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A Single Atom Transistor in Atomic Pipelines
Physicists in Innsbruck and Oxford have invented a way to use a single atom as a transistor; one which would control the flow of atoms in a pipeline made from light.
Physicists in Innsbruck and Oxford have invented a way to use a single atom as a transistor; one which would control the flow of atoms in a pipeline made from light. This single atom transistor is a quantum switch, with the single control atom able to exist in two states simultaneously, one state engineered to completely block a current of other atoms flowing past it ('off'), and the other to be transparent to the atomic current ('on'). Whilst it is somewhat reminiscent of single electron transistors from solid state systems and spintronics systems, the ability to place the single atom transistor in a coherent superposition of 'on' and 'off' states (identical to the '0' and '1' states of a qubit) would allow it to potentially forma a building block for the construction of a quantum computer.
The concept of the single atom transistor and how it can be implemented using techniques already demonstrated in ongoing experiments is the work of Innsbruck physicists Andrea Micheli, Andrew Daley, and Peter Zoller, in collaboration with Dieter Jaksch, a lecturer at the University of Oxford. Their analysis of the system made use of state of the art computer simulation techniques to model the quantum dynamics of the many-body system, and to test the robustness of the setup for realistic experimental conditions.
The resulting scheme is suitable for implementation in current experiments with atoms in optical lattices. These lattices are standing waves of laser light that exert forces on atoms, and can be used either to hold the atoms in particular positions, or to form pipelines which direct a flow of atoms in certain directions. There are already several experiments with optical lattices operating in Europe, and more are under construction. Progress is also being made towards trapping atoms and forming pipelines on atomic microchips.
The single atom transistor could be implemented in optical lattices using the fundamental idea of quantum interference. In this scheme, the collisions between the control atom and the atoms in the pipeline are carefully controlled using lasers or magnetic fields. This produces two different quantum 'paths' past the control atom, that is, two ways for an atom in the pipeline to go from one side of the transistor to the other. Under appropriate circumstances, quantum mechanics allows for these two paths to cancel one another, so that the two combined yield almost zero probability that an atom will pass the transistor. This corresponds to the 'off' state of the switch. Simultaneously, quantum mechanics allows for a different electronic state of the atom to produce paths which interfere constructively, creating an 'on' state by making the transistor transparent to the atomic current flowing past it.
The single atom transistor could play a similar role in atomic circuits to that played by semiconductor transistors in electronics, and could be used both for control of atomic currents and for measurement in such systems. In certain situations, the interactions between the transistor and the atomic current can also be engineered to create an energy filter for the incident atoms. The main feature of atomic circuits is that they allow for coherent superpositions of different quantum states which are required for quantum computing applications. In particular, such parallelism is the basis of sophisticated quantum algorithms such as Shor’s algorithm for factorising large numbers, and of 'quantum simulators', devices used to model complicated systems from other branches of physics, such as high temperature superconductors.
The detailed analysis of the single atom transistor is scheduled to be published the high-visibility American Physical Society journal Physical Review Letters next week.
Work in Innsbruck was performed jointly within the Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences(1) and the Institute for Theoretical Physics of the University of Innsbruck(2), as part of the Spezialforschungsbereich for control and measurement of coherent quantum systems, and was supported by the Austrian Science Foundation, EU Networks, and the Institute for Quantum Information. Work by Dieter Jaksch at the University of Oxford(3) was supported by the IRC on Quantum Information Processing.
(1) Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, Technikerstr. 25, A-6020 Innsbruck, Austria
(2) Institute for Theoretical Physics, University of Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria
(3) Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
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