Sustainable entanglement production from a quantum field

Abstract

We propose a protocol by which entanglement can be extracted repeatedly from a quantum field. In analogy with prior work on entanglement harvesting, we call this protocol entanglement farming. It consists of successively sending pairs of unentangled particles through an optical cavity. Using non-perturbative Gaussian methods, we show that in certain generic circumstances this protocol drives the cavity field towards a non-thermal metastable state. This state of the cavity is such that successive pairs of unentangled particles sent through the cavity will reliably emerge significantly entangled. We calculate thermodynamic aspects of the harvesting process, such as energies and entropies, and also the long-term behavior beyond the few-mode approximation. Significant for possible experimental realizations is the fact that this entangling fixed point state of the cavity is reached largely independently of the initial state in which the cavity was prepared. Our results suggest that reliable entanglement farming on the basis of such a fixed point state should be possible also in various other experimental settings, namely with the to-be-entangled particles replaced by arbitrary qudits and with the cavity replaced by a suitable reservoir system.Comment: V2: Added Journal Reference. Title modified to match published version. 16 pages, 8 figures. RevTex 4.

Quantum signaling in cavity QED

“…Of course, independently of that, the Dyson expansion is not unitary order by order, but instead it is unitary up to the power of the perturbative parameter of the first ignored term in the perturbative expansion. Additionally, it is well known that for very long times we can leave the perturbative regime (where the Dyson expansion is valid) [21]. However, in this paper, we are concerned with time scales smaller or of the order of the light-crossing time of the cavity, and for all the values considered here, the Dyson expansions will be unitary up to at least the fourth (or sixth) power of the perturbative parameter.…”

Thermal amplification of field-correlation harvesting

“…While an interesting theoretical discovery, there has been little hope that this phenomenon may be used as a practical tool for generating entanglement over large distances because the amount of entanglement obtained is typically minuscule. That said, there has very recently been a proposal for a reusable and sustainable entanglement "farming" procedure that may be able to overcome this limitation [26].…”

Extraction of genuine tripartite entanglement from the vacuum

“…The problem was fixed in [5] by adding more field modes and the idea was further developed, providing a useful formalism for the analytical treatment of point-like detectors interacting with the vacuum. This formalism has been extensively used to study various scenarios in the harvesting of entanglement [4][5][6] and more general quantum correlations [7] in the case of bipartite harvesting (i.e. two detectors).…”