A clownfish is made up of various attributes, like size, gender, and swimming speed. Photons also come in different traits: paths, polarization and orbital angular momentum.

Let’s say there are two clownfish that are “entangled” -- one male, one female. You can’t tell which is which just from the outside -- but we do know that if fish #1 is a girl, then fish #2 must be a boy, and vice versa. Until you find out for sure, each clownfish is basically both a boy and a girl -- a phenomenon known in quantum physics as superposition.

Next, you decide to change the gender of one fish. Once you do that, the other fish must immediately turn into the opposite sex. That’s what we call entanglement.

Entangled qubits are like that too -- changing one affects the other, even if they are far apart physically. That’s what Albert Einstein dubbed “spooky action at a distance”.

Entanglement and superposition are some of the weird qualities that quantum computers could make use of to create powerful algorithms, potentially doing what classical computers can’t do.

How China plans to challenge SpaceX with reusable rockets

18-QUBIT ENTANGLEMENT

In their experiment, the Chinese team used six photons, each with three traits (or “degrees of freedom”). That’s equivalent to 18-qubit entanglement (6x3=18): One photon’s trait is related to that same photon’s other traits, plus all traits of the other photons as well.

Each of these 18 qubits have two possible values (just like there are two sexes in clownfish) -- together they represent 218 or 262,144 possibilities. Remember how each qubit can carry both values simultaneously? That means this 18-qubit entangled system can represent hundreds of thousands of values, all linked together, at the same time. That’s a big leap from a classical computer, which can only represent one value at a time.

Study coauthor Pan Jianwei told us, “The ability to coherently control 18 qubits enables experimental access to previously unexplored regimes.”

THE MORE THE MERRIER?

Well-behaved qubits are rare. Without the right temperature and condition, they tend to act like erratic, tantrum-throwing toddlers -- losing their precious quantum qualities quickly.

One big challenge is to have these qubits maintain superposition and entanglement for long enough to complete a task. For instance, trying to entangle 18 particles alone would already be extremely difficult because of how long that would take.

The Chinese team managed to entangle so many qubits because instead of using 18 particles, it used only six. This marks a breakthrough for quantum computers that use only particles instead of so-called superconducting circuits, which are used by researchers at places like IBM and Google.

The quest for quantum supremacy

FATHER OF QUANTUM

The record-breaking experiment was carried out by a team from the University of Science and Technology of China that includes Pan Jianwei -- known in China as the the “Father of Quantum”.

The godfather of Taiwan’s chip industry retires

For more insights into China tech, sign up for our tech newsletters, subscribe to our Inside China Tech podcast, and download the comprehensive 2019 China Internet Report. Also roam China Tech City, an award-winning interactive digital map at our sister site Abacus.