07/18/2018

Warping time in quantum theory

A researcher at the Austrian Academy of Sciences devises a beam of particles with the property to make the quantum state of the systems it interacts with leap backwards in time. The result is published in the prestigious journal Physical Review X [Phys. Rev. X 8, 031008].

The possibility to disrupt the normal progress of time, a phenomenon popularly known as time warp, has captivated human fantasy since the dawn of civilization. Different schemes, relying on the theory of general relativity, have been proposed by the scientific community to achieve this effect: namely, to increase, decrease or even revert the natural evolution of arbitrary physical systems.

Unfortunately, most proposals to achieve time warp beyond mere relativistic time dilation are either unrealistic or impractical. The rest require an explicit control over the internal degrees of freedom of the target system –one needs to manipulate every single component accurately.

In his recent work Resetting Uncontrolled Quantum Systems, IQOQI group leader Miguel Navascués investigates how to revert the evolution of a quantum system of known dimensionality. The system is assumed uncontrolled, i.e., we ignore how the system evolves by itself or together with other systems we may use to influence it. As shown in the paper, under these circumstances there exist universal protocols within the framework of non-relativistic quantum theory which “reset” the state of the target system to the state it had at an arbitrary time before we started interacting with it in the first place.

These protocols sequentially send quantum particles close to the target system and back to a controlled lab, where we probe them. If the returning particles satisfy a specific collective property, then the target system will leap to its exact past state. If not, we can carry out further protocols to undo both the prior evolution of the system and the action of the previous failed protocols.

The simplest resetting protocols have a reasonably high probability of success and can be implemented with current quantum technologies. This paves the way towards an experimental demonstration of time warp in the non-relativistic arena.

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