Pump-free Microwave-Optical Quantum Transduction Generates Time-Bin Bell Pairs Without Optical Pumping

Quantum networks promise revolutionary advances in communication and computation, but building them requires efficient conversion between microwave and optical frequencies, a process known as quantum transduction. Fangxin Li, Jaesung Heo, Zhaoyou Wang, and colleagues at the University of Chicago now demonstrate a significant step towards this goal with a novel pump-free transduction scheme. The team overcomes a key limitation of current approaches, the unavoidable heating caused by optical pumping, by generating entanglement between microwave and optical photons using colour centres and a specially designed resonator. Simulations reveal this method achieves a heralding rate exceeding one kilohertz with near-unity fidelity, establishing a promising new source for the microwave-optical Bell pairs essential for long-distance quantum communication and distributed quantum computing.

This innovative approach utilizes a mechanical resonator to mediate the interaction between these different frequencies, carefully engineered to maximize coupling strength and minimize unwanted noise. This pump-free scheme promises to simplify quantum systems and reduce overall system noise. The team demonstrates a conversion efficiency exceeding ten percent, a significant improvement over previous pump-free methods and approaching the performance of systems that rely on energy-intensive pumps. Furthermore, the system achieves a bandwidth of one megahertz, sufficient for encoding and transmitting quantum information, and the generated optical photons exhibit the characteristics expected of single photons. This advancement paves the way for scalable and practical quantum networks by eliminating the need for complex pump infrastructure.

Microwave-Heralded Entanglement of Color Center Photons

This research details a protocol for generating entangled photon pairs using color centers, specifically, defects in diamond known as Nitrogen-Vacancy (NV), Silicon-Vacancy (SiV), and Tin-Vacancy (SnV) centers. The method relies on detecting a microwave signal to confirm that entanglement has been successfully created, a process known as heralding. The team conducted detailed simulations to optimize the protocol parameters and maximize the rate at which high-fidelity entangled photons are generated. The research demonstrates that the protocol’s success depends on carefully balancing detection time with the overall rate of entanglement. Longer detection times increase the probability of identifying a signal, but also extend the duration of each attempt. Simulations reveal an optimal detection time that maximizes the heralding rate for each color center, with SiV centers offering the highest rate, followed by SnV and NV centers.

Pump-Free Microwave-Optical Entanglement Generation Demonstrated

Researchers have demonstrated a new pump-free method for generating microwave-optical Bell pairs, essential components for distributed quantum computing and networking. By utilizing a single color center in diamond, the team designed a system that coherently converts between microwave and optical frequencies without requiring an energy-intensive optical pump. Simulations indicate this approach can achieve a heralding rate exceeding one kilohertz with near-unity fidelity, establishing a promising source for creating entangled states across different quantum platforms. The team’s design integrates a strongly-coupled microwave resonator with a high-cooperativity optical cavity, enabling efficient conversion between quantum states.

Notably, nitrogen-vacancy (NV) centers slightly outperformed tin-vacancy (SnV) centers in generating Bell pairs, due to a larger magnetic dipole moment, although the SnV center remains viable for applications requiring zero-field operation. This work establishes the feasibility of a novel approach to quantum transduction, potentially overcoming limitations associated with traditional pump-based systems. The authors suggest extending the protocol to utilize an ensemble of emitters to boost coupling rates and highlight the importance of achieving clean interfaces between diamond and superconducting materials, suggesting crystalline dielectrics and niobium as promising materials for future device fabrication.