A photograph of a full moon, created by lights from thousands of hair-thin pipes of glass, won first prize in the Danish National Research Foundation’s photo competition 2018. The picture gives an insight into the thorough methods that scientists use in the hunt for developing quantum technologies that can revolutionize the processing of data and digital security.
The picture looks like a full moon in a clear night sky, but if the viewer looks closer, the moon formation consists of thousands of tiny illuminating dots. Each one is created by light from a so-called optical fiber – a pipe of glass as thin as a human hair. The photograph is called The Rising Fiber Moon, and it is the winning photo in the Danish National Research Foundation’s photo competition 2018. The competition is a new initiative whereby the foundation’s numerous grant holders within the Danish research environment have the opportunity to submit photographs from the world of basic research that awakens our curiosity.
“In the picture we see a projection of the light from a powerful lamp that is transmitted through a bundle of these optical fibers. The bundle has a diameter of approximately one centimeter and contains 10,000 fibers that run closely side by side. At the end, every single output of light from the fibers is magnified onto a wall as dots that together form the moon-like design,” physicist Jonas Schou Neergaard-Nielsen explained. He is the creator of the winning photo and a senior researcher at the DNRF’s Center for Macroscopic Quantum States (bigQ), which is led by professor Ulrik Lund Andersen and anchored at the Technical University of Denmark (DTU).
The lamp and the fiber bundle are normally tools that researchers at bigQ use for powerful illumination of singular fibers, which are handled with care when experimenting with quantum physics. To take the photograph, Neergaard-Nielsen had to almost turn the lamp upside down, since the light output is normally focused on the tip of one single fiber, an area of just one millimeter in diameter.
“In experiments we want a good picture of one of the single fiber’s tips in a microscope, and to do so, we need a very intense lightning of the fiber tip. The reason why we need a clear picture is because we must treat the fiber very precisely with a laser beam in order to make the surface of the fiber curve inwards. If it succeeds, the fiber tip can function as a microscopic mirror in our experiment,” Neergaard-Nielsen explained.
The small mirror is used by Neergaard-Nielsen and his colleagues to create a so-called microcavity. In principle, it is two small mirrors placed a few micrometers from each other, so that light can continuously move back and forth between the mirrors. And the light between the mirrors is exactly what the researchers are interested in.
Light particles are the safe data messengers of the future
To understand exactly why this light is so interesting to Neergaard-Nielsen and his colleagues at bigQ, we need to dig deeper into the world of quantum mechanics. One of the reasons is that light particles – also known as photons – are potentially carriers of data, since, unlike electrons, they can transport data without any resistance and with the speed of light. This enables fast transmission of massive amounts of data. Another reason is that particles like photons can be in a certain state called quantum entanglement. Quantum researchers hope to exploit these photonic qualifications in order to create fast and secure methods of communication.
In the state of quantum entanglement, two photons are entangled into one system, and therefore, each affects the other, even though the photons are far apart. This means that each of the entangled photons can function as an encryption key for an unbreakable connection. In that case, if a trespasser tries to measure one of the photons to intercept data from the connection, the second photon in the entangled system will be affected by the measurement as well, which will reveal the potential eavesdropping.
Thus, in the quantum researchers’ wildest dreams, the photons’ quantum mechanical qualities can be used as the cornerstone in a secure and lightning-fast worldwide quantum internet. However, the challenge is that photons are very fragile and extremely difficult to produce and handle. That is why researchers all over the world, including Neergaard-Nielsen and his colleagues at bigQ, are working on producing large amounts of photons that they can manage and control as they please.
BigQ will make the microscopic quantum world macroscopic
This brings us back to the light that runs back and forth between the two microscopic mirrors. The light originates from what the researchers call N-V centers:
“N-V centers are an impurity in the crystal structure on a very small piece of diamond. This impurity, in principle, acts as one single free atom and can work as a source of single photons. A photon source like this is extremely desirable in quantum physics, for instance, from the perspective of technologies for quantum communication,” Neergaard-Nielsen explained. He added:
“By converting a fiber tip into one of the mirrors in the microcavity, we can capture these single photons in the fiber. And because optic fibers are flexible, we can lead the light wherever we want to and integrate the photons further in our quantum experiments,” Neergaard-Nielsen explained.
BigQ opened in January 2018 with a grant of 63 million DKK from the Danish National Research Foundation. The center is the only place in the world where the laboratory has a special combination of technologies that include quantum optics and N-V centers in diamond. One of the main goals for bigQ is to use this combination to work toward creating macroscopic quantum conditions of light.
“In relation to optic fibers, we would like to try controlling bigger amounts of light by creating numerous microcavities close to each other and, in that way, collecting and working with photons from many different N-V centers. In practice, experiments like these can lead to the development of a quantum internet, for instance, and other applicable technologies based on quantum physics,” Schou Neergaard-Nielsen concluded.