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Оптика и спектроскопия

Highly efficient generation of squeezed states of light based on Laguerre-Gaussian modes in a cavity

E. N. Bashmakova, E. A. Vashukevich, Golubeva T. Yu., Golubev Yu. M

Published Jan 1, 2022• 0 citations
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Abstract

Today, the efficient generation of squeezed states of light seems to be a significant practical problem for various quantum-optical and information applications. In this paper, we investigate the possibility of increasing the efficiency of the generation of states based on the Laguerre-Gaussian light modes in the parametric down conversion due to the optimal choice of the cavity configuration. Analyzing the Heisenberg-Langevin equations for the eigenmodes of the system, we estimate the influence of the geometric parameters of the pump beam and the idler and signal beams on the efficiency of generation of squeezed states and on the degree of squeezing. The calculation for a finite number of modes has shown that the highest theoretically possible degree of squeezing in the system is 15.85 dB. Keywords: squeezed light, Laguerre-Gaussian modes, orbital angular momentum, optimization of PDC geometric parameters.

DOI
10.21883/eos.2022.14.53997.2484-21

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Today, the efficient generation of squeezed states of light seems to be a significant practical problem for various quantum-optical and information applications. In this paper, we investigate the possibility of increasing the efficiency of the generation of states based on the Laguerre-Gaussian light modes in the parametric down conversion due to the optimal choice of the cavity configuration. Analyzing the Heisenberg-Langevin equations for the eigenmodes of the system, we estimate the influence of the geometric parameters of the pump beam and the idler and signal beams on the efficiency of generation of squeezed states and on the degree of squeezing. The calculation for a finite number of modes has shown that the highest theoretically possible degree of squeezing in the system is 15.85 dB. Keywords: squeezed light, Laguerre-Gaussian modes, orbital angular momentum, optimization of PDC geometric parameters.
Orbital angular momentum (OAM) modes are an important resource used in various branches of quantum science and technology due to their unique helical structure and countably infinite basis. Generating light that simultaneously carries high-order orbital angular momenta and exhibits quantum correlations is a challenging task. In this work, we present a theoretical approach to the generation of correlated Schmidt modes carrying OAM via parametric down-conversion (PDC) in cascaded nonlinear systems (nonlinear interferometers) pumped by Laguerre–Gaussian beams. We demonstrate how the number of generated modes and their population can be controlled by varying the pump parameters, the gain of the PDC process, and the distance between the crystals. We investigate the angular displacement measurement uncertainty of these interferometers and demonstrate that it can overcome the classical shot noise limit.
Abstract Light beams with orbital angular momentum (OAM) are convenient carriers of quantum information. They can also be used for imparting rotational motion to particles and providing high resolution in imaging. Due to the conservation of OAM in parametric down-conversion (PDC), signal and idler photons generated at low gain have perfectly anti-correlated OAM values. It is interesting to study the OAM properties of high-gain PDC, where the same OAM modes can be populated with large, but correlated, numbers of photons. Here we investigate the OAM spectrum of high-gain PDC and show that the OAM mode content can be controlled by varying the pump power and the configuration of the source. In our experiment, we use a source consisting of two nonlinear crystals separated by an air gap. We discuss the OAM properties of PDC radiation emitted by this source and suggest possible modifications.
Spatially structured quantum states, such as orbital angular momentum (OAM) squeezing and entanglement, is currently a popular topic in quantum optics. The method of generating and manipulating spatial quantum states on demand needs to be explored. In this paper, we generated OAM mode squeezed states of −5.4 dB for the L G 0 + 1 mode and −5.3 dB for the L G 0 − 1 mode directly by an optical parametric oscillator (OPO) for the first time. Additionally, we demonstrated that the OAM mode squeezed and entangled states were respectively generated by manipulating the nonlinear process of the OPO by controlling the relative phase of two beams of different modes, thus making two different spatial multimode pump beams. We characterized the Laguerre-Gaussian (LG) entangled states by indirectly measuring the squeezing for the H G 10 ( 45 ∘ ) mode and H G 10 ( 135 ∘ ) mode, and directly measuring the entanglement between the L G 0 + 1 and L G 0 − 1 modes. The effective manipulation of the OAM quantum state provides a novel insight into the continuous variable quantum state generation and construction on demand for high-dimensional quantum information and quantum metrology.
ObjectiveQuantum communication is an emerging mode of communication with broad application prospects, combining with classical information science and technology. It offers unconditional security and efficient transmission of information, making it a hot research topic in todayƳs communication field. High-dimensional quantum entanglement often exhibits strong nonlocality, enhancing the security in quantum communication processes and playing a crucial role in quantum communication and computing. To meet the demand for high-dimensional entangled states in quantum information science, this paper proposes a method for generating high-dimensional Bell states based on the Orbital Angular Momentum (OAM) of photons, capable of producing the complete set of Bell state basis vectors with high fidelity.MethodsInitially, the Spontaneous Parametric Down-Conversion (SPDC) process involving photon OAM is studied. Furthermore, a Genetic Algorithm (GA) is employed to optimize the quantum state of the pump light, aiming to obtain the required high-dimensional maximally entangled states. We analyze the characteristics of Laguerre-Gaussian (LG) beams in detail and explore their application in the SPDC process. By optimizing the parameters of the pump light, maximally entangled states are generated in three-dimensional, four-dimensional, and five-dimensional spaces.ResultsA comparison of the spatial mode spectral distribution shows that the optimized entangled states possess higher fidelity to the target states. Additionally, by simulating the generation of 16 Bell states, it is verified that the produced quantum states form a complete basis for a four-dimensional Hilbert space.ConclusionThe proposed scheme not only effectively generates high-dimensional entangled states but also enables longer-distance quantum communication and potentially global quantum communication systems. Moreover, it provides new avenues for the application of high-dimensional entangled states in the fields of quantum communication and computing, significantly contributing to the advancement of quantum information science.
In this article we investigate the orbital angular momentum spectrum of photons produced in parametric down conversion process. We study how the transverse profile of the pump mode affects the spectrum as compared to a gaussian pump beam. We show that using perfect optical vortex mode as pump the spectrum can be highly narrowed down. We further study the entanglement between the two down converted photons in the orbital angular momentum basis. We observe that photons entangled in Laguerre-Gaussian modes exhibit greater higher dimensional entanglement.
We demonstrated that by using a pump field with nonzero orbital angular momentum (OAM) in the polarization self-rotation squeezing process it is possible to generate a squeezed vacuum optical field with the matching OAM. We found a similar level of maximum quantum noise reduction for a first-order Laguerre-Gaussian pump beam and a regular Gaussian pump beam, even though the optimal operational conditions differed in these two cases. Also, we investigated the effect of self-defocusing on the level of the vacuum squeezing by simultaneously monitoring the minimum quantum noise level and the output beam transverse profile at various pump laser powers and atomic densities and found no direct correlations between the increased beam size and the degree of measured squeezing.