The illustration
shows an optical chip embedded with a so-called quantum dot.
The quantum dot
can function as a gateway or transistor for photons.
The drawing on top
shows that if you send a single photon into the quantum dot,
it will be thrown
back – the gateway is closed. The lower drawing shows that if you send
two photons, the
gateway opens the two photons are sent onwards. So the quantum dot
works as a photon
contact and this is an important component when you want to build
complex quantum
photonic circuits on a large scale. Illustration: Alisa Javadi, Niels Bohr
Institute.
(October 23, 2015) There
is tremendous potential for new information technology based on light
(photons). Photons (light particles) are very well suited for carrying
information and quantum technology based on photons – called quantum photonics,
will be able to hold much more information than current computer technology.
But in order to create a network with photons, you need a photon contact, a
kind of transistor that can control the transport of photons in a circuit.
Researchers at the Niels Bohr Institute in collaboration with researchers from
the Korea Institute of Science and Technology have managed to create such a
contact. The results are published in the scientific journal Nature
Communications.
Quantum information can be sent optically, that is to say,
using light, and the signal is comprised of photons, which is the smallest
component (a quantum) of a light pulse. Quantum information is located in
whichever path the photon is sent along – it can, for example, be sent to the
right or to the left on a semi-transparent mirror. It can be compared to the
use of bits made up of 0s and 1s in the world of conventional computers. But a
quantum bit is more than a classical bit, since it is both a 0 and a 1 at the
same time and it cannot be read without it being detected, as it is only a
single photon. In addition, quantum technology can be used to store far more
information than conventional computer technology, so the technology has much
greater potential for future information technology.
Søren Stobbe,
associate professor, Peter Lodahl, professor and
Alisa Javadi,
postdoc in front of the Niels Bohr Institute on Blegdamsvej at
the University of
Copenhagen.
Controlling the light
Light normally spreads in all directions. But in order to
develop quantum technology based on light, you need to be able to control light
down to the individual photons. Researchers in the Quantum Photonic research
group at the Niels Bohr Institute are working on this and to do so, they use an
optical chip embedded with a so-called quantum dot. The optical chip is made up
of an extremely small photonic crystal, which is 10 microns across (1 micron is
a thousandth of a millimetre) and has a thickness of 160 nanometers (1
nanometer is a thousandth of a micron). Embedded in the middle of the chip is a
so-called quantum dot, which is comprised of a collection of atoms.
Alisa Javadi,
postdoc in the Quantum Photonic research group, has worked with the
experiments in the
laboratory at the Niels Bohr Institute, University of Copenhagen.
“We have developed the photonic chip so that the quantum dot
emits a single photon at a time and we can control the photon’s direction. Our
big new achievement is that we can use the quantum dot as a contact for the
photons – a kind of transistor. It is an important component for creating a
complex network of photons,” explains Peter Lodahl, professor and head of the
Quantum Photonic research group at the Niels Bohr Institute at the University
of Copenhagen.