Silicon Spin Qubits: The Semiconductor Path to Quantum Computing

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Earlier posts here covered superconducting, trapped ion, photonic, and neutral atom qubits. Each platform has a different answer to the same problem: how do you isolate a quantum system long enough to do useful computation? Silicon spin qubits take a different approach than all of them. Instead of cooling exotic materials or trapping atoms with lasers, they use ordinary silicon, the same material in every chip your phone and laptop run on.

That is the bet. If you can make a qubit out of silicon, you inherit six decades of semiconductor manufacturing infrastructure.

First, What is a Qubit Refresher

A regular computer stores information as bits. Each bit is either a 0 or a 1, like a light switch that is either off or on. A qubit is a quantum bit. It can be 0, 1, or a combination of both at the same time, a property called superposition. Two qubits can also be entangled, meaning the state of one instantly affects the other no matter how far apart they are.

These properties let quantum computers solve certain types of problems, like simulating molecules or breaking encryption, far faster than any classical computer ever could. But building a reliable qubit is extremely hard. They are fragile and easily disturbed by heat, vibration, or any stray interference from the environment.

The Silicon Idea: Using an Electron's Spin

Every electron has a property called spin. Think of it like a tiny compass needle that can point either up or down. In a silicon spin qubit, the spin-up state represents 1 and the spin-down state represents 0. That single electron, trapped in place inside a silicon chip, is the qubit.

To trap it, engineers build a structure called a quantum dot: a tiny electrical cage, about 30 to 100 nanometers across (roughly 1,000 times smaller than the width of a human hair), formed by applying precise voltages to metal wires patterned on top of the silicon. Those voltages create a pocket in the silicon just deep enough to hold one electron.

Another version uses a phosphorus atom embedded directly in the silicon. The extra electron that comes with the phosphorus atom becomes the qubit. This approach has produced some remarkable results: coherence times (the length of time the qubit stays usable) above 30 seconds, which is far longer than almost any other qubit technology can manage.

Why Silicon is Special

Most quantum computing platforms require exotic materials or unusual setups. Silicon spin qubits are different because silicon is the most well-understood material in the history of electronics. The entire semiconductor industry, the one that makes the chips powering every computer on earth, is built on it.

That matters enormously. Building quantum hardware usually requires custom processes developed from scratch. Silicon spin qubits can, in principle, be manufactured using the same factories and tools already used to make conventional computer chips. A silicon spin qubit device looks structurally similar to a standard transistor.

There is also a materials trick that helps a lot. Natural silicon contains a small amount of a variant called silicon-29, which has a nuclear spin that creates interference for nearby electron spin qubits. By purifying the silicon to remove silicon-29, researchers have dramatically improved how long qubits hold their quantum state without errors. This purified material is now commercially available.

How You Actually Operate Them

To perform a computation, you need to rotate a qubit from one state to another. For silicon spin qubits, you do this by applying a precisely timed microwave pulse, a radio-wave signal at exactly the right frequency to flip or tilt the electron’s spin. This is the same basic principle used in MRI machines, which also use magnetic resonance to probe spin states in atoms.

Single-qubit operations of this kind have achieved accuracy above 99.9%, meaning fewer than 1 error in every 1,000 operations. That is an important benchmark for building reliable quantum computers.

For two qubits to work together (which is required for any real computation), they need to interact. Silicon spin qubits do this through what is called the exchange interaction. When two quantum dots are placed next to each other and the barrier between them is briefly lowered, the two electrons can “sense” each other quantum mechanically. By controlling exactly how long and how strongly this interaction happens, you can perform a two-qubit logic operation.

Two-qubit operations have now exceeded 99% accuracy in silicon, which clears the bar generally considered necessary for quantum error correction to work.

The Challenges

Silicon spin qubits are promising, but they are not ready for prime time yet. Here are the main obstacles:

•       They still need extreme cold. Like most quantum hardware, silicon spin qubits must be cooled to within a fraction of a degree of absolute zero (around minus 273 degrees Celsius) using a machine called a dilution refrigerator. These are expensive and complex. Researchers are working toward versions that operate at slightly higher temperatures, which would make the systems simpler and cheaper.

•       No two quantum dots are identical. Even with precise chip fabrication, tiny variations between quantum dots mean each qubit behaves slightly differently and needs to be individually tuned. At small qubit counts this is manageable. At thousands of qubits it becomes a serious problem. Machine learning tools are being developed to automate this tuning.

•       Electrical noise disrupts the qubits. Random fluctuations in the electrical environment of the chip can shift a qubit out of its intended state. This is called charge noise and it is the main source of errors in current silicon spin qubit devices.

•       Qubit counts are still small. The most advanced silicon spin qubit chips demonstrated as of 2024 have around 6 to 12 qubits. Compare that to IBM’s superconducting systems, which have passed 1,000 qubits. Silicon is behind on this count, though its proponents argue it has a clearer path to catching up.

•       Reading out results is tricky. Measuring the final spin state of an electron requires detecting an extremely small electrical signal. Getting this readout fast and accurate enough for large-scale computing is an active area of research.

Who Is Working on This

Several major players are betting on silicon spin qubits:

•       Intel released a 12-qubit silicon chip called Tunnel Falls in 2023, fabricated on the same 300mm production line used for conventional computer chips. Intel is the most prominent example of a major semiconductor company applying its manufacturing expertise directly to quantum hardware.

•       imec, a Belgian research institute, is developing silicon spin qubit fabrication on industrial 300mm wafer lines. In 2025, imec and Australian company Diraq published results in Nature showing their industrially manufactured qubits consistently hit over 99% accuracy, a first for factory-made silicon quantum devices.

•       QuTech, a research institute in Delft in the Netherlands, has produced some of the highest-fidelity silicon and germanium spin qubit results in the world. Their two-qubit gate accuracy above 99.5% in germanium set a benchmark for the field.

•       Silicon Quantum Computing, a spin-out from the University of New South Wales in Sydney, was founded by Professor Michelle Simmons, who pioneered the approach of placing individual phosphorus atoms in silicon with atomic precision. The company targets commercial-scale quantum computing using this technique.

The Scaling Picture

Silicon spin qubits are small. A single qubit occupies tens of nanometers, compared to hundreds of micrometers for a superconducting transmon qubit. In principle, you could fit millions of spin qubits on a chip the size of a modern processor die. The wiring and control problem at that scale is not solved, but like other methods, it is an engineering problem, not a physics one.