Polarization Degrees Of Freedom Research Articles

Postselection-free, hyperentangled photon pairs in a periodically poled lithium-niobate ridge waveguide

In this paper, we propose the generation of hyperentangled photon pairs using type-II spontaneous parametric down-conversion in a biperiod, 5% MgO-doped lithium-niobate ridge waveguide. The photon pairs are entangled in spatial mode and polarization degrees of freedom. A pulsed laser source at 687 nm, having an antisymmetric Hermite-Gaussian HG (1,0) spatial mode, is considered as the pump. Down-converted photon pairs, with the signal being at the telecommunication wavelength of 1550 nm, are characterized through a joint spectral amplitude analysis of their biphoton state.

Experimental observation of phase-transition-like behavior in an optical simulation of single-qubit game

Phase-transition-like behavior in quantum games has been studied in recent years as a strategy to deal with abrupt changes in the expected payoff of quantum players. More precisely, such behavior is investigated in the context of two-qubit quantum games, where entanglement is used as a resource for quantum players or quantum game referees. In this work, we present the first experimental realization of a single-qubit game where phase-transition-like behavior raises as an immediate consequence of quantum coherence, since no entanglement is present in our game. The game was realized by encoding the qubit in the polarization degree of freedom of an intense laser beam. We investigate the optimal gain of the quantum player as well as a discussion and obtaining of critical points that was experimentally observed, where we had an excellent agreement between theoretical predictions and the experimental results. Due to the power of the quantum-classical analogy between quantum states and optical modes, our platform is adequate to simulate the quantum game and our experiment can be efficiently reproduced in a single-photon experiment.

Visible frequency broadband dielectric metahologram by random Fourier phase-only encoding

In recent years, metasurfaces that enable the flexible wavefront modulation at sub-wavelength scale have been widely used into holographic display, due to its prominent advantages in polarization degrees of freedom, viewing angle, and achromaticity in comparison with traditional holographic devices. In holography, the computational complexity of hologram, imaging sharpness, energy utilization, reproduction rate, and system indirection are all determined by the encoding method. Here, we propose a visible frequency broadband dielectric metahologram based on the random Fourier phase-only encoding method. Using this simple and convenient method, we design and fabricate a transmission-type geometric phase all-dielectric metahologram, which can realize holographic display with high quality in the visible frequency range. This method encodes the amplitude information into the phase function only once, eliminating the cumbersome iterations, which greatly simplifies the calculation process, and may facilitate the preparation of large area nanoprint-holograms.

Robust optical physical unclonable function using disordered photonic integrated circuits

Abstract Physical unclonable function (PUF) has emerged as a promising and important security primitive for use in modern systems and devices, due to their increasingly embedded, distributed, unsupervised, and physically exposed nature. However, optical PUFs based on speckle patterns, chaos, or ‘strong’ disorder are so far notoriously sensitive to probing and/or environmental variations. Here we report an optical PUF designed for robustness against fluctuations in optical angular/spatial alignment, polarization, and temperature. This is achieved using an integrated quasicrystal interferometer (QCI) which sensitively probes disorder while: (1) ensuring all modes are engineered to exhibit approximately the same confinement factor in the predominant thermo-optic medium (e. g. silicon), and (2) constraining the transverse spatial-mode and polarization degrees of freedom. This demonstration unveils a new means for amplifying and harnessing the effects of ‘weak’ disorder in photonics and is an important and enabling step toward new generations of optics-enabled hardware and information security devices.

Continuous angle-tunable birefringence with freeform metasurfaces for arbitrary polarization conversion.

Birefringence occurs when light with different polarizations sees different refractive indices during propagation. It plays an important role in optics and has enabled essential polarization elements such as wave plates. In bulk crystals, it is typically constrained to linear birefringence. In metamaterials with freeform meta-atoms, however, one can engineer the optical anisotropy such that light sees different indices for arbitrary-linear, circular, or elliptical-orthogonal eigen-polarization states. Using topology-optimized metasurfaces, we demonstrate this arbitrary birefringence. It has the unique feature that it can be continuously tuned from linear to elliptical birefringence, by changing the angle of incidence. In this way, a single metasurface can operate as many wave plates in parallel, implementing different polarization transformations. Angle-tunable arbitrary birefringence expands the scope of polarization optics, enables compact and versatile polarization operations that would otherwise require cascading multiple elements, and may find applications in polarization imaging, quantum optics, and other areas.

