Beyond the quantum error correction threshold! Neutral Atom Array Entanglement Gate Makes Major Progress

Quantum computers are expected to achieve speeds and efficiencies that even today's fastest supercomputers cannot. However, largely due to the inability of quantum computers to self-correct errors, this technology has not yet been widely promoted and commercialized. Unlike classical computers, quantum computers cannot correct errors by repeatedly copying coded data. Scientists must find another way.

Recently, a team of researchers from Harvard University, the Massachusetts Institute of Technology, and QuEra Computing, a leader in the field of neutral atom quantum computers, successfully demonstrated a two-qubit entanglement gate with 99.5% fidelity on 60 parallel neutral atom quantum bits. This quantum breakthrough is the result of extensive testing conducted by Harvard University's Department of Physics and the John A. Paulson School of Engineering and Applied Science, QuEra, MIT's Department of Physics and the Electronics Research Laboratory.

Performing low error rate entanglement quantum operations in a scalable manner is a core element of useful quantum information processing. Neutral atom arrays are a recently emerged promising platform for quantum computing with coherent control over hundreds of quantum bits and arbitrary gate-to-arbitrary gate connectivity in flexible, dynamically reconfigurable architectures. To exceed the quantum error correction threshold, fidelity must be higher than 99% (or an error rate of less than 1%), while the highest fidelity previously achieved in this configuration was 97.5%. By achieving high-fidelity operation in a scalable, highly connected system, MIT, Harvard, and QuEra have laid the groundwork for large-scale implementation of quantum algorithms, error-correcting circuits, and digital simulations.

The key to this fidelity breakthrough lies in an innovative approach to quantum computing based on neutral atoms, which incorporates a range of cutting-edge technologies, including:

- Optimal control. Fast single-pulse gates based on optimal control to ensure the precision and efficiency of entanglement operations.

- Atomic dark states. To reduce scattering and error rates, the team utilizes atomic dark states, a key factor in achieving 99.5% high fidelity.

- Enhanced Rydberg excitation and atomic cooling. Key improvements in Rydberg excitation and atomic cooling techniques further enhance the accuracy of quantum manipulation.

In this new paper, the team reports near-perfect performance of its two-qubit entanglement gate with extremely low error rates. For the first time, they demonstrated the ability to entangle atoms at an error rate of less than 0.5%. In terms of quality of operation, this puts the performance of their technique on par with other leading types of quantum computing platforms, such as superconducting quantum bits and captured ion quantum bits.

However, Harvard's approach has a significant advantage over these competitors because of its large system scale, efficient quantum bit control, and ability to dynamically reconfigure the atomic layout.

The Harvard team's advances are reported in the same issue of Nature as other innovations led by former Harvard graduate student Jeff Thompson (now at Princeton University) and former Harvard postdoc Manuel Endres (now at Caltech). Taken together, these advances lay the groundwork for quantum error-correction algorithms and large-scale quantum computation; all of which means that quantum computing on arrays of neutral atoms is showing its promise.

Lukin said, "These contributions open the door to exceptional opportunities in scalable quantum computing, and there are truly exciting times ahead for the entire field."