Quantum jumps are more quantum than quantum diffusion

Abstract

It was recently argued (Wiseman and Gambetta 2012 Phys. Rev. Lett. 108 220402) that the stochastic dynamics (jumps or diffusion) of an open quantum system are not inherent to the system, but rather depend on the existence and nature of a distant detector. The proposed experimental tests involved homodyne detection, giving rise to quantum diffusion, and required efficiencies η of well over 50%. Here we prove that this requirement (η > 0.5) is universal for diffusive-type detection, even if the system is coupled to multiple baths. However, this no-go theorem does not apply to quantum jumps, and we propose a test involving a qubit with jump-type detectors, with a threshold efficiency of only 37%. That is, quantum jumps are 'more quantum', and open the way to practical experimental tests. Our scheme involves a novel sort of adaptive monitoring scheme on a system coupled to two baths.A surprising prediction of quantum entanglement theory is that the stochastic dynamics of individual open quantum systems (e.g. the quantum jumps of atoms) are not inherent to the system, but rather depend upon the presence, and nature, of a distant, macroscopic detector (e.g.

Symmetries and physically realisable ensembles for open quantum systems

“…The case of D=2, describing a 'rebit', actually leads to PREs of the same size as that predicted by equation (28). However, even in the case of D=2, the analysis above leads us to a better understanding of the nature of the PREs; in our upcoming discussion we highlight the symmetry that exists in the D=2 PREs of [1,41].…”

“…This ME was briefly considered, in the context of PREs, in [41]; the reader is also referred to the application discussed in [42] as evidence of its relevance to quantum information. In the Pauli basis we obtain ( ), which lies on the z-axis of the Bloch ball.…”

“…Of course, the portion of the w-axis within 0 U is also an invariant one-dimensional subspace. The case of K=2 is discussed in [41], and it is indeed the case that each of the invariant subspaces contains a K=2 PRE. An infinite number of PREs are parametrised by the azimuthal angle in the w=0 disc, and there is one further PRE consisting of the two points where the w-axis and 0 U intersect.…”

Hitting Statistics from Quantum Jumps

“…We assumed thatL has an inverse in our proof and it is natural to ask what ifL (55). Equations (60) and (61) are obtained from (55) which we have derived using the moment-generating function but they should also be derivable by directly doing the integral in (54) with n = 1 and n = 2 respectively.…”

Hitting statistics from quantum jumps

“…In particular we can choose to ignore jumps for selected channels by setting the detection efficiency for those channels to zero. The multichannel theory of quantum jumps with non-unit detection efficiency has been used to show that quantum jumps are more robust to measurement inefficiencies in disproving the existence of objective pure-state dynamical models [55]. The same formalism has also been used to study parameter estimation from multichannel photon counting 2 [24].…”