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Taming qubits with quantum rings

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November 28, 2010

The latest development in quantum computing might hold the key to taming qubits, the building blocks of quantum systems. Holding these elusive qubits in a controlled state for longer than nanoseconds has proven extremely difficult in the past but researchers have recently discovered a method could see their lifespan reach seconds if not tens of seconds.

Even in the simplest quantum systems, single electron semiconductor, also known as Quantum Dots (QDs) the longest durations have been only fractionally greater than one second. Now researchers have discovered a way to lengthen this duration using Quantum Rings (QRs).

The biggest problem facing quantum computing researchers is holding qubits in the quantum regime. Qubits naturally deteriorate quickly as they interact with the environment – a process known as decoherence – which results in a loss of information from the system. The Catch 22 here is that they need this interaction to be useful as carriers of information as a way to measure and steer electrons, yet decoherence means that the act of reading this information destroys it.

While QDs have been shown to have properties that can hold single electron qubits for slightly over one second this new process, which shapes the QDs into ring-shaped nanostructures called Quantum Rings (QRs), has been pioneered by researchers at the Institute of Physics, University of Silesia, Poland. They have found interesting atom-like properties in these ring-shaped nanostructures that make them good candidates for quantum information processing. They are able to hold multiple electrons in orbit and allow magnetically induced change of the ground state of the electrons.

The ability to build defect free QRs provides strong confidence in measuring the spin states of electrons. While current QR fabrication techniques are chemical using magnetism or gravity to shape nanoparticles into crater-like structures future advancements in nanowire technology might be the next step in building smaller (<10nm) rings. This is important because research shows that smaller rings show less evidence of deterioration due to decoherence – meaning longer durations of stability. This improvement in system stability by using nanowire rings smaller than 10nm is likely allow the production of QRs capable of durations exceeding seconds – up to 10s theoretically.

The research by Elzbieta Zipper, Marcin Kurpas, Maciej M. Maska (University of Silesia) and Janusz Sadowski (MAX-Lab, Lund University / Institute of Physics, Polish Academy of Sciences) was published on November 11.

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