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Washington, An international team of researchers have achieved a 100-fold increase in the ability to maintain control over the spins of electrons in a solid material, which is a key step in the development of ultrafast quantum computers.
Until recently, the best attempts at such control lasted for only a fraction of a second, However, Stephen Lyon and Alexei Tyryshkin from Princeton University have found a way to extend control over the spins of billions of electrons in a silicon chip for up to 10 seconds, far longer than any previous attempt.
Lyon, an electrical engineering professor, said that the key to the new results lies in a highly purified sample of silicon. The experiment uses a small silicon chip the size of a pencil lead made almost entirely of a particular isotope of silicon – silicon-28.
“Partly, it is an improvement in our measurements, but it is mainly the material,” Lyon said.
“This is the purest sample we have ever used,” he said.
In an experiment conducted in the basement of Princeton’s Hoyt laboratory, the researchers suspended the sample of pure silicon inside a cylinder filled with liquid helium, dropping its temperature to 2 kelvin, or just above absolute zero.
They locked the cylinder between two donut-shaped rings about the size of pizza boxes that control the magnetic field around the sample. A click of a computer mouse sent microwaves pulsing across the silicon, and coordinated the spins of about 100 billion electrons.
“The first pulse twists them, the second reverses them, and at some point the sample itself produces a microwave pulse, and we call that the echo,” Lyon said.
“This is the purest sample we have ever used,” he said.
In an experiment conducted in the basement of Princeton’s Hoyt laboratory, the researchers suspended the sample of pure silicon inside a cylinder filled with liquid helium, dropping its temperature to 2 kelvin, or just above absolute zero.
They locked the cylinder between two donut-shaped rings about the size of pizza boxes that control the magnetic field around the sample. A click of a computer mouse sent microwaves pulsing across the silicon, and coordinated the spins of about 100 billion electrons.
“The first pulse twists them, the second reverses them, and at some point the sample itself produces a microwave pulse, and we call that the echo,” Lyon said.
“By doing the second pulse, getting everything to reverse, we get the electrons into phase,” he said.
While describing electrons, scientists use the term spin. But like a lot of things in quantum mechanics, the meaning is a little bit tricky. For subatomic particles like electrons, spin is a fundamental characteristic that can make them behave like incredibly tiny magnets. Lyon’s team uses this magnetic signature in their observations.
Maintaining that phase is what scientists call “coherence”. Unlike objects in the everyday world, subatomic particles, which operate under the rules of quantum mechanics, can be in more than one place at the same time.
A standard computer uses transistors either switched off or on to represent the 0’s and 1’s that are the bits that make up the basis of all computer programs
Instead of this binary language, a quantum computer would incorporate the uncertainty of quantum mechanics into its programming. Instead of bits, the computers will use quantum bits or qubits – a value that is inherently indeterminate.
Mathematicians are still working on ways to take advantage of such a machine. They believe it could be used to factor incredibly large numbers, break cryptographic codes or to simulate the behaviour of molecules.
The study has been published online in online in Nature Materials.
ANI
