Spin doctors create quantum transistor

The invention of the spintronic transistor, which uses the spin of electrons to store information, marks an important step in quantum computing

Canadian researchers have announced the laboratory creation of what they are calling a "spintronic transistor".

According to a paper published in the American Physical Society's Physical Review Letters, physicists at Ottowa's Institute for Microstructural Sciences are the first to connect a quantum dot to spin-polarised leads. Dr Pawel Hawrylak, co-author of the work and a group leader of the quantum theory group at the Institute, told industry paper EE Times: "There is a significant effort to tap into an elusive, quantum property of an electron: its spin. Our device is a prototype showing how a single-spin-based transistor might work."

Like conventional electronics, spintronics uses the flow of electronics to represent signals and logic states. Unlike conventional electronics, which depends on the electrical charge of the electron, spintronics uses an electron's 'spin'. While electrons don't really spin, the idea comes from the discovery in the 1920s that they interact with each other and with other particles as if they do. Each electron can be in one of two states of spin: up or down. Only certain combinations of up and down electrons can share the same area of space.

The Canadian researchers created a quantum dot -- a tiny area that keeps small numbers of electrons together by electrostatic charge. They then hooked up the spin-polarised leads -- two reservoirs of up- and down-spinning electrons.

The quantum dot acted as an artificial atom, and by feeding in electrons one at a time from the reservoirs, the state could be changed. The total spin of the quantum dot depended on which electrons had been fed in, and this affected how easy or hard it was to feed in more electrons. Thus, data could be stored and read back depending on spin state -- the first time this has been done in a single device.

Although this is a very long way from any production device it opens up a whole new field of electronic devices. It is especially significant for quantum computing, where spin state is an integral part of the equations at the heart of much of the work being done. The Institute is now working on more complex devices with several spintronic transistors configured as a quantum computer.

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