Quantum sensing technology is increasingly drawing attention as quantum science moves closer to practical applications. Quantum sensors utilize quantum phenomena such as superposition and coherent evolution, enabling detection of weak signals including magnetic, electric, and gravitational fields with sensitivity surpassing classical sensors. Such capabilities have broad potential applications in fundamental research, precision measurements, materials analysis, mining and navigation technologies. However, factors such as noise, decoherence, complex measurement setups, and quantum state preparation remain significant hurdles, restricting achievable precision. Developing more precise yet simpler quantum sensing methods within existing hardware is therefore a current research priority.
In a recent study published in Science Bulletin , researchers from the Beijing Academy of Quantum Information Sciences, in collaboration with the University of Electronic Science and Technology of China, the Institute of Physics of the Chinese Academy of Sciences, and other institutions, demonstrated a quantum sensing approach using superconducting qubits. This method incorporates both non-equilibrium dynamics and quantum criticality in a Stark-Wannier localization system. The team observed the propagation of quantum excitations within a superconducting qubit chain to precisely measure gradient field strengths with quantum-limit precision. Importantly, the authors developed a technique that combines measurement outcomes collected at different evolution times, enabling highly precise estimates of gradient field strengths with a limited number of samples obtained through simple, experimentally accessible measurements. This approach avoids the complex measurement setups that are usually required to achieve quantum advantage in conventional criticality-based sensing.
Quantum probes at criticality
The researchers built a Stark-Wannier probe, a quantum system designed to explore the interplay between particle tunneling and a linear gradient potential, using a chain of nine superconducting qubits. This physical system exhibits distinct critical behaviors, characterized by extended and localized phases. In the extended phase, quantum excitations propagate freely across the entire chain. In the localized phase, excitations are confined to limited regions. Experimentally, the researchers initialized a quantum excitation at the chain's center, allowing it to evolve under controlled gradient fields. The propagation patterns varied significantly depending on the field strength: the excitation either diffused widely if the system is in the extended phase, or remained confined locally if the probe is in the localized phase. By accurately tracking and analyzing these patterns, the researchers could precisely determine the external gradient field strengths.
Using non-equilibrium dynamics for quantum sensing
Quantum systems, governed by the Schrödinger equation, display increasingly complex behavior as their evolution extends over time. In quantum sensing, measurement precision can theoretically increase quadratically with longer evolution times, achieving quantum-limit precision. Typically, achieving this precision involves using complex, highly entangled quantum states and advanced measurement techniques, posing considerable experimental challenges. To overcome these challenges, the research team adopted an alternative approach. They collected measurement data at multiple distinct time points and integrated these data within a Bayesian estimation framework. By analyzing these snapshots collectively, the team successfully extracted highly accurate information about the external fields, achieving precision approaching the quantum limit. This method improved measurement accuracy and robustness, especially effective in complex localized phases, thereby enhancing the practicality and accessibility of quantum sensing.
This research demonstrates improvements in quantum sensing precision by integrating non-equilibrium dynamics with quantum criticality. It addresses limitations related to measurement complexity and applicable parameter ranges typical in quantum sensing. The findings suggest potential practical applications in fields such as gravitational and magnetic field measurements, representing an important step towards practical quantum technology deployment.
Science Bulletin
Experimental study