Reduction of unitary operators, quantum graphs and quantum channels Salcedo Moreno, Lorenzo Luis This work has been partially supported by MCIN/AEI/10.13039/501100011033 under grant PID2020-114767 GB-I00, and by the Junta de Andalucía under grant No. FQM-225, and Spanish Ministerio de Ciencia, Innovacion y Universidades under grant PID2023-147072N Given a unitary operator in a finite dimensional complex Hilbert space, its unitary reduction to a subspace is defined. The application to quantum graphs is discussed. It is shown how the reduction allows to generate the scattering matrices of new quantum graphs from assembling of simpler graphs. The reduction of quantum channels is also defined. The implementation of the quantum gates corresponding to the reduced unitary operator is investigated, although no explicit construction is presented. The situation is different for the reduction of quantum channels for which explicit implementations are given. 2025-02-18T07:50:39Z 2025-02-18T07:50:39Z 2024-12-11 journal article Published version: Salcedo Moreno, Lorenzo Luis. Reduction of unitary operators, quantum graphs and quantum channels. Journal of Physics A: Mathematical and Theoretical, 58, 3, id.035202, 33 pp. 2025 DOI: 10.1088/1751-8121/ada2c8 https://hdl.handle.net/10481/102430 10.1088/1751-8121/ada2c8 eng http://creativecommons.org/licenses/by/4.0/ open access Atribución 4.0 Internacional IOPScience