Nov 13th: Prof. Scott Aaronson (MIT)

“Forrelation: A Problem that Optimally Separates Quantum from Classical Computing”
Prof. Scott Aaronson, MIT

ROOM 26-214
THURSDAY, NOVEMBER 13, 2014
12:00 PM – 13:00 PM

We achieve essentially the largest possible separation between quantum
and classical query complexities. We do so using a property-testing
problem called Forrelation, where one needs to decide whether one
Boolean function is highly correlated with the Fourier transform of a
second function. This problem can be solved using 1 quantum query,
yet we show that any randomized algorithm needs Omega(sqrt(N) /
log(N)) queries (improving an Omega(N^{1/4}) lower bound of Aaronson).
Conversely, we show that this 1 versus ~Omega(sqrt(N)) separation is
optimal: indeed, any t-query quantum algorithm whatsoever can be
simulated by an O(N^{1-1/2t})-query randomized algorithm. Thus,
resolving an open question of Buhrman et al. from 2002, there is no
partial Boolean function whose quantum query complexity is constant
and whose randomized query complexity is linear. We conjecture that a
natural generalization of Forrelation achieves the optimal t versus
~Omega(N^{1-1/2t}) separation for all t. As a bonus, we show that this
generalization is BQP-complete. This yields what’s arguably the
simplest BQP-complete problem yet known, and gives a second sense in
which Forrelation “captures the maximum power of quantum computation.”

Joint work with Andris Ambainis

“The students in MIT’s new NSF training program will be encouraged to cross disciplines, and develop a common fellowship with their peers. We will also address training for post-academic jobs directly by connecting students to government and industrial members of the iQuISE Consortium.”

—Seth Lloyd, Co-Director, iQuISE, and Professor of Mechanical Engineering and Professor of Engineering Systems