Quantum Computers with Recyclable Qubits: A Solution for Reducing Errors

Quantum computers, utilizing qubits formed from extremely cold atoms, are rapidly increasing in size and may soon surpass classical computers in computational power. However, the frequency of errors poses a significant challenge to their practicality. Researchers have now found a way to replenish and recycle these qubits, enhancing computation reliability.

All existing quantum systems are susceptible to errors and are currently unable to perform calculations that would give them an edge over traditional computers. Nonetheless, researchers are making notable advancements in the creation of error correction methods to address this issue.

One approach involves dividing the components of quantum computers, known as qubits, into two primary categories: operational qubits that manipulate data and auxiliary qubits that monitor errors.

Developing large quantities of high-quality qubits for either function remains a significant technical hurdle. Matt Norcia and his team at Atom Computing have discovered a method to lessen the qubit requirement by recycling or substituting auxiliary qubits. They demonstrated that an error-tracking qubit can be effectively reused for up to 41 consecutive runs.

“The calculation’s duration is likely to necessitate numerous rounds of measurement. Ideally, we want to reuse qubits across these rounds, minimizing the need for a continuous influx of new qubits,” Norcia explains.

The team utilized qubits derived from electrically neutral ytterbium atoms that were chilled close to absolute zero using lasers and electromagnetic pulses. By employing “optical tweezers,” they can manipulate each atom’s quantum state, which encodes information. This method allowed them to categorize the quantum computer into three distinct zones.

In the first zone, 128 optical tweezers directed the qubits to conduct calculations. The second zone comprised 80 tweezers that held qubits for error tracking, or that could be swapped in for faulty qubits. The third zone functioned as a storage area, keeping an additional 75 qubits that had recently been deemed useful. These last two areas enabled researchers to reset or exchange the auxiliary qubit as needed.

Norcia noted that it was challenging to establish this setup due to stray laser light interfering with nearby qubits. Consequently, researchers had to develop a highly precise laser control and a method to adjust the state of data qubits, ensuring they remained “hidden” from specific harmful light types.

“The reuse of Ancilla is crucial for advancing quantum computing,” says Yuval Borger from QuEra, a U.S. quantum computing firm. Without this ability, even basic calculations would necessitate millions, or even billions, of qubits, making it impractical for current or forthcoming quantum hardware, he adds.

This challenge is recognized widely across the atom-based qubit research community. “Everyone acknowledges that neutral atoms understand the necessity to reset and reload during calculations,” Norcia asserts.

For instance, Borger highlights that a team from Harvard and MIT employed similar techniques to maintain the operation of their quantum computer using 3000 ultra-cold rubidium atoms for several hours. Other quantum setups, like Quantinuum’s recently launched Helios machine, which uses ions controlled by light as qubits, also feature qubit reusability.