Researchers from the University of Copenhagen and Ruhr University have figured out how to control two quantum light sources instead of one. A small step from 1 to 2 may sound too anti-climactic to be called a breakthrough, but this new technology could potentially be developed to create universal error-correcting quantum computers, the holy grail of quantum computing.
According to the University of Copenhagen, researchers around the world have been working for years to develop stable quantum light sources to achieve what is known as quantum mechanical entanglement. In the context of photonic quantum computing, entanglement is when two light sources can instantly affect each other, potentially over a large geographical distance. Entanglement is a key concept in developing efficient quantum computers.
The two light sources are entangled, which means that controlling one light source will affect the other light source almost immediately. The technique can then be extended to create entire networks of entangled quantum light sources that can be used to perform “quantum bit operations” just like normal bits in a computer.
Researchers have been unable to create two entangled light sources because of their extreme sensitivity to noise. “The problem is very much ‘charge noise’ of the carriers in the vicinity of the quantum emitter which gives spectral jitter. We overcome this by using very clean materials and applying a low-noise bias voltage across the quantum dot emitter.” Peter Lodahl, co-author of the research paper published in the journal ScienceI have notified indianexpress.com via email.
To accomplish the feat, the researchers used nanochips as large as the diameter of a human hair. Over the past five years, the team has developed this nanochip and eventually improved its performance.
“We start with an ultra-clean material grown in a UHV molecular beam epitaxy chamber by our colleagues in Bochum, Germany. After that, we fabricate the tiny chip devices using a very well-tested dedicated etch process. Finally, we fabricate electrical contacts to the sample and protect the experiment from excessive electrical noise,” Lodahl explained.
According to the researchers, the technology could be adapted to use 20 to 30 entangled quantum light sources that could potentially be used to build “universal error-correcting quantum computers” that tech companies are pouring billions of dollars into.
A portion of the research team is pictured here. From left: Peter Lodahl, Anders Sørensen, Vasiliki Angelopoulou, Ying Wang, Alexey Tiranov, and Cornelis van Diepen. Photo: Ola J. Joensen. (Image credit: Niels Bohr Institute)
According to EU Research and Innovation Magazine, the main difference between classical and quantum computers is their different rule sets. Unlike classical computers, quantum computers do not use 0s and 1s or “bits”. Instead, you work with “qubits”.
Bits can be thought of as light switches. On or off, 1 or 0. Qubits have the special property of being able to exist in the presence of both 0s and 1s. This superposition theoretically allows quantum computers to do things beyond classical computers.
“I think quantum computers will be primarily used to solve difficult quantum problems. For example, in the context of understanding complex chemical reactions such as drug discovery pipelines or new materials engineering. Quantum computers are still immature, and different qubit platforms are being explored around the world, each with their pros and cons,” said Lodahl, referring to the various quantum technologies.
“Photonics is becoming an increasingly serious contender, primarily because it seems easier to scale to large processors compared to some competing approaches. Our work is a key stepping stone towards using deterministic single-photon sources for photonic quantum computing,” added Lodahl.
According to the researchers, it is too expensive for universities to build setups that can control 10, 15 or more light sources. Therefore, it is now up to other actors such as private companies and laboratories to do more research work and find applications for the technology.
