A fast-growing UK startup is quietly making strides in the promising field of quantum photonics. Cambridge-based company Nu Quantum is building devices that can emit and detect quantum particles of light, called single photons. With a freshly secured £2.1 million ($2.71 million) seed investment, these devices could one day underpin sophisticated quantum photonic systems, for applications ranging from quantum communications to quantum computing.
The company is developing high-performance light-emitting and light-detecting components, which operate at the single-photon level and at ambient temperature, and is building a business based on the combination of quantum optics, semiconductor photonics, and information theory, spun out of the University of Cambridge after eight years of research at the Cavendish Laboratory.
"Any quantum photonic system will start with a source of single photons, and end with a detector of single photons," Carmen Palacios-Berraquero, the CEO of Nu Quantum, tells ZDNet. "These technologies are different things, but we are bringing them together as two ends of a system. Being able to controllably do that is our main focus."
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As Palacios-Berraquero stresses, even generating single quantum particles of light is very technically demanding.
In fact, even the few quantum computers that exist today, which were designed by companies such as Google and IBM, rely on the quantum states of matter, rather than light. In other words, the superconducting qubits that can be found in those tech giants' devices rely on electrons, not photons.
Yet the superconducting qubits found in current quantum computers are, famously, very unstable. The devices have to operate in temperatures colder than those found in deep space to function, because thermal vibrations can cause qubits to fall from their quantum state. On top of impracticality, this also means that it is a huge challenge to scale up the number of qubits in the computer.
A photonic quantum computer could have huge advantages over its matter-based counterpart. Photons are much less prone to interact with their environment, which means they can retain their quantum state for much longer and over long distances. A photonic quantum computer could, in theory, operate at room temperature – and as a result, scale up much faster.
The whole challenge comes from creating the first quantum photon, explains Palacios-Berraquero. "Being able to emit one photon at a time is a ground-breaking achievement. In fact, it has become the Holy Grail of quantum optics."
"But I worked on generating single photons for my PhD. That's the IP I brought to the table."
Combined with improved technologies in the fields of nanoscale semi-conductor fabrication, Palacios-Berraquero and her team set off to crack the single-photon generation problem.
Nu Quantum's products come in the form of two little boxes: the first one generates the single photons that can be used to build quantum systems for various applications, and the other measures the quantum signals emitted by the first one. The technology, maintains the startup CEO, is bringing quantum one step closer to commercialization and adoption.
"Between the source and the detector of single photons, many things can happen, from the simplest to the most complex," explains Palacios-Berraquero. "The most complex one being a photonic quantum computer, in which you have thousands of photons on one side and thousands of detectors on the other. And in the middle, of course, you have gates, and entanglement, and… and, and and. But that's the most complex example."
A photonic quantum computer is still a very long-term ambition of the startup CEO. A simpler application, which Nu Quantum is already working on delivering commercially with the UK's National Physical Laboratory, is quantum random number generation – a technology that can significantly boost the security of cryptographic keys that secure data.
The keys that are currently used to encrypt the data exchanged between two parties are generated thanks to classical algorithms. Classical computing is deterministic: a given input will always produce the same output, meaning that complete randomness is fundamentally impossible. As a result, classical algorithms are predictable to an extent. In cryptography, this means that security keys can be cracked fairly easily, given sufficient computing power.
Not so much with quantum. A fundamental property of quantum photons is that they behave randomly: for example, if a single photon is sent down a path that separates in two ways, there is no way of knowing deterministically which way the particle will choose to go through.
The technology that Nu Quantum is developing with the National Physical Laboratory, therefore, consists of a source of single photons, two detectors, and a two-way path linking the three devices. "If we say the right detector is a 1, and the left detector is a 0, you end up with a string of numbers that's totally random," says Palacios-Berraquero. "The more random, the more unpredictable the key is, and the more secure the encryption."
Nu Quantum is now focusing on commercializing quantum random number generation, but the objective is to build up systems that are increasingly complex as the technology improves. Palacios-Berraquero expects that in four or five years, the company will be able to start focusing on the next step.
One day, she hopes, Nu Quantum's devices could be used to connect quantum devices in a quantum internet – a decade-long project contemplated by scientists in the US, the EU, and China, which would tap the laws of quantum mechanics to almost literally teleport some quantum information from one quantum device to the next. Doing so is likely to require single photons to be generated and distributed between senders and receivers, because of the light particles' capacity to travel longer distances.
In the shorter term, the startup will be focusing on investing the seed money it has just raised. On the radar, is a brand-new lab and headquarters in Cambridge, and tripling the size of the team with a recruitment drive for scientists, product team members and business functions.