A new nanoscale diamond structure that better collects and controls light
The novel device produces a ‘nanojet’ of light and holds promise to advance scalable quantum technologies
By Naomi Grosman
Researchers at the Institute for Quantum Computing (IQC) at the University of Waterloo have demonstrated a nanoscale optical device that makes it easier to probe quantum systems with light to enable more efficient quantum sensors and solid-state quantum computing systems. The new device was demonstrated in diamond as a proof of principle.
This optical device has the potential to make quantum sensors better at detecting weak magnetic fields, which could enhance technologies in biomedical imaging or navigation in GPS-denied environments. It could also advance solid-state quantum computing architectures by improving control and readout of individual quantum bits (qubits), and the transfer of quantum information between them.
“Our new approach offers a powerful and practical route to enhance light–matter interaction in solid-state platforms."
-Dr. Behrooz Semnani
Semnani spearheaded the research in Dr. Michal Bajcsy’s group, IQC Faculty and Professor, Department of Electrical and Computer Engineering.
Solid-state quantum platforms such as diamond, silicon carbide, and silicon can host atom-like defects, also known as quantum emitters or color centers, that can serve as qubits. These defects can be initialized, controlled, and read out with laser light, and in many cases can also act as solid-state single-photon sources.
In practice, however, aiming a laser at a single defect can be difficult. Additionally, efficiently collecting the optical signal is challenging because these materials have a high refractive index, causing much of the light emitted by the defects to remain trapped inside the material rather than being collected.
That’s the problem Bajcsy’s group aims to solve with a novel device reported in a new paper Probing Individual Quantum Emitters in Bulk Semiconductors via Photonic Nanojets published in Science Advances.
The group used an automated, inverse design approach to optimize the shape of a two-dimensional structure sculpted into a diamond surface. The structure was designed to funnel light into a highly localized nanoscale beam known as a ‘photonic nanojet’ to isolate and aim at single defects in the diamond crystal. The structure was also optimized to act like an antenna for light to help extract photons emitted by the defects.
To demonstrate this, the group fabricated the structure on a synthetic diamond piece to probe a defect called nitrogen vacancy.
Dr. Michal Bajcsy's group designed a quantum device in diamond that funnels and aims a highly localized beam of photons at single engineered defects in diamond and is optimized to extract photons. Better collecting and controlling light has applications in quantum sensing and solid-state quantum computing architecture.
The group used an automated, inverse design approach to optimize the shape of a two-dimensional structure sculpted into a diamond surface. The device size is about 1 micrometre - 100 times smaller than the width of a human hair.
Side view showing the 'Photonic Nanojet' funneling light.
“Our nanojet structure introduces a lot of new benefits but uses a very common fabrication technique without the difficulties associated with some of the previously reported structures used to couple light in and out of quantum emitters in diamond and other materials," says Semnani, who was IQC Research Associate at the time of the research. "This provides a path towards enhanced efficiency.”
Bajcsy says that they are hoping to expand this work into other materials that contain individual defects suitable for sensing or as qubits.
“With most semiconductor materials, it’s hard to extract photons emitted by embedded defects and we hope that our nanojet structures will enable studies and new applications of less common emitters.”
- Dr. Michal Bajcsy, IQC Faculty and Professor, Department of Electrical and Computer Engineering.
He adds that the results allowed addressing individual defects even in low-quality diamond crystals, instead of expensive high-purity diamond samples often used in quantum experiments. This will help with the development of low-cost quantum sensors.
“The device’s simple fabrication process, minimally invasive geometry, and compatibility with reliable device manufacturing make it especially attractive for scalable quantum technologies,” Semnani says.
The device was fabricated at the Quantum-Nano Fabrication and Characterization Facility at the University of Waterloo. The group says access to the facility’s advanced tools, technical support and adaptable processes gave them a flexible and robust fabrication ecosystem to develop new ideas and iterate the device concept.
The paper’s other co-authors are Sai Sreesh Venuturumilli, IQC PhD student; Dr. Mohammad Soltani, IQC post doc; Dr. Pratik Adhikary, IQC post doc; Abdolreza Pasharavesh, IQC PhD student; Nikolay Videnov IQC PhD student; Dr. Paul Anderson, IQC Post doc; Vinodh Raj Rajagopal Muthu, IQC alumni; and Supratik Sarkar, IQC alumni.
The research was supported in part by the Canada First Research Excellence Fund through the Transformative Quantum Technologies (TQT) program at IQC.