Local spin qubits reveal non-Gaussian magnetic noise in materials

Nitrogen vacancy (NV) centers in diamond now enable magnetic field noise studies with nanometer scale spatial resolution, a precision previously unattainable. Researchers Jonathan Curtis, Amir Yacoby, and Eugene Demler detail methods to move beyond analyzing Gaussian noise processes with spin qubits, allowing measurement of higher-order magnetic noise cumulants locally. The work unveils two protocols for this, and demonstrates how fluctuation dynamics converge towards the central limit theorem as a function of effective bath size using models of both non-interacting two-level systems and systems near a second-order Ising phase transition.

Diamond Spin Qubits Enable Nanoscale Magnetic Noise Study

This advancement unlocks the potential to characterize complex magnetic behaviors that were previously hidden by the limitations of linear-response techniques. The researchers published their findings in the journal Quantum on August 27, 2026, outlining two distinct protocols for achieving this enhanced sensitivity. The first protocol utilizes a single spin qubit and employs varied dynamical decoupling sequences to detect non-Markovian and non-Gaussian spin-echo noise. This approach allows for a more complete picture of the noise environment, moving beyond the simplified assumptions of traditional methods.

Complementing this, the second protocol leverages two-qubit coincidence measurements to investigate spatially non-local cumulants in the magnetic noise, offering insights into correlations that extend beyond the immediate vicinity of the qubits. The ability to probe both local and non-local noise characteristics represents a step forward in materials characterization, potentially revealing subtle magnetic interactions and phenomena.

This convergence is a fundamental concept in statistics, and its observation in a real many-body system provides valuable validation of the methodology. The implications of this work extend to a wide range of materials science applications, particularly in the study of quantum materials and devices. Higher-order nonlinear correlations, now accessible through this method, can directly probe the interactions between magnetic and electronic excitations within a crystal.

This is especially relevant for detecting phase transitions and other critical phenomena, where subtle changes in magnetic noise can signal shifts in the material’s fundamental properties. The use of multiple defect qubits allows for the study of non-local correlations, a feature difficult to achieve with traditional methods. This capability opens doors to understanding how energy, magnetization, charge, and information are transported across a sample, providing a more holistic view of the material’s behavior. The researchers note that this approach builds on previous work.

The team’s work also connects to broader efforts in nanoscale sensing. The ability to combine high spatial resolution with sensitivity to non-Gaussian noise opens up new avenues for exploring the complex interplay between quantum phenomena and material properties. The researchers conclude by discussing promising applications and extensions of their method, suggesting that this technique could become a cornerstone of future materials characterization efforts. The ability to map magnetic noise with nanometer precision and to capture non-Gaussian correlations promises to reveal hidden details about the behavior of quantum materials.

Non-Gaussian Cumulants Measured via Dynamical Decoupling

Dynamical decoupling minimizes the impact of environmental noise on qubit coherence, and by tailoring these sequences, the team can isolate and quantify non-Gaussian contributions to the noise spectrum. This dual approach provides a comprehensive toolkit for dissecting the intricate nature of magnetic noise. The central limit theorem predicts that the sum of many independent random variables will tend towards a Gaussian distribution; deviations from this behavior indicate the presence of correlations or non-linearities in the underlying noise processes.

The ability to probe these correlations with nanometer precision opens up possibilities for studying a wide range of materials, from high-temperature superconductors to complex magnetic systems. The team’s models also considered a bath of non-interacting two-level systems, allowing them to validate their protocols and demonstrate their ability to accurately characterize the noise statistics.

They further extended their analysis to a system near a second-order Ising phase transition, a scenario where strong correlations and critical fluctuations are expected to dominate the noise behavior. They also highlight the potential for combining their technique with other nanoscale probes to create a more complete picture of material properties.

Two-Qubit Coincidence Reveals Spatially Resolved Noise

Investigations into magnetic fluctuations largely relied on analyzing Gaussian noise, a simplification that overlooks crucial details in many materials. This work details methods to measure higher-order magnetic noise cumulants, providing a more complete picture of complex magnetic environments. These advancements promise deeper insights into the behavior of quantum materials and devices, potentially unlocking new avenues for technological innovation. The team’s approach centers on nitrogen vacancy (NV) centers in diamond, defects within the crystal lattice that function as sensitive spin qubits.

These NV centers allow for spatially resolved measurements of magnetic fields at the nanoscale, a level of detail unattainable with conventional techniques. The utility of these protocols was demonstrated through modeling a bath of non-interacting two-level systems, validating the methodology against a relatively simple scenario.

Crucially, the two-qubit coincidence protocol allows for the measurement of spatial correlations in magnetic noise. This is a significant leap forward, as previous techniques were largely limited to characterizing noise at a single point in space. By comparing measurements from two spatially separated qubits, the team can determine how magnetic fluctuations are correlated over nanometer distances.

The implications extend beyond fundamental physics; for example, the team draws connections to earlier investigations into noise magnetometry, including studies of and related phenomena. The team’s models also considered the impact of spatial correlations on the measured noise demonstrating how the technique can be used to extract information about the range and strength of these correlations.

This is particularly important for understanding systems where long-range interactions play a significant role, such as in certain types of magnetic materials. The researchers emphasize that the two-qubit approach is not merely a refinement of existing techniques, but a fundamentally new way to probe magnetic noise, offering access to information previously hidden from view. The researchers also note that the protocols they have developed are not limited to specific materials or systems.

The underlying principles can be applied to a wide range of quantum materials, offering a versatile tool for materials science research. They anticipate that this technique will be particularly valuable for studying systems where non-Gaussian noise is dominant, such as those exhibiting strong electron-electron interactions or complex magnetic ordering.

Non-Interacting Two-Level Systems Model Noise Dynamics

This advancement allows for a more complete understanding of complex magnetic phenomena in materials and devices. The team’s work centers on two distinct protocols for probing non-Gaussian noise. This approach effectively captures the ‘memory’ of the noise, revealing how past fluctuations influence present measurements. To validate these protocols, the researchers modeled systems of non-interacting two-level systems, a common approximation for many disordered materials. Understanding this convergence is crucial for accurately interpreting noise measurements and extracting meaningful information about the underlying physical processes.

Previous methods often relied on simplifying assumptions about the noise or lacked the spatial resolution to probe local fluctuations. The two-qubit approach, in particular, offers a powerful way to disentangle local and non-local contributions to the noise, providing a more complete picture of the system’s behavior.

These interactions are often responsible for a wide range of physical properties, including magnetism, superconductivity, and optical absorption. By measuring higher-order noise cumulants, the team believes it is possible to directly probe these interactions and gain new insights into the behavior of complex materials. The researchers anticipate that their technique will be valuable for studying systems exhibiting non-Gaussian noise, a characteristic often found in strongly correlated materials and disordered systems.

These materials are known to exhibit complex behavior that is difficult to capture with traditional methods. By providing a way to directly measure non-Gaussian noise, the team hopes to unlock new insights into the fundamental physics of these materials and pave the way for the development of new technologies. The researchers’ findings were published in Quantum, and represent an advance in the field of nanoscale magnetic noise characterization.

By combining the sensitivity of NV centers in diamond with novel measurement protocols, they have opened up new possibilities for studying the complex magnetic properties of materials and devices. The ability to probe non-Gaussian noise with nanometer-scale resolution promises to be a powerful tool for materials scientists and quantum technologists alike.