Article link: http://physicsworld.com/cws/article/news/2015/feb/05/photons-simulate-time-travel-in-the-lab
Note: (A)This article talks about using photon aka laser, (B) at the end of article mentioned strong gravitational curvature....
Does it sounds a bit similar to what the John Titor fans have claimed?
"Physicists in Australia claim to have simulated time travel using fairly standard optical equipment on a lab bench. They say they have prepared photons that behave as if they are travelling along short cuts in space–time known as "closed time-like curves", and add that their work might help in the long-sought-after unification of quantum mechanics and gravity. Others, however, argue that the research does little or nothing to establish whether time travel is possible in nature."
"In 1991 David Deutsch of Oxford University showed that the probabilistic nature of quantum mechanics comes to the rescue. Deutsch found that there would always be a state that a quantum particle could assume that would make the particle's trip back in time a safe one. For example, if the particle were to start out in an equal mixture of one and zero, when flipped it would remain in that state – a 50:50 mixture of one and zero."
"In the latest work, Martin Ringbauer and colleagues at the University of Queensland in Brisbane set out to reproduce Deutsch's model in the laboratory. But given the absence of any real closed time-like curves in the vicinity of their lab, they were not able to directly study the interaction between younger and older versions of the same quantum particle. Instead, they used two separate particles. The idea is that the "younger" particle remains in normal space–time, while the "older" one disappears down a simulated wormhole, reappears in the "past" and then interacts with its junior partner.
To implement their scheme, the team generated pairs of single photons by shining a laser beam through a nonlinear crystal. The younger photon was encoded by polarizing it – with horizontal polarization representing zero, vertical polarization representing one and intermediate polarization representing superpositions. That photon then interfered with its older partner in a beamsplitter, and the outcome was recorded by a pair of detectors.
Consistency condition
One of these detectors constitutes the entrance to the "wormhole" and is used to record the state of the older photon to ensure that is in the same state as it is at the beginning of the experiment – the point at which it emerges from the wormhole. In this way, the scheme satisfies the "consistency condition" that Deutsch imposed on his model to remove the paradoxes from time travel – that whatever goes into a wormhole emerges from it unchanged.
Encoding the younger photon arbitrarily with one of 32 different polarizations and fixing the state of the older photon to satisfy the consistency condition, the researchers showed that they could indeed meet this condition. They also found that the presence of a closed time-like curve allows an observer to perfectly distinguish non-orthogonal states of the time-travelling photon, such as horizontal and diagonal polarizations. This is something that cannot normally be done in quantum-mechanical systems.
Encryption buster
According to project leader Tim Ralph, this result suggests a way to break quantum encryption, since any eavesdropper with access to a closed time-like curve would in principle be able to make a perfect copy of the secret key and so avoid revealing his or her presence via quantum measurements. More broadly, he says, the research could provide an insight into the tension between quantum mechanics and general relativity, given that closed time-like curves are only possible with strong gravitational curvature."
Note: (A)This article talks about using photon aka laser, (B) at the end of article mentioned strong gravitational curvature....
Does it sounds a bit similar to what the John Titor fans have claimed?
"Physicists in Australia claim to have simulated time travel using fairly standard optical equipment on a lab bench. They say they have prepared photons that behave as if they are travelling along short cuts in space–time known as "closed time-like curves", and add that their work might help in the long-sought-after unification of quantum mechanics and gravity. Others, however, argue that the research does little or nothing to establish whether time travel is possible in nature."
"In 1991 David Deutsch of Oxford University showed that the probabilistic nature of quantum mechanics comes to the rescue. Deutsch found that there would always be a state that a quantum particle could assume that would make the particle's trip back in time a safe one. For example, if the particle were to start out in an equal mixture of one and zero, when flipped it would remain in that state – a 50:50 mixture of one and zero."
"In the latest work, Martin Ringbauer and colleagues at the University of Queensland in Brisbane set out to reproduce Deutsch's model in the laboratory. But given the absence of any real closed time-like curves in the vicinity of their lab, they were not able to directly study the interaction between younger and older versions of the same quantum particle. Instead, they used two separate particles. The idea is that the "younger" particle remains in normal space–time, while the "older" one disappears down a simulated wormhole, reappears in the "past" and then interacts with its junior partner.
To implement their scheme, the team generated pairs of single photons by shining a laser beam through a nonlinear crystal. The younger photon was encoded by polarizing it – with horizontal polarization representing zero, vertical polarization representing one and intermediate polarization representing superpositions. That photon then interfered with its older partner in a beamsplitter, and the outcome was recorded by a pair of detectors.
Consistency condition
One of these detectors constitutes the entrance to the "wormhole" and is used to record the state of the older photon to ensure that is in the same state as it is at the beginning of the experiment – the point at which it emerges from the wormhole. In this way, the scheme satisfies the "consistency condition" that Deutsch imposed on his model to remove the paradoxes from time travel – that whatever goes into a wormhole emerges from it unchanged.
Encoding the younger photon arbitrarily with one of 32 different polarizations and fixing the state of the older photon to satisfy the consistency condition, the researchers showed that they could indeed meet this condition. They also found that the presence of a closed time-like curve allows an observer to perfectly distinguish non-orthogonal states of the time-travelling photon, such as horizontal and diagonal polarizations. This is something that cannot normally be done in quantum-mechanical systems.
Encryption buster
According to project leader Tim Ralph, this result suggests a way to break quantum encryption, since any eavesdropper with access to a closed time-like curve would in principle be able to make a perfect copy of the secret key and so avoid revealing his or her presence via quantum measurements. More broadly, he says, the research could provide an insight into the tension between quantum mechanics and general relativity, given that closed time-like curves are only possible with strong gravitational curvature."
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