Polarization States Of Photons Research Articles

Influence of Material Properties on Surface Chemistry Induced Circular Dichroism in Halide Perovskite: Computational Insights.

The chirality transfer phenomenon is attractive for enhancing the optical functionality of nanomaterials by inducing sensitivity to the circular polarization states of photons. An underexplored aspect is how material properties of the achiral semiconductor impact the induced chiroptical signatures. Here we apply atomistic time-dependent density functional theory simulations to investigate the material properties that influence the chiroptical signatures of a lead halide perovskite nanocrystal with a chiral molecule bound to the surface. First, we find that both lattice disorder created by surface strain and halide substitution can increase the chiroptical response of the perovskite quantum dots by an order of magnitude. Both phenomena are attributed to a broadening of the density of the electronically excited states. Second, the intensity of the anisotropy spectra decreases with increasing dot size with a power law decay. Overall, these insights can be used to help guide experimental realization of highly resolvable polarized optical features in semiconducting nanomaterials.

Coherent transfer of higher-order polarization state of photons to spin structure state of electrons in a semiconductor

Coherent transfer of higher-order polarization state of photons to spin structure state of electrons in a semiconductor

Phototransformation of achiral metasurfaces into handedness-selectable transient chiral media

Chirality is a geometric property describing the lack of mirror symmetry. This unique feature enables photonic spin-selectivity in light-matter interaction, which is of great significance in stereochemistry, drug development, quantum optics, and optical polarization control. The versatile control of optical geometry renders optical metamaterials as an effective platform for engineered chiral properties at prescribed spectral regimes. Unfortunately, geometry-imposed restrictions only allow one circular polarization state of photons to effectively interact with chiral meta-structures. This limitation motivates the idea of discovering alternative techniques for dynamically reconfiguring the chiroptical responses of metamaterials in a fast and facile manner. Here, we demonstrate an approach that enables optical, sub-picosecond conversion of achiral meta-structures to transient chiral media in the visible regime with desired handedness upon the inhomogeneous generation of plasmonic hot electrons. As a proof of concept, we utilize linearly polarized laser pulse to demonstrate near-complete conversion of spin sensitivity in an achiral meta-platform-a functionality yet achieved in a non-mechanical fashion. Owing to the generation, diffusion, and relaxation dynamics of hot electrons, the demonstrated technique for all-optical creation of chirality is inherently fast, opening new avenues for ultrafast spectro-temporal construction of chiral platforms with on-demand spin-selectivity.

Qudit-based high-dimensional controlled-not gate.

High-dimensional quantum systems expand quantum channel capacity and information storage space. By implementing high-dimensional quantum logic gates, the speed of quantum computing can be practically enhanced. We propose a deterministic 4 × 4-dimensional controlled-not (CNOT) gate for a hybrid system without ancillary qudits required, where the spatial and polarization states of a single photon serve as a control qudit of four dimensions, whereas two electron-spin states in nitrogen-vacancy (NV) centers act as a four-dimensional target qudit. As the control qudits are easily operated employing simple optical elements and the target qudits are available for storage, the CNOT gate works in a deterministic way, and it can be flexibly extended to n × n-dimensional (n > 4) quantum gates for other hybrid systems or different photonic degrees of freedoms. The efficiency and fidelity of the CNOT gate are analyzed aligning with current technological capabilities, finding that they have satisfactory performances.

Quantum field theory for coherent photons: isomorphism between Stokes parameters and spin expectation values

Stokes parameters (S) on the Poincaré sphere are very useful values to describe the polarisation state of photons. However, the fundamental principle on the nature of polarisation is not completely understood, yet, because we have no concrete consensus on how to describe spin of photons, quantum-mechanically. Here, we have considered a monochromatic coherent ray of photons, described by a many-body coherent state, and established a fundamental basis to describe the spin state of photons, in connection with a classical description based on Stokes parameters. We show that a spinor description of the coherent state is equivalent to Jones vector for polarisation states, and obtain the spin operators (Ŝ) of all components based on rotators in an SU(2) group theory. Polarisation controllers such as phase-shifters and rotators are also obtained as quantum-mechanical field operators to change the phase of the wavefunction for polarisation states. We show that the Stokes parameters are quantum-mechanical average of the spin operators, S=⟨Ŝ⟩.

