Quantum Optical Systems

Philippe Grangier

Jacek Długopolski, Marek Życzkowski, Anna Pakuła +4 more

Scientists involved in building quantum computers are currently facing many physical difficulties. Creating qubits, manipulating them and reading their state requires a lot of experience. This paper describes an optical laser system as a test platform for quantum-optical control that enables effective manipulation of an emulated quantum bit. Importantly, it is a reproduction of the system controlling the optical path in real ion traps. This solution makes it possible to study the phenomena occurring in such systems and to learn about the wide range of problems that a designer and an operator of quantum systems may encounter, even before they start building them. The optical system presented in the article uses, among others, a 532 nm laser, acousto-optic modulators (AOMs), ultrafast light detectors, and a programmable FPGA chip. The entire optical system was then attached to the QUBIT emulator and thoroughly tested. The article describes the design and operation of the proposed optical system and shows an example of how to control it using a Python script.

Sintayehu Tesfa

Yakov A. Korennoy, Vladimir I. Man’ko

The evolution equation for the propagator of the quantum system in the optical probability representation (optical propagator) is obtained. The relations between the optical and quantum propagators for the Schrödinger equation and the optical propagator of an arbitrary quadratic system are found explicitly.

Sintayehu Tesfa

Daniil S. Shiryaev, K.R. Razzhivina, A.A. Kundius +3 more

Subject of study. An optical system, composed of transmitting and receiving telescopes, was designed for quantum key distribution, based on the subcarrier wave modulation method, over an atmospheric channel. Aim of study. The aim of the study was to develop an optical system that allowed the use of single-mode fibers as the input and output of the system, ensured the transmission of an ultralow-power optical signal without introducing additional distortion, and implemented a protocol for distributing a quantum key over an atmospheric optical communication channel at a distance of up to 25 m. Method. An experimental setup with an atmospheric quantum communication channel was developed, which showed stable quantum key distribution without interruptions throughout the measurement process. Radiation propagation simulations were also performed to estimate the insertion loss of the optical signal. Main results. Simulations revealed that the optical losses in the quantum key distribution system amounted to approximately 17 dB. The atmospheric communication channel was studied at distances of 5, 10, and 25 m. Considering all optical elements of the system, including the ferrules of the output and input fibers of the quantum key distribution modules, the attenuation of the optical signal was approximately 8, 13, and 18 dB, respectively. Based on the atmospheric optical losses, the quantum key generation rates were of the order of 500, 350, and 190 bits/s with increasing distance and insertion losses. The probability of a quantum error was in the range of 3% to 5%, which was lower than the threshold of 6%, ensuring the legitimacy of the generated key and excluding the possibility of an attack on the communication channel. Practical significance. The compatibility of the developed optical system with single-mode optical fibers allows its integration into the existing infrastructure of data transmission lines without the need for additional optical radiation converters. Owing to the analyzed characteristics of the optical system for distributing a quantum key over an atmospheric communication channel, it can be applied in communication systems based on the Internet of Things, unmanned vehicles, and other moving objects.