Improving interferometric displacement detection with quantum correlations

F. De Martini, G. Denardo, Anton Zeilinger

N. S. Kampel, Robert W. Peterson, Ran Fischer +5 more

When one seeks knowledge of the full dynamics of the displacement of a harmonic oscillator, non-commutation of the two mechanical quadratures requires a minimum added noise equal to the mechanical resonator's zero point motion. This fundamental quantum limit (QL) is a distinct bound from the standard quantum limit (SQL) that is often considered in interferometric displacement measurement. The SQL is a consequence of the non-commutation of the probe's quadratures in a specific measurement configuration and is characterized by a tradeoff between shot noise (SN) imprecision and quantum backaction that are uncorrelated. The QL and SQL reach the same limit when probing at the peak mechanical response, but the QL can be a significantly lower bound off resonance. In studies of micro-mechanical motion, there has been great interest in observing quantum backaction and approaching the SQL on mechanical resonance. However, much of what historically motivates SQL research is displacement monitoring over a wide frequency band, such as gravitational wave searches. One long-standing concept for surpassing the SQL is to introduce correlations by changing the readout quadrature as a function of frequency in a technique known as variational readout. Here we harness quantum correlations in the measurement of a macroscopic resonator by modifying the readout quadrature of an optical interferometer. By using an optomechanical device thermalized to a dilution refrigerator, we measure quantum noise far off resonance where we improve upon the off-resonance SQL for our quantum efficiency.

N. S. Kampel, R. W. Peterson, R. Fischer +5 more

Ultraprecise measurements of displacement and force can run into a limit on precision due to random forces imparted by the photons used for the measurement. An investigation into a technique for modifying the readout of an interferometer to avoid these limits demonstrates sensitivity improvements.

Rui‐Bo Jin, Zi-Qi Zeng, Chenglong You +1 more

Juan F. Hodelin

Pengxiang Ruan, Jun Liu, Dong-Xu Chen

Compared to classical state inputs, using quantum states in interferometers, especially squeezed states, can greatly improve the accuracy of the phase estimation. Here, we propose a scheme based on a Mach-Zehnder interferometer with a displaced two-mode squeezed coherent state input. The scheme employs both intensity difference detection and balanced homodyne detection to achieve high phase sensitivity. The displaced squeezed state exhibits higher accuracy and better robustness by theoretical calculations. For the state, the phase sensitivity of the quantum Cramér-Rao bound and intensity difference detection both exceed the shot noise limit. Additionally, we demonstrate that the proposed state is superior to the two-mode squeezed coherent state by analyzing different displacement operations. Under the presence of both the interferometric transmission loss and the detection loss, higher displacement strength yields higher robustness. To the best of our knowledge, our work provides new ideas for the field of precision measurement.