ALP induced polarization effects on photons from galaxy clusters

Many extensions of the Standard Model of particle physics and in particular superstring and superbrane theories predict the existence of axion-like particles (ALPs). ALPs are very elusive, extremely light and interact primarily with photons. In the presence of an external magnetic field two effects show up: (i) photon-ALP oscillations and (ii) a change of the photon polarization state. The astrophysical context represents the best opportunity to get indirect evidence for the ALP existence thanks to various effects that the photon-ALP interaction produces in the sky. Great attention has been paid so far to photon-ALP oscillations, since they modify the transparency of the crossed media at very high energies and so the final spectra of faraway sources exhibit a flux excess and a characteristic oscillatory behavior. Two hints at the ALP existence have hitherto been discovered. But less interest has been attracted by the modification of the photon polarization. In this paper we address it in the X-ray and in the high energy (HE) bands. Specifically, we analyze the photon degree of linear polarization and the polarization angle induced by the photon-ALP interaction for photons generated in the central region of two galaxy clusters: Perseus and Coma. We find a substantial departure from conventional physics in both considered bands. We conclude that the ALP-induced polarization effects are more likely detectable with the proposed missions like COSI (approved to launch), e-ASTROGAM and AMEGO in the HE range. Still, possible ALP-induced effects on photon polarization could also be detected by IXPE (already operative) and by the proposed eXTP, XL-Calibur, NGXP and XPP in the X-ray band.

Photon-ALP oscillations inducing modifications to photon polarization

Axion-like particles (ALPs) are very light, neutral, spin zero bosons predicted by many theories which try to complete the standard model of elementary particles. ALPs interact primarily with two photons and can generate photon-ALP oscillations in the presence of an external magnetic field. They are attracting increasing interest since photon-ALP oscillations produce deep consequences in very-high-energy (VHE) astrophysics. Two hints for the existence of an ALP have recently been proposed. In this paper, we study another effect of the photon-ALP interaction: the change of the polarization state of photons. In particular, we study the propagation of the photon-ALP beam starting where photons are produced - we consider photons generated in a galaxy cluster or in the jet of a blazar - crossing several magnetized media (blazar jet, host galaxy, galaxy cluster, extragalactic space, Milky Way) up to their arrival at the Earth. In the presence of photon-ALP interaction, we analyze the final photon survival probability $P_{\gamma \to \gamma}$ and the corresponding photon degree of linear polarization $\Pi_L$ for energies in the range $(1-10^{15}) \, \rm eV$. We observe that photons, which are expected as unpolarized in the absence of ALPs, are made partially polarized by photon-ALP interaction. Our findings can be tested by observatories like IXPE (already operative), and by the proposed missions eXTP, XL-Calibur, NGXP and XPP in the X-ray band and by COSI (approved to launch), e-ASTROGAM and AMEGO in the high-energy range. We also discover a peculiar feature in the VHE band, where photons at energies above $ \sim (1-10) \, \rm TeV$ are fully polarized because of photon-ALP interaction. A possible detection of this feature would represent a proof for the existence of an ALP, but, unfortunately, current technologies do not allow yet to detect photon polarization up to so high energies.

Entanglement of Trapped-Ion Qubits Separated by 230Meters.

We report on an elementary quantum network of two atomic ions separated by 230m. The ions are trapped in different buildings and connected with 520(2)m of optical fiber. At each network node, the electronic state of an ion is entangled with the polarization state of a single cavity photon; subsequent to interference of the photons at a beam splitter, photon detection heralds entanglement between the two ions. Fidelities of up to (88.0+2.2-4.7)% are achieved with respect to a maximally entangled Bell state, with a success probability of 4×10^{-5}. We analyze the routes to improve these metrics, paving the way for long-distance networks of entangled quantum processors.

