Dressed-state Hamiltonian Engineering Enhances Spin Ensemble Coherence and Delivers 3 dB Sensitivity Gain in AC Magnetometry

Controlling interactions between individual spins is crucial for advances in quantum sensing and many-body physics, but conventional techniques often weaken these vital connections. Haoyang Gao, Nathaniel T. Leitao, and Siddharth Dandavate, at Harvard University, alongside Lillian B. Hughes Wyatt from University of California, Santa Barbara, and colleagues, now present a new method for directly tuning these interactions within a solid-state spin ensemble.

The team achieves this through a technique called dressed-state qubit encoding, manipulating spins under a specific magnetic field, and demonstrates a significant enhancement in coherence compared to existing approaches. This breakthrough not only boosts sensitivity in AC magnetometry, achieving a decibel improvement, but also allows researchers to probe spin transport over extended timescales, offering a powerful tool for future investigations into interacting quantum systems. In quantum science, controlling interactions between spins is crucial for applications ranging from understanding complex materials to developing highly sensitive sensors. Researchers have now developed a new technique for directly tuning these spin-spin interactions, achieving enhanced sensitivity in quantum sensing. This approach overcomes limitations of conventional methods by maintaining strong coupling between spins while simultaneously manipulating them with tailored electromagnetic fields.

The team successfully implemented this method using nitrogen-vacancy (NV) centers in diamond, demonstrating a significant increase in the effective coupling between spins and an external magnetic field, representing a crucial step towards realising high-precision quantum sensors with improved sensitivity and performance. Controlling NV Center Spin Interactions for Sensing This research details significant advancements in using strongly interacting spin systems, specifically nitrogen-vacancy (NV) centers in diamond, for quantum sensing, metrology, and exploring many-body physics. The focus lies on enhancing sensitivity, extending coherence times, and leveraging collective spin dynamics for applications spanning fundamental physics investigations to biological imaging and precision measurement. Researchers have developed techniques to amplify signals in solid-state quantum sensors, potentially enabling the detection of weaker magnetic fields and improving sensitivity, and demonstrated robust methods for engineering the energy landscape of the spin system, allowing for more precise control over its dynamics and improved sensing performance. Crucially, the ability to tune the interactions between spins allows for optimization of sensing parameters and exploration of different quantum states, paving the way for scalable quantum sensors with many interacting spins working together to achieve higher sensitivity and resolution. To extend the duration for which quantum information can be stored, the team employs dynamical decoupling techniques, using carefully timed pulses to protect the spin states from environmental noise. Furthermore, using diamond with specific isotopic compositions helps reduce nuclear spin noise, further extending coherence. Investigations into disordered spin systems reveal glassy dynamics, providing insights into fundamental physics, while exploring critical phenomena, such as phase transitions, potentially leads to new quantum materials and devices. The concept of superspin renormalization suggests that the collective behavior of many spins can lead to emergent properties, and observing and controlling spin hydrodynamic behavior, where spin excitations behave like a fluid, is a promising avenue for creating robust quantum states. Achieving spin squeezing, a technique that reduces noise in one component of the spin state, further enhances precision measurements. These advancements have implications for nanoscale thermometry and temperature control in biological systems, potentially enabling high-resolution imaging of cellular processes, and open up possibilities for precision measurements in various fields, including materials science and fundamental physics.

Enhanced Dipolar Coupling in Nitrogen-Vacancy Centers Scientists have achieved a breakthrough in controlling interactions between quantum bits, specifically nitrogen-vacancy (NV) centers in diamond, through a novel approach to manipulating their quantum properties. This work demonstrates direct tuning of the native dipolar interaction between NV centers, overcoming limitations inherent in existing techniques.

The team applied a magnetic field perpendicular to the crystal lattice orientation, encoding qubits in resulting dressed states and realizing a significant enhancement of the coherence parameter. This enhancement directly addresses a key challenge in exploring many-body phenomena and achieving sensitive quantum sensing. Experiments revealed that by utilizing this perpendicular field configuration, coupled with a pulsed magnetic field to maintain optical contrast, scientists were able to significantly extend the coherence of the NV ensemble, enabling detailed probing of spin transport at intermediate and late timescales, previously inaccessible due to rapid decoherence. Furthermore, the team demonstrated a substantial increase in sensitivity for detecting alternating magnetic fields by tuning the native interaction to a specific point that preserves spin coherence. The research involved encoding qubits in dressed states created by the perpendicular magnetic field, simplifying the system to a two-level structure and allowing for precise control of spin interactions. Measurements confirm that this technique avoids unwanted couplings between the NV electronic spin and its host nitrogen nuclear spin, leading to faster decay of electronic spin coherence.

The team achieved enhanced coherence and subsequently demonstrated a corresponding increase in sensitivity for detecting alternating magnetic fields. This advancement enables the probing of spin transport phenomena at timescales previously inaccessible due to limitations in coherence. The improved coherence and sensitivity open new avenues for investigating complex quantum many-body physics, including emergent hydrodynamics and finite temperature magnetic ordering. Furthermore, the researchers suggest that combining this technique with existing magnetic field gradient methods could facilitate the experimental realization of collective spin squeezing dynamics, potentially leading to further improvements in quantum sensing capabilities for micro- and nanoscale imaging. The authors anticipate that future work integrating this method with high-fidelity spin readout techniques could further enhance magnetic sensitivity in nanoscale applications, and believe that the approach will extend beyond NV centers to encompass other higher-spin systems. 👉 More information 🗞 Dressed-state Hamiltonian engineering in a strongly interacting solid-state spin ensemble 🧠 ArXiv: https://arxiv.org/abs/2512.09043 Tags: