Evelyn Hu and a team at Harvard’s School of Engineering and Applied Sciences have developed a platform to probe and control quantum systems using a simple electric diode. The device manipulates qubits inside a commercial silicon wafer, allowing researchers to explore how the defect responds to changes in the electric field, tune its wavelength within the telecommunications band, and even turn it on and off. The research, published in Nature Communications, could be a significant step towards building a quantum internet using existing telecommunications technologies and infrastructure. The work was supported by AWS Center for Quantum Networking and the Harvard Quantum Initiative.
Quantum Defects in Silicon: A New Frontier for Quantum Communications
The quantum internet, a concept that has been gaining traction in recent years, could potentially be built using existing telecommunications technologies and infrastructure. This is due to the discovery of defects in silicon, a widely used semiconductor material, that could be harnessed to send and store quantum information over commonly used telecommunications wavelengths. The question that arises, however, is whether these defects in silicon could be the optimal choice to host qubits for quantum communications.
The field of quantum communications is still in its infancy, often referred to as the “Wild West” by researchers. Despite the promising potential of new candidate defects as a quantum memory platform, there is still much to learn about why certain methods are used to create them, how to quickly characterize them and their interactions, and how to fine-tune their behavior so they exhibit identical characteristics.
A New Platform for Probing and Controlling Quantum Systems
A team of researchers led by Evelyn Hu, the Tarr-Coyne Professor of Applied Physics and of Electrical Engineering at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), has developed a platform to probe, interact with, and control these potentially powerful quantum systems. The device uses a simple electric diode, a common component in semiconductor chips, to manipulate qubits inside a commercial silicon wafer.
Using this device, the researchers were able to explore how the defect responds to changes in the electric field, tune its wavelength within the telecommunications band, and even turn it on and off. This approach could be used as a diagnostic and control tool for defects in other material systems, expanding its potential applications.
Quantum Defects: The Key to Quantum Communications
Quantum defects, also known as color centers or quantum emitters, are imperfections in otherwise perfect crystal lattices that can trap single electrons. When these electrons are hit with a laser, they emit photons in specific wavelengths. The defects in silicon that researchers are most interested in for quantum communications are known as G-centers and T-centers.
In this research, the team focused on G-center defects. Unlike other types of defects, G-center defects are made by adding atoms to the lattice, specifically carbon. However, the research team found that adding hydrogen atoms is also critical to consistently forming the defect.
A New Approach to Fabricating Electrical Diodes
The researchers fabricated electrical diodes using a new approach which optimally sandwiches the defect at the center of every device without degrading the performance of either the defect or the diode. The fabrication method can create hundreds of devices with embedded defects across a commercial wafer.
When a negative voltage was applied across the device, the defects turned off and went dark. This understanding of when a change in environment leads to a loss of signal is crucial for engineering stable systems in networking applications.
Tuning Wavelengths and Diagnosing Defects
The researchers also found that by using a local electric field, they could tune the wavelengths being emitted by the defect, which is important for quantum networking when disparate quantum systems need to be aligned.
The team also developed a diagnostic tool to image how the millions of defects embedded in the device change in space as the electric field is applied. This tool provides valuable insights into how defects respond to changes in their environment, which can inform the design of future devices.
The team’s next goal is to use the same techniques to understand the T-center defects in silicon. This research, published in Nature Communications, was supported by the AWS Center for Quantum Networking and the Harvard Quantum Initiative.
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