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Caracterização de um dispositivo de cristal líquido para implementação de operações programáveis sobre o estado de polarização da luz

Erick Ribeiro de Carvalho

Published May 29, 2024• 0 citations
OpenAlex

Abstract

Liquid crystal displays (LCDs) are devices capable of manipulating properties of an incident light beam, such as amplitude, phase, and polarization, based on the voltage applied to their molecules. In this work, we will experimentally characterize the effect of an LCD on light polarization, aiming at its use as a programmable spatial light modulator (SLM) in optics and quantum information experiments. In the first part, we will determine the Mueller matrix of the device and, from it, its polarimetric properties. We will show that the LCD acts only approximately as an ideal retarder plate since it introduces depolarization to the incident light. In the second part, we investigate the behavior of the LCD through the formalism of quantum operations, treating its action as an operation on polarization qubit states. Through process tomography, we determine the matrix characterizing the device's operation and show that it is non-unitary. Next, we derive a general expression for the process matrix of an SLM, given by the combination of the LCD with wave plates. This expression will allow us to implement programmable operations on the polarization states of light based on the configuration of the wave plates and the voltage on the LCD. As an application, we will quantify the fidelity of the actual operation implemented by the SLM with an ideal unitary operation of interest in quantum information protocols.

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Polarization encryption has long been shown to allow simultaneous encryption of 2D images, but with scarce practical implementations or commercial applications to date. Nevertheless, a possible vector for its use in market products may be additive manufacturing (AM). As more complex and diversified technologies use AM in their production chains, intellectual property (IP) protection of shared data is becoming increasingly crucial. Many AM techniques rely on optical systems, therefore, it is essential to analyze the prospects of safeguarding AM processes using advances in optical secrecy. This work demonstrates the use of polarization encoding by employing liquid crystals for physical layer security. We examine the encoding of the information in a signal’s polarization state and show that linear transformations of polarization can be used to encrypt and decrypt data. We further demonstrate the use of off-the-shelf liquid crystal displays (LCD) in a low-cost commercial resin 3D printer to build a "polarization decryptor". The proposed system does not require any software modification and in hardware only the replacement of the printer’s LCD masking screen. This technique provides a promising methodology to secure part of the supply chain for AM operations.

