Quantum computers that are actually useful 1 step closer thanks to new silicon processor that could pack millions of qubits

Scientists say they have reached "a critical inflection point" after developing a technology that makes silicon-based quantum processors more viable.

Quantum computing company Equal1 has created a quantum processing unit (QPU) that can be built using conventional semiconductor manufacturing processes. This negates the complexity and expense typically involved with producing quantum processors using exotic materials or complicated techniques.

The company has also developed what representatives called "the most complex quantum controller chip developed to date." This can operate at ultra-low temperatures and paves the way for millions of qubits on a single chip — meaning it can handle a huge number of quantum bits of information simultaneously while keeping them stable and accurate for calculations.

By contrast, the most powerful quantum chips today only house qubits in the thousands and are built with superconductors, all requiring cooling to near absolute zero in order to perform quantum computations.

Combined, the new technologies "pave the way for the next phase of quantum computing and demonstrate the fastest way to scaling is to leverage existing silicon infrastructure," Equal1 representatives said in a statement.

Quantum impracticalities

Building quantum chips is a notoriously difficult and expensive process. Unlike regular computer chips, which rely on binary bits to process information as 1s or 0s, quantum chips use qubits, which are grounded in the principles of quantum mechanics.

Qubits have special properties that allow them to exist in multiple states simultaneously — a phenomenon called superposition — and to work together in ways traditional bits cannot through a process called entanglement. The resultant parallel processing enables quantum computers to solve problems far beyond the capabilities of classical systems.

However, qubits are incredibly fragile. They only work when they are kept in a state of coherence, meaning they maintain their quantum state long enough to perform calculations. Coherence is easily disrupted by environmental factors like temperature changes or electromagnetic noise — hence the need for extremely low temperatures, to avoid interference.

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Typically, quantum chips are also made using exotic or custom-built materials like superconducting metals, which require expensive and complex manufacturing processes. Equal1’s innovation is its use of silicon — one of the most abundant and widely used materials in the semiconductor industry.

Silicon provides a stable environment for qubits, particularly when using a material blend called silicon germanium (SiGe). In a study published Dec. 2 to the preprint database arXiv, Equal1 scientists explained that SiGe combines silicon’s stability with germanium’s ability to enhance electronic performance, making it well-suited for quantum applications. More importantly, SiGe chips can be produced using the same processes and factories that are already used to manufacture traditional computer chips, potentially making quantum processors cheaper and easier to scale.

Equal1 representatives said its SiGe 6-qubit array — which is the part of the chip where qubits are created and controlled — had broken ground in two key areas: the precision of quantum gate operations and the speed at which those operations are performed.

Specifically, the chip demonstrated a single-qubit gate fidelity of 99.4% with an operation speed of 84 nanoseconds and a two-qubit gate fidelity of 98.4% with a speed of 72 nanoseconds. High accuracy, or fidelity, in quantum gates minimizes errors in calculations, while faster gate speeds reduce the risk of qubits losing their quantum properties during operations. These factors determine the accuracy of quantum computations and the ability of qubits to maintain their quantum states long enough to complete complex operations.

"This result demonstrates the massive benefit of silicon qubits — the ability to achieve the performance required for scaling in two key areas — fidelity and speed of quantum gates." Nodar Samkharadze, chief quantum architect at Equal1, said in the statement.

Putting a spin on it

To ensure reliable quantum operations, Equal1’s device uses "spin qubits." Spin qubits encode information in the spin state of an electron. In their study, the scientists said spin qubits are particularly well-suited for integration with silicon because silicon provides a stable environment for electron spins. This reduces the risk of qubits losing their delicate quantum properties due to interference from their surroundings.

Equal1 also developed a quantum controller chip that uses a multi-tile architecture; this design divides a chip into multiple tiles that can operate semi-independently. This architecture is key to scaling quantum systems because it allows control functions to be distributed across the chip, avoiding the bottlenecks that can occur when relying on a single processing unit.

The controller operates at 300 millikelvin — a temperature just above absolute zero — which allows it to effectively manage qubits while maintaining the conditions needed for coherence. Equal1 representatives said the controller also features artificial intelligence (AI)-driven error correction technology, enabling real-time adjustments that maintain the stability and accuracy of quantum operations.

"Today marks a critical inflection point for Equal1 and the quantum computing industry," added Elena Blokhina, the company's chief scientific officer, in the statement. "Equal1 has always believed that silicon is the vehicle to scale quantum computers and today, with these world leading qubit and control chip results, we have taken a major step towards this vision."