Researchers are developing the world’s smallest quantum light detector on a silicon chip

Researchers at the University of Bristol have made a major breakthrough in scaling quantum technology by integrating the world’s smallest quantum light detector onto a silicon chip. The article “A Bi-CMOS quantum light detector with electronic photonic integrated circuit” was published in Scientific advances.

A pivotal moment in unlocking the information age was when scientists and engineers first succeeded in miniaturizing transistors on cheap microchips in the 1960s.

Now scientists at the University of Bristol have demonstrated for the first time the integration of a quantum light detector – smaller than a human hair – onto a silicon chip, bringing us one step closer to the age of quantum light technologies.

Large-scale manufacturing of powerful electronics and photonics is essential to realizing the next generation of advanced information technologies. Figuring out how to implement quantum technologies in existing commercial facilities is an ongoing international effort undertaken by academic researchers and companies around the world.

Being able to produce powerful quantum hardware at scale could prove crucial to quantum computing, as even a single machine is expected to require a large number of components.

To achieve this goal, researchers at the University of Bristol have demonstrated a type of quantum light detector implemented on a chip with a circuit that occupies 80 micrometers by 220 micrometers.

Crucially, the quantum light detector can be fast due to its small size, which is key to unlocking high-speed quantum communications and enabling high-speed operation of optical quantum computers.

The use of established and commercially accessible manufacturing techniques improves the prospects for early integration into other technologies such as sensing and communications.

“These types of detectors are called homodyne detectors and are popping up everywhere in quantum optics applications,” explains Professor Jonathan Matthews, who led the research and is director of the Quantum Engineering Technology Labs.

“They operate at room temperature and can be used for quantum communications in incredibly sensitive sensors – such as state-of-the-art gravitational wave detectors – and there are designs of quantum computers that would use these detectors.”

In 2021, the Bristol team showed how connecting a photonic chip to a separate electronic chip can increase the speed of quantum light detectors – with a single integrated electronic-photonic chip, the team was now able to increase the speed by a factor of 10 and at the same time reduce the space requirement by a factor of 50.

Although these detectors are fast and small, they are also sensitive.

“The key to measuring quantum light is sensitivity to quantum noise,” explains author Dr. Giacomo Ferranti.

“Quantum mechanics is responsible for a tiny, fundamental level of noise in all optical systems. The behavior of this noise reveals information about what type of quantum light is moving in the system, it can determine how sensitive an optical sensor can be, and it can be used to mathematically reconstruct quantum states. In our study, it was important to show that the size and speed of the detector does not compromise its sensitivity for measuring quantum states.

The authors point out that there is still more exciting research to be done in integrating other breakthrough quantum technology hardware down to chip size. With the new detector, efficiency needs to be improved and there is still a lot of work to be done to test the detector in many different applications.

Professor Matthews added: “We built the detector using a commercially available foundry to make its applications more accessible. While we are incredibly excited about the impact on a range of quantum technologies, it is important that we as a community continue to address the scalable manufacturing challenge of quantum technology.

“Without evidence of truly scalable quantum hardware manufacturing, the impact and benefits of quantum technology will be delayed and limited.”