April Flowers for redOrbit.com – Your Universe Online
Two new studies, both published in Nature this week, outline incredible breakthroughs in the field of quantum mechanics.
Australian engineers led an international team of researchers to create the first working quantum bit based on a single atom in silicon, potentially making another important step toward ultra-powerful quantum computing that theoreticians have dreamt of for decades.
The team describes how they were able to read and write information using the magnetic orientation, or “spin,” of an electron that was bound to a single atom of phosphorus and embedded in a chip made of silicon.
“For the first time, we have demonstrated the ability to represent and manipulate data on the spin to form a quantum bit, or ‘qubit’, the basic unit of data for a quantum computer,” says Scientia Professor Andrew Dzurak.
“This really is the key advance towards realizing a silicon quantum computer based on single atoms.”
The team was led by Dr Andrea Morello and Professor Dzurak from the UNSW School of Electrical Engineering and Telecommunications. The international team also included researchers from the University of Melbourne and University College, London.
“This is a remarkable scientific achievement — governing nature at its most fundamental level — and has profound implications for quantum computing,” explained Dzurak.
According to Dr. Morello, quantum computers may provide a critical tool for solving enormously complicated problems that are now impossible on even the world’s largest supercomputers. Morello explained that such ultra-complex problems include data-intensive issues, such as cracking modern encryption codes, mining vast databases and modeling biological molecules and pharmaceuticals.
This new finding follows a previous study by the same group of researchers in which they demonstrated the ability to read the state of an electron’s spin. The discovery of how to write the spin state now completes the two-stage process that is required to operate a quantum bit.
The new result was achieved by using a microwave field to gain unprecedented control over an electron bound to a single phosphorous atom. The atom was implanted next to a specially-designed silicon transistor. Professor David Jamieson of the University of Melbourne’s School of Physics, led the team that implanted the phosphorous atom into the silicon device.
Jarryd Pla, the lead author of the paper and a PhD student as UNSW, explained, “We have been able to isolate, measure and control an electron belonging to a single atom, all using a device that was made in a very similar way to everyday silicon computer chips.”
According to Dr Morello, “This is the quantum equivalent of typing a number on your keyboard. This has never been done before in silicon, a material that offers the advantage of being well understood scientifically and more easily adopted by industry. Our technology is fundamentally the same as is already being used in countless everyday electronic devices, and that’s a trillion-dollar industry.”
The team’s next goal is to combine pairs of quantum bits to create a two-qubit logic gate, which constitutes the basic processing unit of a quantum computer.
Here in the United States, an international team of scientists led by the University of Florida, is rewriting a page from the quantum physics rulebook using a laboratory once called the coldest spot in the universe.
Most of what science knows about quantum mechanics is theoretical and tested by computer modeling because quantum systems, like electrons zipping around the nucleus of an atom, are difficult to pin down for observation. However, particles can be slowed down and caught in the quantum act by subjecting them to extremely cold temperatures. The new study describes how this freeze-frame approach was recently used to overturn an accepted rule of thumb in quantum theory.
“We are in the age of quantum mechanics,” said Neil Sullivan, a University of Florida physics professor and director of the National High Magnetic Field Laboratory High B/T Facility — home of the Microkelvin Laboratory where experiments can be conducted in temperatures approaching absolute zero.
“If you’ve had an MRI, you have made use of a quantum technology.”
The magnet that powers an MRI scanner is a superconducting coil transformed into a quantum state by very cold liquid helium. Inside the coil, electric current is able to flow free of friction.
Sullivan says that quantum magnets and other strange, almost otherworldly occurrences in quantum mechanics could inspire the next big breakthrough in computer, alternative energy and transportation technologies, such as magnetic levitating trains. However, the practical steps needed bring these technologies into reality cannot be taken without the sign posts and maps that engineers need to navigate the quantum road.
Enter the Microkelvin lab. This is one of the few facilities in the world that is equipped to deliver the extremely cold temperatures needed to slow the “higgledy-piggledy” world of quantum systems at normal temperatures to a manageable pace where it can be observed and manipulated.
“Room temperature is approximately 300 kelvin,” Sullivan said. “Liquid hydrogen pumped into a rocket at the Kennedy Space Center is at 20 kelvin.”
Physicists need to cool things down to 1 millikelvin, one thousandth of a kelvin above absolute zero — that´s -459.67 degrees Fahrenheit — to bring matter into a state where its quantum properties can be explored.
The Bose-Einstein Condensate, an unstable, transitory phase of matter, is one fundamental state of quantum mechanics that scientists are keen to understand more fully. In this state, individual particles that make up a material begin to act as a single coherent unit. The Bose-Einstein Condensate is a tricky condition to induce in a laboratory setting, but one that researchers need to explore if technology is ever to fully exploit the properties of the quantum world.
Tommaso Roscilde at the University of Lyon, France, and Rong Yu from Rice University in Houston, developed the underlying ideas for the study and asked a colleague, Armando Paduan-Filho from the University of Sao Paulo in Brazil, to engineer the crystalline sample used in the experiment.
“Our measurements definitively tested an important prediction about a particular behavior in a Bose-Einstein Condensate,” said Vivien Zapf, a staff scientist at the National High Magnetic Field Laboratory at Los Alamos and a driving force behind the international collaboration.
The team monitored the atomic spin of subatomic particles called bosons in the crystal to see when the transition to Bose-Einstein Condensate was achieved, and then further cooled the sample to document the exact point where the condensate properties decayed. They observed the anticipated phenomenon when they took the sample down to 1 millikelvin.
The experiment used a crystal that had been “doped” with impurities to create a more realistic scenario.
Zapf said. “It’s nice to know what happens in pure samples, but the real world, is messy and we need to know what the quantum rules are in those situations.”
Thanks to prior simulations, the team knew that the experiment would require them to generate temperatures as low as 1 millikelvin.
“You have to go to the Microkelvin Laboratory at UF for that,” explained Zapf. The lab is located in the National High Magnetic Field Laboratory High B/T Facility and is funded by the National Science Foundation (NSF). Other laboratories can get to the extreme temperature required, but none of them can sustain it long enough to collect all of the data needed for the experiment.
“It took six months to get the readings,” said Liang Yin, an assistant scientist in the University of Florida physics department who operated the equipment in the Microkelvin lab.
“Because the magnetic field we used to control the wave intensity in the sample also heats it up. You have to adjust it very slowly.”
Their findings literally rewrote the rule for predicting the conditions under which the transition would occur between the two quantum states.
“All the world should be watching what happens as we uncover properties of systems at these extremely low temperatures,” Sullivan said. “A superconducting wire is superconducting because of this Bose-Einstein Condensation concept. If we are ever to capitalize on it for quantum computing or magnetic levitation for trains, we have to thoroughly understand it.”
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