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arXiv:2004.05369 · Journal of the Optical Society of America B

Engineering continuous and discrete variable quantum vortex states by nonlocal photon subtraction in a reconfigurable photonic chip

David Barral, Jesús Liñares, Daniel Balado

Published Oct 5, 2016• 5 citations
arXivHTMLPDF

Abstract

We study the production of entangled two- and N-mode quantum states of light in optical waveguides. To this end, we propose a quantum photonic circuit that produces a reconfigurable superposition of photon subtraction on two single-mode squeezed states. Under postselection, continuous variable or discrete variable entangled states with possibilities in quantum information processing are obtained. Likewise, nesting leads to higher-dimension entanglement with a similar design, enabling the generation of non-Gaussian continuous variable cluster states. Additionally, we show the operation of the device through the generation of quantum vortex states of light and propose an integrated device that measures their order and handedness. Finally, we study the non-Gaussianity, nonclassicality, and entanglement of the quantum states generated with this scheme by means of the optical field-strength distribution, Wigner function, and logarithmic negativity.

DOI
10.1364/josab.33.002225

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We study the production of entangled two- and N-mode quantum states of light in optical waveguides. To this end, we propose a quantum photonic circuit that produces a reconfigurable superposition of photon subtraction on two single-mode squeezed states. Under postselection, continuous variable or discrete variable entangled states with possibilities in quantum information processing are obtained. Likewise, nesting leads to higher-dimension entanglement with a similar design, enabling the generation of non-Gaussian continuous variable cluster states. Additionally, we show the operation of the device through the generation of quantum vortex states of light and propose an integrated device that measures their order and handedness. Finally, we study the non-Gaussianity, nonclassicality, and entanglement of the quantum states generated with this scheme by means of the optical field-strength distribution, Wigner function, and logarithmic negativity.
A quantum photonic circuit with the ability to produce continuous variable quantum vortex states is proposed. This device produces two single-mode squeezed states which go through a Mach-Zehnder interferometer where photons are subtracted by means of weakly coupled directional couplers towards ancillary waveguides. The detection of a number of photons in these modes heralds the production of a quantum vortex. Likewise, a measurement system of the order and handedness of quantum vortices is introduced and the performance of both devices is analyzed in a realistic scenario by means of the Wigner function. These devices open the possibility of using the quantum vortices as carriers of quantum information.
In this paper, we propose a versatile integrated optical chip with the ability to generate both coherent and squeezed Bell-like states for quantum information processing purposes. This is a reconfigurable quantum photonic circuit in a lithium niobate substrate, which produces both non-local addition and subtraction of photons on squeezed vacuum states with directional couplers and post-selection. Setting appropriately phases and powers of the input beams, as well as electro-optic phase shifts, coherent and continuous variable Bell-like states are obtained. An analysis of the device operation in both the ideal and realistic scenarios is presented.
Nonclassicality of optical fields are the key resources in quantum information processing.Recently, Agarwal [New J. Phys., 13, 073008(2011)] proposed a method for engineering of a two-mode vortex state, a non-Gaussian state, by subtracting a photon from a two-mode squeezed state produced by down-converter from idler mode via a beam splitter with low reflectivity and detection of one photon by the avalanche photo diode (APD), or even better by a single-photon detector.We study the nonclassicalities of this state in terms of squeezing, antibunching, photon number correlation and distribution of photon number.In addition, we study higher-order nonclassical properties, viz., sum squeezing.We find that the non-Gaussian state shows strong nonclassical effects.
The generation of large-scale entangled states is crucial for quantum technologies, such as quantum computation1, communication2 and metrology3. Integrated quantum photonics that enables on-chip encoding, processing and detection of quantum light states offers a promising platform for the generation and manipulation of large-scale entangled states4,5. Generating entanglement between qubits encoded in discrete variables within single photons is challenging, owing to the difficulty of making single photons interact on photonic chips6–11. Devices that operate with continuous variables are more promising, as they enable the deterministic generation and entanglement of qumodes, in which information is encoded in light quadratures. Demonstrations so far have been limited to entanglement between two qumodes12–20. Here we report the deterministic generation of a continuous-variable eight-mode entanglement on an integrated optical chip. The chip delivers a quantum microcomb that produces multimode squeezed-vacuum optical frequency combs below the threshold. We verify the inseparability of our eight-mode state and demonstrate supermode multipartite entanglement over hundreds of megahertz sideband frequencies through violation of the van Loock–Furusawa criteria. By measuring the full matrices of nullifier correlations with sufficiently low off-diagonal noises, we characterize multipartite entanglement structures, which are approximate to the expected cluster-type structures for finite squeezing. This work shows the potential of continuous-variable integrated photonic quantum devices for facilitating quantum computing, networking and sensing. Deterministic generation of a continuous-variable eight-mode entanglement on an integrated optical chip is reported.
Abstract Entanglement is an essential feature of quantum theory and the core of the majority of quantum information science and technologies. Quantum computing is one of the most important fruits of quantum entanglement and requires not only a bipartite entangled state but also more complicated multipartite entanglement. In previous experimental works to demonstrate various entanglement‐based quantum information processing, light has been extensively used. Experiments utilizing such a complicated state need highly complex optical circuits to propagate optical beams and a high level of spatial interference between different light beams to generate quantum entanglement or to efficiently perform balanced homodyne measurement. Current experiments have been performed in conventional free‐space optics with large numbers of optical components and a relatively large‐sized optical setup. Therefore, they are limited in stability and scalability. Integrated photonics offer new tools and additional capabilities for manipulating light in quantum information technology. Owing to integrated waveguide circuits, it is possible to stabilize and miniaturize complex optical circuits and achieve high interference of light beams. The integrated circuits have been firstly developed for discrete‐variable systems and then applied to continuous‐variable systems. In this article, we review the currently developed scheme for generation and verification of continuous‐variable quantum entanglement such as Einstein‐Podolsky‐Rosen beams using a photonic chip where waveguide circuits are integrated. This includes balanced homodyne measurement of a squeezed state of light. As a simple example, we also review an experiment for generating discrete‐variable quantum entanglement using integrated waveguide circuits.