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.Scott

Homework Helper

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## Main Question or Discussion Point

The title of this thread is the title to this Phys.org article posted today:

https://phys.org/news/2017-08-physicists-complementary-properties-quantum-clones.html

First, correct me if I'm wrong, but the problem is not that complementary states cannot be both measured, but that the there is a limit (##\hslash/2##) describing how measuring one results in a trade-off in what can be measured in the other.

Here is their claim:

From any normal view of QM, complementary states cannot be measured because they don't both exist - there simply isn't that much information in the system to measure. So I'm putting this article into the same category as perpetual motion machines.

Of course, if I'm wrong, I'm sure I'll hear about it.

https://phys.org/news/2017-08-physicists-complementary-properties-quantum-clones.html

First, correct me if I'm wrong, but the problem is not that complementary states cannot be both measured, but that the there is a limit (##\hslash/2##) describing how measuring one results in a trade-off in what can be measured in the other.

Here is their claim:

Why am I so thoroughly skeptical of this?"In our daily lives, information is often copied, such as when we photocopy a document, or when DNA is replicated in our bodies," Thekkadath explained. "However, at a quantum level, information cannot be copied without introducing some noise or imperfections. We know this because of a mathematical result known as the no-cloning theorem. This has not stopped physicists from trying. They developed strategies, known as optimal cloning, that minimize the amount of noise introduced by the copying process. In our work, we go one step further. We showed that it is possible to eliminate this noise from our measurements on the copies using a clever trick that was theoretically proposed by Holger Hofmann in 2012. Our results do not violate the no-cloning theorem since we never physically produce perfect copies: we only replicate the measurement results one would get with perfect copies."

From any normal view of QM, complementary states cannot be measured because they don't both exist - there simply isn't that much information in the system to measure. So I'm putting this article into the same category as perpetual motion machines.

Of course, if I'm wrong, I'm sure I'll hear about it.