Quantum Thermometric Sensing Achieves Precision Bounds Via Coupled Qubits and Fisher Information Analysis

Precise temperature measurement, or thermometry, remains a critical challenge across diverse scientific and technological fields, and researchers are continually seeking ways to improve sensor sensitivity and accuracy. Seyed Mohammad Hosseiny, Abolfazl Pourhashemi Khabisi, Jamileh Seyed-Yazdi, and colleagues investigate novel approaches to quantum thermometry, focusing on the fundamental limits of precision achievable with coupled quantum sensors. The team explores both direct, local temperature estimation and a more complex remote method utilising quantum teleportation, demonstrating that direct measurement consistently outperforms remote techniques due to the benefits of immediate sensor-environment interaction. This work, which models sensor behaviour using principles of quantum mechanics and statistical thermodynamics, reveals key relationships between sensor parameters, such as energy levels and coupling strength, and overall temperature sensitivity, offering pathways to optimise future quantum thermometry devices. The findings represent a significant step towards developing highly accurate and efficient temperature sensors for applications ranging from materials science to biological imaging.

Quantum thermometry leveraging quantum sensors is investigated, with an emphasis on fundamental precision bounds derived from quantum estimation theory. The proposed sensing platform consists of two dissimilar qubits coupled via a capacitor, which exhibit quantum oscillations in response to thermal environments. Researchers modelled thermal equilibrium states using the Gibbs distribution to accurately characterize sensor behaviour. The sensitivity of this quantum thermometer was rigorously assessed using both the Quantum Fisher Information (QFI) and the Hilbert-Schmidt Speed (HSS), serving as stringent criteria for performance.

Qubit Coupling Enables Precision Quantum Thermometry

This work presents a breakthrough in quantum thermometry, demonstrating a highly sensitive method for measuring temperature using coupled qubits. Scientists achieved precise temperature estimation by leveraging the quantum properties of these sensors. Systematic analysis revealed a crucial relationship between key parameters, qubit energies and coupling strengths, and the resulting temperature sensitivity, providing pathways for optimization. Experiments demonstrate that increasing the mutual coupling energy between qubits enhances sensor sensitivity, while increasing Josephson energies diminishes it.

Researchers investigated two distinct thermometry paradigms: direct temperature estimation by the sensor itself, and remote estimation via quantum teleportation. Results demonstrate a clear advantage for direct measurement, yielding superior sensitivity compared to remote estimation, due to the direct interaction between the sensor and the thermal environment. This direct coupling allows for a more precise measurement of temperature, while the teleportation process introduces noise that degrades sensitivity. This study establishes a crucial trade-off between direct sensing and remote state transfer in quantum metrology.

Scientists confirmed that the fidelity criterion, a measure of successful quantum state transfer, remains intact throughout the process. This research has broad implications for applications requiring ultra-precise temperature measurements, including cryogenic thermometry, in vivo nano-thermometry, on-chip hot-spot mapping, distributed environmental monitoring, and point-of-use thermal validation. This research delivers a significant advancement in quantum sensing technology, paving the way for more accurate and efficient temperature measurements across diverse scientific and technological fields.

Remote Thermometry Beats Classical Limits

This research presents a detailed investigation into quantum thermometry, focusing on the fundamental limits of precision achievable with a novel sensor architecture. Scientists developed a platform consisting of two dissimilar qubits coupled via a capacitor, which oscillates in response to thermal environments. Through rigorous analysis using quantum estimation theory, specifically the quantum Fisher information and Hilbert-Schmidt speed, the team identified key parameters influencing sensor sensitivity, demonstrating how optimization of qubit energies and coupling strengths can maximize thermal resolution. The study compared two distinct thermometry approaches: direct, local temperature estimation and remote estimation facilitated by quantum teleportation.

Results consistently show that direct measurement provides superior sensitivity, owing to the direct interaction between the sensor and the thermal environment, which minimizes noise. Importantly, the analysis reveals that increasing Josephson energies reduces sensor sensitivity, while stronger capacitive coupling between the qubits enhances it. These findings have implications for a range of applications, including ultra-precise cryogenic thermometry, nanoscale biological temperature measurement, on-chip thermal profiling, environmental monitoring, and thermal validation processes. The authors acknowledge that the performance of remote estimation is suppressed at higher temperatures, potentially due to increased thermal noise or limitations in the quantum channel. Future work could explore strategies to mitigate these effects and further refine the sensor design for improved performance across a wider temperature range. This research establishes a strong foundation for developing advanced quantum sensors with unprecedented precision and broad applicability in diverse scientific and technological fields.