Electric control of spin transitions at the atomic scale.

Electric control of spins has been a longstanding goal in the field of solid state physics due to the potential for increased efficiency in information processing. This efficiency can be optimized by transferring spintronics to the atomic scale. We present electric control of spin resonance transitions in single TiH molecules by employing electron spin resonance scanning tunneling microscopy (ESR-STM). We find strong bias voltage dependent shifts in the ESR signal of about ten times its line width. We attribute this to the electric field in the tunnel junction, which induces a displacement of the spin system changing the g-factor and the effective magnetic field of the tip. We demonstrate direct electric control of the spin transitions in coupled TiH dimers. Our findings open up new avenues for fast coherent control of coupled spin systems and expands on the understanding of spin electric coupling.

Microwave excitation of atomic scale superconducting bound states.

Magnetic impurities on superconductors lead to bound states within the superconducting gap, so called Yu-Shiba-Rusinov (YSR) states. They are parity protected, which enhances their lifetime, but makes it more difficult to excite them. Here, we realize the excitation of YSR states by microwaves facilitated by the tunnel coupling to another superconducting electrode in a scanning tunneling microscope (STM). We identify the excitation process through a family of anomalous microwave-assisted tunneling peaks originating from a second-order resonant Andreev process, in which the microwave excites the YSR state triggering a tunneling event transferring a total of two charges. We vary the amplitude and the frequency of the microwave to identify the energy threshold and the evolution of this excitation process. Our work sets an experimental basis and proof-of-principle for the manipulation of YSR states using microwaves with an outlook towards YSR qubits.

Combining electron spin resonance spectroscopy with scanning tunneling microscopy at high magnetic fields.

The continuous increase in storage densities and the desire for quantum memories and computers push the limits of magnetic characterization techniques. Ultimately, a tool that is capable of coherently manipulating and detecting individual quantum spins is needed. Scanning tunneling microscopy (STM) is the only technique that unites the prerequisites of high spatial and energy resolution, low temperature, and high magnetic fields to achieve this goal. Limitations in the available frequency range for electron spin resonance STM (ESR-STM) mean that many instruments operate in the thermal noise regime. We resolve challenges in signal delivery to extend the operational frequency range of ESR-STM by more than a factor of two and up to 100 GHz, making the Zeeman energy the dominant energy scale at achievable cryogenic temperatures of a few hundred millikelvin. We present a general method for augmenting existing instruments into ESR-STM to investigate spin dynamics in the high-field limit. We demonstrate the performance of the instrument by analyzing inelastic tunneling in a junction driven by a microwave signal and provide proof of principle measurements for ESR-STM.