Classically entangled Ince–Gaussian modes

Complex vector light modes, classically entangled in their spatial and polarization degrees of freedom (DoF), have become ubiquitous in a vast diversity of research fields. Crucially, while polarization is limited to a bi-dimensional space, the spatial mode is unbounded, and it can be specified by any of the sets of solutions the wave equation can support in different coordinate systems. Here, we report on a class of vector beams with elliptical symmetry where the spatial DoF is encoded in the Ince–Gaussian modes of the cylindrical elliptical coordinates. We outline their geometric representation on the higher-order Poincaré sphere, demonstrate their experimental generation, and analyze the quality of the generated modes via Stokes polarimetry. We anticipate that such vector modes will be of great relevance in applications, such as optical manipulations, laser material processing, and optical communications among others.

Topological edge and corner states in a two-dimensional photonic Su-Schrieffer-Heeger lattice

Abstract Implementation of topology on photonics has opened new functionalities of photonic systems such as topologically protected boundary modes. We theoretically present polarization-dependent topological properties in a 2D Su-Schrieffer-Heeger lattice by using a metallic nanoparticle array and considering the polarization degree of freedom. We demonstrate that when eigenmodes are polarized parallel to the plane of the 2D lattice, it supports longitudinal edge modes that are isolated from the bulk states and transverse edge modes that are overlapped with the bulk states. Also, the in-plane polarized modes support a second-order topological phase under an open boundary condition by breaking the four-fold rotational symmetry. This work will offer polarization-based multifunctionality in compact photonic systems that have topological features.

Determining the non-separability of vector modes with digital micromirror devices

The non-separability between the spatial and polarization Degrees of Freedom (DoF) of complex vector light fields has drawn significant attention in recent times. Key to this is its remarkable similarities with quantum entanglement, with quantum-like effects observed at the classical level. Crucially, this parallelism enables the use of quantum tools to quantify the coupling between the spatial and polarization DoFs, usually implemented with polarization-dependent spatial light modulators, which requires the splitting of the vector mode into two orthogonal polarization components. Here, we put forward an alternative approach that relies on the use of Digital Micromirror Devices (DMDs) for a fast, cheap, and robust measurement, while the polarization-independent nature of DMDs enables a reduction in the number of required measurements by 25%. We tested our approach experimentally on cylindrical vector modes with arbitrary degrees of non-separability, of great relevance in a wide variety of applications. Our technique provides a reliable way to measure in real time the purity of vector modes, paving the way for a wide variety of applications where the degree of non-separability can be used as an optical sensor.

Determining the Cosmological Constant Using Gravitational Wave Observations

It is shown in Einstein gravity that the cosmological constant Lambda introduces a graviton mass m into the theory, a result that will be derived from the Regge-Wheeler-Zerilli problem for a particle falling onto a Kottler-Schwarzschild mass with Lambda. The value of m is precisely the Spin-2 gauge line appearing on the Lambda versus m2 phase diagram for Spin-2, the partially massless gauge lines introduced by Deser & Waldron and described as the Higuchi bound. Note that this graviton is unitary with only four polarization degrees of freedom (helicities plus & minus 2 and 1, but not 0 because a scalar gauge symmetry removes it). The conclusion is drawn that Einstein gravity (with Lambda) is a partially massless gravitation theory which has lost its helicity 0 due to a scalar gauge symmetry. That poses a challenge for gravitational wave antennas as to whether they can measure the loss of this gauge symmetry. Also, given the recent results measuring the Hubble constant Ho from LIGO-Virgo data, it is then shown that Lambda can be determined from the LIGO results for the graviton mass m and Ho. This is yet another multi-messenger source for determining the three parameters Lambda, m, and Ho in astrophysics and cosmology, at a time when there is much disparity in measurements of Ho.

