The process, say the researchers, manufactures and integrates "artificial atoms" - created by atomic-scale defects in microscopically thin slices of diamond - with photonic circuitry. The artificial atoms, which can be prodded with visible light and microwaves to emit photons that carry quantum information, are the qubits in the new chip.
To create the chip, the researchers used carefully selected "quantum micro chiplets" containing multiple diamond-based qubits that are placed on an aluminum nitride photonic integrated circuit. The approach, say the researchers, demonstrates a viable way to scale up quantum processor production.
Using their hybrid method, the researchers were able to build a 128-qubit system - said to be the largest integrated artificial atom-photonics chip yet. The qubits are stable and long-lived, and their emissions can be tuned within the circuit to produce spectrally indistinguishable photons. The accomplishment, say the researchers, "marks a turning point" in the field of scalable quantum processors.
"In the past 20 years of quantum engineering, it has been the ultimate vision to manufacture such artificial qubit systems at volumes comparable to integrated electronics," says Dirk Englund, an associate professor in MIT's Department of Electrical Engineering and Computer Science. "Although there has been remarkable progress in this very active area of research, fabrication and materials complications have thus far yielded just two to three emitters per photonic system."
The artificial atoms in the chiplets consist of color centers in diamonds - defects in diamond's carbon lattice where adjacent carbon atoms are missing, with their spaces either filled by a different element or left vacant. In the MIT chiplets, the replacement elements are germanium and silicon.
Each center functions as an atom-like emitter whose spin states can form a qubit. The artificial atoms emit colored particles of light, or photons, that carry the quantum information represented by the qubit.
While diamond color centers make good solid-state qubits, say the researchers, the bottleneck with this platform is actually