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Journal of Physics Conference Series

Computation of optical waveguide interaction for quantum gates implementation

Alexander A. Lytaev, I. Yu. Popov

Published Dec 1, 2021• 0 citations
Publisher

Abstract

Abstract The system of two coupled optical dual-mode waveguides is considered. The coupling of the system is studied to find a circuit for building a control switch for two qubit gates. The classical coupled mode theory is applied and the exact expressions for coupling coefficients are derived. The parameters of the system for performing the desired operations are numerically computed and analysed. The system describing the influence of intermodal interactions is solved numerically. The distortions are analysed.

DOI
10.1088/1742-6596/2086/1/012153

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Abstract The system of two coupled optical dual-mode waveguides is considered. The coupling of the system is studied to find a circuit for building a control switch for two qubit gates. The classical coupled mode theory is applied and the exact expressions for coupling coefficients are derived. The parameters of the system for performing the desired operations are numerically computed and analysed. The system describing the influence of intermodal interactions is solved numerically. The distortions are analysed.
The paper is devoted to simulation of interactions in the system of two symmetrical slab optical waveguides, that guide exactly two guided modes with the aim to use the directional coupler as a switcher for CNOT gate in the waveguide model of quantum-like computations. The coupling mode theory is used to solve the system of Maxwell equations. The asymptotic analysis is applied to simplify the system of differential equations, so an approximate analytic solution can be found. The solution obtained is used for the quick directional coupler parameters adjusting algorithm, so the power exchange in the system occurs as that of correctly working CNOT-gate switcher. Moreover, the finite difference method is used to solve the stricter system of equations, that additionally takes into account the process of power exchange between different order guided modes, so the computational error of the device can be estimated. It was obtained, that the possible size of the device may not exceed 1 mm in the largest dimension, while the computational error does not exceed 3%.
Abstract We provide an approach to realize an optical switch using an induced transparency phenomenon in double-cavity structures. Our system consists of two directly coupled cavities, each coupled to a different waveguide. The system is pumped by a control field and a signal field propagating in the waveguides. We analyze the excitation spectra of the cavities, as well as corresponding transmission and reflection coefficients for the signal field. We find that induced transparency or an absorption phenomenon for the signal field can be established in this system, depending on the parameters of the control field. Thus, the transport properties for the signal field are highly controllable. Under appropriate parameters the system can behave as a nearly perfect optical switch for the signal field. The influence of dissipations on the efficiency of the switch is also discussed. The device studied here is suitable for on-chip integrations, and may have broad applications in future quantum networks.
Quantum logic operations are the elemental operations for quantum computing and have been implemented in various time-evolved atomic systems. Here, we present a scheme to simulatively implement the typical quantum NOT- and Hadamard gates operations, alternatively with the coupled three-waveguide structure (rather than the usual atomic levels); two modes in sinuous waveguides encoding the two logic states of a qubit and the mode in the center straight waveguide serve as auxiliary the coupler. Based on the Lewis-Riesenfeld invariant theory, we show that the desired mode conversions for implementing the NOT gate and mode split to realize the Hadamard gate are fast achieved by engineering the coupling parameters between the optical waveguides. The implementations of the logic gates demonstrated here relay on the structure parameters of the waveguides, rather than the durations of time evolutions with the usual driven atomic systems, and thus should be feasible robustly with the current integrated optical technology.
The use of silicon photonics in the context of quantum technologies has been widely discussed in the fields of communication, engineering, computation, biology, chemistry, and metrology due to its scalability, stability, room-temperature control, and system miniaturization capabilities. In this paper, in the context of using photonic chips for application in quantum information protocols, we focus on multiple waveguide encoding of qudits, that is, a multi-level quantum computational unit, instead of the usual two-level qubit. Given the complexity of constructing control gates and designing systems using qubits, we show a method where we use coupled-mode theory in the small perturbation approximation, so that we can describe the coupling matrix of n-waveguides that can be used in the context of interferometers in photonic chips, to find optimal parameters for describing operations using qudits.
We propose a method for implementation of a quantum computer using artificial molecules. The artificial molecule consists of two coupled quantum dots stacked along z direction and one single electron. One-qubit and two-qubit gates are constructed by one molecule and two coupled molecules, respectively.The ground state and the first excited state of the molecule are used to encode the |0> and |1> states of a qubit. The qubit is manipulated by a resonant electromagnetic wave that is applied directly to the qubit through a microstrip line. The coupling between two qubits in a quantum controlled NOT gate is switched on (off) by floating (grounding) the metal film electrodes. We study the operations of the gates by using a box-shaped quantum dot model and numerically solving a time-dependent Schridinger equation, and demonstrate that the quantum gates can perform the quantum computation. The operating speed of the gates is about one operation per 4ps. The reading operation of the output of the quantum computer can be performed by detecting the polarization of the qubits.
We propose a method for implementing a quantum computer using artificial molecules. The artificial molecule consists of two coupled quantum dots stacked along the z direction and one single electron. One-qubit and two-qubit gates are constructed by one molecule and two coupled molecules, respectively. The ground state and the first excited state of the molecule are used to encode the |0> and |1> states of a qubit. The qubit is manipulated by a resonant electromagnetic wave that is applied directly to the qubit through a microstrip line. The coupling between two qubits in a quantum-controlled NOT gate is switched on (off) by floating (grounding) the metal film electrodes. We study the operations of the gates using a box-shaped quantum dot model and numerically solving a time-dependent Schrödinger equation, and demonstrate that the quantum gates can perform quantum computations. The operating speed of the gates is about one operation per 4 ps. The reading operation of the output of the quantum computer can be performed by detecting the polarization of the qubits.