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Karen Chiu

This article originally appeared on ABACUS
A true quantum computer can potentially transform encryption and cybersecurity, but right now there’s still a long way to go.
One thing that needs to happen first: Getting enough qubits (or quantum bits) to entangle in a way that people can actually control.
Now a group of Chinese physicists say they’ve managed to achieve 18-qubit entanglement, while still being able to control each qubit -- setting a new record.
But... what does that mean?
Can China solve its water problem with rain-making furnaces?
SPOOKY ACTION
Let’s go back a bit. This experiment uses photons (the particles that light is made up of) -- so for the moment, let’s think of photons as like... clownfish. (Sorry, I just watched Finding Nemo again.)
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.
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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.”
In April, a European team said they were able to generate entanglement in a system of 20 qubits. But that experiment was different in that it only detected entanglement in groups of two to five within those 20 qubits.

THE MORE THE MERRIER?
You might have heard of quantum computers with way more qubits than just 18. But here’s the thing. As Quantum Computing Report points out, not all qubits are created equal.
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”.
Named Time Magazine’s 100 Most Influential People this year and Nature’s 10 people who mattered in 2017, Pan is best known for the world’s first intercontinental video call using quantum encryption.
Relying on the curious properties of quantum physics, Pan and his team successfully ran a virtually unhackable video conference with counterparts in Austria, paving the way for a new form of highly secure communication.
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.



Chinese scientists broke a quantum computing record

A European team observed entanglement between neighboring qubits in pairs (blue), groups of three (pink), groups of four (red) and groups of five (yellow). (Picture: IQOQI) 


Chinese scientists broke a quantum computing record

But what does 18-qubit entanglement exactly mean?

Can China solve its water problem with rain-making furnaces?

SPOOKY ACTION