Symmetry-based Quantum Sensing Enables High-Precision Measurements, Outperforming GHZ States

The pursuit of measurement precision beyond conventional limits is driving innovation in quantum sensing, and new research explores how critical systems can be harnessed for this purpose. Yinan Chen, Sara Murciano, and Pablo Sala, alongside Jason Alicea and colleagues from the California Institute of Technology and Université Paris-Saclay, demonstrate interferometric protocols utilising critical wavefunctions to achieve enhanced sensitivity. Their work introduces a symmetry-based algorithm to optimise measurement strategies in magnetic systems and Rydberg atom arrays, revealing how inherent symmetries can be exploited as a metrological resource. Significantly, the researchers show that these critical systems maintain advantages even when subjected to realistic imperfections like decoherence and qubit loss, suggesting a pathway towards robust and practical quantum sensors. This builds upon recent advances in preparing these critical states, positioning interferometry with critical systems as a highly promising avenue for future quantum technologies.

The research focuses on understanding how symmetries, imperfections and decoherence affect the performance of these sensors, specifically exploring their sensitivity to external perturbations. Their approach combines analytical calculations with numerical simulations to characterise the influence of these factors on the sensing capabilities of critical systems. This work contributes a detailed analysis of symmetry-protected gapless modes and their susceptibility to disorder, revealing how imperfections can both hinder and, surprisingly, enhance sensing precision in certain scenarios.

The study examines the impact of various decoherence mechanisms on the quantum sensor’s performance, modelling these effects through open quantum system dynamics. Researchers specifically consider dephasing and dissipation, demonstrating how these processes limit the achievable sensitivity and coherence time of the sensor. They present results showing that certain types of decoherence can be mitigated through careful design of the critical system and the sensing protocol. Furthermore, the team explores the interplay between symmetry, imperfections and decoherence, identifying parameter regimes where robust sensing is possible despite the presence of these detrimental factors.

A key contribution of this research is the development of a theoretical framework for quantifying the sensitivity of critical systems to weak external fields. This framework accounts for the unique properties of critical systems, such as their diverging correlation length and the presence of gapless excitations. By analysing the response of these systems to perturbations, the authors establish a connection between the system’s critical exponents and the achievable sensing precision. Numerical simulations, utilising both exact diagonalisation and density matrix renormalisation group techniques, validate the analytical predictions and provide insights into the behaviour of more complex systems.

The authors demonstrate that the presence of quenched disorder can significantly alter the sensing characteristics. They find that for weak disorder, the sensing sensitivity is reduced, while for strong disorder, novel sensing mechanisms can emerge. Importantly, the research highlights that specific types of disorder can actually enhance the sensor’s response to certain external fields, offering a pathway towards improved sensing performance. This counterintuitive result stems from the creation of localised states that are particularly sensitive to the target perturbation. Finally, the study provides concrete examples of how these findings can be applied to the design of practical quantum sensors based on critical systems. They consider specific material platforms, such as topological insulators and superconducting nanowires, and discuss the challenges and opportunities associated with realising these sensors in the laboratory. The research concludes by outlining future directions, including the exploration of more complex decoherence models and the development of adaptive sensing protocols that can optimise performance in the presence of noise and imperfections.

Symmetry-Enhanced Interferometry with Critical Wavefunctions

The research details a novel interferometric approach to high-precision sensing, leveraging the unique properties of entangled many-body states. Scientists engineered protocols based on critical wavefunctions, comparing their performance against established benchmarks like Greenberger-Horne-Zeilinger (GHZ) and spin-squeezed states to demonstrate potential advantages. A symmetry-based algorithm was introduced, designed to pinpoint optimal measurement strategies for both magnetic systems exhibiting internal symmetries and Rydberg-atom arrays with spatial symmetries, effectively harnessing symmetry as a metrological resource. Experiments employed one-dimensional systems to estimate a parameter imprinted on a critical many-body state via a unitary rotation.

The study pioneered a method for determining the minimum phase uncertainty, revealing it reaches a minimum at an intermediate angle, scaling as δθ ∼L−5/8. Researchers established a practical criterion for quantum metrology improvement, requiring the quantum uncertainty to be smaller than the initial phase window, and demonstrated a clear quantum advantage in the XXZ model where the achievable δθ significantly outperformed the classical resolution. To assess robustness, the work investigated the impact of non-unitary deformations, including symmetry-preserving and symmetry-breaking decoherence, and qubit loss, on critical systems. This analysis identified regimes where critical systems outperform GHZ states, and surprisingly, showed that non-unitary deformation could even enhance precision.

The team developed a decoding protocol where the imprinting operation explicitly depends on measurement outcomes, revealing an enhancement beyond the SQL for deformed critical states. Furthermore, the study examined the effects of decoherence, finding that preserving the Z2 symmetry of the system maintains sensitivities between the SQL and the Heisenberg limit. This research builds upon recent advances in log-depth preparation of critical wavefunctions, suggesting a promising path towards practical implementation. The error-propagation formula was used to identify optimal observables dictated by internal or spatial symmetries, ensuring saturation of the Cramer-Rao bound. The scaling of the Quantum Fisher Information (QFI) for a subsystem in a critical Ising chain was found to match the full system, while the minimum achievable δθ was determined to be ∼L−5/8.

Critical Wavefunctions Enhance Quantum Magnetic Sensing Scientists have

Scientists have achieved a breakthrough in quantum sensing, developing interferometric protocols based on critical wavefunctions that demonstrate high-precision measurements beyond the standard quantum limit. The research focuses on exploiting entangled many-body states to enhance the estimation of physical quantities, such as magnetic fields, at the atomic scale. Experiments revealed that systems tuned to a quantum phase transition exhibit enhanced sensitivity due to long-range entanglement inherent in their ground state, offering a robust alternative to traditional sensing methods. The team measured the quantum Fisher information (QFI) to quantify the sensitivity of quantum systems to infinitesimal changes in a parameter of interest, establishing that precision in estimating this parameter is inversely proportional to the square root of the QFI.

Results demonstrate that critical systems outperform Greenberger-Horne-Zeilinger (GHZ) states in specific regimes, with the research identifying conditions where non-unitary deformation can actually enhance sensing precision. Critical states, unlike fragile GHZ states, coherently superpose polarized domains across all length scales, providing resilience against local perturbations. Further investigation involved studying the robustness of criticality under various decoherence mechanisms, including symmetry-preserving and symmetry-breaking decoherence, as well as qubit loss. Measurements confirm that critical systems maintain their enhanced sensitivity even when subjected to these disturbances, a significant advantage over GHZ states which are easily disrupted by environmental factors.

Data shows that the scaling of the QFI with system size is a key metric for optimal precision, and the work introduces a symmetry-based algorithm to identify optimal measurement strategies for both magnetic systems and Rydberg-atom arrays. The breakthrough delivers a pathway towards interferometric sensing with log-depth preparation of critical wavefunctions, suggesting increasingly promising applications in areas like atomic clocks and high-resolution microscopy. Scientists recorded that the accumulation of phase difference in critical states grows with the number of spins, yielding a sensitivity enhancement, while the coherent superposition of domains at all length scales provides a more resilient probe than macroscopic superpositions. This research establishes a foundation for developing quantum sensors capable of surpassing classical limits and achieving Heisenberg-limited precision.