Using quantum light to boost microphone sensitivity
Researchers in Germany have developed a microphone that uses the quantum effects of light to reduce the signal to noise ratio to record low levels.
A research group led by Dr. Florian Kaiser at the Institute of Physics 3 at the University of Stuttgart is investigating the fundamental limit up to which noise can be suppressed using quantum technologies.
The group developed a laser microphone similar to that used for monitoring industrial machinery. However this classical laser microphone was limited in its performance capability by electrical noise present during the measurement process. In the next step, the classical laser light was replaced by specially-adapted quantum light, which directly improved the signal-to-noise ratio by 0.57 decibels. This is a significant improvement in low signal-to-noise environments, such as those commonly found in the communication between flight controllers and airplane pilots.
To conduct the measurements, researchers teamed up with the Olgahospital in Stuttgart to conduct a medically-approved speech recognition trial on 45 subjects. The aim of the study was to determine the minimum required sound level, above which patients correctly understood 50 percent of the words. The study found that more than 71% of the subjects were able to immediately recognize the improvement provided by the quantum microphone.
“These results are mainly based on the high rate at which we generate entangled photons, as well as the subsequent quantum state conversion from a multi-photon state to a single-photon state,” said Kaiser. “The resulting increase in measurement rates by a factor of 10,000 compared to previous approaches enabled us to increase measurement rates up to 100 kHz, which allowed us to comfortably cover the audio band (20 Hz – 20 kHz). Additionally, thanks to the quantum state conversion, we can now use the same cost-effective detectors that we use for the classical laser microphone. This is or course very interesting from a commercial perspective.”
“Our approach is not limited to use in quantum microphones,” added doctoral researcher Raphael Nold. “We also see great potential for our technology in imaging examinations of light-sensitive biospecimens. Our current work already clearly demonstrates that competitive quantum imaging is possible with commercially available enhancements.”
Although the commercialization of this approach is still a long way off, due to the high energy consumption required to generate the quantum light, the concept of quantum state conversion before light detection has the potential to become a game changer for future research studies.
“Our next steps will involve benefiting from the tremendous advancements made in integrated quantum photonics to implement the entire setup on a photonic chip,” said Kaiser. “Having such compact systems at hand would enable a plethora of applications, covering fundamental research, bio-imaging, to effective public exhibitions and experiments in which people can directly experience quantum technologies.”
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