Magnetized matter effects on dilaton photon mixing

Dilatons [$\ensuremath{\phi}(x)$] are a class of bosonic scalar particles associated with scaling symmetry and its compensation (under the violations of the same). They are capable of interacting gravitationally with other massive bodies. As they have coupling to two photons ($\ensuremath{\gamma}$), they are (also) capable of decaying to the two photons. However, the decay time is long and that makes them a good candidate for dark matter. Furthermore due to two photon coupling, they can produce optical signatures in a magnetic field. In a vacuum or plain matter they couple to one of the transversely polarized states of the photon. But in magnetized matter, they couple to both the transversely polarized state of photons (due to the emergence of a parity violating part of the photon self-energy contribution from magnetized matter). Being spin zero scalar, they could mix with spin zero longitudinal part of photons but they do not. A part of this work is directed towards understanding this issue of mixing the scalar with various polarization states of photons in a medium (magnetized or unmagnetized) due to the constraints from different discrete symmetries, e.g., charge conjugation ($\mathbf{C}$), parity ($\mathbf{P}$) and time reversal ($\mathbf{T}$) associated with the interaction. Based on these symmetry aided arguments, the structure of the mixing matrix is found to be $3\ifmmode\times\else\texttimes\fi{}3$, as in the case of neutrino flavor mixing matrix. Thus there exists nonzero finite probabilities of oscillation between different polarization states of photon to dilaton. Our analytical and numerical analysis show no existence of periodic oscillation length either in temporal or spatial direction for the most general values of the parameters in the theory. Possible astrophysical consequences of these results can be detected through the discussed observations.

Fast and accurate measurement of the polarization-dependent detection efficiency of superconducting nanowire single photon detectors.

Superconducting nanowire single photon detectors (SNSPDs) have been extensively investigated due to their superior characteristics, including high system detection efficiency, low dark count rate and short recovery time. The polarization sensitivity introduced by the meandering-type superconductor nanowires is an intrinsic property of SNSPD, which is normally measured by sweeping hundreds of points on the Poincaré sphere to overcome the unknown birefringent problem of the SNSPD's delivery fiber. In this paper, we propose an alternative method to characterize the optical absorptance of SNSPDs, without sweeping hundreds of points on the Poincaré sphere. It is shown theoretically that measurements on the system detection efficiencies (SDEs) subject to cases of four specific photon polarization states are sufficient to reveal the two eigen-absorptances of the SNSPD. We validate the proposed method by comparing the measured detection spectra with the spectra attained from sweeping points on the Poincaré sphere and the simulated absorption spectra.

Engineering a strong and stable ultraviolet chiroptical effect in a large-area chiral plasmonic shell.

Ultraviolet chiral metamaterials (UCM) are highly desired for their strong interaction with the intrinsic resonance of molecules and ability in manipulating the polarization state of high energy photons, but rarely reported to date due to their small feature size and complex geometry. Herein, we design and fabricate a kind of novel ultraviolet chiral plasmonic shell (UCPS) by combing the stepwise Al deposition and colloid-sphere assembled techniques. The cancellation effect originated from the disorder lattices of micro-domains in the colloid monolayer has been successfully overcome by optimizing the deposition parameters, and a strong CD signal of larger than 1 deg in the UV region is demonstrated both in simulation and experiment. This strong ultraviolet chiroptical resonances mainly come from the surface chiral lattice resonance mode, the whispering gallery mode and also the interaction between neighbor shells, and can be effectively tuned by changing structural parameters, for example, the sphere diameter, or even slightly increasing the deposition temperature in experiment. To improve the stability, the fabricated UCPSs are protected by N2 in the deposition chamber and then passivated by UV-ozone immediately after each deposition step. The formed UCPS show an excellent stability when exposing in the atmospheric environment. The computer-aided geometrical model, electromagnetic modes, and the tunable chiroptical resonance modes have been systematically investigated.

