So... I have finally finished reading this paper:
And my conclusion is, the hype is not exaggerated
So to start off, this is a quantum optics experiment consists of a coupled three level system $\lvert D\rangle,\lvert B\rangle,\lvert G\rangle$. Here, rabi drives were used to cause transitions between $DG$ and $BG$ respectively, with $DG$ proceed at a slower rate than $BG$
What they observed in the experiment is that, whenever the clicks die out from 0-2 $\mu s$ it is an indication that the state is trying to jump to $\lvert D\rangle$ from $\lvert G\rangle$ and hence a warning that a quantum jump had occurred
While the initiation of such warning to jump is stochastic and unpredictable, it was found that whenever the warning occurred, the jump will occur in a deterministic fashion with the ensemble passing through essentially the same trajectory in Hilbert space as it made its way from $\lvert G\rangle$ to $\lvert D\rangle$
This deterministic schrodinger equation like dynamics due to the coherence of the evolution of the jump at the short time scale (in contrast with the stochastic behaviour of the initiation of the warning at long time scales of the order 10), thus allows the experiment to use the warning to initiate some Bloch sphere operations into the system so that the jump trajectory can be reversed midway, returning the ensemble to $\lvert G\rangle$
and thus achieving the controlled reversal of a quantum jump, something that is commonly believed to be purely stochastic
Therefore, while the occurrence of the warning is stochastic, the jump evolutions that followed after those are deterministic, thus allowing them to be intercepted. This also reconcile Bohr's conception of quantum jumps with schrodinger's, that the stochastic and coherence of a quantum jump coexists at two different time scales of the dynamics
The experiment predictions are thus consistent with that of quantum trajectory theory.
So what is quantum trajectory theory?
arxiv.org/abs/1405.6694 Here is a good review of this model that is commonly used in quantum optics. Roughly speaking:
Quantum trajectory theory arises from the increasing need to model open quantum systems, systems where the quantum state of interest is coupled strongly to the environment, and that properties of the environment are sufficiently well understood that the environment played an important role in controlling the quantum state in question
What result from this is that the whole system need to be described as if the environment is a bath coupled to the quantum state, and hence an open system. In order to describe what happens to the quantum state as it evolves in time, one need to wrote the change in the density matrix in terms of all the dephasing, couplings and other interactions between the quantum system and the environment.
This forms something called the master equation, which describes how the quantum system evolves under the action of the environment
Quantum trajectory theory, which has many different versions developed by many different authors, are approaches in simplifying the computation of this master equation. All of them are based on the principle that rather than trying to compute the whole density matrix, you pick an ensemble of pure states, to be evolved in time steps through Hilbert space, and these samplings will reflect the average behaviour of the density matrix you want to compute
From these you can then deduce a lot of things from which route a state took in order to move from A to B in Hilbert space, to the observables that is expected to be measured such as when and how spontaneous emission will occur when a quantum system is coupled to a laser field
Therefore, quantum trajectory theory is not to be confused with Bohmian mechanics, though in principle, I do not see any problem that it can be used in the bohmian context
And finally, that paper is consistent with all interpretations, though that quantum jumps have a deterministic component seemed to be surprising enough for me, sharing a similar comment as the authors in the paper
It may open the door as to whether all such jumps have a warning period, or just really coherent systems like this three level rabi driven system does that, and whether they have durations that are as given by quantum trajectory theory. In the supplementary info, however, it is said that some jumps still reverses unpredictably, thus according for that 23% failure rate in the graph
Philosophically, I still think this experiment is significant. Even though it said absolutely nothing about quantum interpretations, that we can experimentally demonstrated that there is a nonzero period of determinacy that follows after almost every warning to jump can have implications on how to control what is essentially random phenomenon right when they occur
@vzn @PM2Ring @Semiclassical etc. Sorry for my extremely lengthly comment. What do you guys think of my thoughts about that experiment?
