Trapped ion qubits have the best coherence times and the highest fidelity entangling gate operations of all platforms. In addition to the gates between nearby trapped ion qubits through their Coulomb interaction, they can also be entangled at a distance through photonic interconnects. Over the past few decades, we have improved the photonic entanglement rate by almost 6 orders of magnitudes, recently hitting 250 Hz. While this seems pretty slow, it is still the fastest photonic interconnect between quantum memories ever demonstrated. We use sympathetic cooling of a different species ion to absorb the heating from the repeated atom excitation, and collect photons with NA-0.8 obectives. By encoding photonic qubits with time-bin wavepackets, we eliminate many errors from conventional polarization encoding, and demonstrate an entanglement fidelity >97%, with much higher fidelities expected in the future. In the course of this research, we discovered a new error source stemming from residual recoil between the two atomic qubits, and show how to eliminate it by synchronizing the atomic motion with the time bins, or adding auxliary operations that “rewind” the recoil.
- “Entanglement fidelity limits of photonically-networked atomic qubits from recoil and timing,” Yichao Yu, Sagnik Saha, Mikhail Shalaev, George Toh, Jameson OReilly, Isabella Goetting, Ashish Kalakuntla, Christopher Monroe, arXiv:2503.19818 (2025).
- “Fast photon-mediated entanglement of continuously-cooled trapped ions for quantum networking,” J. O’Reilly, G. Toh, I. Goetting, S. Saha, M. Shalaev, A. Carter, A. Risinger, A. Kalakuntla, T. Li, A. Verma, and C. Monroe, Phys. Rev. Lett. 133, 090802 (2024).
- “High-fidelity remote entanglement of trapped atoms mediated by time-bin photons,” S. Saha, M. Shalaev, J. O’Reilly, I. Goetting, G. Toh, A. Kalakuntla, Y. Yu, and C. Monroe, Nature Comm. 16, 2533 (2025).
- “Ion Trap with In-Vacuum High Numerical Aperture Imaging for a Dual-Species Modular Quantum Computer,” A. L. Carter, J. O’Reilly, G. Toh, S. Saha, M. Shalaev, I. Goetting, and C. Monroe, Rev. Sci. Instrum. 95, 033201 (2024),
