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Physicists find that entanglement concentration is irreversible, in contrast with previous research

Posted October 8, 2013
Several different types of entangled states can be used in quantum information processes, and these states can be converted into one another using a variety of conversion processes. While previous research has suggested that one of the most common types of conversions, called entanglement concentration, is reversible, a new paper shows for the first time that it is irreversible due to a trade-off relation between performance and reversibility. The finding could have implications for future developments in quantum information applications.
Physicists find that entanglement concentration is irreversible, in contrast with previous research
A diagram of entanglement concentration and its recovery operation, entanglement dilution. Scientists have found that an initial entangled state cannot be completely recovered after the concentration process. Credit: Kumagai, et al. ©2013 American Physical Society

The physicists, Wataru Kumagai at Tohoku University in Sendai, Japan, and Nagoya University in Nagoya, Japan; and Masahito Hayashi at Nagoya University and the National University of Singapore, have published their paper on the irreversibility of entanglement concentration in a recent issue of Physical Review Letters.

In quantum information processes, entanglement concentration is used to convert multiple copies of an entangled pure state into multiple copies of an entangled EPR state. Another conversion process, called entanglement dilution, does the opposite; that is, it converts copies of the EPR state into copies of a pure state.

Due in part to the fact that the optimal rates of entanglement concentration and entanglement dilution are the same, physicists have previously thought that entanglement concentration may be reversible. If this were true, reversible entanglement concentration could be used to compress multiple copies of an entangled pure state in a lower dimensional storage system, and later the initial state could be recovered using entanglement dilution.

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