Nu Quantum CEO and co-founder Carmen Palacios-Berraquero was invited to take part in a podcast with Physics World, the membership magazine of the Institute of Physics. During the interview, Carmen explained why single-photons are necessary in Quantum technologies and how Quantum Key Distribution systems (QKD) use them.
She told Physics World’s online editor, Hamish Johnston:
“Single-photons can be used as qubits to store Quantum information. Because they do not interact very readily with their environment, they can travel for hundreds of kilometres and still store this Quantum information without it degrading as much as matter-stored qubits would.
“Single-photons are the basis of any Quantum photonics technology. They are the only flying qubit that we know of. And they will underpin the Quantum Internet and be fundamental to some of the Quantum computing approaches currently being developed. In the same way that lasers and photo detectors underpin global communication technologies and the Internet, sources of single-photons and detectors of single-photons will underpin the Quantum Internet.
“At the moment, we are working with firms like BT and Arkit to make Quantum communications systems that employ sources and detectors of single-photons. And we are looking at integrating our technology into these systems – in particular, Quantum Random Number Generator and Quantum Key Distribution systems. We are building with BT and other partners in the UK a QKD system that can interface with the 5G testbed that BT has at Adastral Park, Suffolk.”
Carmen also gave an overview of the technology that Nu Quantum is developing – how our systems create and detect single-photons.
“Starting with the single-photon source: We use small atomic defects in a material that is a very thin insulator. These point defects are particularly active and they emit single-photons. You can excite them with light or with a current, and they will emit a photon when they relax. We have used these materials alongside an optical microcavity to enhance the emission in all respects in terms of quality and rate. And we have built a photonic and electronic system or module around this material which is also tackling excitation and read-out optics as well as cavity-locking mechanisms – all to form a module that ideally enables you to get a photon out at the press of a button.
“Our technology is very unique, and we are hoping to have the world’s first room temperature single-photon source product.”
Turning to detecting single-photons, Carmen explained:
“The traditional way of detecting single-photons is by using avalanche photodiodes (APDs): Semiconductor structures that create a very large electric field inside the semiconductors, such that when a photon comes in and is absorbed and forms an electron-hole pair, you have such a large electric field that can separate the electron and hole. The electron hole then dislocates other charges and this leads to an avalanche process, which, in turn, leads to a detectable current. That is the traditional room temperature way of detecting single-photons, and we have a take on that. At Nu Quantum, we are all about making APDs better by looking at that semiconductor structure, how you package and how you design the electronics around it. And, in that, there is a lot of scope to improve the design of these modules for particular use cases.”