Polarization-Independent Coherent Spatial-Temporal Interface with Low Loss

A coherent interface between temporal and spatial degrees of freedom (DOFs) empowers photons to take advantage of both DOFs in quantum information processing. Such interfaces have either suffered from a typical loss of 1--3 dB or disturbed the polarization DOF in the conversion process. The authors realize a low-loss, polarization-independent, coherent interface between temporal and spatial DOFs (specifically time-bin and path modes), which promises applications like the postselection-loophole-free Bell inequality test, and can be put into a cavity to boost the generation rates of multiphoton polarization-entangled sources, or to enhance the scalability of sequential quantum metrology.

Orthogonally polarized frequency combs in a mode-locked VECSEL

We introduce a spin–flip model for a vertical-external-cavity surface-emitting laser (VECSEL) with a saturable absorber. We demonstrate the possibility, due to the spin–flip dynamics, to generate two orthogonally linearly polarized frequency combs in the mode-locked regime. The two combs are shifted in wavelength due to the birefringence in the VECSEL gain and/or saturable absorption mirror. We show that the polarization degree of freedom may also lead to several pulses being generated per roundtrip in the two orthogonal linear polarizations and to more complicated dynamics with both linear polarizations excited.

The analysis of high-capacity quantum secure direct communication using polarization and orbital angular momentum of photons

Higher channel capacity and noise elimination are the key requirements for the implementation of long-distance quantum communication. As the additional degrees of freedom (DoF) of photons can be employed to achieve higher channel capacity and security beyond the polarizations DoF of photons, the photonic qubits are always employed as the flying qubits in quantum communication and quantum information processing. Here, exploiting the multiple DoFs of photons, we present an efficient quantum secure direct communication protocol based on the coding and manipulation of qubits on both the polarization and the orbital angular momentum of photons. Also, the numerical simulation is studied to further clarify the improvement of the channel capacity and the security. It is found that the channel capacity and the error rate (caused by eavesdropping) of the QSDC protocol which encoded on the polarization DoF and the OAM DoF is significantly higher than that of coding on only polarization DoF. We believe this work could provide more evidence for the applications of higher-dimensional qubits in quantum information science.

Simulating Markovian quantum decoherence processes through an all-optical setup

We investigate through both theory and experiment quantum decoherence processes. By considering a qubit under the effect of Markovian channels, we analytically obtain expressions for the $$l_1$$-norm of coherence and for the corresponding maximal coherence measure in terms of the initial state and decoherence parameters. In particular, we examine under which conditions such quantum coherence quantifiers exhibit the eternal freezing phenomenon, and we find that this property is more common in maximal quantum coherence compared to quantum coherence. We implement an all-optical setup with an intense laser to perform the experimental simulation of the quantum channels, where the qubit was encoded in polarization degree of freedom and the environment was encoded in the propagation path.

State-independent contextuality in classical light

State-independent contextuality is a fundamental phenomenon in quantum mechanics, which has been demonstrated experimentally in different systems in recent years. Here we show that such contextuality can also be simulated in classical optical systems. Using path and polarization degrees of freedom of classical optics fields, we have constructed the classical trit (cetrit), here the term ‘cetrit’ is the classical counterpart of a qutrit in quantum systems. Furthermore, in classical optical systems we have simulated the violations of several Yu-Oh-like noncontextual inequalities in a state-independent manner by implementing the projection measurements. Our results not only provide new physical insights into the contextuality and also show the application prospects of the concepts developed recently in quantum information science to classical optical systems and optical information processes.

Experimental orthogonalization of highly overlapping quantum states with single photons

We experimentally realize a nonlinear quantum protocol on single-photon qubits with linear optical elements and appropriate measurements. The quantum nonlinearity is induced by post-selecting the polarization qubit based on a measurement result obtained on the spatial degree of freedom of the single photon which plays the role of a second qubit. Initially, both qubits are prepared in the same quantum state and an appropriate two-qubit unitary transformation entangles them before the measurement on the spatial part. We analyze the result by quantum state tomography on the polarization degree of freedom. We then demonstrate the usefulness of the protocol for quantum state discrimination by iteratively applying it on either one of two slightly different quantum states which rapidly converge to different orthogonal states by the iterative dynamics. Our work opens the door to employ effective quantum nonlinear evolution for quantum information processing.

