Researchers have demonstrated a method for measuring visible light particles nondestructively. The method could be used to investigate the quantum properties of light.
The researchers coupled a single trapped ion to an optical cavity dispersively to extract information about the cavity photon-number distribution in a non-destructive way.
The team placed an ionized calcium atom between two hollow mirrors (see how diamond turning can machine mirrors), creating a cavity through which visible laser light was guided. The ion has only a weak influence on the light. The researchers took quantum measurements of the ion. Based on these measurements, they were able to make statistical predictions about the number of light particles in the chamber.
They used the measurements first to obtain the ion-cavity interaction strength. Then they reconstructed the cavity photon-number distribution for coherent states and for a state with mixed thermal-coherent statistics, finding overlaps above 99% with the calibrated states.
The new method to measure visible light particles could be used to generate specially tailored light fields by feeding the measurement results back into the system via a feedback loop, thus establishing the desired states. The researchers have limited themselves to classical states. In the future, this method could also be used to measure the quantum states of light.