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),
Typical qubit gate operations are binary, involving operations with up to just two qubits. While this can be universal, it is more efficient for almost all quantum circuits to directly entangle qubits with N-body interactions. With trapped ions, gates are typically realized by applying optical state-dependent displacements to the ions. By instead using state-dependent squeezing forces, the workhorse quantum gate between pairs of trapped ions is extended to an N-qubit gate. This is an important shortcut for most quantum circuits such as quantum error-correction encoding and quantum optimization circuits, while also providing direct N-body interactions for quantum simulations of many-body quantum systems.
![Encoding and stabilizer readout schematic for the Bacon-Shor [[9,3,1]] error correction process.](https://iontrap.duke.edu/files/2021/10/FTQEC-1024x331.jpg)
Profs. Christopher Monroe and Michael Raymer spearheaded the U.S. National Quantum Initiative (NQI
In one of the largest quantum simulations ever performed, up to 53 trapped ion qubits have been used to simulate properties of many body magnetic interactions. The qubits are each prepared with individual control, and measured in a single shot with nearly 100% efficiency. This allows the observation of arbitrary correlation functions that cannot be calculated. This restricted quantum computer becomes fully programmable and reconfigurable with straightforward modifications in the control lasers.
Connectivity between qubits in a quantum computer may be as important as clock speed and gate fidelity when it comes time to build large-scale quantum computers. We run several quantum algorithms on two 5-qubit programmable quantum computers: 