Quantum protocol achieves Heisenberg-limited measurement precision with robust spin states

Researchers from the National University of Singapore (NUS) have achieved exciting progress in quantum metrology, a field that harnesses quantum effects to make measurements with unprecedented accuracy. Their newly developed protocol could potentially benefit emerging technologies such as navigation and sensing of extremely weak signals.

Quantum metrology exploits the unique properties of quantum systems to achieve sensitivities far exceeding classical limits. Pushing beyond the so-called standard quantum limit (SQL) to reach the ultimate Heisenberg limit (HL) typically requires highly entangled quantum states, such as Greenberger–Horne–Zeilinger (GHZ) states. However, these states are extremely challenging to generate, maintain, and measure, as they are highly susceptible to environmental noise and readout errors, which are major obstacles for practical deployment.

Led by Professor Gong Jiangbin from the Department of Physics at the NUS Faculty of Science, the research team has developed a novel strategy that eliminates these roadblocks. Their method leverages quantum resonance dynamics in a periodically driven spin system, a well-studied model called the quantum kicked top.

Instead of beginning with a fragile, highly entangled state, their protocol starts with a robust and easily prepared SU(2) spin coherent state. Through precisely designed periodic interactions, this simple initial state evolves naturally into strongly entangled states that encode quantum information. At special resonance conditions, the system returns to its original coherent state due to quantum recurrence, enabling both straightforward preparation and robust readout.

The research findings were published in the journal Physical Review Letters on 11 June 2025.

Prof Gong said, “This round-trip evolution means we can start and end with a stable, experimentally friendly state, while still harnessing the quantum-enhanced sensitivity typically associated with more challenging entangled states.”

The team showed that their protocol achieves Heisenberg-limited measurement precision. The quantum Fisher information (QFI), a fundamental quantity that determines the best achievable precision, grows quadratically with both the number of particles (spins) and the sensing time.

Unlike earlier approaches, this optimal scaling can be sustained over extended durations and remains robust even in the presence of Markovian noise, a common form of environmental decoherence in quantum systems. Even under such noise, the protocol maintains near-Heisenberg scaling with the number of spins, marking a significant advance in practical quantum metrology.

One of the major advantages of this approach is its experimental feasibility. The protocol can be implemented using existing quantum hardware, including platforms based on trapped ions or cold atoms, simply by tuning operating parameters, and no specialized equipment or complex state preparation is required.

“This work demonstrates that ultra-precise quantum measurements are achievable without the usual difficulties. By avoiding complicated state preparation and improving resilience to noise, our approach opens new possibilities for practical and scalable quantum sensing,” added Prof Gong.

This development represents a conceptual advancement in quantum metrology, providing an experimentally accessible and noise-resilient route to Heisenberg-limited measurement precision. By leveraging quantum resonance dynamics with simple initial states, the protocol overcomes longstanding obstacles of state preparation and readout, paving the way for practical implementation in next-generation quantum sensing technologies.