The quantum computer is growing up: Repetitive error correction in a quantum processor

May 26, 2011
The quantum bit (blue) is entangled with the auxiliary qubits (red). If an error occurs, the state of the defective quantum bit is corrected. Graphics: Harald Ritsch

( -- A team of physicists at the University of Innsbruck, led by Philipp Schindler and Rainer Blatt, has been the first to demonstrate a crucial element for a future functioning quantum computer: repetitive error correction. This allows scientists to correct errors occurring in a quantum computer efficiently. The researchers have published their findings in the scientific journal Science.

A general rule in data processing is that disturbances cause the distortion or deletion of information during data storage or transfer. Methods for conventional computers were developed that automatically identify and correct errors: Data are processed several times and if errors occur, the most likely correct option is chosen. As are even more sensitive to environmental disturbances than , a quantum computer requires a highly efficient algorithm for error correction.

The research group of Rainer Blatt from the Institute for Experimental Physics of the University of Innsbruck and the Institute for and Quantum Information of the Austrian Academy of Sciences has now demonstrated such an algorithm experimentally. “The difficulty arises because quantum information cannot be copied,“ explains Schindler. “This means that we cannot save information repeatedly and then compare it.“ Therefore, the physicists use one of the peculiarities of quantum physics and use quantum mechanical entanglement to perform error correction.

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The Innsbruck physicists demonstrate the mechanism by storing three calcium ions in an ion trap. All three particles are used as quantum bits (qubits), where one ion represents the system qubit and the other two ions auxiliary qubits. “First we entangle the system qubit with the other qubits, which transfers the to all three particles,” says Philipp Schindler. “Then a quantum algorithm determines whether an error occurs and if so, which one. Subsequently, the algorithm itself corrects the error.“ After having made the correction, the auxiliary qubits are reset using a laser beam. “This last point is the new element in our experiment, which enables repetitive error correction,“ says Rainer Blatt. “Some years ago, American colleagues demonstrated the general functioning of quantum error correction. Our new mechanism allows us to repeatedly and efficiently correct errors.“

Disturbances cause the distortion or deletion of information during data storage or transfer. Graphics: Graphics: Harald Ritsch

“For a quantum computer to become reality, we need a quantum processor with many quantum bits,“ explains Schindler. “Moreover, we need quantum operations that work nearly error-free. The third crucial element is an efficient error correction.“ For many years Rainer Blatt’s research group, which is one of the global leaders in the field, has been working on realizing a quantum computer. Three years ago they presented the first quantum gate with fidelity of more than 99 percent. Now they have realized another key element: repetitive .

Explore further: Hype and cash are muddying public understanding of quantum computing

More information: Experimental repetitive quantum error correction. Philipp Schindler, Julio T. Barreiro, Thomas Monz, Volckmar Nebendahl, Daniel Nigg, Michael Chwalla, Markus Hennrich, Rainer Blatt. Science, 27 May 2011. DOI: 10.1126/science.1203329

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1 / 5 (3) May 26, 2011
I've only been saying every circuit should be built this way for 10 years. they have known the advantages for years, but they don't want anything to last forever, they want u to keep buying new ones. if this is done right u would be able to switch the bad circuit without ever turning off or interrupting the circuits tasks. it will be awesome to be able to fix things before they break completely and without shutting them down for maintenance.
5 / 5 (1) May 26, 2011
??? WHAT ARE YOU TALKING ABOUT ??? circuits have no need for error correction they are hard coded by being physical to beahve exactly the same way with voltage and current.
5 / 5 (2) May 26, 2011
error correction in the classical sense is for fixing misinterpretations of variing voltage in a circuit as it applies to logic carried out by a processor like system.

5 / 5 (6) May 26, 2011
I think he is mistakenly interpreting "error correction" as "self repair".

"Error correction" is where you have extra circuits which double check the work of the first circuits, or else the first circuits re-do their own work to double check it.

"Self Repair" is currently non-existent in computer technology, at least to my knowledge. This would require some form of nano-assembly.
3.7 / 5 (3) May 27, 2011
Error correction is required in digital systems due to electrical noise that can cause logic circuits to switch to the wrong state.

Error detection in logic circuits is typically implemented using an even/odd parity bit that allows single bit errors to be detected. When an error is detected the circuit typically stops and requires a reset. In more complex logic circuits like CPUs, an error may trigger an interrupt that executes error handling code. Logic circuits are very reliable and single bit errors within the circuits are rare. Consequently, in this case, the cost/benefit ratio of error correction is unfavorable.

In a digital communication channel, a cyclic redundancy check is used. A CRC allows both detection and correction of multi-bit errors and is efficiently implemented in communication hardware. Communication channels are generally not reliable and it may not always be possible or desirable to re-transmit a message. Consequently, Cost/benefit ratio is favorable.

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