Important Step towards the Quantum Computer

03. Jan 2007  — A team of quantum physicists lead by Anton Zeilinger have managed to outsmart the quantum world, thereby boosting a quantum computers speed and efficiency. The latest study is featured in the current issue of the weekly science magazine NATURE and marks an important step in the world-wide quest to realize a quantum computer. Nature 445, 65-69 (4 January 2007)


Important Step towards the Quantum Computer

Foto by Robin Riegler


In the actual experiment, the research team (Robert Prevedel, Philip Walther, Felix Tiefenbacher, Pascal Böhi, Rainer Kaltenbaek, Thomas Jennewein and Anton Zeilinger) first of all prepared a so-called cluster-state, which acts as the “resource” for the computation. This cluster state is made up of entangled quantum bits (“qubits” for short), in which each qubit was realized by a photon in the experiment. Such an initial cluster state is so rich in information, that in principle, it contains all the possible outcomes of the calculation one intents to perform.

Based on a theoretical proposal of Raussendorf and Briegel (IQOQI Innsbruck), the Austrian research team outsmarted the fundamental principle of measurement randomness with a clever trick:


The problematic randomness of the measurement result can be disarmed if one adapts the choice of subsequent measurements in such a way that the introduced error in the computation is corrected for (so-called error correction). Loosely speaking, one adapts the software of the computer in real-time, so that the quantum randomness does not effect the computation any more. The process of quickly adapting the subsequent measurements is called “active feed-forward”, which due to the speed of light, has to be as fast as possible.

The study was the result of a collaboration of physicists from the Institute for Experimental Physics of the University of Vienna, the Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences in Vienna as well as with a researcher from the Harvard University (USA). This research was supported by the Austrian Science Fund (FWF), the DTO of the U.S. Army Research Offices as well as by the QAP-Project of the European Commission.

 

High-speed linear optics quantum computing using active feed-forward