Many-Body Quantum Lock-In Amplifier

Achieving high-precision detection of time-dependent signals within noise is a ubiquitous issue in physics and a critical task in metrology. Lock-in amplifiers are detectors that can extract alternating signals within extreme noise via a known carrier frequency. Here we present a protocol for achieving an entanglement-enhanced lock-in amplifier via use of many-body multipulse quantum interferometry. The many-body quantum lock-in amplifier is implemented by application of a periodic multi-sr-pulse sequence during the interrogation. Our analytic results show that, by our choosing suitable input states and readout operations, the frequency and amplitude of an unknown alternating field can be simultaneously extracted via population measurements. The lock-in point can be determined via the symmetry of the signal during a single interrogation time or the time-averaged signals for multiple interrogation times. We find that the measurement signal at the lock-in point is independent of the interrogation time. In particular, if we input spin cat states and apply interaction-based readout operations, the measurement precisions for frequency and amplitude can both approach the Heisenberg limit. Moreover, our many-body quantum amplifier is also robust with regard to extreme stochastic noise. Our study paves a new way for measuring time-dependent signals with many-body quantum systems, and provides a feasible method for achieving Heisenberg-limited detection of alternating signals.

Automated summary

The study introduces a new approach for achieving high-precision detection of time-dependent signals using many-body quantum systems. The many-body quantum lock-in amplifier extracts frequency and amplitude of unknown alternating field by applying a multi-pulse sequence, with measurement signal at the lock-in point being independent of the interrogation time.