Quantum mechanics does not only allow superposition of quantum states but also superposition
of quantum gates. It was shown that superimposing two quantum gates A and B,
an unordered quantum computation can run more efficiently than a well-defined
order quantum computation (Copyright: Philip Walther Group, University of Vienna).
Unordered quantum computation: improved efficiency
(August 11, 2015) A team of physicists from the University of Vienna and the Austrian Academy of Sciences have demonstrated a new quantum computation scheme in which operations occur without a well-defined order. The researchers led by Philip Walther and Caslav Brukner used this effect to accomplish a task more efficiently than a standard quantum computer. Moreover, these ideas could set the basis for a new form of quantum computing, potentially providing quantum computers with an even larger computational speed-up. Their results will be published in an upcoming issue of "Nature Communications".
Since its conception, quantum mechanics has defied our natural way of thinking, and it has forced physicists to come to grips with peculiar ideas. Although they may be difficult to digest, quantum phenomena are real. What’s more, in the last decades, scientists have shown that these bizarre quantum effects can be used for many astonishingly powerful applications: from ultra-secure communication to hacking existing secure communications, and from simulating complex quantum systems to efficiently solving large systems of equations.
One of the most exciting and most difficult proposed quantum technologies is the quantum computer. Quantum logic gates are the basic building blocks of a quantum computer, but constructing enough of them to perform a useful computation is difficult. In the usual approach to quantum computing, quantum gates are applied in a specific order, one gate before another. But it was recently realized that quantum mechanics permits one to "superimpose quantum gates". If engineered correctly, this means that a set of quantum gates can act in all possible orders at the same time. Surprisingly, this effect can be used to reduce the total number of gates required for certain quantum computations.