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Quantum computer research reaches ‘significant milestone’

Scientists make major advancements in the development of a large scale quantum computer

Scientists at Santa Barbara University have announced major advancements in the development of a large scale quantum computer, as well as a breakthrough in the quantum control of light.

The team, which included scientists from Zhejiang University in China and NEC, Japan, used a superconducting quantum integrated circuit to generate unique quantum states of light known as NOON states. These states, generated from microwave frequency photons (the quantum unit of light), were created and stored in two physically separated microwave storage cavities.

According to Haohua Wang, postdoctoral fellow in physics at Santa Barbara University, the quantum NOON states were created using one, two, or three photons. All of these photons were placed in one cavity, leaving the other empty. This was simultaneous with the first cavity being empty, with all the photons stored in the second cavity. "This seemingly impossible situation, allowed by quantum mechanics, led to interesting results when we looked inside the cavities," he said. "There was a 50% chance of seeing all the photons in one cavity and a 50% chance of not finding any – in which case all the photons could always be found in the other cavity."

However, Wang found that if one of the cavities was gently probed before looking inside, thus changing the quantum state, the effect of the probing could be seen, even if that cavity was subsequently found to be empty. "It's kind of like the states are ghostly twins or triplets," he said. "They are always together, but somehow you never know where they are. They also have a mysterious way of communicating, so they always seem to know what is going to happen."

Wang likened these types of states with what Einstein termed 'spooky action at a distance', whereby prodding or measuring a quantum state in one location affects its behaviour elsewhere. "The quantum integrated circuit, which includes superconducting quantum bits in addition to the microwave storage cavities, forms part of what could become a quantum computational architecture in the future," concluded Wang.

The research has been published in the 7 February edition of the journal Physical Review Letters.

Laura Hopperton

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