Person:

Zhang, Mian

The uncontrolled interaction of a quantum system with its environment is detrimental for quantum coherence. For quantum bits in the solid state, decoherence from thermal vibrations of the surrounding lattice can typically only be suppressed by lowering the temperature of operation. Here, we use a nano-electro-mechanical system to mitigate the effect of thermal phonons on a spin qubit – the silicon-vacancy colour centre in diamond – without changing the system temperature. By controlling the strain environment of the colour centre, we tune its electronic levels to probe, control, and eventually suppress the interaction of its spin with the thermal bath. Strain control provides both large tunability of the optical transitions and significantly improved spin coherence. Finally, our findings indicate the possibility to achieve strong coupling between the silicon-vacancy spin and single phonons, which can lead to the realisation of phonon-mediated quantum gates and nonlinear quantum phononics.

Efficient frequency shifting and beam splitting is important for a wide range of applications, including atomic physics1,2, microwave photonics3–6, optical communication7,8, and photonic quantum computing9–14. However, realizing gigahertz-scale frequency shifts with high efficiency, low loss, and tunability, in particular using a miniature and scalable device, is challenging since it requires efficient and controllable nonlinear processes. Existing approaches based on acousto-optics6,15–17, all-optical wave mixing10,13,18–22, and electro-optics23–27 are either limited to low efficiencies or frequencies, or are bulky. Furthermore, most approaches are not bi-directional, which renders them unsuitable for frequency beam splitters. Here we demonstrate electro-optic frequency shifters that are controlled using only continuous and single-tone microwaves. This is accomplished by engineering the density of states of, and coupling between, optical modes in ultra-low loss waveguides and resonators in lithium niobate nanophotonics28. Our devices, consisting of two coupled-ring-resonators, provide frequency shifts as high as 28 GHz with an ~90% on-chip conversion efficiency. Importantly, the devices can be reconfigured as tunable frequency-domain beam splitters. Using the device, we also demonstrate a non-blocking and efficient swap of information between two frequency channels. Finally, we propose and demonstrate a scheme for cascaded frequency shifting that allows shifts of ~120 GHz using a ~30 GHz continuous and single-tone microwave signal. Our devices could become building-blocks for future high-speed and large-scale classical information processors7,29 as well as emerging frequency-domain photonic quantum computers9,11,14.