Physics · Units and Measurements

Consider the following statements regarding the ongoing efforts to redefine the SI unit of time: I. Optical atomic clocks are more precise than caesium atomic clocks and are expected to redefine the second by around 2030. II. The frequency used in optical clocks lies in the microwave range of the electromagnetic spectrum, similar to caesium clocks. III. International clock comparison experiments are essential to ensure that optical clocks across countries agree within uncertainties of up to 10-18. Which of the statements given above is/are correct?