Measuring nanomechanical motion with an imprecision below the standard quantum limit

Abstract

We report a room-temperature measurement of nanomechanical motion with an imprecision below the standard quantum limit (SQL), using cavity-enhanced optical near fields. Fundamental thermodynamical cavity frequency fluctuation limits the total imprecision to 3 dB below the SQL at room temperature [corresponding to (530 am/ √ Hz)2 in absolute units] and is expected to reduce to negligible values at moderate cryogenic temperatures. Coupling strengths exceeding those required to reach the SQLby more than two orders of magnitude are achieved, allowing a shot-noise limited imprecision more than 10 dB below the SQL. The transducer, thus, in principle, allows access to the quantum backaction dominated regime, a prerequisite for exploring quantum backaction, measurement-induced squeezing, and obtaining sub-SQL sensitivity using backaction evading techniques