Converting qubits

Michel Le Bellac

В. А. Калмычков, L. V. Kurganskaya, Е. А. Шестова +2 more

The article provides an approach of modeling quantum states which determine the properties of an abstract system, means the design and simulation environment Matlab, as well as means of instrumental package Simulink. Describes the representation of a quantum system in two ways: in the form of the state vector and in the form of density matrices. Considered unary, binary and ternary logical operations on qubits, called quantum converters. The process of assignment of qubits, the method of imaging, the use of quantum transformation to qubits, and visualization of results of converters in the environment Matlab are described. Developed a model that shows the use of the converter two qubits converter controlled NOT (CNOT), followed by visualization of the results of his work in the visual simulation system Simulink. Conclusions are drawn on applicability of the Matlab/Simulink environments to problems of modeling of quantum systems.

Xiaosong Ren, Zhanping Jin, Xiaotong Zou +6 more

The development of quantum internet demands on-chip quantum processor nodes and interconnection between the nodes. Path-encoded photonic qubits are suitable for on-chip quantum information processors, while time-bin encoded ones are good at long-distance communication. It is necessary to develop an on-chip converter between the two encodings to satisfy the needs of the quantum internet. In this work, a quantum photonic circuit is proposed to convert time-bin-encoded photonic qubits to path-encoded ones via a thin-film lithium niobate high-speed optical switch and low-loss matched optical delay lines. The performance of the encoding converter is demonstrated by the experiment of time-bin to path encoding conversion on the fabricated sample chip. The converted path qubits have an average fidelity higher than 97%. The potential of the encoding converter on applications in quantum networks is demonstrated by the experiments of entanglement distribution and quantum key distribution. The results show that the on-chip encoding converter can serve as a foundational component in the future quantum internet, bridging the gap between quantum information transmission and on-chip processing based on photons.

K. S. Melnik, Mansur M. Minnegaliev, Sergey A. Moiseev

Abstract The conversion of photonic qubits between different physical encodings is a necessary condition for the creation of hybrid quantum networks. We propose and demonstrate a network scheme for a photonic qubit state converter from phase-frequency to polarization encoding, implemented in a Sagnac loop topology over a distance of 25 km. The obtained results of photonic qubit conversion with a fidelity of ( 0.99 ± 0.01 ) open up the possibility of creating photonic qubit converters that are more resistant to external noise and can be integrated into a subcarrier wave quantum communication network with independent detection.