Programmable quantum computer milestone in development

American researchers have built the world’s first fully reprogrammable quantum computer that can solve multiple algorithms without the need to change the hardware for every task. 

The research, described in the latest issue of the journal Nature, presents a milestone towards the realisation of quantum computing, which is believed to be able to solve complex computing operations far more quickly than current transistor-based computers.

The quantum computer by a team from the University of Maryland consists of five qubits, or quantum bits, which encode information into the states of subatomic particles instead of the conventional zeros and ones in electronic computers.

“Small quantum algorithms have been demonstrated on multiple quantum computing platforms, many specifically tailored in hardware to implement a particular algorithm or execute a limited number of computational paths 1-10,” the researchers wrote in the Nature article. “Here we demonstrate a five-qubit trapped-ion quantum computer that can be programmed in software to implement arbitrary quantum algorithms by executing any sequence of universal quantum logic gates.”

The five electrically charged atoms at the heart of the device are suspended in a magnetic field, which allows the researchers to modify their characteristics with precisely targeted laser beams. This way, the researchers can cause subatomic particles in the qubits to enter multiple quantum states at the same time – a phenomenon known as superposition – which is behind the technology’s ability to solve computational tasks with out-of-this-world speed and ease.

During experiments, the researchers used the quantum computer to solve a complex calculation in a single step. A conventional computer would have to carry out several steps to achieve the same.

The team also managed to demonstrate the so-called quantum Fourier transform (QFT), a mathematical operation that could be used to break highly secure encryption codes.

Out of the three algorithms the researchers tested, two ran with a 90 per cent accuracy, while the QFT ran with a 70 per cent success rate. However, the researchers said none of the errors involved were fundamentally insurmountable.

"Our experiment brings high-quality quantum bits up to a higher level of functionality by allowing them to be programmed and reconfigured in software," said quantum physicist Professor Christopher Monrow, who led the team.

The researchers believe the technology could be easily scaled up to accommodate a larger number of qubits and could be expanded by connecting several modules.

The machine uses its laser-manipulated ytterbium ions to drive the so-called quantum logic gates - the equivalent of the switches and transistors that power ordinary computers.

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