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We might finally have a way to build circuits for the world's first quantum computers

We are getting so close.

BEC CREW
8 JUL 2016
 

The computers of today have just about hit their limits, and scientists around the world are scrambling to build the first viable quantum computer - a machine that could increase processing speeds 100-million-fold.

The biggest challenge in scaling up a quantum computer is figuring out how to entangle enough quantum bits (qubits) to perform calculations, but a team of engineers in the US say they might finally have a solution.

 

Quantum computers are set to revolutionise how we process data in the future, because they’re not limited to the 1s and 0s of binary code that today’s computers rely on. That binary code is holding us back, because if you can only use a combination of 1s and 0s, there’s a finite amount of data that can be processed, no matter how fast you go.

Instead, quantum computers use qubits, which can essentially take the state of 0, 1, or a 'superposition' of the two. So rather than having bits that can only be 1 or 0 at any given moment, qubits can be anything and everything. 

As Todd Jaquith explains for Futurism:

"Quantum computers exploit three very unusual features that operate at the quantum scale - that electrons can be both particles and waves, that objects can be in many places at once, and that they can maintain an instantaneous connection even when separated by vast distances (a property called 'entanglement’)."

This means that quantum computers can perform many calculations simultaneously, giving them - quite literally - limitless potential. But we have to figure out how to build them first.

Despite what Google’s been saying about its controversial new D-Wave 2X quantum computing machine, no one’s been able to build a 'proper' quantum computer, because of how difficult it is to entangle a large number of qubits on a circuit, and control them in any reliable way.

 

Once derided by Einstein himself as "spooky action at a distance", quantum entanglement is a strange phenomenon where two quantum particles interact in such a way that they become deeply linked, and essentially 'share' an existence.

This means that what happens to one particle will directly and instantaneously affect the other - even if it’s many light-years away.

Getting a bunch of entangled particles in the one place is crucial to the development of quantum computers, and researchers from Penn State University say they’ve come up with a technique that could get this done.

First they used beams of laser light to build a three-dimensional lattice array, which could trap and hold onto a bunch of quantum particles, forcing them into a cubic arrangement of five stacked planes. Think of it like a five-layer sandwich with grids of atoms held inside each layer, says Katherine Noyes from PC World. 

Each layer in the circuit could hold 25 equally spaced atoms, and once they were all in position, microwaves were used to switch individual qubits from one quantum state to another without altering the states of the other atoms in the cubic array.

As Noyes explains:

"The scientists filled some of the possible locations in the array with qubits consisting of neutral caesium atoms possessing no positive or negative charge. Then, they used crossed beams of laser light to target individual atoms in the lattice, causing a shift in the energy levels of those atoms.

When the scientists then bathed the whole array with a uniform wash of microwaves, the state of the atoms with the shifted energy levels changed, while the states of all the other atoms did not."

The team, led by physicist David S. Weiss, tested their ability to change the quantum state of these individual atoms by switching the states of selected atoms across three of the stacked planes to spell out the letters P, S, and U (for Penn State University).

"We changed the quantum superposition of the PSU atoms to be different from the quantum superposition of the other atoms in the array," Weiss says in a press release. "We have a pretty high-fidelity system. We can do targeted selections with a reliability of about 99.7 percent, and we have a plan for making that more like 99.99 percent."

So... next step, quantum computers?

Unfortunately, there are two major limitations here - the system needs to be seriously scaled up, because 125 atoms aren't going to do us much good in the real world, and the quantum particles used in the system hadn't been entangled. As we found out last month, when Chinese physicists quantum entangled 10 photon pairs to set a new world record, entangling multiple particles is hard.

But Weiss's team is confident that they can build on the system they have, both in teams of scale and spooky entanglement action. 

"Filling the cube with exactly one atom per site and setting up entanglements between atoms at any of the sites that we choose are among our nearer-term research goals," he says.

Our fingers are crossed for the computers of the future.

The results have been published in Science.

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