Optics Continuum•Mar 10, 2023•1 citation
Liquid crystal displays (LCDs) are devices capable of manipulating properties of an incident light beam, such as amplitude, phase, and polarization, based on the voltage applied to their molecules. In this work, we will experimentally characterize the effect of an LCD on light polarization, aiming at its use as a programmable spatial light modulator (SLM) in optics and quantum information experiments. In the first part, we will determine the Mueller matrix of the device and, from it, its polarimetric properties. We will show that the LCD acts only approximately as an ideal retarder plate since it introduces depolarization to the incident light. In the second part, we investigate the behavior of the LCD through the formalism of quantum operations, treating its action as an operation on polarization qubit states. Through process tomography, we determine the matrix characterizing the device's operation and show that it is non-unitary. Next, we derive a general expression for the process matrix of an SLM, given by the combination of the LCD with wave plates. This expression will allow us to implement programmable operations on the polarization states of light based on the configuration of the wave plates and the voltage on the LCD. As an application, we will quantify the fidelity of the actual operation implemented by the SLM with an ideal unitary operation of interest in quantum information protocols.
Spatial light modulators are versatile devices employed in a vast range of applications to modify the transverse phase or amplitude profile of an incident light beam. Most experiments are designed to use a specific polarization which renders optimal sensitivity for phase or amplitude modulation. Here we take a different approach and apply the formalism of quantum information to characterize how a phase modulator affects a general polarization state. In this context, the spatial modulators can be exploited as a resource to couple the polarization and the transverse spatial degrees of freedom. Using a quasimonochromatic single-photon beam obtained from a pair of twin photons generated by spontaneous parametric down conversion, we performed quantum process tomography in order to obtain a general analytic model for a quantum channel that describes the action of the device on the polarization qubits. We illustrate the application of these concepts by demonstrating the implementation of a controllable phase flip channel. This scheme can be applied in a straightforward manner to characterize the resulting polarization states of different types of phase or amplitude modulators and motivates the combined use of polarization and spatial degrees of freedom in innovative applications.
Spatial light modulators (SLMs) are widely used to coherently control quantum states of light.When carrying out these experiments, some assumptions are made.For instance, it is supposed that the position-momentum correlations between twin photon pairs are not affected by the use of a liquid crystal display (LCD) as a SLM.Furthermore, it is assumed that the characterization of such devices performed with an intense laser source, is still valid in the single photon regime.In this work, we show that such assumptions are acceptable, within the experimental uncertainties, for a liquid crystal on silicon (LCoS) display.This is especially important when considering the use of this kind of displays for the coherent control of quantum states based on twin photon sources.
In this thesis we demonstrate experimentally the implementation of quantum processes and simulation of complex dynamics, through the manipulation of a quantum system. Pairs of entangled photons generated by spontaneous parametric down conversion (SPDC) were used as the quantum system. The entangled state in the transversal path has been manipulated using programmable spatial light modulators (SLM). A nonlinear crystal with phase matching type I and a continuouslaser beam with wavelength in the violet region were used for the generation of twin photons in entangled path states that allow us to vary the Hilbert space dimension. Three quantum protocols were experimentally studied in this thesis: minimum Deutsch algorithm, entanglement concentration and simulation of dissipative dynamics. In the Deutsch algorithm implementation were used twin photons generated by SPDC and a double slit to encode a spatial qubit were used. The second photon was used as a trigger to prepare a conditional state of the first. The SLM was used as the oracle mentioned in the algorithm, i. e., it is responsible for implementing the balancedand constant functions. The entanglement concentration protocol for two-qutrit states was also implemented. Partially entangled path states were generated using SPDC along with a SLM that modules amplitude only. A second SLM phase modulator inside a Sagnac interferometer was used to implement the protocol using the method known as Procustean. The third protocol demonstrated experimentally was the simulation of two dissipative dynamics in qudits: dephasing and amplitude. One of the photons passes through a noisy channel, implemented using a SLM, and the transmitted state is characterized allowing us to identify the noisy channel properties.
Generation of particular polarization states of light, encoding information in polarization degree of freedom, and efficient measurement of unknown polarization are the key tasks of many applications in optical metrology, optical communications, polarization-sensitive imaging, and photonic information processing. Liquid crystal devices have proved to be indispensable for these tasks, though their limited precision and the requirement of a custom design impose a limit of practical applicability. Here we report fast preparation and detection of polarization states with unprecedented accuracy using common twisted nematic liquid-crystal displays. To verify the performance of the device we use it to prepare dozens of polarization states with average fidelity 0.999(1) and average angle deviation 0.5(3) deg. Using four-projection minimum tomography as well as six-projection Pauli measurement, we measure polarization states employing the reported device with the average fidelity of 0.997(1). Polarization measurement data are processed by the maximum likelihood method to reach a valid estimate of the polarization state. In addition to the application in classical polarimetry, we also employ the reported liquid-crystal device for full tomographic characterization of a three-mode Greenberger--Horne--Zeilinger entangled state produced by a photonic quantum processor.
This work has as a main goal the implementation of the experimental minimal quantum tomography in spatial variables using a spatial light modulator. To produce the two photons states entangled in spatial variables we use the properties of the photons produced by Spontaneous Parametric Down Conversion (SPDC) and double slits. A theoricaldescription was necessary for the understanding of the minimal tomography method. Four states which describe a tetrahedron in the Bloch sphere were chosen and associated to these states, were built four operators, making it a POVM set for tomography. For the experimental implementation of these operators, it took two calibrations of the spatial light modulator. Values of grayscales and polarization angles of input and output polarizers were determined in order to apply dierent phases and/or specific amplitude diferences between the beams that pass through each slit path. Thus, through the studyof minimal tomography and the knowledge of the operation of the modulator and their calibration, it was possible to experimentally perform the minimal quantum tomography for one and two qubits in spatial variables.
Polarization encryption has long been shown to allow simultaneous encryption of 2D images, but with scarce practical implementations or commercial applications to date. Nevertheless, a possible vector for its use in market products may be additive manufacturing (AM). As more complex and diversified technologies use AM in their production chains, intellectual property (IP) protection of shared data is becoming increasingly crucial. Many AM techniques rely on optical systems, therefore, it is essential to analyze the prospects of safeguarding AM processes using advances in optical secrecy. This work demonstrates the use of polarization encoding by employing liquid crystals for physical layer security. We examine the encoding of the information in a signal’s polarization state and show that linear transformations of polarization can be used to encrypt and decrypt data. We further demonstrate the use of off-the-shelf liquid crystal displays (LCD) in a low-cost commercial resin 3D printer to build a "polarization decryptor". The proposed system does not require any software modification and in hardware only the replacement of the printer’s LCD masking screen. This technique provides a promising methodology to secure part of the supply chain for AM operations.