Quantum Sensing: Coherent Nuclear Spin Dynamics Unveiled Using Diamond’s Nitrogen-Vacancy Centers

The interaction of a central spin qubit with surrounding spins is crucial in quantum information processing (QIP). A study has used an ensemble of nitrogen-vacancy (NV) centers in diamond to probe the coherence of P1 centers and detect interactions between P1 spins and 13C nuclei. The results reveal a remarkably coherent interaction within a many-body spin bath, which could be of interest to schemes that use P1 spins as reporter spins or probes of many-body physics. This could lead to the development of more efficient and precise quantum sensing and information processing systems.

What is the Significance of Sensing Coherent Nuclear Spin Dynamics?

The study of how a central spin qubit interacts with a bath of surrounding spins is a prominent feature in quantum sensing. This interaction is crucial in quantum information processing (QIP) where precise knowledge and control of the spin environment facilitates a resource for storing, entangling, and measuring quantum states. Diamond, a widely studied widebandgap semiconductor, hosts spin qubits with applications in quantum sensing and information processing. The optically active nitrogen-vacancy (NV) center in diamond can be used to measure and control the optically inactive manybody spin environment surrounding it.

For natural abundance diamond, the dominant spin environment is composed of spin-12 13C nuclei and substitutional neutrally charged nitrogen impurities (P1 centers). Much effort has been invested in schemes to eliminate the influence of these spins on the NV coherence for quantum sensing. The 13C spins around individual NV centers, however, weakly couple to magnetic fields and as such possess intrinsically long spin coherence times that are highly amenable to schemes for storing, processing, and retrieving quantum information.

The ability to control, polarize, and entangle P1 centers near NVs has positioned the P1 itself as a potential platform for quantum information processing. The tunable coupling of the P1 center to both control fields and other spins in the diamond can be utilized for enhanced sensing schemes in which the P1 electron spins act as useful ancillae or reporter sensors.

How are Nitrogen-Vacancy Centers Used in Quantum Sensing?

In this work, an ensemble of NV centers in diamond is used to probe the coherence of the optically dark P1 centers and detect coherent interactions between the P1 spins and 13C nuclei, despite having no initialization of either spin ensemble. Periodic collapses and revivals in the coherence of the P1 spins are observed, and these modulations are induced by coherent interactions between the P1 centers and a local bath of 13C nuclear spins.

Interestingly, the local 13C spins surrounding the probing NV centers are independent from the P1 coupled nuclear spin bath. This is shown by varying the degree to which dynamical decoupling protocols isolate the NV center from the combined spin bath. The observations are well explained by numerical simulations of the P1-13C spin bath. Clear 13C revivals are observed without initialization or controlled polarization of the P1 spins and despite the presence of room-temperature Jahn-Teller reorientation, strong anistropic hyperfine broadening, and the proximal NV center.

What are the Implications of this Study?

These results reveal a remarkably coherent interaction at play within a many-body spin bath. This will be of interest to schemes that employ P1 spins as reporter spins or as probes of many-body physics. It could also serve as a remote electronic spin node in an NV-13C quantum information processing network.

The study should further stimulate the renewed theoretical attention devoted to the spin physics of P1 centers. The ability to control, polarize, and entangle P1 centers near NVs has positioned the P1 itself as a potential platform for quantum information processing. The tunable coupling of the P1 center to both control fields and other spins in the diamond can be utilized for enhanced sensing schemes in which the P1 electron spins act as useful ancillae or reporter sensors.

How was the Experiment Conducted?

The experiment considered an ensemble of spin-1 NV centers interacting with an ensemble of P1 centers and a bath of 13C nuclear spins. A diamond sample with a 1.1% natural abundance of 13C and a nitrogen concentration of 1 ppm was used. A magnetic field was applied along the 111 crystallographic axis, spectrally selecting out a single NV orientation class. The magnetic field lifts the degeneracy of the mS=1 spin states of the NVs, allowing work in the effective spin-1/2 subspace. Microwaves for NV driving and rf for P1 control were synthesized using an arbitrary waveform generator.

What are the Future Directions of this Research?

The results of this study offer new insight into the interactions within a many-body system. The ability to sense coherent nuclear spin dynamics with an ensemble of paramagnetic nitrogen spins opens up new possibilities for quantum sensing and information processing. Future research could focus on further understanding the interactions between P1 centers and their own 13C spin bath, which has been somewhat overlooked despite several works revealing nontrivial effects such as P1-13C-mediated hyperpolarization and spin torques. This could lead to the development of more efficient and precise quantum sensing and information processing systems.