Tackling the type of question usually reserved for science fiction, researchers from IQC and IBM recently investigated whether time travel can be utilized to solve difficult computational problems.IBM researchers Charles Bennett, Graeme Smith and John Smolin and IQC faculty member Debbie Leung examined whether "closed timelike curves" (CTCs), in which a particle's path through spacetime returns to its point of origin, can allow a computer to more efficiently solve difficult problems.
Although some prior research has suggested this feat may be possible in certain circumstances, Bennett, Leung, Smith and Smolin demonstrated that such research was problematic because conclusions accounted for only fixed input states, but do not work when input consists of a distribution of states. Thus, the speedup was possible only when the question is known upfront. Any computational advantage is dubious and unproven when a more physically relevant computational model is considered.
The study indicates that CTCs do not make computations more efficient in a physically motivated computation model, and calls into question other conclusions about nonlinear extensions of quantum mechanics. The researchers' conclusions were summarized in a recent edition of Nature Physics. Though CTCs have not yet been shown to exist beyond the sci-fi realm, they have proven theoretically interesting.
The work by Bennett, Leung, Smith and Smolin shows that it is unlikely that one can use a too-good-to-be-true computational advantage to rule out a variety of nonlinear theory of quantum mechanics.
About IQC: Founded in 2002, the mission of the Institute for Quantum Computing (IQC) is to aggressively explore and advance the application of quantum mechanical systems to a vast array of relevant information processing techniques.
A part of the University of Waterloo, Waterloo, Ont., Canada, IQC creates a truly unique environment fostering cutting-edge research and collaboration between researchers in the areas of computer, engineering, mathematical and physical sciences.
At the time of this release, IQC has 17 faculty members, 22 postdoctoral fellows and over 55 students and research assistants, as well as a support staff of 18.
The Institute for Quantum Computing acknowledges the support of the Government of Canada through Industry Canada and the Government of Ontario through the Ministry of Research and Innovation.