In the race to build practical quantum computers, researchers are turning to an unlikely hero: silicon-28. This isotope of silicon, long overlooked in the semiconductor industry, is emerging as a potential game-changer in quantum computing. Its unique properties offer promising solutions to some of the field’s most challenging obstacles, particularly in scaling up quantum systems and maintaining qubit coherence.
Understanding Silicon-28
Silicon is the bedrock of modern electronics, but not all silicon atoms are created equal. Most natural silicon is a mixture of three isotopes: silicon-28 (92.2%), silicon-29 (4.7%), and silicon-30 (3.1%). What makes silicon-28 special is its nuclear spin.
In standard silicon, the presence of silicon-29 and silicon-30, both of which have non-zero nuclear spins, creates a noisy magnetic environment. This noise interferes with the delicate quantum states of qubits, causing them to lose coherence quickly — a phenomenon known as decoherence. In contrast, silicon-28 has zero nuclear spin, making it magnetically “quiet.”
Quantum Computing’s Silicon-28 Advantage
The quest for practical quantum computing faces two primary challenges: maintaining qubit coherence and scaling up systems. Silicon-28 offers compelling solutions to both.
1. Enhanced Coherence Times
— Silicon-28’s zero nuclear spin dramatically reduces magnetic noise.
— This quiet environment allows qubits to maintain their quantum states much longer.
— Researchers have observed coherence times exceeding one second in silicon-28-based qubits — a significant leap from milliseconds in other materials.
2. Scalability
— Silicon-28 is compatible with existing CMOS (Complementary Metal-Oxide-Semiconductor) technology.
— This compatibility allows quantum chips to be fabricated using the same processes as classical chips.
— Leveraging the mature silicon industry infrastructure enables cost-effective, large-scale production.
3. Low Error Rates
— Longer coherence times translate to lower error rates.
— In 2022, a team at UNSW Sydney achieved a 99.95% fidelity rate using silicon-28 qubits.
— This approaches the 99.99% threshold needed for fault-tolerant quantum computing.
4. Temperature Advantages
— Many quantum systems require ultra-low temperatures, near absolute zero.
— Silicon-28 qubits can operate at slightly higher temperatures (around 1 Kelvin).
— This reduces the complexity and cost of cooling systems.
Current Implementations
1. Princeton’s Single-Atom Qubits
— Researchers embedded phosphorus atoms in a silicon-28 crystal.
— The phosphorus nucleus serves as the qubit, shielded by the “quiet” silicon-28.
— They achieved record-breaking coherence times exceeding 39 minutes.
2. Intel’s Horse Ridge Cryogenic Chip
— Intel uses silicon-28 in its quantum control chip, Horse Ridge.
— This chip manages multiple qubits at low temperatures.
— It demonstrates silicon-28’s potential in both quantum and classical roles within a quantum system.
3. UNSW Sydney’s Two-Qubit Gates
— Scientists created high-fidelity two-qubit gates in silicon-28.
— These gates, fundamental to quantum operations, showed 99.95% fidelity.
— The work paves the way for more complex quantum circuits.
Future Progress and Practical Solutions
1. Isotopically Pure Silicon-28
— Producing large quantities of pure silicon-28 is crucial.
— Collaborations with nuclear research facilities, like in Russia, are underway.
— Advanced centrifuge technology is being adapted for silicon-28 production.
2. Hybrid Quantum-Classical Systems
— Future designs may integrate silicon-28 qubits with classical silicon chips.
— This “system on a chip” approach simplifies architecture.
— It could lead to more compact, efficient quantum computers.
3. Room-Temperature Operations
— Research is ongoing to operate silicon-28 qubits at room temperature.
— Techniques like using donors with deep energy levels show promise.
— Room-temperature operation would revolutionize accessibility.
4. Error Correction at Scale
— Silicon-28’s low error rates support quantum error correction.
— Researchers are designing silicon-28-based topological qubits.
— These could enable large-scale, fault-tolerant quantum computing.
5. Integration with Photonics
— Silicon photonics is a growing field.
— Coupling silicon-28 qubits with photonic circuits is being explored.
— This could enable quantum networks and distributed quantum computing.
Conclusion
Silicon-28 represents a convergence of quantum physics and semiconductor engineering. Its nuclear quietness, combined with the silicon industry’s mature infrastructure, offers a unique pathway to scale quantum computing. From enhancing coherence times to enabling room-temperature operations, silicon-28 is helping to transform quantum computing from a lab curiosity into a practical technology.
While challenges remain, particularly in isotope production and error correction at scale, the progress is undeniable. Silicon-28 isn’t just another material in quantum computing — it’s a bridge between the quantum future and our silicon-based present. As research advances, we may find that the key to unlocking quantum computing’s potential has been in our electronic devices all along.
Citations:
[1] https://www.nature.com/articles/s41534-023-00679-8
[2] https://www.advancedsciencenews.com/worlds-purest-silicon-chip-could-make-quantum-computers-error-free/
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[6] https://www.technologynetworks.com/applied-sciences/news/worlds-purest-silicon-brings-scientists-one-step-closer-to-scaling-up-quantum-computers-386543
[7] https://thequantuminsider.com/2024/05/10/worlds-purest-silicon-brings-scaling-up-quantum-computers-closer/
[8] https://en.wikipedia.org/wiki/Silicon
[9] https://www.nist.gov/news-events/news/2020/01/spotlight-silicon-28-quantum-computers
[10] https://www.nature.com/articles/s43246-024-00498-0
[11] https://byjus.com/chemistry/silicon/
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[14] https://pubchem.ncbi.nlm.nih.gov/compound/Silicon-28
[15] https://www.quantumgrad.com/article/736
