A Weinberg: detecting changes to QM using atomic clocks

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Steven Weinberg has lately been critical of QM. He now also has a technical paper out called 'Lindblad Decoherence in Atomic Clocks', available on arxiv. Here is the abstract:

It is shown how possible corrections to ordinary quantum mechanics described by the Lindblad equation might be detected by exploiting the great precision of atomic clocks.

It's a short paper (6 pgs of text), arguing for objective collapse (a la GRW/Diosi-Penrose/etc) instead of Copenhagen/MWI. Based on Ramsey-method atomic clocks frequency measurements, Weinberg gives upper limits (based on Ramsey transition times) for objective collapse below which the scheme is already ruled out experimentally. He also proposes two different ways in which objective collapse can be sought out further in future atomic clock experiments.

 

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If Γ has similar values for all transitions, then we should look at clocks
for which the Ramsey time T is as long as possible. Modern atomic clocks
typically have T of the order of seconds, but a clock[12] using a microwave-
frequency transition in trapped 171Yb+ ions has operated with T > 600
seconds. Hence we can conclude that in this transition Γ < 10^−18 eV. This
upper limit shows that environmental effects make it hopeless to look for
departures from quantum mechanics on macroscopic scales, where the en-
ergy of interaction with the environment is presumably always much greater
than 10^−18 eV. On the other hand, this upper bound is enormous compared
with the difference between energies of discrete states of macroscopic ob-
jects that are free from all external influences. For instance, according to
quantum mechanics, the successive energy eigenstates of a pointer of mass
one gram and length one centimeter that swivels freely in two dimensions is
about 10^−42 eV. Thus departures from ordinary quantum mechanics with Γ
less than the limit 10^−18 eV derived from atomic clocks might still have a
powerful effect on the quantum states of macroscopic systems if they could
somehow be isolated from their environment.

This passage in particular (describing one of the two ways forward experimentally) seems very interesting. It is somewhat reminiscent of the Marshall et al. proposal of putting a tiny mirror in superposition in order to detect or rule out the Diosi-Penrose objective reduction scheme.

From what I last heard from Penrose (past November), Dirk Bouwmeester is currently still hard at work on this experiment and we will have an answer within a decade.

 

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Here is a somewhat recent review of the theory and experiment of decoherence, both environmental and intrinsic, concomitantly offering a Feynman path integral approach:

Stamp 2012, Environmental Decoherence versus Intrinsic Decoherence

Spoiler: Abstract

We review the difference between standard environmental decoherence and 'intrinsic decoherence', which is taken to be an ineluctable process of Nature. Environmental decoherence is typically modeled by spin bath or oscillator modes - we review some of the unanswered questions not captured by these models, and also the application of them to experiments. Finally, a sketch is given of a new theoretical approach to intrinsic decoherence, and this scheme is applied to the discussion of gravitational decoherence.

Of particular interest for the current thread, in light of the Lindblad equation, are the following passages, especially the highlighted part:

It has [become] quite common in some fields to approximate the effect of an environment by coupling the system to an external ’noise’ source, ie., to approximate the full Hamiltonian in (1) by a form $H(t) = H_o(P, Q) + VN (Q;t)$, where the time-dependent potential $VN$ contains a random force acting on $Q$, and the effects of this force are averaged over, using some technique (Langevin, Lindblad, Fokker-Planck, etc.). But it [is] well known that such models can never fully capture the effect of integrating out a dynamical environment [14]. They only describe the real part of the influence functional, which itself completely characterizes the effect of the dynamic environment on the system [1, 14]; moreover, when approximated by, eg., Markovian processes, they also lose the long-time correlations which are characteristic of the influence functional of many environments. Physically, it is clear that a key part of the environmental effect on the central system dynamics is via a time-retarded ’back-reaction’ on this system. We note that the results may sometimes be quite counter-intuitive. The example of a particle moving on a lattice while coupled to a spin bath [15] provides an example: the particle density matrix shows simultaneous ballistic motion and anomalous diffusion, reminiscent of weak localization. Further discussion of all this is quite technical.

It doesn't seem Weinberg has taken this into account either...

NB: Reference 1 and 14 are two works by Feynman from during the 60s:
[1] Feynman, R. P., & Vernon, F. L. (1963). The theory of a general quantum system interacting with a linear dissipative system. Annals of physics,24, 118-173.
[14] Feynman, R. P., & Hibbs, A. R. (1965).Quantum mechanics and path integrals [by] RP Feynman [and] AR Hibbs. McGraw-Hill.