Quantum Metrology with Cubic Phase States Surpasses Gaussian Limits for Precision Measurements

Quantum precision measurements stand to gain significantly from exploiting the unique properties of light, and researchers are continually seeking ways to push the boundaries of sensitivity. Jiajie Guo, Shuheng Liu, and Boxuan Jing, all from Peking University, alongside colleagues including Qiongyi He and Manuel Gessner from the Instituto de F ́ısica Corpuscular, have demonstrated a pathway to surpass existing limits using a special type of light known as cubic phase states. The team reveals that these states offer a distinct advantage over conventional approaches, achieving greater precision in phase sensing than any light source described by Gaussian statistics, even with modest initial squeezing. This breakthrough establishes cubic phase states as a promising resource for quantum-enhanced measurements, potentially unlocking improvements in diverse fields reliant on high-precision sensing.

Cubic Phase States Enhance Measurement Precision

Researchers are developing new methods to enhance the precision of measurements, particularly those limited by the standard quantum limit. They demonstrate that utilising cubic phase states, a specific type of quantum state of light, allows for measurements to surpass these limitations, achieving a sensitivity improvement of 1. 6 decibels compared to coherent states and 0. 8 decibels compared to squeezed states when estimating the phase shift of a weak optical field. This improvement arises from the unique, higher order non-classical behaviour of cubic phase states. This work represents a significant advancement in quantum metrology, establishing a practical method for achieving measurement precision beyond conventional limits and paving the way for more sensitive sensors and measurement devices with potential applications in areas such as gravitational wave detection and precision spectroscopy. Cubic phase states provide a valuable non-Gaussian resource for continuous-variable quantum computing and offer significant potential for quantum metrology, surpassing the phase-sensing sensitivity of all Gaussian states.

Nonclassical Light Boosts Rotation Sensing Precision

Researchers are investigating how non-classical states of light can improve the precision of rotation sensors, crucial for applications like inertial navigation and fundamental physics experiments. They are exploring whether quantum mechanics can overcome the limitations of classical sensors by utilising states of light that don’t behave like ordinary light, focusing on cubic phase states theoretically predicted to offer superior sensitivity for rotation sensing. The research demonstrates that it is possible to create states that approximate cubic phase states using realistic experimental techniques, consistently achieving higher sensitivity than traditional squeezed vacuum states. Three main approaches were explored: a repeat-until-success protocol, a Kerr-based Hamiltonian with Gaussian channels, and a trisqueezing interaction, with the repeat-until-success protocol proving most effective at approaching the sensitivity of ideal cubic phase states as the number of iterations increases. Key concepts include squeezing, displacement, the Kerr effect, Gaussian channels, and cubic phase states, with performance quantified using metrics like quantum Fisher information, variance, and metrological sensitivity.

Cubic Phase States Enhance Metrology Sensitivity

Researchers have demonstrated that cubic phase states offer a significant advantage in quantum metrology, surpassing the sensitivity achievable with standard Gaussian states when measuring phase. This improvement stems from the non-Gaussian nature of cubic phase states, which effectively utilises quantum resources beyond those available in Gaussian approaches, with sensitivity closely linked to the squeezing of fourth-order quadrature observables, a property proving reasonably robust against experimental imperfections like signal loss and detection noise. Importantly, the research indicates that practical, experimentally achievable methods can generate cubic phase states with sufficient fidelity to realise these metrological benefits on current continuous-variable platforms. While trisqueezed states exhibit superior sensitivity at low signal levels, cubic phase states maintain their advantage as signal strength increases, offering a scalable path towards enhanced precision measurements, and suggesting further research could explore optimisation of generation schemes and investigate potential applications in other quantum sensing areas.