Quantum Limit to Measurement Precision Confirmed with Novel Optical Technique

Researchers experimentally verified a fundamental limit to measurement precision – the shot-noise limit – using an intensity-product technique applied to subfields of a Mach-Zehnder interferometer. This approach, leveraging independent and identically distributed photon statistics, enhances precision in optical sensing without altering phase sensitivity.

The precision of optical measurements is fundamentally constrained by the statistical nature of light and the limits imposed by the Fisher information principle. Researchers are continually seeking methods to circumvent these limitations without compromising the sensitivity of the measurement itself. A team led by S. Kim and Byoung S. Ham from the Gwangju Institute of Science and Technology, alongside J. Stöhr from SLAC National Accelerator Laboratory and Stanford University, report in this issue on an experimental demonstration of enhanced resolution in interferometry through a novel intensity-product measurement technique.

Their work, titled ‘Enhanced interferometric resolution via N-fold intensity-product measurements without sacrificing phase sensitivity’, details how dividing the output of a Mach-Zehnder interferometer (MZI) into N subfields and measuring the product of their intensities allows for improved resolution while maintaining the original phase sensitivity. This approach, predicated on satisfying the conditions for independent and identically distributed (i.i.d.) measurements, offers potential benefits for applications such as fibre-optic gyroscopes and high-precision wavelength meters.

Enhanced Optical Sensing via Intensity-Product Measurement

Researchers have experimentally validated an enhancement in precision for optical sensing through the application of an intensity-product measurement technique. By dividing the output of a Mach-Zehnder interferometer (MZI) into N subfields and calculating the product of their intensities, the study achieves a sensitivity approaching the established shot-noise limit (SNL). This confirms theoretical predictions regarding the potential to surpass conventional phase sensitivity bounds in interferometric systems, opening new avenues for precision measurement.

The principle relies on satisfying the criteria for Fisher information, specifically the requirement of independent and identically distributed (i.i.d.) measurement events. The N-division of the MZI output ensures this i.i.d. condition, given the Poisson-distributed nature of photon statistics, which is crucial for accurate data analysis. Consequently, the intensity-product method effectively enhances precision without compromising the inherent phase sensitivity of the optical field.

Experimental results confirm the presence of a shot-noise-like feature in the resolution of an unknown signal when employing this technique, validating its effectiveness. The study centres on an intensity-product measurement applied to the outputs of a Mach-Zehnder interferometer (MZI) divided into N subfields, providing a clear demonstration of the technique.

The study confirms that, under conditions of independent and identically distributed (i.i.d.) measurement events, this approach yields a resolution approaching the SNL, a fundamental limit in phase sensitivity for conventional interferometry. This validation solidifies the potential of this technique for applications such as quantum metrology and imaging.

Researchers meticulously designed and executed the experiments, confirming that the intensity-product technique achieves resolution comparable to the SNL, demonstrating its potential to improve the performance of existing optical sensing technologies. Applications include fiber-optic gyroscopes, which rely on precise phase measurements to detect rotation, and wavelength meters, used for accurate spectral analysis.

Future research will focus on optimising the experimental parameters and exploring the potential of this technique for other applications. The team plans to investigate the effects of noise and imperfections on the performance of the system and develop strategies to mitigate these effects. This work will contribute to the development of more sensitive and accurate optical sensors, enabling new scientific discoveries and technological advancements.