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Physicists Make Quantum Leap



Physicists at UCSB recently published a paper in the journal Nature that could pave the way to building the first quantum computer.

UCSB physicist John Martinis led the project to model theories in quantum mechanics using quantum circuits, to represent qubits — quantum bits of information. Martinis, UCSB physics professor Andrew Cleland and graduate student Matthew Neeley studied entanglement, which gives qubits the properties that scientists hope to harness one day to produce a quantum computer.

“It’s definitely not witchcraft,” Cleland said.

Qubits can be represented in many ways, such as with electrons or photons. Atoms, which also display quantum behavior, often do not interact with anything. To ensure the quantum circuits would function like atoms, they had to be placed in a sterile environment with no air, friction or light.The qubits could then be measured electronically to see which state they exist in. When the qubit is observed, it is forced to choose one of the three states to reveal itself in. The measuring equipment used in this study forces the qubits to choose a state by interacting with, or “observing” them.

What makes this research unique is that the experiments used parts regularly found on an electrical circuit, giving the research a degree of practicality, as it is closer to a common computer than more theoretical representations, such as those using magnetic fields or photons.

“Like a classical computer, we make electronic circuits on a chip,” Neeley said. “But in our case, when cooled very close to absolute zero, the circuits become superconducting and behave quantum mechanically.”

The study involved measuring three entangled qubits in two states, GHZ and W. GHZ entanglement is so fragile that measuring it causes the qubits to untangle. Measuring W, however, shows that observing any of the three qubits causes all of them to reveal themselves to be in the same state.

According to Martinis, while it seems unrealistic that quantum computers, if developed, would be available at a consumer level, they could still be used by the government as a kind of mainframe computer, similar to those used in the 1970s to lend processing power to other computers hooked up to its network. However, the possibility is still there.

“When regular computers were developed, it was hard for people to imagine that everyone would have them,” Martinis said.

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One Response to Physicists Make Quantum Leap

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