Researchers at Penn State University claim to have devised a better way to build circuits for quantum computers, enabling more quantum computing power to be packed into a smaller space, and with greater control than ever before.
The research, led by Penn State University professor of physics David S. Weiss, used a 3D array of atoms in states called quantum bits, or qubits.
The new technique uses laser light and microwaves to precisely control the switching of selected individual qubits from one quantum state to another, without altering the states of the other atoms in the cubic array.
The new technique demonstrates the potential use of atoms as the building blocks of circuits in future quantum computers.
The scientists invented an innovative way to arrange and precisely control the qubits, which are necessary for doing calculations in a quantum computer.
"Our result is one of the many important developments that are still needed on the way to achieving quantum computers that will be useful for doing computations that are impossible to do today, with applications in cryptography for electronic data security and other computing-intensive fields," said Weiss.
The technique is described in detail in the latest issue of the academic journal Science. The achievement is also expected to be useful to scientists pursuing other approaches to building a quantum computer, including those based on other atoms, ions, or atom-like systems in one or two dimensions.
"If this technique is adopted in those other geometries, they would also get this robustness," said Weiss.
The university explained that to arrange the quantum atoms into an orderly 3D pattern for their experiments, the research team constructed a lattice made by beams of light to trap and hold the atoms in a cubic arrangement of five stacked planes, each with room for 25 equally spaced atoms.
The arrangement forms a cube with an orderly pattern of individual locations for 125 atoms. The scientists filled some of the possible locations with qubits consisting of neutral (without a positive or a negative charge) caesium atoms.
Unlike the bits in a normal computer, which are typically ones or zeros, each of the qubits in the experiment has the ability to be in more than one state at the same time, a central feature of quantum mechanics called ‘quantum superposition'.
Weiss and his team then used two crossed beams of laser light to target individual atoms in the lattice. The focus of these two ‘addressing' beams' on a targeted atom shifts some of that atom's energy levels by about twice as much as it does for those of any of the other atoms in the array, including those that were in the path of one of the addressing beams on its way to the target.
The scientists then bathed the whole array in a uniform wash of microwaves, changing the state of the atoms with the shifted energy levels but not the others.
"We have set more qubits into different, precise quantum superpositions at the same time than in any previous experimental system," said Weiss.
The other members of the research team were graduate students Yang Wang, Aishwarya Kumar and Tsung-Yao Wu.
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