In a June 28 publication in Physical Review Letters, Chinese researchers presented a new record in quantum entanglement. The team demonstrated 18-qubit entanglement in photons.

The ability to entangle quantum objects (qubits) is vital to developing quantum computers. Two (or more) qubits are considered entangled when their states are correlated. To put it another way, their states depend on each other.

As an example, say we have two electrons which we want to use as qubits. Recall that one property of electrons is their spin, which can be clockwise or counterclockwise (that’s a little simplified, but bear with me).

Now let’s say these two electrons are entangled (correlated). If we measure the state of one electron and find it spinning clockwise, we would know that the other electron is also spinning clockwise.

Alternatively, we could also make these two electrons “anti-correlated”. This would mean if we measured one electron and found it spinning clockwise, we would know that the other electron would be spinning counterclockwise. Both situations (correlated and anti-correlated) are examples of quantum entanglement.

One fascinating characteristic of quantum entanglement is that this correlation is not dependent on the distance between the two electrons. They could be miles apart, but we would still see this correlation.

Going back to the China team’s results, they used three different properties (paths, polarizations, and orbital angular momentum) of six different photons to give 18 total entangled bits of quantum information (qubits). In their experiments, they made what is called a GHZ state, which is a correlated state (like our first electron example).

They also showed quantum logic and readout protocols, making their experiments even closer to quantum computing applications.

It’s definitely a cool achievement, and another step in the quantum marathon.

Reference:

Xi-Lin Wang, Yi-Han Luo, He-Liang Huang, Ming-Cheng Chen, Zu-En Su, Chang Liu, Chao Chen, Wei Li, Yu-Qiang Fang, Xiao Jiang, Jun Zhang, Li Li, Nai-Le Liu, Chao-Yang Lu, and Jian-Wei Pan, 18-Qubit Entanglement with Six Photons’ Three Degrees of Freedom,

Phys. Rev. Lett. 120, 260502 – Published 28 June 2018 arxiv:1801.04043