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发帖数: 19049 | 1 Some particles such as photons and electrons, when brought together and then
separated, can become “entangled” and exist in the same quantum
mechanical state.
This quantum mechanical state, prior to any form of measurement, possesses
indefinite properties such as position in space, spin, and polarization.
Such properties remain indefinite until they are measured, at which point
they take on definite values such as a particular location in space or a
clockwise spin. After one such entangled particle has been measured, the
other member of the pair can be seen to have taken on the appropriately
paired value.
Thus when one member of a pair is measured and takes on a counterclockwise
spin, the other member of the pair will take on a clockwise pair.
Interestingly, there are not range constraints on this interaction; quantum
entanglement events can take place over arbitrarily large distances. Quantum
entanglement allows for the “remote control” of quantum states, which is
essential for many aspects of quantum communication, cryptography, and
computation.
Entanglement, though very useful, can be quite difficult to work with.
Highly sensitive systems can often be influenced and disrupted by outside
forces. According to a new article titled “Quantum discord as resource for
remote state preparation” in the journal Nature Physics, quantum
entanglement may not be the only way to achieve this “remote control” of
quantum states. Physicists Caslav Brukner and Philip Walther demonstrate
that certain non-entangled quantum states can perform even better than
entangled states in some circumstances.
Though physicists do not completely understand the correlation between
certain pairs of non-entangled quantum states, it involves an interaction
labeled by physicists as “quantum discord,” or the disturbance experienced
by correlated particles when one member of a pair is measured.
Mr. Walther and Mr. Brukner experimented largely with two-photon states with
the goal of characterizing and manipulating how the quantum state of one
photon changed in response to the measurement of the correlated photon’s
quantum state.
“By measuring the polarization state of a certain photon we prepare the
state of the respective partner photon remotely. In the experiment we
observe how the quality of our remotely prepared quantum state is affected
by changes in the quantum discord,” says Mr. Walther, according to R&D
Magazine.
Such experimentation is important as it may prove to be less restrictive and
less resource-intensive than similar work done with entangled particles.
Such limitations are major barriers to progress in fields such as quantum
communications and quantum computing. Quantum discord could provide a new
and very useful tool for the preparation of quantum remote states over a
distance.
The team of physicists found that discord is similar to shared quantum
static and that more ‘music’ can be extracted from this simulcast with the
right quantum tools. Quantum discord has been shown to be present in many
systems, and might previously have been characterised as unwanted noise.
This has made some scientists sceptical that it could be useful. The new
results suggest otherwise. The experiment demonstrated isn’t considered a
quantum computation, but it shows that discord has potential that can be
unlocked for quantum technologies.
Collaborators from the physics faculty at the University of Vienna, the
Vienna Center for Quantum Science and Technology, the Institute for Quantum
Optics and Quantum Information, the Center for Quantum Technologies at the
University of Singapore and the University of Oxford conducted the project’
s research and theoretical work. |
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