Resetting entanglement in biomolecules

85266_largeSteady state entanglement in open and noisy quantum systems at high temperature

L. Hartmann, W. Dur, & H.J. Briegel, Innsbruck University

Phys Rev A, vol. 74, issue 5 (dated May 15 2011)

This paper is significant in moving away from a Tegmark type orthodoxy of rapid decoherence in high temperature systems, towards a recognition that systems far from thermal equilibrium, such as biomolecules, are capable of resetting entanglement by drawing new particles from the environment.

This paper demonstrates how quantum entanglement can be sustained in open and noisy environments that are far from thermal equilibrium, despite the tendency of such systems to decoherence. Such a system has a large number of interacting particles, and can also interact with and exchange particles with the environment. The impact of decoherence is counteracted by resetting of some of these particles to their initial state.

The situation of entanglement in macroscopic solids and fluids with large numbers of particles interacting with one another and the environment has been unclear. Studies have shown that entanglement is present in such systems, but this only referred to very low temperatures at which particles were close to their ground state. The main question which the authors address here is what happens in systems that are far from thermal equilibrium and exchange particles with the environment. This involves systems where individual particles are subject to decoherence, and particles are exchanged with the environment. Such systems include biomolecular processing within cells. The past expectation, as with the well-known Tegmark (2000) paper, is that decoherence would quickly destroy entanglement in such a system.

The authors identify a mechanism which can allow entanglement in systems that are not close to their ground state. This involves particles from the environment replacing particles in the system. In combination with particles already in the system, the ‘fresh’ particle is able to create entanglement. The system is described as being coupled to two reservoirs, a high temperature reservoir creating decoherence, and a second low temperature reservoir from which ‘fresh’ particles are drawn. This described a system far from thermal equilibrium.

All the authors results, which also involved simulating the system on a computer, produced the same conclusion that entanglement could persist in systems that are far from thermal equilibrium. Thus there is a sharp distinction made by the authors between systems at thermal equilibrium where entanglement can only occur at very low temperatures, and those that are far from equilibrium where entanglement can be sustained at high temperatures. Entanglement is suggested to persist in the middle ground where it has time to build up, but decoherence is not too fast. In the case of biomolecules that are far from thermal equilibrium, and where there are fluctuations in the number of particles in the system, ‘fresh’ particles from the environment are seen as likely to be responsible for the reset mechanism.

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