Sensing remote nuclear spins (1204.6513v1)

Abstract: Sensing single nuclear spins is a central challenge in magnetic resonance based imaging techniques. Although different methods and especially diamond defect based sensing and imaging techniques in principle have shown sufficient sensitivity, signals from single nuclear spins are usually too weak to be distinguished from background noise. Here, we present the detection and identification of remote single C-13 nuclear spins embedded in nuclear spin baths surrounding a single electron spins of a nitrogen-vacancy centre in diamond. With dynamical decoupling control of the centre electron spin, the weak magnetic field ~10 nT from a single nuclear spin located ~3 nm from the centre with hyperfine coupling as weak as ~500 Hz is amplified and detected. The quantum nature of the coupling is confirmed and precise position and the vector components of the nuclear field are determined. Given the distance over which nuclear magnetic fields can be detected the technique marks a firm step towards imaging, detecting and controlling nuclear spin species external to the diamond sensor.

• The paper demonstrates the detection of remote single nuclear spins by applying the CPMG sequence to amplify weak magnetic signals.
• It employs NV centers in diamond to filter background noise and achieve sensitivity capable of detecting hyperfine couplings as weak as 500 Hz.
• The results extend nuclear spin imaging beyond the immediate diamond vicinity, opening avenues for advanced quantum computing and precision sensing.

Sensing Remote Nuclear Spins: A Detailed Review

The paper "Sensing Remote Nuclear Spins," authored by Nan Zhao, Jan Honert, Berhard Schmid, Junichi Isoya, Mathew Markham, Daniel Twitchen, Fedor Jelezko, Ren-Bao Liu, Helmut Fedder, and Jörg Wrachtrup, presents a significant advancement in the field of quantum sensing. The paper addresses the challenging detection of remote single nuclear spins, specifically in a system involving nitrogen-vacancy (NV) centers in diamonds surrounded by nuclear spin baths.

Remote Nuclear Spin Detection

The paper focuses on single nuclear spin detection, which is a pivotal issue in magnetic resonance imaging techniques due to the inherently weak signals generated by nuclear spins. These signals are typically indistinguishable from background noise when employing conventional methods. This paper introduces an innovative technique using a nitrogren-vacancy (NV) center in a diamond to overcome such limitations. By utilizing dynamical decoupling techniques, specifically the Carr-Purcell-Meiboom-Gill (CPMG) sequence, the researchers amplify the weak magnetic fields from a single nuclear spin located approximately 3 nm from the NV center.

Key Methodological Advances

The significance of this work lies in utilizing the CPMG control sequence to selectively amplify the signal of specific frequencies and suppress unwanted noise, thus drastically enhancing the sensitivity and range of nuclear spin detection. By maintaining high sensitivity and filtering out background noise, the researchers successfully detect single C nuclear spins with hyperfine coupling as weak as 500 Hz. The advanced signal processing allows for the detection of nuclear magnetic fields over a considerable distance, marking an essential development toward nuclear spin imaging and control using diamond defects.

Results and Implications

The paper reports the detection of remote single nuclear spins and confirms the quantum nature of this coupling. This development significantly widens the detection range of nuclear spins beyond the strong coupling regime typically necessary with diamond defects. Consequently, this allows the expansion of nuclear spin imaging techniques beyond the diamond's immediate vicinity. The capability to isolate and measure individual nuclear spins also opens new avenues in quantum information processing, where nuclear spins are used as quantum registers or in a quantum memory context.

The sensitivity improvements allow nuclear spins to be detected at distances up to 10 times greater than previously possible, with more than three orders of magnitude better sensitivity. The research thus facilitates progress in various applications, including structural analysis in life sciences and material research, driven by the ability to discern single nuclear spins with high precision.

Quantum Mechanisms and Decoherence

The paper delineates the quantum nature of the detected signal, as evidenced by negative coherence dips resolved under increased CPMG pulse sequences, which contradict classical decoherence models. The identification of quantum coupling mechanisms attests to the coherent interaction between electrons and nuclear spins, paving the way for more complex quantum manipulations and the incorporation of quantum spin qubits for enhanced quantum computing applications.

Future Directions

The implications of these findings are profound, suggesting that further enhancements to the spatial resolution and sensitivity of NV-based systems could achieve high-resolution single nuclear spin imaging. Immediate future research may involve optimizing NV centers near the diamond surface to detect external nuclear spins. Integrating these techniques into existing NMR methodologies could potentiate advanced nuclear spin control and expand the number of quantum bits around a diamond electron spin, crucial for the development of quantum computing technologies.

Overall, this paper contributes substantially to the field of quantum sensing and imaging, providing a foundation for further studies toward practical applications of NV centers in quantum technologies and spin-based sensing.