Researchers Overcome Key Barrier to Quantum-Enhanced Measurements
Scientists have solved a longstanding detection problem that has blocked quantum-sensing applications at infrared wavelengths used by gravitational-wave observatories. By amplifying quantum signals before they're measured, the team doubled the effective sensitivity of detectors at 2 micrometers, opening a pathway to next-generation quantum measurement systems that could improve precision in both scientific instruments and industrial sensing.
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Squeezed states of light enable quantum-enhanced measurements but are limited by optical loss, particularly at 2 μm where photodiode efficiency is low. We report the first loss-tolerant, audio-band squeezed light detection at 1984 nm by using a phase-sensitive amplifier to amplify the squeezed vacuum prior to detection. This technique increases the effective detection efficiency from 74% to 95% and increases the observed squeezing from 4 to 8 dB, the highest level of squeezing observation reported at this wavelength. Additionally, the vacuum to dark-noise clearance increases, extending the effective measurement bandwidth toward lower frequencies. This approach is largely wavelength independent, extending high-fidelity quantum measurements to future gravitational-wave detectors and related quantum technologies.