Paper: To catch and reverse a quantum jump in flight

[Swamp Thing]

This video www.youtube.com/watch?v=j5HyMNNSGqQ and the paper it refers to https://www.nature.com/articles/s41586-019-1287-z
(available also at : http://qulab.eng.yale.edu/documents/papers/zlatko_paper.pdf )

... talks about how a quantum transition can be monitored and manipulated in real time. A couple of questions came to mind:

[1] The reported experiment involves an energy level transition. Is it possible to monitor and manipulate other kinds of states that don't involve energy jumps, like photon polarization or electron spin? For example, as an electron makes its way between the poles of a Stern-Gerlach magnet, can we (at least in principle) monitor and sense that it's about to head upwards, and then coax it to go downwards instead --- using principles like weak measurement and quantum state control?

[2] If two experimenters apply these techniques to a pair of entangled particles, how would it play out? Would both of them be able to sense that it's about to head towards state |A> |B>, say? If yes, then what if one experimenter decided to intervene and reverse the process and push it towards |Not A> |Not B> ? Or would weak measurement (however weak) totally destroy the entanglement?

[3] Is it possible for energy transitions occurring in different places to be entangled with each other? Or is it the case that entanglement normally involves observables other than energy?

 

[eljose79]

I find this forum post and the referenced video and paper very interesting. To answer your questions:

[1] The experiment described in the paper and video does indeed involve an energy level transition, but the principles of weak measurement and quantum state control can be applied to other types of states as well. For example, photon polarization and electron spin can also be monitored and manipulated using these principles. In fact, there have been experiments where weak measurements have been used to monitor and control the spin of a single electron in a quantum dot. So, in principle, it is possible to monitor and manipulate different types of states using weak measurement and quantum state control.

[2] If two experimenters apply these techniques to a pair of entangled particles, they would both be able to sense that it's about to head towards state |A> |B>. However, if one experimenter decides to intervene and reverse the process, it would not necessarily destroy the entanglement. The key is to make sure that the intervention is done in a way that does not disturb the entanglement. This can be achieved by carefully designing the experimental setup and using techniques such as quantum error correction.

[3] It is possible for energy transitions occurring in different places to be entangled with each other. In fact, entanglement can occur between any quantum systems, not just energy levels. Entanglement can be created between particles with different energy levels, different spins, or even different types of particles. So, it is not necessary for entanglement to involve observables other than energy.

Overall, the research presented in the paper and video is a significant step towards real-time monitoring and manipulation of quantum states. It opens up new possibilities for studying and controlling quantum systems, and has potential applications in fields such as quantum computing and quantum communication.