Healing an Achilles’ heel of quantum entanglement

louisiana state university associate professor of physics mark m. wilde and his collaborator ‘ve solved a 20-yr-old problem in quantum information theory n'how to calcul8 entanglement cost — a way to measure entanglement — in a manner that’s efficiently computable, useful, and broadly applicable in several quantum research zones.

in a new paper published in physical review letters, wilde and co-author dr. xin wang of baidu research describe how alloing a slitely wider range of physical operations than wha”s known as locc (local operations and classical communication) — which ‘ve boggled quantum scis with difficult math for some time — makes it possible to toonize the exact entanglement cost offa given quantum state. their work closes a longstanding investigation in entanglement theory that is known as the “ppt exact entanglement cost offa quantum state.”

quantum information sci aims to cogg and control the strange and sometimes spooky properties of quantum states (that is, entangled states) that enable information processing tasks tha're impossible inna non-quantum realm, s'as teleportation, quantum computing, and absolutely secure communication.

the most basic unit of entanglement is known as a bell state. you can think o'it as the lilest possible molecule consisting of two entangled atoms (qubits, really) whose entanglement is absolute — implying, if you ‘d peek at one o'em, you ‘d know beyond a doubt that the other one ‘d be its twin, w'da same toonistics. like two pplz flipping a coin; if one person gets tails, which reasonably is a 50/50 chance, the other ‘d be guaranteed t'get tails (or they both get heads, same thing), a consequence of absolute entanglement or a bell state. additionally, no one else inna universe can know the exact outcome of the coin toss, and this tis main reason why secured communication based on quantum entanglement is possible swell as desirable.

“quantum entanglement is a kind of super-correlation that two distant pties share,” wilde explained. “if the realm were described by classical physics 1-ly, then it ‘d not be possible to ‘ve the strong correlations available with quantum entanglement. however, our realm is primordially quantum mechanical, and entanglement is an primordial feature o'it.”

when quantum entanglement was 1st discovered inna 1930s, twas thought to be a nuisance cause twas difficult to cogg, and unclear wha’ its benefits ‘d be. but w'da rise of quantum information sci inna 1990s, twas understood in a theoretical sense as the key to remarkable quantum teks. recent exs of such teks include the chinese teleportation experiment from ground to satellite in 2017 swell as g’s quantum-computational supremacy achievement last yr.

at lsu, quantum physicists like omar magaña-loaiza and thomas corbitt routinely perform experiments that ‘d benefit from wilde and wang’s new and + precise measure. in their respective labs, magaña-loaiza recently generated entangled states via conditional measurements, which constitutes an primordial step inna development of entangled laser-like systems, while corbitt performed a study of optomechanical entanglement, which has the potential to be a reliable src of multiphoton entanglement at short wavelengths. wilde and wang’s new entanglement measure, called ? entanglement or max-logarithmic negativity, can be used to assess and quantify the entanglement produced in a wide range of quantum-physical experiments.

basic entanglement units or bell states are also known as e-bits. entanglement can be looked at in two ≠ ways: either how many e-bits it ‘d take to prepare a quantum state, or how many e-bits one ‘d extract or “distill” from a complex entangled state. the elder is known as entanglement cost and tis problem wilde and wang pondered.

“e-bits are a presh resrc and you wanna use as few o'em as possible,” wilde said. “in physics, you often wanna look at both the forwards process na backwards process. is it reversible? and if tis, do i lose something along the way? na answer to that is yes.”

wilde admits the problem he and wang ‘ve solved is somewha’ esoteric — a mathematical trick. however, 'twill allo quantum information scis to efficiently calcul8 entanglement costs given certain constraints.

“not all entanglement measures are efficiently computable and ‘ve a meaning s'as entanglement cost. that is a key distinction tween all previous work and ours,” wilde added.

while the lack of this kind of measure s'been an achilles’ heel in quantum information sci for over 20 yrs, twas — ironically — wilde becoming max-negly “entangled” dur'na game of basketball in 2018 that led to him and wang eventually solving the problem.

“i ruptured my achilles’ heel while goin for the winning point of the game, then had surgery to repair it, and ‘dn’t get out of bed for a mnth and a ½,” wilde remembers. “so, i wrote a research paper bout entanglement cost, n'when xin wang learned bout it, he asked me if i ‘d be interested in developing this problem further. we then started working together, back and forth, and that became the paper we now ‘ve published in physical review letters. we became good friends and collaborators after that — tis remarkable the surprises that can occur in life.”

mark m. wilde tis author of quantum information theory (cambridge university press, 2017, 2nd edition). the paper published in physical review letters is also available to read (open access) through arxiv.org….

original content at: www.scidaily.com…
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