Researchers have developed a new error correction system for quantum computers that uses qLDPC codes and reconfigurable atomic arrays to reduce physical qubit requirements, making them more scalable and efficient. Credit: SciTechDaily.com
Researchers at the Pritzker School of Molecular Engineering have developed a new quantum computer that uses “reconfigurable atoms.” These mobile qubits can communicate efficiently with multiple neighboring qubits, enhancing error correction capabilities.
A team from the University of Chicago has developed a new quantum computing model that uses innovative qLDPC codes and reconfigurable atomic arrays to improve efficiency and scalability, while reducing the number of qubits used to correct errors.
The delicate qubits of quantum computers offer powerful computational tools, but they also pose a challenge: How can engineers create practical, functioning quantum systems from bits that can be easily perturbed and have their data erased by slight changes in their environment?
Engineers have long been working on ways to make quantum computers less error-prone, often by developing ways to detect and correct errors rather than preventing them in the first place. But many such error-correction schemes require replicating the information across hundreds or thousands of physical qubits simultaneously, which quickly becomes difficult to scale up in an efficient way.
Now, a team of scientists led by researchers at the University of Chicago’s Pritzker School of Molecular Engineering (PME) has developed a blueprint for a quantum computer that can correct errors more efficiently. The system uses a new framework based on quantum low-density party-check (qLDPC) codes, which can detect errors by examining the relationships between bits, and new hardware that includes reconfigurable atomic arrays. This allows qubits to communicate with more of their neighbors, allowing qLDPC data to be encoded with fewer qubits.
“This proposed blueprint reduces the overhead required for quantum error correction and opens new avenues for scaling up quantum computers,” said Liang Jiang, professor of molecular engineering and lead author of the new research paper published in the journal Nature Physics.
Intrinsic Noise
While standard computers encode data using digital bits that are either in an on or off position, qubits can exist in a superposition of states, allowing them to tackle new computational problems. However, the unique properties of qubits make them highly sensitive to their environment, changing state based on the temperature and electromagnetism of their surroundings.
“Quantum systems are inherently noisy. There is no practical way to build an error-free quantum machine,” said Qian Xu, a PME graduate student who led the new research. “If we want to scale up quantum systems and make them useful for practical tasks, we need a way to do active error correction.”
For the past few decades, scientists have relied primarily on one type of error correction for quantum systems, called surface codes. These systems simultaneously encode the same logical information into many physical bits arranged in a large two-dimensional grid. Errors can be inferred by comparing a qubit with its direct neighbors. A mismatch indicates that one qubit has malfunctioned.
“The problem with this is that it requires a huge resource overhead,” Xu says. “In some of these systems, you need 1,000 physical qubits for every logical qubit, and we don’t think this can be scaled to very large computers in the long term.”
Reduced redundancy
In their new system, Jiang, Xu and their colleagues from Harvard University, California Institute of Technology, the University of Arizona and QuEra Computing aimed to correct the errors instead using qLDPC codes. This type of error correction has long been considered but never implemented in a realistic blueprint.
In qLDPC codes, a qubit’s data is compared not only with its direct neighbors, but also with qubits that are farther away. This allows a smaller qubit grid to be used to perform the same number of comparisons for error correction. However, this long-distance communication between qubits has always been a problem in implementing qLDPC.
The researchers came up with a solution in the form of new hardware: reconfigurable atoms that can be moved by lasers to allow qubits to communicate with new partners.
“Today’s reconfigurable atomic array systems can control and manipulate over a thousand physical qubits with high fidelity, connecting qubits that are far apart,” said Harry Zhou of Harvard University and QuEra Computing. “By matching the quantum code structure with these hardware capabilities, these more advanced qLDPC codes can be implemented with just a few control lines, making them achievable in today’s experimental systems.”
Combining qLDPC codes with reconfigurable neutral atomic arrays allowed the team to achieve better error rates than using surface codes with just a few hundred physical qubits. When scaled up, quantum algorithms involving thousands of logical qubits can be realized with fewer than 100,000 physical qubits, far more efficient than gold-standard surface codes.
“There’s still some redundancy in terms of encoding data across multiple physical qubits, but the idea is to significantly reduce that redundancy,” Xu said.
This framework is still theoretical, but scientists are rapidly developing atomic array platforms to enable practical applications of error-corrected quantum computing. The PME team is now working to further fine-tune the blueprint, enabling computations to use logical qubits that rely on qLDPC codes and reconfigurable atomic arrays.
“In the long term, we think this will enable us to build very large quantum computers with low error rates,” Xu said.
Reference: “Constant-overhead fault-tolerant quantum computing with reconfigurable atomic arrays,” Qian Xu, J. Pablo Bonilla Ataides, Christopher A. Pattison, Nithin Raveendran, Dolev Bluvstein, Jonathan Wurtz, Bane Vasić, Mikhail D. Lukin, Liang Jiang, Hengyun Zhou, 29 April 2024, Nature Physics.
DOI: 10.1038/s41567-024-02479-z
