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A novel way to make frequency-dependent squeezed light

AEI team shows first time generation of frequency dependent squeezed light from a detuned optical parametric oscillator

May 02, 2022

Quantum mechanics fundamentally limits highest precision force measurements, such as those employed in gravitational-wave detectors. The resulting random noise is a combination of shot noise and quantum back-action noise and defines the “standard quantum limit” of interferometry. This limit can be overcome with frequency-dependent squeezed light. While gravitational-wave detectors have been using “simple” squeezed light for more than a decade, they are only now starting to implement frequency-dependent squeezing. The current implementation uses squeezed light sources and filter cavities and cannot entirely cancel quantum back-action noise. Now, a team of AEI researchers has demonstrated for the first time a new method of generating frequency-dependent squeezed light. It is based on detuning the optical parametric oscillator in a squeezed light source, and can entirely evade back-action noise. The novel method is unlikely to replace the combination of squeezers and filter cavities in gravitational-wave detectors. It could, however, be a useful add-on for third-generation detectors such as the Einstein Telescope and might also have applications in other opto-mechanical precision experiments and coherent quantum noise cancellation.

Paper abstract

Top row: Tomographically reconstructed Wigner functions. The dashed circle indicates the shot noise levels as a reference. Bottom row: The projections of the Wigner function are measured at four different detection angles shown by the colored traces (blue: ψ=-153°, red: ψ=-88°, yellow: ψ=-15°, violet ψ=-6°). The black dashed traces are simulations of σ ̃11(ψ − ψ0) for these four specific angles. The solid black traces show simulations when the detection angle is aligned to the maximum squeezing/anti-squeezing axis at each measurement frequency σ ̃11(ψω) and σ ̃22(ψω). — Top row: Tomographically reconstructed Wigner functions. The dashed circle indicates the shot noise levels as a reference. Bottom row: The projections of the Wigner function are measured at four different detection angles shown by the colored traces (blue: ψ=-153°, red: ψ=-88°, yellow: ψ=-15°, violet ψ=-6°). The black dashed traces are simulations of σ ̃₁₁(ψ − ψ0) for these four specific angles. The solid black traces show simulations when the detection angle is aligned to the maximum squeezing/anti-squeezing axis at each measurement frequency σ ̃₁₁(ψ_ω) and σ ̃₂₂(ψ_ω).

Top row: Tomographically reconstructed Wigner functions. The dashed circle indicates the shot noise levels as a reference. Bottom row: The projections of the Wigner function are measured at four different detection angles shown by the colored traces (blue: ψ=-153°, red: ψ=-88°, yellow: ψ=-15°, violet ψ=-6°). The black dashed traces are simulations of σ ̃₁₁(ψ − ψ0) for these four specific angles. The solid black traces show simulations when the detection angle is aligned to the maximum squeezing/anti-squeezing axis at each measurement frequency σ ̃₁₁(ψ_ω) and σ ̃₂₂(ψ_ω).

Frequency-dependent squeezing is a promising technique to overcome the standard quantum limit in opto-mechanical force measurements, e.g. gravitational wave detectors. For the first time, we show that frequency-dependent squeezing can be produced by detuning an optical parametric oscillator from resonance. Its frequency-dependent Wigner function is reconstructed quantum-tomographically and exhibits a rotation by 39°, along which the noise is reduced by up to 5.5 dB. Our setup is suitable for realizing effective negative-mass oscillators required for coherent quantum noise cancellation.