Quantum chip scale-up

A process at MIT researchers to produce “artificial atoms” created by atomic-scale defects in microscopically thin slices of diamond and integrate them with photonic circuits to produce the largest quantum chips of that type. Was developed.

Dirk Englund, associate professor of the Department of Electrical Engineering and Computer Science at MIT, points to a “breaking point” in the field of scalable quantum processors. Millions of quantum processors are needed to build quantum computers, and new research shows a viable way to scale up processor production, he and his colleagues point out.

Unlike traditional computers, which use bits represented by either 0s or 1s to process and store information, quantum computers represent qubits or qubits that can represent 0s, 1s, or both at the same time. Use and work. This strange property allows quantum computers to perform multiple computations at the same time, solving problems that are awkward on traditional computers.

The new chip qubit is an artificial atom made from a defect in a diamond that uses visible light and microwaves to emit photons that carry quantum information. The process Englund and his team describe today Nature, Is a hybrid approach in which carefully selected “quantum microchiplets” containing multiple diamond-based qubits are placed on an aluminum nitride photonic integrated circuit.

“For the last 20 years in quantum engineering, the ultimate vision has been to manufacture such artificial qubit systems in quantities comparable to integrated electronics,” says Englund. “There have been tremendous advances in this very active area of ​​research, but so far the complexity of manufacturing and materials has only produced a few emitters per photonic system.”

Englund et al. were able to build a 128 qubit system using a hybrid approach. This is the largest integrated artificial atom photonics chip.

“It’s very exciting in terms of technology,” says Marko Lončar, a professor of electrical engineering at Harvard University Thien Cyrin who wasn’t involved in the study. “They were able to get a stable emitter on the photonic platform while maintaining a very good quantum memory.”

Other authors of Nature The papers include MIT researchers, Noel H. Wang, Tung Jur, Kevin C. Chen, Michael P. Walsh, Matthew E. Trasheim, Lorenzo de Santis, Eric A. Vercin, Isaac B. Harris, Sarah L. Moradian, Ian R. Kristen; with Edward S. Biellejek at Sandia National Laboratory.

Chiplet quality control

Chiplet artificial atoms consist of diamond color centers, defects in the carbon lattice of diamond lacking adjacent carbon atoms, whose spaces are either filled with another element or are vacant. In MIT Chiplet, the replacement elements are germanium and silicon. Each center acts as an atom-like emitter whose spin state can form the qubit. Artificial atoms emit colored particles of light or photons that carry the quantum information represented by qubits.

“The bottleneck of this platform is actually building system and device architectures that can scale to thousands and millions of qubits,” says Diamond Color Center, which creates great solid-state qubits. ”Explains Wang. “Artificial atoms are in solid crystals, and unwanted contamination can affect important quantum properties such as coherence time. In addition, variations in the crystal can cause qubits to differ from each other, Scaling these systems becomes difficult.”

Instead of trying to build large quantum chips entirely out of diamond, researchers decided to take a modular and hybrid approach. “We use semiconductor manufacturing technology to create these small chiplets of diamonds, from which we select only the highest quality qubit modules,” says Wang. “Then, we’re integrating these chiplets one by one into another chip, and “wiring” the chiplets into a larger device. “

The integration is done in photonic integrated circuits. It is similar to electronic integrated circuits, but uses photons rather than electrons to convey information. Photonics provides a low-loss basic architecture for routing and switching photons between modules in a circuit. The circuit platform is aluminum nitride rather than the traditional silicon of some integrated circuits.

Using this hybrid approach of photonic circuits and diamond tiplets, researchers were able to connect 128 qubits on one platform. According to Wan et al., qubits are stable, have a long life, and their emission can be tuned in-circuit to produce spectrally indistinguishable photons.

Modular approach

The platform provides a scalable process for manufacturing artificial atomic photonics chips, but the next step is to “turn it on” and test its throughput.

“This proves that solid-state qubit emitters are a highly scalable quantum technology,” says Wan. “The next step in processing quantum information is controlling these numerous qubits and causing interactions between them.”

Qubits of this type of tip design do not have to be centered on these particular diamonds. Other chip designers may choose other types of diamond color centers, atomic defects in other semiconductor crystals such as silicon carbide, specific semiconductor quantum dots, or crystalline rare earth ions. “The integrated approach is hybrid and modular, so instead of relying on the natural properties of only one material, we can choose the best material for each component. Can be combined into one system.” Lou

Researchers need to find ways to automate the process and demonstrate further integration with optoelectronic components such as modulators and detectors, which are needed for modular quantum computers and multi-channel quantum repeaters that transport qubits over long distances. He says it will be needed to build larger chips.