Balanced homodyne detection of squeezed light in three papers

Short answer: Balanced homodyne detection measures one quadrature of a light field with a sensitivity set by shot noise, and it is the standard way to see squeezed light directly. Three papers cover it: a title-level report of 13.8 dB squeezed vacuum detection, a 2022 tabletop interferometer with 10 dB sensitivity enhancement, and a 2025 study of gigahertz-bandwidth squeezing of about 3 dB. These are laboratory demonstrations.

What is being measured?

The 2025 New Journal of Physics abstract explains why squeezed vacuum matters. It says squeezed vacuum states with gigahertz bandwidth are required for ultrafast quantum sensors, for high-speed continuous-variable one-sided device-independent quantum key distribution and for continuous-variable optical quantum computers. The introduction adds that the first measurements of squeezed light from resonator-enhanced parametric down-conversion were made in 1987, and that up to 15 dB were directly measured in 2016 at 1064 nm.

What did the 2022 interferometer experiment show?

The 2022 Physical Review Letters abstract says future gravitational-wave detectors target an effective quantum noise reduction of 10 dB using squeezed states of light, and that in the last joint observation run the large detectors already used squeezing, though with moderate efficiency. The authors report the first successful 10 dB sensitivity enhancement of a shot-noise-limited tabletop Michelson interferometer with squeezed light in the fundamental Gaussian laser mode. They also implement the balanced homodyne detection scheme planned for the third generation of detectors. They achieved a similarly strong quantum noise reduction when the interferometer was operated in higher-order Hermite-Gaussian modes, which have been discussed for thermal noise mitigation. They describe the results as an important step towards the targeted quantum noise level, and as progress for nonclassical states in higher-order modes for interferometry, spatial resolution and multichannel sensing. These are the authors' assessments.

What did the gigahertz-bandwidth study show?

The 2025 paper investigates the current performance limits of the established method for generating and directly measuring squeezed light with gigahertz bandwidth. The authors present squeeze factors of diffraction-limited laser beams from monolithic periodically poled KTP resonators, measured with two laboratory-built balanced homodyne detectors with gigahertz bandwidth. They build two complete systems without selecting optical or electronic components, to test reproducibility without rejects. The systems show clear spectral differences, but both reach directly measured squeeze factors of about 3 dB over a gigahertz bandwidth, which the authors say is achieved here for the first time. They add that the speed of continuous-variable protocols scales with the bandwidth used, so their detector layout is suitable for speeding up such protocols.

What about the 13.8 dB paper?

A paper titled "Detection of 13.8 dB squeezed vacuum states by optimizing the interference efficiency and gain of balanced homodyne detection" was on the source list. Only its title and author block could be read, so the 13.8 dB figure is quoted as its title says, and nothing else is claimed about the method or its results.

How to read this

The three results measure different things: a very large squeeze factor in a title, a sensitivity gain in an interferometer, and a squeeze factor over a wide bandwidth, so they do not rank against each other. Decibel values are the authors' own. This post is based on abstracts and visible introductions, and full texts were not checked. It makes no claim about products or operating detectors. For background, see our posts on squeezed light in gravitational-wave detectors and on squeezed states in metrology.

FAQ

What does a decibel of squeezing mean?

Noise reduction below the shot-noise level in one quadrature, as used in the three papers.

What did the 2022 experiment show?

A 10 dB sensitivity enhancement of a tabletop Michelson interferometer.

Why does bandwidth matter?

The 2025 authors say the speed of continuous-variable protocols scales with it.

Was 13.8 dB confirmed here?

Only as a paper title, because its text was not readable.