Last week there was a report that scientists in China have managed to keep particle states entangled out to a distance of 10 miles. That means that changes to an entangled particle in the lab should be instantly transmitted to the particle 10 miles away. But this doesn’t mean that we can now send a signal faster than the speed of light. At least not yet…
The problem in entanglement is that while the particles change state instantly, any attempt to observe the state destroys the entanglement. Which then means that while the information travels faster than the speed of light, the observation of the information is lightspeed limited, because the lab has to signal to the external observer that the state has changed so that the correlation can be measured.
But there’s a paper today that reports that there is hope that not all quantum properties are destroyed when observed. In particular researchers in Finland are publishing a paper this week that shows that a certain class of quantum correlations propagate out to classical length scales. The claim that these represent the transitional cases between quantum decoherence and macroscopic classical behavior:
“This particular correlation can be found, for example, in quantum systems comprising of two qubits. ‘These qubits, each with different properties, such as different polarizations, have to interact with a type of noise that doesn’t change the energy of the qubits,’ Maniscalco explains. ‘Instead of changing the energy, the noise just changes the phase, such as flipping polarizations. The type of noise that we have considered is one that contains all frequencies in a way that is very similar to white noise.’
While this discovery is theoretical, Maniscalco says that it has an experimental basis as well. ‘A very recent experiment has confirmed a type of quantum correlation that is not affected by the environment. And this is not a weird type of environment; it’s a natural environment that we could work in right now.’ (For more on this experiment, see Jin-Shi Xu, et. al., ‘Experimental investigation of classical and quantum correlations under decoherence,’ Nature Communications (April 2010). Doi:10.1038/ncomms1005.)
In the last 20 years, Maniscalco points out, technology has advanced to the point where it is possible to use single atoms or photons to build quantum logic gates for future quantum computers, or perform communication, measurement and cryptography tasks. ‘We’ve learned that it is possible to exploit the quantumness of the microscopic state, but in order for us to succeed, the quantum properties have to remain intact for a long time. That is a challenge, since once the properties are lost through interaction with the environment, a device can’t exploit quantumness.’
This discovery that certain quantum correlations are not lost in presence of the environment could lead an increased ability to exploit the quantum world for use in technological devices. Maniscalco points out that the idea that all quantum properties need not be lost through interaction with the environment presents more than interesting fundamental implications. ‘While this work has a surprising fundamental aspect,’ she says, ‘it opens up a whole range of possibilities with applications in quantum technology, including computing, communications, metrology and cryptography.’”
Read the full article here.
An ansible is a tool that allows for a faster than light communication. The term was coined by Ursula K. Le Guin but it’s appeared in numerous novels since. It’s a pretty obvious concept assuming that you actually measure an entangled quantum state without destroying the entanglement. Call the up-state a 1 and the down-state a 0. It’s a relatively simple project then to use a field on one end of the entangled state to flip the states up and down, and then use fields on the other end to measure the result. Since the states are entangled, the signal travels instantly – faster than the speed of light. You have a superluminal modem. Which means that we can talk to people in orbit around Saturn in real time, with out any light-flight induced delay.
Sub-space radio, here we come!