All-optical coherent quantum-noise cancellation in cascaded optomechanical systems

Coherent quantum-noise cancellation (CQNC) can be used in optomechanical sensors to surpass the standard quantum limit (SQL). In this paper, we investigate an optomechanical force sensor that uses the CQNC strategy by cascading the optomechanical system with an all-optical effective negative-mass oscillator. Specifically, we analyze matching conditions and losses and compare the two possible arrangements in which either the optomechanical or negative-mass system couples first to light. While both of these orderings yield a sub-SQL performance, we find that placing the effective negative-mass oscillator before the optomechanical sensor will always be advantageous for realistic parameters. The modular design of the cascaded scheme allows for better control of the subsystems by avoiding undesirable coupling between system components while maintaining a performance similar to the integrated configuration proposed earlier. We conclude our work with a case study of a micro-optomechanical implementation.