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Category: quantum physics

The significant advance, by a team at the University of New South Wales (UNSW) in Sydney appears today in the international journal Nature.

“What we have is a game changer,” said team leader Andrew Dzurak, Scientia Professor and Director of the Australian National Fabrication Facility at UNSW.

“We’ve demonstrated a two-qubit logic gate — the central building block of a quantum computer — and, significantly, done it in . Because we use essentially the same device technology as existing computer chips, we believe it will be much easier to manufacture a full-scale processor chip than for any of the leading designs, which rely on more exotic technologies.

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For decades, researchers have been trying to build a computer that harnesses the enormous potential of quantum mechanics. Now engineers from the University of New South Wales (UNSW) in Australia have overcome the final hurdle, by creating a quantum logic gate in silicon — the same material that today’s computer chips are made from.

The newly developed device allows two quantum bits — or qubits — to communicate and perform calculations together, which is a crucial requirement for quantum computers. Even better, the researchers have also worked out how to scale the technology up to millions of qubits, which means they now have the ability to build the world’s first quantum processor chip and, eventually, the first silicon-based quantum computer.

Right now, regular computer chips store information as binary bits, which are either in a 0 or 1 state. This system works well, but it means that there’s a finite amount of data that can be processed. Qubits, on the other hand, can be in the state of 0, 1, or both at the same time, which gives quantum computers unprecedented processing power… if we can work out how to build them.

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A Game Changer in Quantum Computing:
The ingredients for superfast computers could be nearly in place. For the first time, researchers have demonstrated that two silicon transistors acting as quantum bits can perform a tiny calculation.

The advance represents the final physical component needed to realise the promise of super-powerful silicon quantum computers, which harness the science of the very small — the strange behaviour of subatomic particles — to solve computing challenges that are beyond the reach of even today’s fastest supercomputers. Potentially transforming fields like encryption and the search for new pharmaceuticals.

The significant advance, by a team at the University of New South Wales (UNSW) in Sydney appears today in the international journal Nature (“A two-qubit logic gate in silicon”).

“What we have is a game changer,” said team leader Andrew Dzurak, Scientia Professor and Director of the Australian National Fabrication Facility at UNSW.

“We’ve demonstrated a two-qubit logic gate — the central building block of a quantum computer — and, significantly, done it in silicon. Because we use essentially the same device technology as existing computer chips, we believe it will be much easier to manufacture a full-scale processor chip than for any of the leading designs, which rely on more exotic technologies.

“This makes the building of a quantum computer much more feasible, since it is based on the same manufacturing technology as today’s computer industry,” he added.

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What are the properties of the vacuum, the absolute nothingness? So far, physicists have assumed that it is impossible to directly access the characteristics of the ground state of empty space. Now, a team of physicists led by Prof. Alfred Leitenstorfer at the University of Konstanz (Germany) has succeeded in doing just that. They demonstrated a first direct observation of the so-called vacuum fluctuations by using short light pulses while employing highly precise optical measurement techniques. The duration of their light pulses was ensured to be shorter than half a cycle of light in the spectral range investigated. According to quantum physics, these oscillations exist even in total darkness, when the intensity of light and radio waves completely disappears. These findings are of fundamental importance for the development of quantum physics and will be published in the journal Science; an advance online version has appeared on October 1, 2015.

The existence of vacuum fluctuations is already known from theory as it follows from Heisenberg’s uncertainty principle, one of the main pillars of quantum physics. This principle dictates that electric and magnetic fields can never vanish simultaneously. As a consequence, even total darkness is filled with finite fluctuations of the electromagnetic field, representing the quantum ground state of light and radio waves. However, until now direct experimental proof of this basic phenomenon has been considered impossible. Instead, it is usually assumed that vacuum fluctuations are manifested in nature only indirectly. From spontaneous emission of light by excited atoms e.g. in a fluorescent tube to influences on the structure of the universe during the Big Bang: these are just some of the instances that highlight the ubiquitous role the concept of vacuum fluctuations plays in the modern physical description of the world.

An experimental setup to measure electric fields with extremely high temporal resolution and sensitivity has now made it possible to directly detect vacuum fluctuations, despite all contrary assumptions. World-leading optical technologies and ultrashort pulsed laser systems of extreme stability provide the know-how necessary for this study. The research team at the University of Konstanz developed these technologies in-house and also an exact description of the results based on quantum field theory. The temporal precision achieved in their experiment is in the femtosecond range — a millionth of a billionth of a second. The sensitivity is limited only by the principles of quantum physics. “This extreme precision has enabled us to see for the first time that we are continuously surrounded by the fields of electromagnetic vacuum fluctuations” sums up Alfred Leitenstorfer.

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Google and NASA are continuing to test quantum computers and this week entered into a new agreement to work with a series of updated systems.

D-Wave Systems, a quantum computing company based in Burnaby, British Columbia, announced this week that it had signed a deal to install a succession of D-Wave systems at NASA’s Ames Research Center in Moffett Field, California. NASA and Google on Wednesday also confirmed the deal.

NASA and the Universities Space Research Association (USRA) are collaborating on the project, which is focused on advancing artificial intelligence and machine learning.

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New findings published by quantum scientists in Germany could pave the way towards computer chips that use light instead of electricity to control their internal logic. Where today’s silicon-based electrical computer chips are capable of speeds in the gigahertz range, the German light-based chips would be some 1,000,000 times faster, operating in the petahertz range.

Rather than focusing on an exciting new semiconductor, or some metamaterial that manipulates light in weird and wonderful ways, this research instead revolves around dielectrics. In the field of electronics, materials generally fall into one of three categories: charge carriers (conductors), semiconductors, and dielectrics (insulators). As the name suggests, a semiconductor only conduct electricity some of the time (when it receives a large enough jolt of energy to get its electrons moving). In a dielectric, the electrons are basically immobile, meaning electricity can’t flow across them. Apply too much energy, and you destroy the dielectric. As a general rule, there’s no switching: A dielectric either insulates, or it breaks.

Basically, the Max Planck Institute and Ludwig Maximilian University in Germany have found that dielectrics, using very short bursts of laser light, can be turned into incredibly fast switches. The researchers took a small triangle of silica glass (a strong insulator), and then coated two sides with gold, leaving a small (50nm) gap in between (see below). By shining a femtosecond infrared laser at the gap, the glass started conducting and electricity flowed across the gap. When the laser is turned off, the glass becomes an insulator again.

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According to scientists photons can travel through time. They already have simulated directing quantum light particles to the past for the first time in the history. University of Queensland scientists learned that a simulation of two wormhole-travelling photons might interrelate; signifying hopping through time is conceivable at smallest scales. Their study might help to comprehend how time-travel could be conceivable in the quantum realm. PhD student Martin Ringbauer spoke to The Speaker: “For the first, ‘photon one’ would travel through a wormhole into the past and interact with its older version. In the second, ‘photon two’ travels through normal space-time but interacts with a photon that is stuck in a time-travelling loop through a wormhole, known as a closed timelike curve (CTC).”

Tim Ralph, UQ Physics Professor, said: “We used single photons to do this, but the time-travel was simulated by using a second photon to play the part of the past incarnation of the time travelling photon.”

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