Enhancing qubit connectivity in spin-based quantum computers

The quantum bits involved in quantum computing normally interact at very short distances. Before quantum computers can be effectively realized, they should ideally have “all-to-all connectivity” between their bits, such that the spins comprising those bits are coupled over both small and large distances. Extending this range, however, has been challenging.

Borjans et al. have successfully demonstrated the coupling of two distant spins using a microwave-frequency photon. The study builds on the lab’s previous work, which was the first to demonstrate the long-range coupling between a single spin and photon.

To achieve long-range coupling between multiple spins, the authors retooled a device design they utilized for their previous work, a hybrid semiconductor-superconductor sample that did not easily allow for the coupling of more than one spin to a photon.

The lab replaced the single plunger gate electrode of the device with a split-gate design that could be tuned to bring more than one spin from the semiconductor part of the device into resonance with a photon trapped in a superconducting cavity. They demonstrated the versatility of the new split-gate design by measuring the interaction between a single charge trapped beneath the split-gate and the photon trapped in the cavity.

Co-author Jason Petta said that the lab hopes to continue fine tuning the quality of their results.

“Our research efforts show that long-range, spin-spin entanglement is feasible,” Petta said. “However, significant device improvements will be required before we can achieve high fidelity coupling of distant spins. In the near term, we’ll be focused on improving the spin-photon interaction rate and cavity quality factor.”

Source: “Split-gate cavity coupler for silicon circuit quantum electrodynamics,” by F. Borjans, X. Croot, S. Putz, X. Mi, S. M. Quinn, A. Pan, J. Kerckhoff, E. J. Pritchett, C. A. Jackson, L. F. Edge, R. S. Ross, T. D. Ladd, M. G. Borselli, M. F. Gyure, and J. R. Petta, Applied Physics Letters (2020). The article can be accessed at https://doi.org/10.1063/5.0006442 .