Quantum Sensor Measures Heat and Forces Together

Scientists are developing increasingly precise methods for measuring physical parameters using quantum phenomena, and a new study by Lucas Ferreira R. de Moura and Daniel Y. Akamatsu from the Instituto de Física, Universidade Federal de Goiás, alongside G. D. de Moraes Neto from the Faculty of Civil Engineering and Mechanics, Kunming University of Science and Technology, and Norton G. de Almeida from the Instituto de Física de São Carlos, Universidade de São Paulo, details a novel dispersive quantum thermometry protocol. This collaborative research establishes a metrological hierarchy for estimating both inverse temperature and interaction strength simultaneously, demonstrating that the performance relies on thermal visibility and its derivative. The significance of this work lies in identifying robust quantum states, specifically squeezed and cat states, that outperform ideal states like NOON states in practical sensing scenarios, and validating these predictions through implementation on IBM’s quantum hardware, thereby benchmarking fundamental trade-offs in multiparameter quantum sensing. Scientists are edging closer to exquisitely sensitive detectors capable of measuring multiple properties of quantum systems at once. This advance promises to unlock new possibilities in fields ranging from materials science to medical diagnostics, demonstrating a pathway towards robust quantum sensors that can function reliably even with imperfect equipment. Researchers have developed a new protocol for simultaneously measuring both temperature and the strength of light-matter interactions with enhanced precision. This dispersive quantum thermometry technique employs a nonlinear Mach-Zehnder interferometer coupled to a thermal ancilla, a quantum system used as a reference, to jointly estimate inverse temperature and a dispersive interaction strength. The research establishes that the performance of this method depends solely on the thermal visibility of the system and how that visibility changes, offering a streamlined approach to optimisation. Crucially, the resulting optical state remains simple, allowing for globally optimal measurements using only photon counting, and fully saturating the fundamental quantum limits without requiring complex adaptive feedback mechanisms. Moving beyond theoretical ideals, the study rigorously assesses the protocol’s resilience to realistic noise, specifically concurrent amplitude and phase damping, common sources of error in quantum systems. By analysing the Fisher Information Susceptibility, researchers have established a clear hierarchy of performance for different quantum states. While NOON states, highly entangled states of light, offer the highest theoretical sensitivity, they are exponentially vulnerable to photon loss, rendering them impractical for real-world applications. Squeezed vacuum states emerge as a robust choice for continuous, steady-state sensing, while cat states demonstrate promise for transient thermometry by maintaining significant coherence even when photons are lost. To validate these predictions, the team implemented the protocol as a digital quantum circuit on IBM’s \texttt{ibm_torino} processor. Experimental results confirm the predicted relationship between Fisher information and system parameters, while also revealing systematic noise-induced biases. This demonstrates that even current, noisy intermediate-scale quantum (NISQ) hardware can effectively benchmark the fundamental trade-offs inherent in multiparameter quantum sensing. The work highlights a pathway towards building more versatile and robust quantum sensors capable of simultaneously characterising multiple physical properties. Metrological performance limitations imposed by state fragility and damping Closed-form expressions for the quantum Fisher information matrix reveal that metrological performance depends solely on the thermal visibility and its derivative. Photon counting is a globally optimal measurement strategy, saturating the multiparameter quantum Cramér-Rao bound without requiring adaptive feedback, as the output state remains diagonal in the photon-number basis, simplifying the measurement process and maximising information extraction. Analysis of protocol robustness under concurrent amplitude and phase damping establishes a clear hierarchy of performance among different quantum states. NOON states, while theoretically offering maximal sensitivity, exhibit exponential fragility to loss, with a cubic susceptibility to amplitude damping quantified by χAD F ∝N3, severely limiting their practical application. In contrast, squeezed vacuum states emerge as robust candidates for steady-state sensing, demonstrating resilience against decoherence. Standard cat states prove compelling for transient thermometry, retaining significant coherence even after experiencing photon loss. Digital quantum circuit implementation on IBM’s \texttt{ibm_torino} processor validates these predictions, confirming the predicted Fisher information landscape and revealing systematic noise-induced biases inherent in current hardware.

Fisher Information Susceptibility analysis highlights the impact of decoherence, showing that phase damping induces a quadratic sensitivity for NOON states (χPD F ∝N2). This detailed comparison of state sensitivities provides a crucial guide for selecting optimal quantum states for specific sensing applications and environmental conditions, establishing a framework for understanding and mitigating the effects of noise in multiparameter quantum sensing. Dispersive thermometry via photon counting in a nonlinear Mach-Zehnder interferometer A nonlinear Mach-Zehnder interferometer served as the core of this work’s dispersive quantum thermometry protocol. This interferometer was coupled to a thermal ancilla, allowing for simultaneous determination of both inverse temperature and interaction strength. Closed-form expressions for the quantum Fisher information matrix were derived, demonstrating that the precision of these estimations depends solely on the thermal visibility and its derivative. The study leveraged the unique property of the output state remaining diagonal in the photon-number basis. This configuration renders photon counting a globally optimal measurement strategy, achieving the multiparameter quantum Cramér-Rao bound without requiring adaptive feedback mechanisms. To assess the protocol’s resilience, researchers analysed its performance under concurrent amplitude and phase damping, simulating realistic experimental imperfections. Methodological innovation was introduced through the use of Fisher Information Susceptibility, enabling a comparative analysis of different quantum states. NOON states, while theoretically offering maximal sensitivity, are exponentially fragile to photon loss. Squeezed vacuum states were identified as robust candidates for steady-state sensing, while cat states proved promising for transient thermometry due to their retained coherence even after photon loss. Validation of these theoretical predictions was achieved through digital quantum circuit implementation on IBM’s \texttt{ibm_torino} processor, confirming the predicted Fisher information landscape and revealing systematic noise-induced biases. Joint quantum estimation of temperature and interactions using robust non-classical states The persistent challenge of accurately measuring multiple physical parameters simultaneously has long vexed precision sensing. Existing techniques often suffer from fundamental trade-offs, where improving sensitivity to one property degrades the ability to discern others. This work offers a notable advance by demonstrating a quantum thermometry protocol capable of jointly estimating both temperature and interaction strength, sidestepping some of those limitations. The ingenuity lies in leveraging a nonlinear interferometer and a carefully chosen thermal state, achieving performance that skirts the usual quantum limits without requiring complex adaptive measurements. What distinguishes this approach is its robustness. While highly sensitive “NOON” states are theoretically appealing, their extreme fragility in the face of even minor disturbances renders them impractical for real-world applications. Squeezed vacuum and cat states emerge as viable alternatives, offering a compelling balance between sensitivity and resilience to photon loss, a critical consideration for any practical device. The validation of these predictions on IBM’s quantum hardware is particularly encouraging, suggesting that current technology is capable of benchmarking these fundamental trade-offs. However, the observed systematic noise-induced biases highlight a crucial area for future work. While the digital quantum circuit confirms the predicted theoretical landscape, mitigating these biases will be essential to unlock the full potential of this protocol. Looking ahead, the focus will likely shift towards developing more sophisticated error correction strategies and exploring alternative ancilla states to further enhance both sensitivity and stability. Ultimately, this research contributes to a growing toolkit for building practical quantum sensors capable of tackling complex measurement problems beyond the reach of classical devices. 👉 More information 🗞 The Multiparameter Frontier: Metrological Hierarchy and Robustness in Dispersive Quantum Interferometry 🧠 ArXiv: https://arxiv.org/abs/2602.14420 Tags: