On-chip electro-optic frequency shifters and beam splitters.

Efficient frequency shifting and beam splitting are 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 because 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 ultralow-loss waveguides and resonators in lithium niobate nanophotonics28. Our devices, consisting of two coupled ring-resonators, provide frequency shifts as high as 28 gigahertz with an on-chip conversion efficiency of approximately 90 per cent. Importantly, the devices can be reconfigured as tunable frequency-domain beam splitters. We also demonstrate a non-blocking and efficient swap of information between two frequency channels with one of the devices. Finally, we propose and demonstrate a scheme for cascaded frequency shifting that allows shifts of 119.2 gigahertz using a 29.8 gigahertz 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.

Relaxation of the electro-optic response in thin-film lithium niobate modulators.

Thin-film lithium niobate (TFLN) is a promising electro-optic (EO) photonics platform with high modulation bandwidth, low drive voltage, and low optical loss. However, EO modulation in TFLN is known to relax on long timescales. Instead, thermo-optic heaters are often used for stable biasing, but heaters incur challenges with cross-talk, high power, and low bandwidth. Here, we characterize the low-frequency (1 mHz to 1 MHz) EO response of TFLN modulators, investigate the root cause of EO relaxation and demonstrate methods to improve bias stability. We show that relaxation-related effects can enhance EO modulation across a frequency band spanning 1kHz to 20kHz in our devices - a counter-intuitive result that can confound measurement of half-wave voltage (V π) in TFLN modulators. We also show that EO relaxation can be slowed by more than 104-fold through control of the LN-metal interface and annealing, offering progress toward lifetime-stable EO biasing. Such robust EO biasing would enable applications for TFLN devices where cross-talk, power, and bias bandwidth are critical, such as quantum devices, high-density integrated photonics, and communications.

Optically Heralded Entanglement of Superconducting Systems in Quantum Networks.

Networking superconducting quantum computers is a longstanding challenge in quantum science. The typical approach has been to cascade transducers: converting to optical frequencies at the transmitter and to microwave frequencies at the receiver. However, the small microwave-optical coupling and added noise have proven formidable obstacles. Instead, we propose optical networking via heralding end-to-end entanglement with one detected photon and teleportation. This new protocol can be implemented on standard transduction hardware while providing significant performance improvements over transduction. In contrast to cascaded direct transduction, our scheme absorbs the low optical-microwave coupling efficiency into the heralding step, thus breaking the rate-fidelity trade-off. Moreover, this technique unifies and simplifies entanglement generation between superconducting devices and other physical modalities in quantum networks.

Rare event molecular dynamics simulations of plasma induced surface ablation.

The interaction of thermal Ar plasma particles with Si and W surfaces is modeled using classical molecular dynamics (MD) simulations. At plasma energies above the threshold for ablation, the ablation yield can be calculated directly from MD. For plasma energies below threshold, the ablation yield becomes exponentially low, and direct MD simulations are inefficient. Instead, we propose an integration method where the yield is calculated as a function of the Ar incident kinetic energy. Subsequent integration with a Boltzmann distribution at the temperature of interest gives the thermal ablation yield. At low plasma temperatures, the ablation yield follows an Arrhenius form in which the activation energy is shown to be the threshold energy for ablation. Interestingly, equilibrium material properties, including the surface and bulk cohesive energy, are not good predictors of the threshold energy for ablation. The surface vacancy formation energy is better, but is still not a quantitative predictor. An analysis of the trajectories near threshold shows that ablation occurs by different mechanisms on different material surfaces, and both the mechanism and the binding of surface atoms determine the threshold energy.

Controlling the coherence of a diamond spin qubit through its strain environment.

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.