QuTech has developed an improvement to diamond nitrogen-vacancy (NV) centre qubits, significantly boosting photon collection probability. Their new device achieves a 0.5 percent probability, a ten-fold increase over existing 0.05 percent rates. This advancement could raise future entanglement rates and contribute to more realistic, practical quantum networks.
Fabry–Pérot Microcavity Boosts NV Centre Photon Extraction
A Fabry–Pérot microcavity integrated with a diamond nitrogen-vacancy (NV) centre significantly enhances photon extraction for quantum networking. This device uses two highly reflective mirrors—one on a chip and one on an optical fibre—creating a resonant cavity tuned to the NV centre’s optical transition. Consequently, the probability of collecting useful photons increases to 0.5 percent, a ten-fold improvement over previous solid immersion lens designs which operated at 0.05 percent. This boosted photon collection directly addresses a major bottleneck in building quantum networks by enabling faster entanglement between distant NV qubits.
Researchers demonstrated the system’s ability to generate spin–photon states and even a three-qubit GHZ state, confirming its functionality as a complete quantum network node. Furthermore, measurements suggest a potential to exceed one percent detection probability with improved excitation, paving the way for scalable quantum repeater designs.
Integrated Microwave Control Maintains Spin Coherence
Maintaining the diamond NV centre’s functionality as a qubit required integrating microwave control directly into the device. A microwave stripline embedded within the mirror substrate enables fast, coherent spin rotations at approximately ten megahertz. Crucially, Ramsey and Hahn-echo measurements confirmed spin coherence exceeding one hundred microseconds – sufficient timing for generating spin-photon states despite the added complexity. This integrated approach ensures the qubit’s reliability isn’t compromised while boosting photon collection. The system maintains spin coherence even with the microwave components present, allowing for both control of the qubit and efficient photon emission. This balance is essential for creating a functional quantum network node capable of fast entanglement generation and, ultimately, practical long-distance quantum communication.
For years, the community has known that NV centres have the right stability and coherence for quantum networks. What held us back was the limited number of useful photons we could extract.
Ronald Hanson
Demonstrated GHZ State Generation Verifies Quantum Networking Potential
The team successfully generated a three-qubit GHZ state, demonstrating the platform’s capacity for complex quantum operations essential for networking. This GHZ state relied on correlations between the spin of the NV centre and two emitted photons, confirming the system functions as a complete spin-photon interface. Observing the expected correlations between photon arrival times and spin outcomes verified its suitability for creating entanglement. This advancement addresses a core limitation in quantum networking by boosting photon collection probability to 0.5 percent—a ten-fold improvement. Measurements suggest even higher probabilities, exceeding one percent per pulse, are achievable with further refinement of the optical excitation.
