One small step for computer designers, one microscopic leap for computer design. University researchers have developed a chip that uses quantum mechanics, that can process information faster than classical computers.

Jess Cox
Graphic by Gervis Menzies

Physics Prof. Christopher Monroe and a team that included physics graduate student Daniel Stick, published a paper in Nature Physics demonstrating proof of principle for the fabrication of advanced computers. Monroe’s research relies on manipulating properties of the atom to enhance traditional computer chips. Quantum chips, which are capable of processing information faster than classical chips, could propel computer design to the next level.

The researchers have found a way to augment microscopic quantum computer chips – using a unique application of existing fabrication techniques. Although quantum computers are still far from our desktops, the development may lead to more advances in quantum physics.

In the past, Monroe and his colleagues have been able to trap ions or isolate ions from the immediate environment – making them “hover” – using individually tuned and controlled electrodes to keep the ion stable.

Prior to publication of this paper, no one had figured out how to incorporate a large number of ion traps into a single chip or miniaturized electronic circuit. “Previous chips would have only four or five trap zones, but over 1000 trap zones are needed for quantum applications,” Stick said.

The group found a way to use an existing fabrication technique called photo lithography to build chips with these ion traps on board.

This finding is important because, “making one ion trap in this fashion, implies with existing manufacturing technologies, that the design can be scaled up to include several more traps,” Stick said.

Quantum computers, therefore will store information in a unique way. Individual atoms can store quantum bits of information called qubits. Each qubit can hold the number 1 or 0, or even both 1 and 0 simultaneously, Stick said. Conventional computer chips store 1s and 0s individually.

Why does it work this way?

“It’s just a strange fact of quantum mechanics,” Stick said.

According to quantum theory, the orbit of an electron around a nucleus is based on the energy of the electron. Changing orbits is a very specific process. Imagine that you want to cross a river which has a stone path across it. You must jump from one stone to the next stone in order to cross the river. However, jumping costs energy – spend too much energy and you will jump past the next stone. Spend too little energy and you will fall short.

The quantum catch is that the distance between each stone is increasing with a known rate. In order for an electron to become excited, or jump from a low energy state to a high energy state, it must receive exactly the right amount of energy, just like a person crossing the river. If the electron receives the wrong amount of energy, it will miss its jump and go back to its pre-jump position.

Lasers emit light that is of energy equal to these specific quantum transitions – the jumps – can be used to send signals to the ions.

Because each quantum transition occurs at a specific energy, lasers can be tuned to target different transitions, thus allowing multiple inputs. Similar quantum properties can then be exploited to cause ions to emit photons, which can then be recorded by a sensitive camera.

Because the idea behind quantum computing is to take an electrically active ion and physically isolate it from the rest of the system, it is absolutely essential that ions are trapped. Stick employed the ion-trapping technique, which uses electromagnetic waves to suspend a single ion in free space.

Monroe said that though it is simple in principle to add more atoms, “it turns out to be terribly difficult to have complete control of even just a few isolated atoms.”

“Although we know exactly what to do to scale this to a more interesting size, it will take a great deal of technical firepower, mostly in the area of lasers, to achieve this,” he said.

In the process of photo lithography, the technique used to construct the chips, patterns are etched into a thin skin of semiconductor material called a wafer. Usually, wafers are composed of silicon. However, Stick said the ion trap chips use gallium arsenide – a compound used for cell phones – because it is a more efficient conductor than silicon.

Basically, gallium arsenide can function at 250 GHz, a much faster rate than silicon. Traditionally, silicon was preferred over the faster gallium arsenide because silicon is cheaper and more versatile due to its higher strength.

Although programming multiple inputs to work in harmony may be difficult, Stick said scientists know how to program a quantum computer composed of trapped ions. Monroe was able to solve the problem of trapping a single ion. The next step for scientists is to trap multiple ions,

For now, the computer industry is staying away from this type of research, at least “until they see a market for it,” Monroe said. Unfortunately, quantum computers are still decades away. Monroe said that someday it may turn into an arms race, in which case, the quantum field will benefit because it will be driven by industry.

“Quantum mechanics is so bizarre that it will always be a fascinating research topic,” Monroe said.

“Quantum mechanics allows things like atoms and molecules to be in two places at the same time. It allows us to ‘teleport’ simple quantum particles from one place to another without any physical contact. Now that’s cool.”

Monroe added that the future for this research could hold revolutionary results.

“Einstein never truly believed in quantum physics, so maybe, someday we will find that he was right and it breaks down at some level,” Monroe said, “I wouldn’t count on it, but this could be much more interesting than a quantum computer!”

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