Achieving high-precision detection of weak alternating signals in noisy environments is a fundamental challenge in metrology. Given that the lock-in amplification technique has been successfully applied to facilitate sensitive detection of various unknown weak signals, in this study, we investigate the extension of this technique, termed quantum lock-in amplification, for precise detection of an unknown alternating signal. With a generalized spin-oscillator hybrid quantum system, we show that the target signal driving the oscillator can be precisely locked in by modulating the $\pi$ pulses that drive the spin, while the amplification of the signal is simultaneously achieved by alternatively driving the probe (i.e., oscillator), similar to its classical counterpart. Unlike previous methods that utilize $\pi$ pulses solely for signal accumulation and amplification, the quantum lock-in amplification scheme proposed here simultaneously harnesses both the spin-oscillator entanglement resources and the quantum squeezing of the oscillator. Notably, the simultaneous use of entanglement and squeezing can achieve greater noise compression compared to the case using entanglement only. Consequently, the spin state, characterized by large phase accumulation, can be measured with significantly high sensitivity even under the noisy environment, allowing for precise locking and amplification of the unknown weak signal.

Close

PrevNext

View figure in article

• Quantum harmonic oscillator
• Quantum measurements
• Quantum metrology
• Quantum parameter estimation
• Quantum protocols