Electrically switched nanowire qubit for both memory and processing
Researchers at the University of Basel in Switzerland have developed a new type of qubit that can switch between storage and processing in a quantum computer.
The silicon germanium nanowires would also allow a large number of qubits to be combined into a powerful quantum computer, as researchers from the University of Basel and TU Eindhoven have reported in the journal Nature Nanotechnology.
Produced at TU Eindhoven, the wire has a 20nm diameter and so in principle millions or even billions of these qubits could fit on a chip.
“The spin can be coherently flipped from up to down in as little as a nanosecond,” said Professor Dominik Zumbühl from the Department of Physics at the University of Basel. “That would allow up to a billion switches per second. Spin qubit technology is therefore already approaching the clock speeds of today’s conventional computers.”
Compared with conventional bits, qubits are much more fragile and can lose their information content very quickly. The challenge for quantum computing is to keep the sensitive qubits stable over a prolonged period of time, while at the same time finding ways to perform rapid quantum operations.
The qubit has a stable but slow state that is suitable for storing quantum information. However, the researchers were also able to switch the qubit into a much faster but less stable manipulation mode by applying an electrical voltage. In this state, the qubits can be used to process information quickly.
Next: Qubit structure
In their experiment, the researchers created the qubits in the form of “hole spins”. These are formed when an electron is deliberately removed from a semiconductor, and the resulting hole has a spin that can adopt two states, up and down – analogous to the values 0 and 1 in classical bits. In the new type of qubit, these spins can be selectively coupled – via a photon, for example – to other spins by tuning their resonant frequencies.
This capability is vital, since the construction of a powerful quantum computer requires the ability to selectively control and interconnect many individual qubits. Scalability is particularly necessary to reduce the error rate in quantum calculations. The researchers were also able to use the electrical switch to manipulate the spin qubits at record speed.
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