Two Nature articles demonstrate for the first time new ways to eliminate errors in quantum computers!

While errors in quantum devices are often hard to detect, researchers have shown that with careful control, some errors can make atoms glow. The researchers took advantage of this ability by performing a quantum simulation using an array of atoms and a laser beam, as shown here. The experiments showed that they could discard the glowing error atoms and make the quantum simulation run more efficiently.

Adam Shaw, co-first author of the new study and a graduate student in the lab of Manuel Endres, a professor of physics at Caltech, said, "It's often hard to detect errors in quantum computers because the mere act of looking for them leads to more errors. But our research shows that with some careful control, we can pinpoint and erase certain errors without any consequences, which is where the name erasure comes from."

Quantum computers are based on the laws of physics in the subatomic realm, such as entanglement, a phenomenon in which particles remain interconnected and mimic each other without direct contact. In this new study, the researchers focused on a quantum computing platform that uses arrays of neutral atoms, or uncharged atoms. Specifically, they manipulated individual alkaline-earth neutral atoms enclosed in "tweezers" made of lasers. These atoms were excited to a high-energy state, known as the "Rydberg" state: a state in which neighboring atoms begin to interact with each other.

Pascal Scholl, the study's other co-first author, explains, "The atoms in our quantum system talk to each other and become entangled."

Entanglement is the key to quantum computers outperforming classical computers. However, nature doesn't "like" to maintain this state of quantum entanglement, Scholl explains: "Eventually, errors will occur that will destroy the entire quantum state. These entangled states can be thought of as a basket full of apples, and the atoms are the apples. Over time, some of the apples will begin to rot, and if these apples are not taken out of the basket and replaced with fresh ones, then all of the apples will rapidly rot. It's not clear how to completely prevent these errors from occurring, so the only feasible way is to detect and correct them."

The new error-catching system is designed in such a way that errant atoms fluoresce or glow when exposed to laser light. Scholl says, "We have images of the glowing atoms that tell us where the errors are, so we can either exclude them from the final statistics or use additional laser pulses to actively correct them."

The theory of implementing erasure detection in neutral atom systems was first proposed by Jeff Thompson, a professor of electrical and computer engineering at Princeton University, and colleagues, and the team recently reported on the technique in the journal Nature.

By eliminating and localizing errors in their system of Rydberg atoms, the Caltech team says they can improve the overall rate or fidelity of entanglement. In the new study, the team reports that only one out of 1,000 pairs of atoms failed to entangle - a tenfold improvement over previous results and the highest rate of entanglement observed in such systems.

Ultimately, these results bode well for quantum computing platforms using the Rydberg Neutral Atom Array. Shaw said, "Neutral atoms are the most scalable type of quantum computer, but until now they have not had high entanglement fidelity."

[4]https://www.nature.com/articles/s41586-023-06516-4