental protection of quantum coherence by using a phase-tunable image drive, Scientific Reports 10, 1 (2020)

[2] De Raedt, H.; Miyashita, S.; Michielsen, K.; Vezin, H.; Bertaina, S.U.; Chiorescu, I., Sustaining Rabi oscillations by using a phase-tunable image drive, European Physical Journal B, 95 (9), 158 (2022)

[3] M. Blencowe, Quantum computing: Quantum RAM, Nature 468, 44 (2010).

[4] Franco-Rivera, G.; Cochran, J.R.; Miyashita, S.; Bertaina, S.U.; Chiorescu, I., Strong Coupling of a Gd3+ Multilevel Spin System to an On-Chip Superconducting Resonator, Physical Review Applied, 19, 024067 (2023).