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By A.J. Roan
For Metal Tech News 

Quantum computing closer with germanium

Original transistor semiconductor gets new quantum life


Last updated 3/24/2020 at 12:50pm

Quantum computer circuit quantum bits qubits germanium transistors

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A quantum computer use quantum bits, or qubits, which are much like the zeros and ones of a binary system but the information exists in either state at the same time.

The future of computing may be seeing a transition back to germanium, a material that is at the same time the past and future of quantum computing.

While today's computers have become exponentially faster, smaller and more powerful than their World War II predecessors, they work much the same way – carrying out complex computations with binary code, a stream of zeros and ones.

The very first of these computers used vacuum tubes to switch on and off the flow of electricity, creating one when power flowed through and zero when there was none.

After the war, through the 1950s, a second generation of computers would use transistors instead of vacuum tubes – a much faster and more reliable means of creating the binary language of computers.

While software and hardware advances over the following six decades have made computers that we hold in the palm of our hand millions of times more powerful than the rooms full of mainframes during the 1950s, binary code being dutifully spit out by transistors remains the basis for computation.

Quantum computing, however, may fundamentally change the way computers carry out their calculations – a shift in speed and form that has the potential to make today's computers look like the giant mainframes of the 1960s.

Albeit, this quantum leap in computing will still lean on the transistor and go back to the material used to make the very first one – germanium.

Schrödinger's computer

To understand how different quantum computers are from conventional machines, it can best be likened to Schrödinger's cat, a thought experiment posited by Dr. Erwin Schrödinger to explain quantum mechanics.

This idea is simple in all that it requires is a radioactive atom, a Geiger counter, a hammer and a container filled with cyanide and, oddly enough, a cat in a box.

Radiation from the decaying atom is picked up by the Geiger counter, which triggers the hammer to fall and break the container of cyanide – killing the cat. The scenario presents a hypothetical cat that may be simultaneously both alive and dead in the box (quantum realm), yet when one looks into the box it is observed that the cat is either dead or alive, not both.

This model was used to demonstrate that simple confusions of quantum theory could lead to absurd results which do not match the real world.

It also happens to work quite well as a comparison to represent a principle of quantum mechanics called superposition, which means an atom's electrons are at the same time decayed and intact.

Much like Schrödinger's cat, which is not known to be dead or alive until the box is opened.

Quantum computing uses a term called quantum bits, or qubits, which are much like the zeros and ones found in our present system of binary, yet the information exists in either state at the same time.

This means the usually understood zero or one, is either a zero or a one or both at the same time.

This superposition of qubits is what gives quantum computers their inherent parallelism. This parallelism is what allows a quantum computer to work on a million computations at once, while your desktop PC works on one.

A 30-qubit quantum computer would equal the processing power of a conventional computer that could run at 10 teraflops (trillions of floating-point operations per second) and a typical desktop computer of today runs at speeds measured in gigaflops (billions of floating-point operations per second).

The power and potential of future quantum computers is nearly as unfathomable as the heavy mechanics and physics that go into them.

Germanium transistors return

Transistors are the key active components in practically all modern electronics, which is why many consider these semiconductor switches to be one of the greatest inventions of the 20th century.

Simply put, transistors are tiny on and off switches that represent the standard computer binary system – off being a zero state and on being the one state.

Transistors, however, do not use moving parts to carry out their endless stream of zeros and ones. Instead, they use the special properties of semiconductor materials such as silicon or germanium to flick the switch.

Due to the atomic structure of these semiconducting materials, the electrons rarely escape their bonds.

Taking advantage of this wonder of physics, today's smartphones and laptops contain millions of these transistors dutifully switching off and on.

The world's first transistor was made from a rare metalloid, or semi-metal, that geologically tends to be found with zinc. Due to the limitations of manufacturing germanium during the transistor's early years, silicon became the material of choice.

There are some good reasons why silicon dominated though. For one thing, silicon is far more abundant and thus a lot cheaper.

Silicon also has a wider bandgap, the energy hurdle that must be overcome for a transistor to carry current, to flip the switch, so to speak. The larger the bandgap, the harder it is for current to leak across the device when it is supposed to be off, draining power.

As an added benefit, silicon also has better thermal conductivity, making it easier to draw away heat so that circuits don't burn.

Given all those advantages, it is natural to wonder why scientists are resurrecting germanium as a transistor material for quantum computing.

The answer lies in mobility. Electrons move nearly three times as readily in germanium as they do in silicon when these materials are close to room temperature. And the holes-the space that is lacking in an electron-move about four times as easily.

This means the flipping of the switch is much faster in a germanium transistor than a silicon transistor.

Which makes germanium the more potent material for operating with qubits, that basic unit of quantum information.

QuTech breakthrough

Researchers at QuTech, an advanced research center for quantum computing and quantum internet, have made a significant breakthrough towards making these cutting-edge technologies a reality with transistors based on germanium.

"We have been working with transistors as the building blocks for a quantum computer for some time now," says Nico Hendrickx, first author and PhD student at QuTech. "Until now, however, it hasn't been possible to perform quantum calculations using only transistors. Other elements were needed as well, and this provided a limitation for upscaling. We now show that a single transistor can function as a quantum bit by using germanium."

The QuTech researchers have long considered germanium as a superb material for making quantum bits, but manufacturing with this material has been challenging.

These hurdles have now been overcome and the team has now demonstrated they "can perform reliable and extremely fast quantum calculations with germanium."

Quantum computer circuit quantum bits qubits germanium transistors


An illustration of two quantum bits made of germanium transistors for a quantum computer.

"This means that germanium has matured in about a year's time from constructing the material to a platform on which quantum calculations can be carried out," says Menno Veldhorst, leader of the discovery team. "This development is unprecedentedly fast and that is extremely promising on the road to a functional quantum computer."

The results from Veldhorst team's work was published in Nature, a British multidisciplinary scientific journal, earlier this year.

With the work done by the QuTech team, the future of quantum computers is something to look forward to and the possibility of this next leap in computer technology becoming a reality within our lifetime is an even more exciting prospect.

And much like Schrödinger's cat, the germanium transistor is both dead and alive until we are able to fully observe the world of quantum computing and quantum internet.


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