Toward single atom qubits on a surface: Pump-probe spectroscopy and electrically-driven spin resonance
William Paul, IBM Research
Single Fe atoms placed on a thin MgO film have exceptional magnetic properties: Their spin relaxation lifetime can extend to many milliseconds, and their quantum state can be coherently manipulated by RF electric fields. In this talk, we will discuss a scanning tunneling microscopy (STM) investigation of the dynamics of spin-relaxation and the electric-field-driven spin resonance of individual Fe atoms on a MgO/Ag(001) surface. The energy relaxation time, T1, of single spins on surfaces can be measured by spin-polarized pump-probe STM [1]. To date, the relaxation times reported for Fe-Cu dimers on Cu2N insulating films have been of the order ~100 ns [1]. A three-order-of-magnitude enhancement of lifetime, to ~200 us, was recently demonstrated for Co on a single-monolayer of MgO [2]. Here, we show that the T1 lifetime of single Fe atoms on MgO can exceed 10 ms under certain conditions, and can be tuned by adjusting the thickness of insulating MgO film grown on Ag(001). Next, we demonstrate electron spin resonance of an individual single Fe atom, driven by a gigahertz-frequency electric field applied across the tip-sample junction, and detected by a spin-polarized tunneling current [3]. The principle parameters of the spin resonance experiment, namely the phase coherence time T2 and the Rabi rate, are characterized for Fe atoms adsorbed to the monolayer MgO film. We conclude with an outlook toward quantum devices built with atomic precision on surfaces.
[1] Loth et al., Science 329, 1628 (2010)
[2] Rau and Baumann et al., Science 344, 988 (2014)
[3] Baumann and Paul et al., Science 350, 417 (2015)