How long does entanglement last?

[San K]

once entangled photons are created (via say SPDC or quantum dots etc) ...how long does the entanglement last?

there is so much noise in the environment
so many things the entangled photons would interact with,
so many ways to transfer/exchange momentum with the surroundings

 

[bohm2]

I'm not sure if someone has recorded longer than this for this size objects?

By combining the dissipative mechanism with a continuous measurement, steady state entanglement is continuously generated and observed for up to an hour.

Entanglement Generated by Dissipation and Steady State Entanglement of Two Macroscopic Objects
http://prl.aps.org/abstract/PRL/v107/i8/e080503
http://lanl.arxiv.org/pdf/1006.4344.pdf (full article pre-print)

 

[VantagePoint72]

once entangled photons are created (via say SPDC or quantum dots etc) ...how long does the entanglement last?

there is so much noise in the environment
so many things the entangled photons would interact with,
so many ways to transfer/exchange momentum with the surroundings

You've more or less answered your own question: entanglement lasts as long as you can effectively mitigate those external factors. The larger the system is, the more difficult this is to do for extended periods.