Researchers develop platform to control qubits in silicon defects for quantum communications

The dream of a , one capable of unprecedented levels of security and computational power, is tantalizingly close. Making this dream a reality would be significantly more feasible if we could harness existing telecommunications technologies and infrastructure. Recently, researchers have made significant strides in this direction by exploring defects in —a ubiquitous semiconductor material—as potential hosts for qubits in quantum communications. These defects could potentially allow for the transmission and storage of over the same wavelengths used in current telecommunications systems. The pressing question remains: are these silicon defects the optimal choice among various promising candidates for qubit hosts?

“It's still a Wild West out there,” says Evelyn Hu, the Tarr-Coyne Professor of Applied Physics and Electrical at Harvard's John A. Paulson School of Engineering and Applied Sciences (SEAS).

Hu elaborates, “Even though new candidate defects show promise as platforms, we often lack detailed knowledge about why certain fabrication methods are used, how to rapidly characterize these defects and their interactions, and how to fine-tune their behaviors to ensure consistency. If we ever hope to develop a viable technology from these possibilities, we must improve our methods of characterization—making them better, faster, and more efficient.”

To address these challenges, Hu and her team have developed a novel platform to probe, interact with, and control these . Their innovative device utilizes a simple electric diode—one of the most common semiconductor components—to manipulate qubits within a commercial silicon . This groundbreaking approach allows the researchers to explore how the defects respond to changes in the electric field, fine-tune their emission wavelengths within the telecommunications band, and even control their activation states.

“One of the most exciting aspects of working with these defects in silicon is that it allows us to use well-established like diodes in a familiar material to explore new quantum systems and achieve novel outcomes,” says Aaron Day, a Ph.D. candidate at SEAS and co-leader of the project alongside Madison Sutula, a research fellow at Harvard.

Their research, published in Nature Communications, reveals that while the team's approach was initially focused on characterizing silicon defects, it holds potential as a diagnostic and control tool for defects in other material systems as well.

Quantum defects, also known as color centers or quantum emitters, are imperfections within an otherwise perfect that can trap single . When these electrons are excited by a laser, they emit photons at specific wavelengths. The defects of particular interest for quantum communications in silicon are known as G-centers and T-centers. These defects emit photons in the O-band wavelength, a range widely used in telecommunications.

In their research, the team concentrated on G-center defects. Their first challenge was to determine how to create these defects. Unlike other types of defects, which involve removing an atom from the crystal lattice, G-center defects are formed by adding atoms—in this case, carbon—to the lattice. The researchers discovered that the addition of hydrogen atoms is also critical to consistently forming these defects.

The ability to create, control, and understand these quantum defects in silicon could pave the way for integrating quantum technologies with existing telecommunication infrastructure, significantly advancing the development of a quantum internet. As research progresses, these advancements could eventually lead to a robust, scalable quantum communication network, bringing the quantum internet from a theoretical possibility to a practical reality.

Source: Harvard John A. Paulson School of Engineering and Applied Sciences