SU(2)-in-SU(1,1) Nested Interferometer for High Sensitivity, Loss-Tolerant Quantum Metrology.

Area of Science:

• Quantum optics
• Interferometry
• Quantum sensing

Background:

• Standard quantum limit (SQL) restricts interferometer sensitivity.
• Photon loss in detectors degrades interferometer performance.
• SU(1,1) interferometers offer enhanced sensitivity but are susceptible to losses.

Purpose of the Study:

• To introduce a novel nested interferometer topology (SISNI).
• To achieve high signal-to-noise ratio (SNR) and sensitivity beyond SQL.
• To demonstrate tolerance to photon losses for practical applications.

Main Methods:

• Nesting a SU(2) interferometer within a SU(1,1) interferometer.
• Implementing SU(1,1) with parametric amplifiers via four-wave mixing (FWM) in Rb vapor.
• Utilizing a laser-fed Mach-Zehnder SU(2) interferometer.

Main Results:

• Achieved 2.2 dB sensitivity beyond SQL.
• Demonstrated high SNR at power levels two orders of magnitude higher than previous loss-tolerant interferometers.
• Experimentally determined optimal FWM gains, agreeing with quantum noise models.

Conclusions:

• The SISNI topology offers simultaneous high SNR, sub-SQL sensitivity, and loss tolerance.
• This approach can enhance the practical sensitivity of high-power interferometers, such as those for gravitational wave detection.
• Enables quantum-enhanced interferometry at wavelengths lacking efficient detectors.