Models for quantum computation with circuit connections subject to the quantum superposition principle have recently been proposed. In them, a control quantum system can coherently determine the order in which a target quantum system undergoes N gate operations. This process, known as the quantum N-switch, is a resource for several information-processing tasks. In particular, it provides a computational advantage - over fixed-gate-order quantum circuits - for phase-estimation problems involving N unknown unitary gates. However, the corresponding algorithm requires an experimentally unfeasible target-system dimension (super)exponential in N. Here, we introduce a promise problem for which the quantum N-switch gives an equivalent computational speedup with target-system dimension as small as 2 regardless of N. We use state-of-the-art multicore optical-fiber technology to experimentally demonstrate the quantum N-switch with N=4 gates acting on a photonic-polarization qubit. This is the first observation of a quantum superposition of more than N=2 temporal orders, demonstrating its usefulness for efficient phase estimation.
CITATION STYLE
Taddei, M. M., Cariñe, J., Martínez, D., García, T., Guerrero, N., Abbott, A. A., … Lima, G. (2021). Computational Advantage from the Quantum Superposition of Multiple Temporal Orders of Photonic Gates. PRX Quantum, 2(1). https://doi.org/10.1103/PRXQuantum.2.010320
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