Researchers dream of quantum computers. Incredibly fast super computers which can solve such extremely complicated tasks that it will revolutionise the application possibilities. But there are some serious difficulties. One of them is the transistors, which are the systems that process the signals.
Today the signal is an electrical current. For a quantum computer the signal can be an optical one, and it works using a single photon which is the smallest component of light.
“To work, the photons have to meet and “talk”, and the photons very rarely interact together” says Anders Søndberg Sørensen who is a Quantum Physicist at the Niels Bohr Institute at Copenhagen University. He explains that light does not function like in Star Wars, where the people fight with light sabres and can cross swords with the light. That is pure fiction and can’t happen. When two rays of light meet and cross, the two lights go right through each other. That is called linear optics.
What he wants to do with the light is non-linear optics. That means that the photons in the light collide with each other and can affect each other. This is very difficult to do in practice. Photons are so small that one could never hit one with the other. Unless one can control them – and it is this Anders Sørensen has developed a theory about.
Light collisions at the quantum level
Instead of shooting two photons at each other from different directions and trying to get them to hit each other, he wants to use an atom as an intermediary. The atom can only absorb one photon (such are the laws of physics). If you now direct two photons towards the atom it happens that they will collide on the atom. It is exactly what he wants.
The atom is however very small and difficult to hit. So the photons have to be focussed very precisely. In a previous experiment researchers had discovered that microwaves could be focussed on an atom via a superconducting nano-wire. They got the idea that the same could happen with visible light.
The theoretical model shows that it works. The atom is brought close to the nanowire. Two photons are sent towards the atom and when they hit it an interaction occurs between them, where one imparts information to the other. The information is sent in bits which are either a one or zero digit, and the order of digits produces the message. (Today we can send information via an optic cable and each bit is made up of millions of photons.) In quantum optics each bit is just one photon. The photon has now received its message and the signal continues on its way. It is a step on the way to building a photon-transistor for a quantum computer.
Source: University of Copenhagen
Related stories:
Can a single molecule behave as a mirror?
(PhysOrg.com) -- “We have shown for the first time, theoretically, that a single molecule can behave as a perfect mirror,” Mario Agio tells
PhysOrg.com. “Imagine that your mirror at home becomes a single molecule and that you put a strong lens between you and it. Well, you could still see the image of your face reflected…[A]mazing if you think that a molecule is just about a nanometer in size.”
Watching Electrons with Lasers
(PhysOrg.com) -- A team of researchers from the Stanford PULSE Institute for Ultrafast Energy Science at SLAC National Accelerator Laboratory has recently moved a step closer to visualizing the motions of electrons in molecules using a technique called high harmonic generation, or HHG.
MIT quantum discovery could lead to better detectors
(PhysOrg.com) -- A bizarre but well-established aspect of quantum physics could open up a new era of electronic detectors and imaging systems that would be far more efficient than any now in existence, according to new insights by a leader in the field that will appear in the journal
Science.
Light touch: Controlling the behavior of quantum dots
Researchers from the National Institute of Standards and Technology and the Joint Quantum Institute (JQI), a collaborative center of the University of Maryland and NIST, have reported a new way to fine-tune the light coming from quantum dots by manipulating them with pairs of lasers. Their technique, published in
Physical Review Letters, could significantly improve quantum dots as a source of pairs of “entangled” photons, a property with important applications in quantum information technologies.
Researchers make milestone discovery in quantum mechanics
Researchers at UC Santa Barbara have recently reached what they are calling a milestone in experimental quantum mechanics.
Europe gets together to harness quantum physics
The long cherished goal of applying the strange properties of quantum mechanics to the macroscopic world we inhabit has been brought closer by a series of recent developments. The exciting progress was made in the important field of quantum optics and discussed recently at a high level conference organised by the European Science Foundation in collaboration with the Fonds zur Förderung der wissenschaftlichen Forschung in Österreich (FWF) and the Leopold-Franzens-Universität Innsbruck (LFUI).
First measurement of entangled states in nitrogen
When atoms form molecules, they share their outer electrons and this creates a negatively charged cloud. Here, electrons buzz around between the two positively charged nuclei, making it impossible to tell which nucleus they belong to. They are delocalized. But is this also true for the electrons located closer to the nucleus?
Quantum computers take step toward practicality with demonstration of new device
Computers based on the powerful properties of quantum mechanics have the potential to revolutionize information technology and security, but for decades they have remained more theoretical than practical, and difficult to scale up. That is changing, however, as demonstrated in a report this week in the journal
Science.
