MIT Lincoln Laboratory Creates The First Trapped-Ion Quantum Chip With Integrated Photonics

Most experts agree that quantum computing is still in an experimental era. The current state of quantum technology has been compared to the same stage that  classical computing was in during the late 1930s.

Quantum computing uses various computation technologies, such as superconducting, trapped ion, photonics, silicon-based, and others. It will likely be a decade or more before a useful fault-tolerant quantum machine is possible. However, a team of researchers at MIT Lincoln Laboratory has developed a vital step to advance the evolution of trapped-ion quantum computers and quantum sensors.

Most everyone knows that classical computers perform calculations using bits (binary digits) to represent either a one or zero. In quantum computers, a qubit (quantum bit) is the fundamental unit of information. Like classical bits, it can represent a one or zero. Still, a qubit can also be a superposition of both values when in a quantum state.

Superconducting qubits, used by IBM and several others, are the most commonly used technology. Even so, trapped-ion qubits are the most mature qubit technology. It dates back to the 1990s and its first use in atomic clocks. Honeywell and IonQ are the most prominent commercial users of trapped ion qubits. 

Trapped-Ion quantum computers

Honeywell and IonQ both create trapped-ion qubits using an isotope of rare-earth metal called ytterbium. In its chip using integrated photonics, MIT used an alkaline metal called strontium. The process to create ions is essentially the same. Precision lasers remove an outer electron from an atom to form a positively charged ion. Then, lasers are used like tweezers to move ions into position. Once in position, oscillating voltage fields hold the ions in place. One main advantage of ions lies in the fact that it is natural instead of fabricated. All trapped-ion qubits are identical. A trapped-ion qubit created on earth would be the perfect twin of one created on another planet.

Dr. Robert Niffenegger, a member of the Trapped Ion and Photonics Group at MIT Lincoln Laboratory, led the experiments and is first author on the Nature paper. He explained why strontium was used for the MIT chip instead of ytterbium, the ion of choice for Honeywell and IonQ. “The photonics developed for the ion trap are the first to be compatible with violet and blue wavelengths,” he said. “Traditional photonics materials have very high loss in the blue, violet and UV. Strontium ions were used instead of ytterbium because strontium ions do not need UV light for optical control.”

All the manipulation of ions takes place inside a vacuum chamber containing a trapped-ion quantum processor chip. The chamber protects the ions from the environment and prevents collisions with air molecules.

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