Hyper-parallel nonlocal CNOT operation with hyperentanglement assisted by cross-Kerr nonlinearity

Implementing CNOT operation nonlocally is one of central tasks in distributed quantum computation. Most of previously protocols for implementation quantum CNOT operation only consider implement CNOT operation in one degree of freedom(DOF). In this paper, we present a scheme for nonlocal implementation of hyper-parallel CNOT operation in polarization and spatial-mode DOFs via hyperentanglement. The CNOT operations in polarization DOF and spatial-mode DOF can be remote implemented simultaneously with hyperentanglement assisited by cross-Kerr nonlinearity. Hyper-parallel nonlocal CNOT gate can enhance the quantum channel capacity for distributed quantum computation and long-distance quantum communication. We discuss the experiment feasibility for hyper-parallel nonlocal gate. It shows that the protocol for hyper-parallel nonlocal CNOT operation can be realized with current technology.

Generation of concentric perfect Poincar\xe9 beams

We theoretically propose and experimentally verify a method to generate new polycyclic beams, namely concentric perfect Poincaré beams (CPPBs), by using an encoded annular phase mask. The proposed beams consisting of multiple polarization structured fields can be simultaneously generated in one concentric mode, which are respectively mapped by fundamental Poincaré sphere (PS), high-order Poincaré sphere (HOPS), and hybrid-order Poincaré sphere (HyPS). Moreover, the ring radius, numbers and polarization orders of the CPPBs at arbitrary positions on arbitrary PS are independently controlled. This work enriches the mode distributions of perfect vortex and introduces a new polarization degree of freedom, which has the potential to implement more information beyond the orbital angular momentum multiplexing in optical communication.

Efficient hyperentanglement purification for three-photon systems with the fidelity-robust quantum gates and hyperentanglement link.

We present an efficient and faithful hyperentanglement purification protocol (hyper-EPP) for three-photon system in mixed hyperentangled Greenberger-Horne-Zeilinger states with bit-flip errors in both spatial-mode and polarization degrees of freedom (DOFs), resorting to the fidelity-robust quantum gates and hyperentanglement link. Our high-efficiency hyper-EPP comes from two aspects. One is to pump the higher-fidelity hyperentanglement from different three-photon systems into the same three-photon system with fidelity-robust swap gates, the other is to reproduce some hyperentangled three-photon systems from hyperentangled two-photon subsystems based on hyperentanglement link. Moreover, as the infidelity originating from imperfect single-photon scattering can be heralded as a failure by triggering a detector, our hyper-EPP operates faithfully with the present quantum circuits. Furthermore, our hyper-EPP can be directly extended to purify multiple photon systems entangled in one DOF or hyperentangled in multiple DOFs.

Measurement-device-independent quantum key distribution with hyper-encoding

Measurement device-independent quantum key distribution (MDI-QKD) protocols are immune to all possible attacks on the photon detectors during quantum communication, but their key generation rates are low compared with those of other QKD schemes. Increasing each individual photons channel capacity is an efficient way to increase the key generation rate, and high-dimensional (HD) encoding is a powerful tool for increasing the channel capacity of photons. In this paper, we propose an HD MDI-QKD protocol with qudits hyper-encoded in spatial mode and polarization degrees of freedom (DOFs). In the proposed protocol, keys can be generated using the spatial mode and polarization DOFs simultaneously. The proposed protocol is unconditionally secure, even for weak coherent pulses with decoy states. The proposed MDI-QKD protocol may be useful for future quantum secure communication applications.

High-Fidelity Hyperentangled Cluster States of Two-Photon Systems and Their Applications

An efficient scheme is proposed in this study to prepare four symmetric hyperentangled cluster states in the polarization degrees of freedom (DOF) and spatial DOF with a two-photon system. This system consists of two nitrogen-vacancy (NV) centers which are coupled to two microtoroidal resonators. The two-photon polarization-spatial hyperentangled cluster states can be generated with our system by virtue of the input and output process. Compared with previous works, our quantum circuit for preparing the hyperentangled cluster states is simple and economic. Moreover, our scheme works deterministically and does not need any extra qubits, making it applicable to existing technologies. Our calculations show that our scheme has high fidelity with current technology, which can help hyperentangled cluster states to play a very useful role in quantum communication networks with long distances and high capacity.