First use of quantum technology to create a random number generator that is both tiny and fast
Random number generators are crucial to the encryption that protects our privacy and security when engaging in digital transactions such as buying products online or withdrawing cash from an ATM. For the first time, engineers have developed a fast random number generator based on a quantum mechanical process that could deliver the world’s most secure encryption keys in a package tiny enough to use in a mobile device.
In The Optical Society’s journal for high impact research, Optica, the researchers report on their fully integrated device for random number generation. The new work represents a key advancement on the path to incorporating quantum-based random number generators — delivering the highest quality numbers and thus the highest level of security — into computers, tablets and mobile phones.
“We’ve managed to put quantum-based technology that has been used in high profile science experiments into a package that might allow it to be used commercially,” said the paper’s first author, Carlos Abellan, a doctoral student at ICFO-The Institute of Photonic Sciences, a member of the Barcelona Institute of Science and Technology, Spain. “This is likely just one example of quantum technologies that will soon be available for use in real commercial products. It is a big step forward as far as integration is concerned.”
The new device operates at speeds in the range of gigabits per second, fast enough for real-time encryption of communication data, such as a phone or video calls, or for encrypting large amounts of data traveling to and from a server like that used by a social media platform. It could also find use in stock market predictions and complex scientific simulations of random processes, such as biological interactions or nuclear reactions.
Shrinking the truly random
The random number generators used today are based on computer algorithms or the randomness of physical processes — essentially complex versions of rolling dice over and over again to get random numbers. Although the numbers generated appear to be random, knowing certain information, such as how many “dice” are being used, can allow hackers to sometimes figure out the numbers, leaving secured data vulnerable to hacking.
The new device, however, generates random numbers based on the quantum properties of light, a process that is inherently random and thus impossible to predict no matter how much information is known. Although other researchers have developed quantum random number generators, they have all been either larger or slower than the device reported in the Optica paper.
“We have previously shown that the quantum processes taking place exhibit true randomness,” said Valerio Pruneri, who led the collaborative research effort. “In this new paper, we made a huge technological advance by using a new design that includes two lasers that interfere with each other in a confined space. This makes the device smaller while keeping the same properties that were used in the past experiments.”
Creating a practical device
The researchers used photonic integrated circuit (PIC) technology to create two quantum number generators that together measure 6 by 2 millimeters. PIC technology offers a way to integrate photonic components — such as the lasers and detectors used by the new quantum random generator — onto a chip with a small footprint and low power consumption. Most importantly, PIC-based devices can be integrated with traditional electronics, which could allow the random number generator to be used with the driving, reading and processing electronics necessary for computation or communications.
“We proved that quantum technologies are within practical reach by exploiting PICs,” said Pruneri. “Quantum random number generation as well as quantum cryptography and other quantum-based technologies will benefit from PIC-based technology because it allows one to build commercial and innovative products. Ours is a first demonstration.”
Electrons reveal their quantum properties when they are confined to small spaces. Scientists from TU Wien (Vienna), Aachen and Manchester have created tiny quantum dots in Graphene
In a tiny quantum prison, electrons behave quite differently as compared to their counterparts in free space. They can only occupy discrete energy levels, much like the electrons in an atom – for this reason, such electron prisons are often called “artificial atoms”. Artificial atoms may also feature properties beyond those of conventional ones, with the potential for many applications for example in quantum computing. Such additional properties have now been shown for artificial atoms in the carbon material graphene. The results have been published in the journal “Nano Letters”, the project was a collaboration of scientists from TU Wien (Vienna, Austria), RWTH Aachen (Germany) and the University of Manchester (GB).
Building Artificial Atoms
“Artificial atoms open up new, exciting possibilities, because we can directly tune their properties”, says Professor Joachim Burgdörfer (TU Wien, Vienna). In semiconductor materials such as gallium arsenide, trapping electrons in tiny confinements has already been shown to be possible. These structures are often referred to as “quantum dots”. Just like in an atom, where the electrons can only circle the nucleus on certain orbits, electrons in these quantum dots are forced into discrete quantum states.
Even more interesting possibilities are opened up by using graphene, a material consisting of a single layer of carbon atoms, which has attracted a lot of attention in the last few years. “In most materials, electrons may occupy two different quantum states at a given energy. The high symmetry of the graphene lattice allows for four different quantum states. This opens up new pathways for quantum information processing and storage” explains Florian Libisch from TU Wien. However, creating well-controlled artificial atoms in graphene turned out to be extremely challenging.
Cutting edge is not enough
There are different ways of creating artificial atoms: The simplest one is putting electrons into tiny flakes, cut out of a thin layer of the material. While this works for graphene, the symmetry of the material is broken by the edges of the flake which can never be perfectly smooth. Consequently, the special four-fold multiplicity of states in graphene is reduced to the conventional two-fold one.
Therefore, different ways had to be found: It is not necessary to use small graphene flakes to capture electrons. Using clever combinations of electrical and magnetic fields is a much better option. With the tip of a scanning tunnelling microscope, an electric field can be applied locally. That way, a tiny region is created within the graphene surface, in which low energy electrons can be trapped. At the same time, the electrons are forced into tiny circular orbits by applying a magnetic field. “If we would only use an electric field, quantum effects allow the electrons to quickly leave the trap” explains Libisch.
The artificial atoms were measured at the RWTH Aachen by Nils Freitag and Peter Nemes-Incze in the group of Professor Markus Morgenstern. Simulations and theoretical models were developed at TU Wien (Vienna) by Larisa Chizhova, Florian Libisch and Joachim Burgdörfer. The exceptionally clean graphene sample came from the team around Andre Geim and Kostya Novoselov from Manchester (GB) – these two researchers were awarded the Nobel Prize in 2010 for creating graphene sheets for the first time.
The new artificial atoms now open up new possibilities for many quantum technological experiments: “Four localized electron states with the same energy allow for switching between different quantum states to store information”, says Joachim Burgdörfer. The electrons can preserve arbitrary superpositions for a long time, ideal properties for quantum computers. In addition, the new method has the big advantage of scalability: it should be possible to fit many such artificial atoms on a small chip in order to use them for quantum information applications.
Learn more: “Artificial Atom“ Created in Graphene
In this month’s issue of Physics World, Jon Cartwright explains how the revelation that the US National Security Agency (NSA) is developing quantum computers has renewed interest and sparked debate on just how far ahead they are of the world’s major labs looking to develop the same technology.
Read more: NSA pursues quantum technology