Researchers at the University of Paderborn and the University of Ulm in Germany have collaborated to develop the first programmable optical quantum memory. The new technique works like an entangled “assembly line” in which entangled photon pairs are sequentially created and combined with stored photons. The research was published as an “Editor’s Pick” in the latest issue of Physical Review Letters.
This year, the Nobel Prize in Physics was awarded to three scientists who have made important contributions to quantum entanglement experiments. Quantum entanglement refers to two or more particles in an entangled state in quantum mechanics, some of which behave as if they were a whole even when separated by great distances. Entangled systems that can contain multiple quantum particles have significant advantages in implementing quantum algorithms that have the potential to be used for communications, data security or quantum computing.
But previously, trying to entangle more than two particles resulted in very inefficient entanglement. In some cases, if researchers want to link two particles with other particles, they need to wait a long time, because the interconnections that facilitate this entanglement work only with limited probability. This means that once the next suitable particle arrives, the photon is no longer part of the experiment, as storing qubit states represents a significant experimental challenge.
“We have now developed a programmable optically buffered quantum memory that dynamically switches back and forth between different modes – storage mode, interference mode and final release mode,” the researchers explained.
In the experimental setup, a small quantum state can be stored until another state is created, and the two can then be entangled. This enables a large, entangled quantum state to “grow” particle by particle. The research team used this method to entangle four and six particles, making it more efficient than any previous experiment, with 9 and 35 times the success rate, respectively, of conventional methods.
The researchers explained: “Our system allows progressively larger and larger entangled states to be built up – which is faster, more reliable and more efficient than any previous method. For us, this represents a milestone that enables us to The practical application of large entangled states of useful quantum technology is getting closer.” The new method can be combined with all common sources of photon pairs, which means that scientists in other fields can also benefit from this method.
