Super-resolving refractive index measurements with even coherent state source and parity detection

Abstract High-precision refractive index measurement has become a research hotspot in recent years. However, traditional refractive index measurement often adopts intensity detection, whose performance is restricted by classical detection limit and thus hard to be further improved. In order to break through this limitation, we propose a quantum-enhanced refractive index sensing scheme utilizing even coherent state sources in combination with parity detection and analyze its detection performance. Due to the inevitable photon loss in practical applications, the effects of photon loss on resolution and sensitivity are also investigated. Numerical results show that the resolution of proposed strategy breaks through the Rayleigh limit and realizes super-resolving refractive index measurement. Relative to the existing coherent state schemes, our strategy possesses twofold resolution improvement. Furthermore, the physical roots of the super-resolution are analyzed.