Michelle Simmons illustrates how to build single atom qubit quantum computers

The smallest transistor ever built – in fact, the smallest transistor that can be built was created using a single phosphorous atom by an international team of researchers at the University of New South Wales, Purdue University, the University of Melbourne and the University of Sydney.

A controllable transistor engineered from a single phosphorus atom has been developed by researchers at the University of New South Wales, Purdue University and the University of Melbourne. The atom, shown here in the center of an image from a computer model, sits in a channel in a silicon crystal. The atomic-sized transistor and wires might allow researchers to control gated qubits of information in future quantum computers. (Purdue University image)

The technical meat of the TedX video is about 12 minutes into this 16 minute video

Although single atoms serving as transistors have been observed before, this is the first time a single-atom transistor has been controllably engineered with atomic precision. The structure even has markers that allow researchers to attach contacts and apply a voltage, says Martin Fuechsle, a researcher at the University of New South Wales and lead author on the journal paper.

“The thing that is unique about what we have done is that we have, with atomic precision, positioned this individual atom within our device,” Fuechsle says.

Simmons says this control is the key step in making a single-atom device. “By achieving the placement of a single atom, we have, at the same time, developed a technique that will allow us to be able to place several of these single-atom devices towards the goal of a developing a scalable system.”

The single-atom transistor could lead the way to building a quantum computer that works by controlling the electrons and thereby the quantum information, or qubits. Some scientists, however, have doubts that such a device can ever be built.

At the start of 2012. Professor Michelle Simmons’ lab announced it had created 1-atom tall and 4-atom-wide nanowires.

They embedded a wire in crystalline silicon to isolate the dopant atoms from surfaces and interfaces that caused this deactivation. They predicted this would give us highly conductive wires, and this is what happened.

The key to making these wires was combining scanning tunneling microscopy, a technique to image and manipulate individual atoms, with molecular beam epitaxy, a way of growing perfect crystals. It gave us great precision in all three dimensions, and when combined with a high density of the dopant atoms, allowed us to create these highly conductive nanowires.

Nature Nanotechnology – A single-atom transistor

a, Perspective STM image of the device, in which the hydrogen-desorbed regions defining source (S) and drain (D) leads and two gates (G1, G2) appear raised due to the increased tunnelling current through the silicon dangling bond states that were created. Upon subsequent dosing with phosphine, these regions form highly phosphorus-doped co-planar transport electrodes of monatomic height, which are registered to a single phosphorus atom in the centre of the device. Several atomic steps running across the Si(100) surface are also visible. b, Close-up of the inner device area (dashed box in a), where the central bright protrusion is the silicon atom, which is ejected when a single phosphorus atom incorporates into the surface. c, Schematic of the chemical reaction to deterministically incorporate a single phosphorus atom into the surface. Saturation dosing of a three-dimer patch (I) at room temperature (RT) followed by annealing to 350 °C allows successive dissociation of PH3 (II–IV) and subsequent incorporation of a single phosphorus atom in the surface layer, ejecting a silicon adatom in the process (V).

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