Atomic nuclei intimately entangled by a quantum measurement
19 Oct 2012
Scientists from the Netherlands and the UK have brought two atomic nuclei in a diamond into a quantum entangled state.
Quantum entanglement is one of the most intriguing phenomena in physics. When two particles are entangled their properties are so strongly connected that they lose their own identity.
Measuring both particles yields fully correlated outcomes, even when the particles are very far apart. Einstein famously called this feature ’spooky action at a distance’.
Today, quantum entanglement is recognised as a resource for revolutionary new technologies that could provide secure communication and ultra-fast computation.
Atomic nuclei as quantum bits
Atomic nuclei in synthetic diamond are promising building blocks for a quantum computer. These nuclei behave like a tiny magnet. The two possible orientations of the spin (up or down) can be used to encode quantum information.
Scientists from Delft University of Technology reported last year in Nature that they could control and read out individual nuclear spins.
Furthermore, using chemical vapour deposition techniques, the Element Six team (UK) produced synthetic diamond, where due to its exceptional purity the quantum states of the nuclear spins were well protected from their environment.
However, interactions between nuclear spins in synthetic diamond are weak, making it challenging to create the entanglement required for quantum computing.
The scientists from Delft, working in partnership with Element Six, have now overcome this challenge by exploiting a special property of quantum measurements.
Entangled by measurement
Instead of probing the spin state of each nucleus separately, researchers measured a joint property of the two nuclei without gaining any knowledge on the individual states. In particular, the measurement forced the nuclei to either assume the same spin orientation or opposite ones, thus imprinting the desired correlations.
Towards teleportationThe scientists proved that the nuclei were entangled by violating the famous Bell inequality; the first demonstration with spins in a solid. The team now plans to use the entanglement to demonstrate basic quantum algorithms that have no classical counterpart, such as the teleportation of spin states.
