World’s smallest data memory: a single atom

Researchers at the Max Planck Institute of Quantum Optics have created the world’s smallest data memory, storing quantum information in a single atom.

They successfully wrote the quantum state of single photons into a rubidium atom and read it out again after a certain storage time.

The technique could in theory be used to design powerful quantum computers and network them with each other across large distances.

Using a single atom as a storage unit has several advantages – the extreme miniaturization being only one, says researcher Holger Specht. The stored information can be processed by direct manipulation on the atom, which is important for the execution of logical operations in a quantum computer.

“In addition, it offers the chance to check whether the quantum information stored in the photon has been successfully written into the atom without destroying the quantum state,” he says. This makes it possible to check at an early stage if a computing process needs to be repeated because of a storage error.

Until now, it’s been impossible to exchange quantum information between photons and single atoms, because the interaction between them is very weak. But the Max Planck team achieved this by placing a rubidium atom between the mirrors of an optical resonator, and then using weak laser pulses to introduce single photons into the resonator.

The mirrors of the resonator reflected the photons to and fro several times, which strongly enhanced the interaction between photons and atom.

The storage time – ie, the time the quantum information in the rubidium can be retained – was measured at around 180 microseconds.

“This is comparable with the storage times of all previous quantum memories based on ensembles of atoms,” says Stephan Ritter.

But the team acknowledges that a much longer storage time would be necessary for the method to be used in a quantum computer or a quantum network.

The storage time is mainly limited by magnetic field fluctuations from the laboratory surroundings, says Ritter. “It can therefore be increased by storing the quantum information in quantum states of the atoms which are insensitive to magnetic fields,” he suggests.