In a collaboration between Aarhus University and the University of Southern Denmark, researchers have discovered a way to subtract a single quantum of light from a laser beam.
This work has recently been published and selected as an Editor's Suggestion in Physical Review Letters.
This method paves the way towards future quantum communication and computation using the subtle aspects of quantum mechanics for technological applications.
Light is made up of little indivisible packets of energy, or particles, known as photons. A defining property of photons is that they are non-interacting, they simply pass through each other totally unaffected.
In the context of quantum communication, this is a very useful feature, as it ultimately enables low-loss transmission of optically encoded data over very large distances. However, many emerging ideas for quantum information processing would greatly benefit from the ability to make two photons interact, whereby one can affect the propagation or state of another.
Over the past years, ultracold atomic gases have proven to provide an ideal medium in which to manipulate light. For example, using a technique known as electromagnetically induced transparency, one can drastically modify the velocity of light propagation and slow light down to astonishingly slow speeds of just a few meters per second.
Perhaps even more remarkably, one can bring light to a full halt by converting the photons into atomic excitations within the medium. By reversing this process, and mapping the excitations back onto photons, this procedure realises a photonic quantum memory, where photons can be temporarily stored and retrieved on demand.
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