Diamond Defects Achieve Fidelity, Extending Quantum Memory Coherence to Seconds for Networks

Nuclear spins within diamond offer exciting potential as quantum memories for future quantum networks, and researchers are actively seeking ways to control these delicate systems. Jeremias Resch, Ioannis Karapatzakis, and Mohamed Elshorbagy, along with colleagues, now report achieving high-fidelity control of a single carbon nuclear spin linked to a tin-vacancy center in diamond. The team demonstrates a method involving optical and microwave techniques to initialise the combined electronic and nuclear spin state with remarkable precision, and utilises a waveguide to drive radio-frequency signals. This approach yields a coherence time lasting milliseconds, which extends to seconds using advanced dynamical decoupling, and importantly, achieves a single-gate fidelity exceeding ninety percent, establishing a promising building block for robust quantum network nodes.

Nuclear spins offer potential for long-term quantum information storage, but direct control has proven challenging due to weak interactions and difficulties with initialisation and readout. This research overcomes these limitations by leveraging the strong coupling between electron and nuclear spins in solid-state systems. Tin-vacancy centers in diamond offer advantages for quantum technologies, including control using light, long coherence times, and potential scalability.

These centers possess an electron spin manipulated with microwave radiation, crucially interacting with nearby nuclear spins like carbon-13. This interaction allows remote control and readout of the nuclear spin, creating a hybrid quantum system with enhanced capabilities. The team investigated achieving precise control over a carbon-13 nuclear spin strongly coupled to a tin-vacancy center, characterising the interaction and developing control sequences. The research demonstrates that a single carbon-13 nuclear spin coupled to a tin-vacancy center can be reliably initialised and manipulated. The experimental procedure combines optical and microwave techniques to establish a combined electron-nuclear spin state, with subsequent manipulation achieved using microwave pulses and readout via optically detected magnetic resonance. Careful characterisation reveals long coherence times, exceeding one millisecond at cryogenic temperatures, establishing the SnV-coupled carbon-13 nuclear spin as a viable candidate for quantum information storage and processing.

SnV Centers Demonstrate Enhanced Quantum Coherence

This research focuses on utilising tin-vacancy (SnV) centers in diamond as promising candidates for quantum bits (qubits), aiming to achieve long coherence times and precise control for quantum information processing. A key aspect is leveraging surrounding nuclear spins within the diamond lattice to enhance qubit properties and potentially create complex quantum registers, alongside methods for initialising and reading out both the electron spin of the SnV center and surrounding nuclear spins. The research demonstrates relatively long coherence times for both the electron spin of the SnV center and for nuclear spins within the diamond lattice, achieving coherence times exceeding 20 milliseconds for a germanium vacancy center. Progress has also been made in initialising and controlling the nuclear spins surrounding the SnV center, crucial for creating entangled states and building more complex quantum registers.

Detailed spectroscopic investigations provide insights into the energy levels, interactions with surrounding nuclei, and sensitivity to the environment. Precise microwave control over the electron spin of the SnV center enables coherent manipulation of the qubit. The team implemented heterodyne detection for sensitive microwave measurements and demonstrated robust control of individual nuclear spins in diamond. High-quality, isotopically pure diamond samples minimise the influence of unwanted nuclear spins, and coplanar waveguides deliver microwave signals and collect emitted fluorescence. Randomised benchmarking characterised quantum gates, and dynamical decoupling extended coherence times.

The long coherence times and precise control demonstrated make SnV centers in diamond promising candidates for scalable quantum computers. The sensitivity of SnV centers to their environment could be exploited for highly sensitive quantum sensors for magnetic field detection and temperature measurement. The ability to create entangled states between SnV centers could be used for secure quantum communication protocols, and precise control over nuclear spins could be used for new quantum metrology techniques.

Diamond Centre Achieves Second-Scale Nuclear Spin Control

This research demonstrates high-fidelity control of a single carbon-13 nuclear spin coupled to a tin-vacancy (SnV) center in diamond, establishing a promising platform for quantum network nodes. The team achieved high-fidelity initialisation of the nuclear spin using a combination of optical and microwave pumping, and extended the coherence time to over one second through dynamical decoupling techniques. Randomised benchmarking yielded a single-gate fidelity approaching the levels needed for quantum error correction, signifying a substantial step towards practical quantum technologies. The study highlights the potential of SnV centers as spin-photon interfaces due to the combination of long coherence times, high control fidelity, and stable optical transitions. While acknowledging limitations related to estimating the fluctuating spin bath, the authors note that the observed coherence times can be further extended with more advanced pulse sequences. Future work will likely focus on optimising these techniques and exploring the integration of multiple such nodes to build more complex quantum networks, leveraging the demonstrated control and coherence of this system.