Experimental computational advantage from superposition of multiple temporal orders of quantum gates
Abstract
Advanced models for quantum computation where even the circuit connections are subject to the quantum superposition principle have been recently introduced. There, a control quantum system can coherently control the order in which a target quantum system undergoes $N$ gate operations. This process is known as the quantum $N$switch, and has been identified as a resource for several informationprocessing tasks. In particular, the quantum $N$switch provides a computational advantage  over all circuits with fixed gate orders  for phaseestimation problems involving $N$ unknown unitary gates. However, the corresponding algorithm requires the targetsystem dimension to grow (super)exponentially with $N$, making it experimentally demanding. In fact, all implementations of the quantum $N$switch reported so far have been restricted to $N=2$. Here, we introduce a promise problem for which the quantum $N$switch gives an equivalent computational speedup but where the targetsystem dimension can be as small as 2 regardless of $N$. We use stateoftheart multicore optical fiber technology to experimentally demonstrate the quantum $N$switch with $N = 4$ gates acting on a photonicpolarization qubit. This is the first observation of a quantum superposition of more than 2 temporal orders, and also demonstrates its usefulness for efficient phaseestimation.
 Publication:

arXiv eprints
 Pub Date:
 February 2020
 arXiv:
 arXiv:2002.07817
 Bibcode:
 2020arXiv200207817T
 Keywords:

 Quantum Physics
 EPrint:
 Main text: 7 pages, 3 figures