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JSAP-OSA Joint Symposia

Quantum Antibunching in Nonlinear Coupler Using Wigner Representation

Mohd Syafiq M. Hanapi, Abel-Baset M. A. Ibrahim, P. K. Choudhury

Published Jan 1, 2024• 0 citations
Publisher

Abstract

Antibunching, a key characteristic of single-photon sources, is crucial for quantum cryptography and quantum computing [1]. Nonlinear couplers have significant potential as generators of nonclassical light [2,3]. However, Limited research has been reported on antibunching in nonlinear couplers [4,5]. This study investigates antibunching in an innovative design of a nonlinear coupler (as fig. 1 shows) featuring three nonlinear waveguides, each comprising a material that exhibits the second-order nonlinearity.

DOI
10.1364/jsapo.2024.20a_c43_5

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Antibunching, a key characteristic of single-photon sources, is crucial for quantum cryptography and quantum computing [1]. Nonlinear couplers have significant potential as generators of nonclassical light [2,3]. However, Limited research has been reported on antibunching in nonlinear couplers [4,5]. This study investigates antibunching in an innovative design of a nonlinear coupler (as fig. 1 shows) featuring three nonlinear waveguides, each comprising a material that exhibits the second-order nonlinearity.
Quantum antibunching, vital for single-photon sources, enables applications in quantum technology, such as secure communication and quantum computing. This study investigates photon antibunching generation in a Nonlinear coupler (NLC) comprising two coupled waveguides: one linear and one with the second-order nonlinearity. Each waveguide is excited by a coherent laser source, with the second harmonic generation enhancing antibunching. Using the Schrödinger picture, the system's Hamiltonian is transformed into a master equation via the Liouville–von Neumann equation. The master equation is further translated into a Fokker–Planck equation using the positive-P representation and subsequently mapped to stochastic differential equations via Ito rules for numerical analysis. The effects of input parameters on antibunching behavior are examined, showcasing the potential of simple systems like NLCs for precise single-photon manipulation, advancing quantum technology.
Higher-order nonclassical properties of fields propagating through a codirectional asymmetric nonlinear optical coupler which is prepared by combining a linear waveguide and a nonlinear (quadratic) waveguide operated by second harmonic generation are studied. A completely quantum mechanical description is used here to describe the system. Closed form analytic solutions of Heisenberg's equations of motion for various modes are used to show the existence of higher-order antibunching, higher-order squeezing, and higher-order two-mode and multimode entanglement in the asymmetric nonlinear optical coupler. It is also shown that nonclassical properties of light can transfer from a nonlinear waveguide to a linear waveguide.
Possible squeezed states generated in a three-waveguide nonlinear coupler operating with second harmonic generation is discussed. This study is carried out using two well-known techniques; the phase space method (based on positive-P representation) and the Heisenberg-based analytical perturbative (AP) method. The effects of key design parameters were investigated under various conditions, including full frequency matching, symmetrical and asymmetrical waveguide initialization, and both codirectional and contr-adirectional propagation. The system consistently produced long-lasting oscillatory squeezed states across all three waveguides, even when only one waveguide was pumped with coherent light while the others were in a vacuum state. Also, the performance and capacities of both methods are critically evaluated. For low levels of key design parameters and in the early stages of evolution, a high level of agreement between the two methods is noticed. In the new era of quantum-based technology, the proposed system opens a new avenue for utilising nonlinear couplers in nonclassical light generation.
It has recently been shown that multiphoton absorption in cavities containing an emitter and a nonlinear mirror or a two photon absorber can be used to create antibunched photons (i.e. nonclassical light). We investigate the generation of nonclassical photon states using nonlinear laser cavities where the excitation has been modified so that it consists of short current pulses. The light fields in the studied setups are ideally formed of superpositions of zero photon and one photon states. Our goal is to study and develop single photon sources which are needed e.g. in quantum information processing and quantum computing, and fundamental quantum optical experiments. We investigate the effect of exciting the photon emitter with time dependent current pulses to provide single-photon-on-demand sources. We maximize the probability of the single photon state by optimizing the strengths of linear losses, nonlinear absorption, photon emission, and the length of the current injection pulse into the amplifier. Furthermore, we analyze the output photon statistics and waiting times using Monte Carlo simulations. This type of a setup is technologically attractive since it potentially provides room temperature realization of photon antibunching with essentially standard optoelectronic materials and processing techniques.
We investigate both codirectional and contradirectional nonlinear couplers composed of two nonlinear waveguides operating by second- and third-order nonlinear optical processes. We take into account possible mismatches inside the waveguides and between them. Quantum statistical characteristics, such as photon number distribution, its factorial moments, quadrature and integrated intensity variances and quadrature uncertainty product demonstrate generation and transmission of nonclassical light in nonlinear couplers. Incident beams are assumed to be coherent, squeezed and mixed with external noise. Nonclassical behavior of beams generated by the nonlinear waveguides can be transferred to linear waveguides and controlled by linear signal and by linear and nonlinear mismatches. In the contradirectional regime of propagation asymptotic nonclassical states can be obtained.
Abstract In this work, we examine the quantum features of a multi-waveguide nonlinear coupler exploiting the second-and third-order nonlinearities. The considered system contains four identical channels, each with a single fundamental transverse mode. The essence of this type of nonlinear coupler is to examine the effect of two or more competing nonlinearities on the generated nonclassical features in this class of devices. Here, we consider the case of second harmonic generation, wherein the fundamental harmonic (FH) fields are up-converted in pairs to double-frequency second harmonic (SH) fields, which are then evanescently coupled with the fields from other Kerr nonlinear waveguides. Using the positive P representation of the phase space, the time-evolution of the density matrix could be mapped to the corresponding Fokker–Planck equation of a classical quasiprobability distribution. Using Langevin stochastic equation, an exact representation of the system in phase space led to the demonstration of sub-Poissonian property, squeezing, and entanglement. With more effective squeezing achieved in all channel waveguides, the present system with χ(2)–χ(3) interaction can be a more efficient alternative to other versions of nonlinear couplers such as the quantum optical dimer (QOD) and Kerr nonlinear coupler (KNC). Furthermore, such a structure offers more flexibility in coupled-mode interactions in the form of correlation between the modes in different waveguides. This provides a better mechanism for the generation of enhanced nonclassical effects.