British quantum computing startup OQC today announced that it has raised £260 million, or $350 million, in new funding. 

Bullhound Capital led the oversubscribed Series C round. It was joined by more than a dozen others, including the British Business Bank, the U.K. government’s economic development bank, and the startup investment arms of several universities.

“This gives us the capital to scale internationally, advance our technology roadmap and meet increasing demand from customers seeking secure, scalable access to quantum computing infrastructure,” said OQC Chief Executive Officer Gerald Mullally.

OQC, officially Oxford Quantum Circuits Ltd., makes quantum computers based on a qubit design known as the transmon. The core component of a transmon is a structure called a Josephson junction. It comprises a layer of insulating material sandwiched between two superconductors.

Usually, electricity can’t pass through a Josephson junction’s insulating layer. When the structure is cooled near absolute zero, electrons organize themselves into pairs and thereby gain the ability to jump through the insulator. Transmon-based quantum computers harness that phenomenon to perform calculations.

OQC builds quantum chips by placing transmon qubits atop a thin layer of sapphire. According to the company, its engineers create the qubits using photolithography techniques and an electron beam. The other side of the sapphire substrate hosts devices called resonators that are responsible for extracting calculation results from qubits.

Quantum computers are prone to making errors that can disrupt processing if left unaddressed. Mitigating those mistakes requires engineers to place conductive pillars in the sapphire qubit substrate. Historically, they went about the task by drilling through the substrate with a high-powered laser beam.

Lasers produce a significant amount of heat, which can complicate quit manufacturing. OQC says that it has worked around the issue by finding a way to drill through sapphire using a CNC machine. Such machines, which are widely used in industrial manufacturing, produce significantly less heat than a laser. Processing sapphire with CNC machines was historically challenging because it’s one of the world’s toughest materials. 

OQC says its technology has several advantages over competing quantum computer designs.

Increasing the computing capacity of a quantum system usually requires researchers to link together multiple standalone qubit chips. That arrangement can lead to a decrease in processing accuracy. According to OQC, its technology makes it possible to implement all of a quantum computer’s qubits on a single wafer and thereby avoids accuracy trade-offs.

The company’s chip architecture also reduces processing errors in other ways. It includes mechanisms that mitigate amplitude damping, one of the main sources of processing mistakes in quantum computers. Amplitude damping occurs when the amount of energy in a qubit decreases to such an extent that the data it contains changes.

OQC’s chip architecture is in its third iteration. The company is currently developing a fourth-generation version with 16 logical qubits, circuits that each comprise multiple physical qubits. It plans to follow up the chip with a system called Titan that is expected to launch in 2028 with 200 logical qubits. 

Image: OQC