Floquet Dynamics in Three-Qubit Systems Enables Selective Metrology and Enhanced Sensitivity to Ising Interactions

Periodically driven quantum systems offer exciting possibilities for precision measurement, and a team led by Asghar Ullah, Hasan Mermer, and Melih Özkurt from Koc University, alongside collaborators including Igor Lesanovsky from Universitat Tubingen and Özgür E. Müstecaplıoğlu from Koc University and TUBITAK Research Institute for Fundamental Sciences, now demonstrates how to exploit these systems for selective metrology. The researchers investigate a three-qubit system and reveal a unique dynamical phase where sensitivity to external parameters becomes sharply asymmetric. This means the system excels at precisely measuring the strength of interactions between qubits while simultaneously minimising sensitivity to unwanted magnetic fields, effectively acting as a parameter filter. By identifying and harnessing this period-doubling phase, the team shows how to tailor quantum systems for targeted sensing applications, offering a pathway towards more robust and accurate quantum technologies.

Period-Doubling Enhances Parameter Estimation Precision

Scientists demonstrate that periodically driven quantum systems can function as highly selective filters for parameter estimation, achieving this capability within a three-qubit system governed by the transverse-field Floquet Ising model. Their work identifies a period-doubling (PD) dynamical phase exhibiting a stark asymmetry in sensitivity to both the magnetic field applied to the qubits and the coupling strength between them. This PD phase originates from a phenomenon termed “-pairing”, where the initial state strongly overlaps with -paired Floquet eigenstates, resulting in robust period-doubled dynamics and enhanced sensitivity. Analysis reveals that the PD regime significantly enhances precision when estimating the Ising interaction strength, while simultaneously suppressing sensitivity to the transverse magnetic field.

Conversely, non-PD regimes prove optimal for sensing the transverse field, establishing a clear trade-off in sensing capabilities. This research reveals a new approach to quantum sensing, where the system’s dynamics are tailored to selectively enhance the measurement of specific parameters. The team investigated a three-qubit system driven by a repeating force and discovered that a particular state, called period-doubling, dramatically improves the ability to measure the strength of interactions between the qubits. Simultaneously, this state minimizes the system’s response to external magnetic fields.

Non-period-doubling states, conversely, excel at measuring magnetic fields, creating a clear trade-off in sensing capabilities. The team confirmed that this selective sensitivity persists even as the system grows larger, suggesting scalability for future quantum sensors. They demonstrated that the observed improvements are quantifiable using readily measurable properties, such as magnetization and correlations between qubits. This means the metrological advantage is not merely theoretical, but can be extracted using standard measurement techniques on existing quantum computing platforms like trapped ions or superconducting circuits. These findings position small-scale Floquet systems as powerful, tunable tools for near-term quantum sensing, offering a pathway to targeted sensing applications by harnessing distinct dynamical regimes.

Selective Precision via Periodically Driven Systems

This research demonstrates that periodically driven quantum systems can function as selective parameter filters, enhancing precision for estimating specific system properties while suppressing sensitivity to others. By investigating a three-qubit system governed by the transverse-field Floquet Ising model, scientists identified a period-doubling dynamical phase exhibiting a stark asymmetry in its response to magnetic fields and qubit coupling strength. Analysis reveals that this period-doubling phase significantly improves the precision with which the Ising interaction strength can be estimated, simultaneously reducing sensitivity to the transverse magnetic field, a behaviour reversed in non-period-doubling regimes. The team’s findings represent a key achievement in quantum sensing, showing how complex interactions within a few qubits can be harnessed for precise measurements.

They discovered that by carefully controlling the way the system is driven, they could selectively enhance the ability to measure certain parameters while minimizing the influence of others. This selective control is crucial for building sensors that can operate effectively in noisy environments. The researchers confirmed that the observed improvements are experimentally accessible through measurements of readily observable quantities like magnetization and two-qubit correlations. This means the metrological advantage is not merely theoretical, but can be extracted using standard measurement techniques on existing quantum computing platforms.

While acknowledging this work as a proof-of-concept, the authors note that further investigation is needed to assess the stability of these period-doubling signatures against environmental noise and imperfections in the driving force. Future research will focus on exploring how this metrological advantage scales with system size and employing optimal control techniques to enhance both stability and selectivity. Ultimately, these findings could contribute to the development of many-body time crystals and other advanced quantum technologies.