The fundamental quantum limit, or the quantum Cramér-Rao bound, defines the sensitivity limit for quantum measurements. For linear measurement systems, such as gravitational-wave detectors, it is inversely proportional to the noise spectrum of the dynamical variable that couples to the measured signal. Defining a physically meaningful spectrum, however, requires that the system is stable and a steady state exists. We relax such a stability requirement and prove that the fundamental quantum limit can be derived simply by considering the open-loop dynamics in the Fourier domain.
Fundamental quantum limit for linear measurements with instability
Note: This paper is part of the APL Special Collection on Gravitational Wave Detectors.
Haixing Miao, Joe Bentley, Hendra Nurdin, Yanbei Chen; Fundamental quantum limit for linear measurements with instability. Appl. Phys. Lett. 27 March 2023; 122 (13): 134001. https://doi.org/10.1063/5.0139740
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