Engineers are developing commercial microphones focus on eliminating technical sources of noise, such as that found in the signal amplifiers. But even when the technical noise sources are addressed, there is still a fundamental noise stemming from the quantum nature of any measurement.
For high-sensitivity microphones that can perform close to this fundamental noise level, laser-based devices are top candidates. They measure the slightest displacements of microphone membranes in a fashion that resembles a microscopic version of gravitational wave interferometers. Such devices are currently being used for measuring wear in industrial machines, as well as in espionage.
Entangled photons can make use of quantum correlations to measure small displacements with an improved signal-to-noise ratio compared to laser light. However, the generally complex experimental setting of quantum physics experiments leads to a tremendous resource overhead and complicated data processing, which results in measurement rates of a few data points per second, at most. This is obviously incompatible with recording sound, where at least tens of thousands of data points per second need to be recorded to reconstruct the waveform.
Scientists found a new method that combines several fundamental quantum optics concepts to realize a quantum optical displacement sensor that is simple, robust, and operates below the classical noise limit at sampling rates up to 100 kHz.
The team wanted to show that this high measurement rate can actually be useful. Thus, they used a loudspeaker, placed it in front of our membrane, and then played 26,400 words from a medically approved speech recognition test. They then recorded the membrane displacements with a classical laser sensor and with their quantum optical sensor. Unsurprisingly, the data revealed that the signal-to-noise ratio was improved using quantum light. (ScienceX)
The study has been published in PRX Quantum.
