Microwave amplification with nanomechanical resonators

Use of nanomechanical resonators has the potential to offer microwave amplification with the minimum possible added noise, namely that due to quantum fluctuations. Noise-free amplification of weak radio signals In order to compensate for energy losses, the radio signals used in telecommunications and detection technologies require occasional electrical amplification. For specific applications, sensitive amplifiers have been demonstrated that operate near the quantum limit — where the only noise added is due to fundamental quantum fluctuations. This paper describes a new concept for amplifying weak electrical signals close to this fundamental limit, using a nanomechanical resonator. The system uses a resonator irradiated with microwave light of a frequency tuned so that it sets the resonator in motion with tiny vibrations; these amplify the signal. In this proof-of-principle study, signal amplification of 25 decibels is demonstrated, with only 20 fundamental noise quanta added. This mechanical amplification approach has the attraction that it is conceptually simple and could feasibly be used in integrated electrical circuits. The sensitive measurement of electrical signals is at the heart of modern technology. According to the principles of quantum mechanics, any detector or amplifier necessarily adds a certain amount of noise to the signal, equal to at least the noise added by quantum fluctuations 1 , 2 . This quantum limit of added noise has nearly been reached in superconducting devices that take advantage of nonlinearities in Josephson junctions 3 , 4 . Here we introduce the concept of the amplification of microwave signals using mechanical oscillation, which seems likely to enable quantum-limited operation. We drive a nanomechanical resonator with a radiation pressure force 5 , 6 , 7 , and provide an experimental demonstration and an analytical description of how a signal input to a microwave cavity induces coherent stimulated emission and, consequently, signal amplification. This generic scheme, which is based on two linear oscillators, has the advantage of being conceptually and practically simpler than the Josephson junction devices. In our device, we achieve signal amplification of 25 decibels with the addition of 20 quanta of noise, which is consistent with the expected amount of added noise. The generality of the model allows for realization in other physical systems as well, and we anticipate that near-quantum-limited mechanical microwave amplif