Opening The Gate To Robust Quantum Computing

April 9, 2012

A team led by an Ames Laboratory scientist develops new technique for solid-state quantum information processing




This power of quantum information processing also poses a major challenge: even a minor “bump” off course causes qubits to lose data. And qubits tend to interact quite sensitively with their environment, where multiple forces bump them off track.



Solid-state hybrid systems are useful for quantum information processing because they are made up of different types of qubits that each perform different functions, much like different parts of a car combine to move it down the road. In the case of Dobrovitski´s work, the hybrid system includes magnetic moments of an electron and a nucleus.

“This type of hybrid system may be particularly good for quantum information processing because electrons move fast, can be manipulated easily, but they also lose quantum information quickly. Nuclei move very slow, are difficult to manipulate, but they also retain information well,” said Dobrovitski. “You can see an analogy between this hybrid quantum system and the parts of a classical computer: the processor works fast but doesn´t keep information long, while the memory works slowly but stores information for a long time.”



“The solution is applying a certain pattern of kicks to the electron´s magnetic moment, so that tiny rotations between each kick accumulate and coincide with the rotation of the nucleus,” said Dobrovitski. “We can separate out this particular single electron movement from thousands of others because it is synchronized with the motion of the nuclear magnetic moment.”

As a result, the electron´s and nucleus´ movements stay linked, while they are both protected from being bumped off course and retain their quantum information processing capabilities.


The researchers took the technique one step further and showed that it can be used for small-scale quantum information processing. Scientists at Delft and UCSB successfully carried out Grover´s quantum search algorithm, a method for searching random lists. In this case, they used the solid-state hybrid system to correctly search a list of four random items.

“This is the first time a robust quantum computation has been demonstrated using a solid-state system with individual spins,” said Dobrovitski. “We showed that even with the inevitable imperfections of experiments, we can use this system to do quantum information processing in a way that beats its classical counterpart. Indeed, for a list of four items, the quantum device finds with certainty the desired entry by looking into the list only once, while classically we must inspect all four items one by one.”

While a four-item list is a small list, consider the possibility of a random list of a million entries. Using classical computing, 500,000 queries would be needed. But, using quantum information processing, only 1,000 queries are required, showing just how much faster tomorrow´s quantum information processing will be than today´s classical computers.

The research conducted at Ames Laboratory was funded by the DOE´s Office of Science.



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