Room temperature entanglement between distant single spins in diamond (1212.2804v1)

Abstract: Entanglement is the central yet fleeting phenomena of quantum physics. Once being considered a peculiar counter-intuitive property of quantum theory it has developed into the most central element of quantum technology providing speed up to quantum computers, a path towards long distance quantum cryptography and increased sensitivity in quantum metrology. Consequently, there have been a number of experimental demonstration of entanglement between photons, atoms, ions as well as solid state systems like spins or quantum dots, superconducting circuits and macroscopic diamond. Here we experimentally demonstrate entanglement between two engineered single solid state spin quantum bits (qubits) at ambient conditions. Photon emission of defect pairs reveals ground state spin correlation. Entanglement (fidelity = 0.67 \pm 0.04) is proven by quantum state tomography. Moreover, the lifetime of electron spin entanglement is extended to ms by entanglement swapping to nuclear spins, demonstrating nuclear spin entanglement over a length scale of 25 nm. The experiments mark an important step towards a scalable room temperature quantum device being of potential use in quantum information processing as well as metrology.

• The paper achieves room temperature entanglement between distinct NV spin qubits with a validated fidelity of 0.67 ± 0.04.
• It employs engineered nitrogen implantation, optical control, and double-quantum transitions to entangle spins over 20–25 nm separations.
• It introduces entanglement swapping from electron to nuclear spins, significantly extending coherence times for scalable quantum processors.

Room Temperature Entanglement Between Distant Single Spins in Diamond

This paper reports a significant achievement in the experimental realization of entanglement between two distinct solid-state spin qubits at room temperature. By utilizing the nitrogen vacancy (NV) centers in diamond, the researchers effectively demonstrate entanglement between electron spins and further successful entanglement swapping to nuclear spins over a spatial separation of approximately 25 nm. This paper marks a critical progression in solid-state quantum technology, particularly emphasizing the capacity to maintain entangled states in ambient conditions without necessitating cryogenic environments.

Methodology and Results

The implementation of entangled stationary qubits using defect pair engineering in diamond and the room temperature operation is of paramount importance. Nitrogen ions $(^{15}N^{+})$ are implanted at a kinetic energy of 1 MeV to create proximal NV center pairs, achieving distances of less than 20 nm. The experimental setup leverages optical and spin physics, where the dipolar interaction between defects forms the basis for entanglement. Employing quantum state tomography, the entanglement is validated with a fidelity of $0.67 \pm 0.04$. The resultant Bell state is generated through the specific series of operations that control the NV center states using microwave pulses. Additionally, the paper highlights the innovative use of double-quantum transitions (DQ) to enhance coupling strength between spins, facilitating precise entanglement at measured distances.

A sophisticated entanglement swapping mechanism is introduced, wherein electron spin entanglement is transferred to nuclear spins, thereby extending the lifetime of the entangled states. The successful extension of nuclear spin coherence times underscores the reliability and potential scalability of diamond-based quantum processors at room temperature.

Implications and Future Directions

The implications of this work are profound for both quantum information processing and quantum metrology. The robust entanglement between spins at room temperature suggests feasibility for real-world applications, bridging laboratory experiments and practical implementations. The scalability potential is emphasized, suggesting pathways toward the development of more complex and larger quantum architectures. Optimize NV center creation through enhanced positional accuracy and density gradient control of implanted nitrogen ions seem to be promising routes for scaling.

One challenging aspect remains the limitation imposed by decoherence mechanisms inherent in the system. Future studies could explore methods to suppress these effects, possibly by leveraging continuous optical excitation which projects increased coherence times into the seconds range. Enhancing coherence properties through improved defect engineering—such as by thinner implantation and advanced surface treatment—will be instrumental.

Overall, this paper makes compelling advances toward establishing a framework for scalable quantum systems operating under ambient conditions and lays the foundation for further exploration into room temperature quantum entanglement applications.