CEA-Leti Announces a Fundamental Breakthrough in Fabricating Quantum Bits

CEA-Leti, a French technology research institute of the French Alternative Energies and Atomic Energy Commission (CEA) and the Institute for Nanoscience and Cryogenics (Inac) fundamental research institute, has announced a breakthrough towards large-scale fabrication of quantum bits, or qubits, the building blocks of future quantum processors.

CEA-Leti demonstrated a new level of isotopic purification in a film deposited by chemical vapor deposition on a 300-mm preindustrial platform, enabling the creation of qubits in thin layers of silicon using ²⁸Si, a high-purity silicon isotope, which produces a crystalline quality comparable to thin films usually made of natural silicon.

“Using the isotope ²⁸Si instead of natural silicon is crucial for the optimization of the fidelity of the silicon spin qubit,” said Marc Sanquer, a research director at Inac. “The fidelity of the spin qubit is limited to small values by the presence of nuclear spins in natural silicon. But spin qubit fidelity is greatly enhanced by using ²⁸Si, which has zero nuclear spin. We expect to confirm this with qubits fabricated in a preindustrial CMOS platform at CEA-Leti.”

Qubits can be made in a broad variety of material systems, but when it comes to the crucial issue of large-scale integration, the range of possible choices narrows significantly. Silicon spin qubits are small and compatible with CMOS technology, presenting advantages for large-scale integration compared to other types of qubits.

Since 2012, when the first qubits that relied on electron spins were reported, the introduction of isotopically purified ²⁸Si has led to significant enhancement of the spin coherence time. The longer spin coherence lasts, the better the fidelity of the quantum operations. Quantum effects are essential to understanding how basic silicon microcomponents work, but the most interesting quantum effects, such as superposition and entanglement, are not used in circuits. The CEA-Leti and Inac results showed that these effects can be implemented in CMOS transistors operated at low temperature.

CEA-Leti is a research institute for electronics, nanotechnologies, and information technologies.