This work fits into the line of research aimed at improving the sensitivity of quantum measurements by suppressing backaction. Nearby in the archive are works on suppressing instabilities in gravitational wave detectors, on quantum sensors that beat their own noise, and on quantum tricks for finding quiet signals. These studies share the goal of bypassing fundamental quantum limits, but this paper stands out by considering a resonant force and using an asymmetric three-mode scheme where the asymmetry of the couplings becomes a resource for eliminating noise.
We consider a Fabry–Perot cavity with one mirror attached to a mechanical oscillator. Three optical modes are excited in the cavity with frequencies ω0, ω+ = ω0 + ωm, and ω− = ω0 − ωm, where ωm is the mechanical oscillator frequency. The central mode is pumped by a laser, and the two side modes, generated by optomechanical interaction, are detected independently at the output. Using the input-output formalism and Fourier transforms, the relation between the output quadratures and the input signal is derived. Then a linear combination of the measured quadratures is constructed with weights depending on the coupling coefficients g±, which, for a certain parameter relation, completely eliminates the contribution of optical noise.
It is shown that when the condition g+ = g− (where g± = C0² η±² / γ±) is satisfied, backaction is completely suppressed. Moreover, by choosing G = γm (where G = g+ − g−, and γm is the mechanical damping rate), the measured quantity becomes proportional to an amplified combination of the signal force and thermal noise, with the amplification factor given by G+ = g+ + g−. In the limit of infinitely long measurement (Ω → 0), the output signal contains neither shot noise nor backaction. For finite frequencies, the noise spectral density can be below the standard quantum limit, as shown in the plots: in the symmetric lossless case it decreases with increasing optical power, and in the asymmetric case with G = γm, even greater noise suppression is achieved at low frequencies. The presence of small optical losses (γe/γ0 = 0.01) is not critical for sensitivity.
Unlike neighboring works, which usually consider symmetric systems or broadband forces, here asymmetry plays a key role: different decay rates and different overlap integrals for the side modes. It is this asymmetry that creates additional damping that compensates for backaction. This approach expands the toolkit of quantum nondemolition measurement methods and shows that asymmetric optomechanical transducers can be more efficient than traditional balanced schemes.
The proposed scheme can be implemented using higher-order modes in a Fabry–Perot cavity, where the frequency spacing between modes can be made small, and the overlap integrals with the mechanical mode can be made different. To separate the modes at the output, mode sorters are proposed, which have demonstrated experimental efficiencies above 80%. Further research could focus on optimizing the cavity geometry and mechanical mode to achieve the required asymmetry, as well as accounting for thermal noise and finite measurement duration.
The method could find applications in precision measurements of weak forces, such as gravitational wave detectors, atomic force microscopy, and quantum sensors. Noiseless signal amplification is also useful for quantum communication and information processing.
Experimental implementation of the three-mode scheme using higher-order modes and mode sorters. Testing the robustness of the method to real optical losses and thermal noise.
This work is directly related to the fundamental problem of overcoming the standard quantum limit in optomechanical measurements. It proposes a new way to completely eliminate backaction and shot noise through asymmetry, which could be extended to other types of quantum transducers and help create more sensitive sensors.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The paper proposes a scheme for noiseless signal amplification in an optomechanical transducer based on three optical modes in a Fabry–Perot cavity, where the asymmetry in decay rates and coupling coefficients allows simultaneous suppression of backaction and shot noise, while the signal is amplified beyond the standard quantum limit.
Where its strength is
The key strength is using the asymmetry of couplings as a resource to completely suppress backaction while maintaining signal amplification, which paves the way for quantum nondemolition measurements of resonant forces.
Where it could go next
Worth trying
Why this may matter
Further development of this approach could lead to new types of quantum sensors that surpass the standard quantum limit in weak-force measurements, which is important for precision metrology and fundamental experiments.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.53, against a usual 0.64. It looks like few have drilled nearby.
The scheme uses three optical modes whose frequencies are spaced exactly by the mechanical oscillator frequency. This 'optical triplet' resembles a musical chord, where the central note is the pump and the two side notes are the response to an external force.
The idea of noiselessly amplifying weak signals echoes the concept of 'quantum nondemolition measurement' from Greg Egan's novel 'Quarantine': there, characters use quantum effects to observe without disturbing the state. In this paper, a similar principle is applied to a classical force acting on a quantum oscillator.