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A team of physicists from ICTP-Trieste and IQOQI-Innsbruck has come up with a surprisingly simple idea to investigate quantum entanglement of many particles. Instead of digging deep into the properties of quantum wave functions - which are notoriously hard to experimentally access - they propose to realize physical systems governed by the corresponding entanglement Hamiltonians. By doing so, entanglement properties of the original problem of interest become accessible via well-established tools. This radically new approach could help to improve understanding of quantum matter and open the way to new quantum technologies.
Quantum entanglement forms the heart of the second quantum revolution: it is a key characteristic used to understand forms of quantum matter, and a key resource for present and future quantum technologies.
Physically, entangled particles cannot be described as individual particles with defined states, but only as a single system. Even when the particles are separated by a large distance, changes in one particle also instantaneously affect the other particle(s). The entanglement of individual particles - whether photons, atoms or molecules - is part of everyday life in the laboratory today.
The physicists turn the concept of quantum simulation upside down by no longer simulating a certain physical system in the quantum simulator, but directly simulating its entanglement Hamiltonian operator, whose spectrum of excitations immediately relates to the entanglement spectrum.
"Instead of simulating a specific quantum problem in the laboratory and then trying to measure the entanglement properties, we propose simply turning the tables and directly realizing the corresponding entanglement Hamiltonian, which gives immediate and simple access to entanglement properties, such as the entanglement spectrum" explains Marcello Dalmonte. "Probing this operator in the lab is conceptually and practically as easy as probing conventional many-body spectra, a well-established lab routine." Furthermore, there are hardly any limits to this method with regard to the size of the quantum system.
This could also allow the investigation of entanglement spectra in many-particle systems, which is notoriously challenging to address with classical computers. Dalmonte, Vermersch and Zoller describe the radically new method in a current paper in Nature Physics and demonstrate its concrete realization on a number of experimental platforms, such as atomic systems, trapped ions and also solid-state systems based on superconducting quantum bits.
(Score: 0) by Anonymous Coward on Thursday May 24 2018, @01:08PM
Not quite so simple. These kind of experiments also have a variable defining the measurement to be made on each particle, akin to choosing whether to ask the particle if it is X/Y or rather A/B. (It can't ask both - blame Heisenberg's uncertainty principle.) This choice of measurement is made randomly after the entangled particles have travelled so far from each other that they could not tell each other (limited by lightspeed) which question they were asked. Yet they still somehow respond as if they all knew! The only way for that to equate to a question of "which universe" (aka the particular values of "local hidden variables") is if the "random" measurement choice was predetermined.
While with current technology we must use machines to make this measurement choice randomly (based on quantum mechanical principles that we believe are nondeterministic), there are not-unrealistic proposals that involve transmitting quantum states to/from the moon which could feasibly have a human make the choice. If the experimental results are unchanged (and there's presently no reason to expect they won't be), your picture, though possibly correct, would nevertheless have some interesting/awkward implications for the concept of free-will.