Knowledge of the superposition of states

[Gerinski]

Is it completely impossible, even in principle, that eventually there can be a device by which we could know about the superposition of states without collapsing it?
For example, being able to know that an atom is in a 30% probability of being unexcited and a 70% probability of being excited, without actually collapsing it in either of both states?

 

[ZapperZ]

But there ARE already!

All you need to do is measure a non-commuting observable. That's what the Delft and Stony Brook experiment did, by measuring the energy gap instead of the "current directions" in a superconducting junction.

From a previous thread:

The SQUID experiments conducted recently at Stony Brook[1] and at Delft[2] CLEARLY showed a case where the supercurrent was flowing in BOTH DIRECTIONS simultaneously. It is the ONLY means to attain the two separate states. If the supercurrent is flowing either in one direction OR the other, the effect will NOT be detected.

The same can be said about a 2-slit experiment. It is a superposition of the path through BOTH slits simultaneously. This is the only means to get the interference pattern, implicating that a single photon is interfering with itself. A photon that goes through EITHER one slit or the other will NOT produce the identical interference pattern.

I have mentioned this reference before, but I highly recommend a topical review on this issue by Tony Leggett.[3] There is a huge, substantial but subtle issue that is involved here when discussing the Schrodinger Cat-type states. One cannot fully understand and appreciate QM without knowing and understanding the issues surrounding quantum superposition. When Feynman stated that when you understand the double-slit, you'll understand QM, this is exactly the principle he was referring to!

Zz.

[1] J.R. Friedman et al., Nature v.406, p.43 (2000).
[2] C.H. van der Wal et al., Science v.290, p.773 (2000).
[3] A.J. Leggett J. Phys: Cond. Matt. v.14, p.415 (2002).

 

[denian]

I cannot definitively say whether it is completely impossible or not for a device to be developed that can measure the superposition of states without collapsing it. However, based on our current understanding of quantum mechanics, it is highly unlikely that such a device could be created.

The principle of superposition states that a quantum system can exist in multiple states simultaneously until it is measured or observed, at which point it collapses into one of those states. This is a fundamental aspect of quantum mechanics and has been extensively tested and confirmed through experiments.

In order to measure the superposition of states without collapsing it, the device would need to interact with the system in a way that does not disturb or influence it in any way. This is a major challenge, as any interaction with the system, no matter how small, can cause it to collapse.

Additionally, the act of measuring itself involves the transfer of information, which can also cause the system to collapse. This is known as the measurement problem in quantum mechanics.

While it is always important to keep an open mind and continue exploring new possibilities, at this point in time, it seems highly unlikely that we will be able to know the superposition of states without collapsing it. However, advancements in technology and further research in quantum mechanics may one day lead to a better understanding of this phenomenon.