Experimental superposition of orders of quantum gates

Authors/others:Procopio, Lorenzo M.; Moqanaki, Amir; Araujo, Mateus (Österreichische Akademie der Wissenschaften (ÖAW)); Costa, Fabio (Österreichische Akademie der Wissenschaften (ÖAW)); Calafell, Irati Alonso; Dowd, Emma G. (Universität Wien); Hamel, Deny R.; Rozema, Lee A.; Brukner, Caslav (Österreichische Akademie der Wissenschaften (ÖAW)); Walther, Philip
Abstract:Quantum computers achieve a speed-up by placing quantum bits (qubits) in superpositions of different states. However, it has recently been appreciated that quantum mechanics also allows one to 'superimpose different operations'. Furthermore, it has been shown that using a qubit to coherently control the gate order allows one to accomplish a task-determining if two gates commute or anti-commute-with fewer gate uses than any known quantum algorithm. Here we experimentally demonstrate this advantage, in a photonic context, using a second qubit to control the order in which two gates are applied to a first qubit. We create the required superposition of gate orders by using additional degrees of freedom of the photons encoding our qubits. The new resource we exploit can be interpreted as a superposition of causal orders, and could allow quantum algorithms to be implemented with an efficiency unlikely to be achieved on a fixed-gate-order quantum computer.
Number of pages:6
Date of publication:8.2015
Journal title:Nature Communications
Peer reviewed:true
Digital Object Identifier (DOI):http://dx.doi.org/10.1038/ncomms8913
Publication Type:Article