![]() ![]() "More precisely, we show that any quantifier of entanglement gives rise to a quantifier of coherence. "The significance of our work lies in the fact that we prove the close relation between entanglement and coherence not only qualitatively, but on a quantitative level," coauthor Alex Streltsov, of ICFO-The Institute of Photonic Sciences in Barcelona, told. As the scientists explained, this is possible because the new results allowed them to define and quantify one resource in terms of the other. For example, the new knowledge has already allowed the physicists to settle an important open question concerning the geometric measure of coherence: since the geometric measure of entanglement is a "full convex monotone," the same can be said of the associated coherence measure. Consequently, all of the comprehensive knowledge that researchers have obtained about entanglement can now be directly applied to coherence, which in general is not nearly as well-researched (outside of the area of quantum optics). For one, it means that quantum coherence can be measured through entanglement. This discovery of the conversion between coherence and entanglement has several important implications. The physicists arrived at this result by showing that, in general, any nonzero amount of coherence in a system can be converted into an equal amount of entanglement between that system and another initially incoherent one. ![]() In a paper to be published in Physical Review Letters, physicists led by Gerardo Adesso, Associate Professor at the University of Nottingham in the UK, with coauthors from Spain and India, have provided a simple yet powerful answer to the question of how these two resources are related: the scientists show that coherence and entanglement are quantitatively, or operationally, equivalent, based on their behavior arising from their respective resource theories. Like coherence, quantum entanglement also plays an essential role in quantum technologies, such as quantum teleportation, quantum cryptography, and super dense coding. The intrigue of entanglement lies in the fact that the two entangled particles are so intimately correlated that a measurement on one particle instantly affects the other particle, even when separated by a large distance. ![]() But in this case, the states in a superposition are the shared states of two entangled particles rather than those of the two split waves of a single particle. The second phenomenon, quantum entanglement, also involves superposition. When such a state experiences decoherence, however, all of its quantumness is typically lost and the advantage vanishes. Coherence also lies at the heart of quantum computing, in which a qubit is in a superposition of the "0" and "1" states, resulting in a speed-up over various classical algorithms. This concept of superposition is famously represented by Schrödinger's cat, which is both dead and alive at the same time when in its coherent state inside a closed box. If an object's wave-like nature is split in two, then the two waves may coherently interfere with each other in such a way as to form a single state that is a superposition of the two states. ![]() Quantum coherence deals with the idea that all objects have wave-like properties. It's well-known that quantum coherence and quantum entanglement are both rooted in the superposition principle-the phenomenon in which a single quantum state simultaneously consists of multiple states-but in different ways. Although physicists have known that coherence and entanglement are close relatives, the exact relationship between the two resources has not been clear. ![]()
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