Cost-Effective ML-Powered Polarization-Encoded Quantum Key Distribution

Secure communications have become a requirement for virtually all kind of applications. Currently, two distant parties can generate shared random secret keys by using public key cryptography. However, quantum computing represents one of the greatest threats for the finite complexity of the mathematics behind public key cryptography. In contrast, Quantum Key Distribution (QKD) relies on properties of quantum mechanics, which enables eavesdropping detection and guarantees the security of the key. Among QKD systems, polarization encoded QKD has been successfully tested in laboratory experiments and recently demonstrated in closed environments. The main drawback of QKD is its high cost, which comes, among others, from: <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</i> ) the requirements for the quantum transmitters and receivers; and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ii</i> ) the need of carefully selecting the fibers supporting the quantum channel to minimize the environmental effects that could dramatically change the polarization state of photons. In this paper, we propose a Machine Learning (ML) -based polarization tracking and compensation that is able to keep shared secret key exchange to high rates even under large fiber stressing events. Exhaustive results using both synthetic and experimental data show remarkable performance, which can simplify the design of both quantum transmitter and receiver, as well as enable the use of aerial optical cables, thus reducing total QKD system cost.

Statistical features of multiple Compton scattering in a strong magnetic field

Compton scattering is a key process shaping spectra formation and accretion flow dynamics in accreting strongly magnetized neutron stars. A strong magnetic field affects the scattering cross section and makes it dependent on photon energy, momentum, and polarization state. Using Monte Carlo simulations, we investigate statistical features of Compton scattering of polarized x-ray radiation in a strong magnetic field. Our analysis is focused on photon gas behavior well inside the scattering region. We take into account the resonant scattering at the fundamental cyclotron frequency, thermal distribution of electrons at the ground Landau level, and bulk velocity of the electron gas. We show that (i) the photons scattered around the cyclotron energy by the electron gas at rest tend to acquire the final energy close to the cyclotron one with very small dispersion measure; (ii) the redistribution of photons within the Doppler core of cyclotron resonance differs significantly from the complete redistribution; (iii) the efficiency of momentum transfer from photons to the electron gas is affected by the temperature of electron gas both for photons at cyclotron energy and below it; (iv) the momentum transfer from photons to the electron gas of nonzero bulk velocity is more efficient in the case of magnetic scattering.

Quantum state interferography with heralded single photons

Quantum state tomography is the standard method used for quantum state reconstruction. Recently, a new technique called, quantum state interferography, has been introduced for the direct single-shot measurement of the quantum state of a qubit [Phys. Rev. Lett. 125 (2020) 123601]. In the present work, we report a first-of-its-kind experimental demonstration of quantum state interferography of legitimate single photon polarization states derived from spontaneous parametric down conversion source. Further, we provide a more general and a simpler mathematical treatment of the QSI technique. While the theoretical treatment with d-dimensional state vectors in the earlier work is limited only to pure qudits, our approach readily lends itself to the case of mixed qudit systems. The basic arguments and the results of this extension are presented with a qutrit state as an example.

Photon-ALP interaction as a measure of initial photon polarization

Axion-like particles (ALPs) are very light, neutral, spin zero bosons predicted by superstring theory. ALPs interact primarily with two photons and in the presence of an external magnetic field they generate photon-ALP oscillations and the change of the polarization state of photons. While well motivated from a theoretical point of view, hints on ALP existence come from astrophysics. In this paper, we state and demonstrate some theorems about a strict relationship between initial photon polarization and photon-ALP conversion probability - which can be extrapolated by observed astrophysical spectra - so that, in the presence of ALPs, flux-measuring observatories become also porarimeters.

Fractal Superconducting Nanowires Detect Infrared Single Photons with 84% System Detection Efficiency, 1.02 Polarization Sensitivity, and 20.8 ps Timing Resolution

The near-unity system detection efficiency (SDE) and excellent timing resolution of superconducting nanowire single-photon detectors (SNSPDs), combined with their other merits, have enabled many classical and quantum photonic applications. However, the prevalent design based on meandering nanowires makes SDE dependent on the polarization states of the incident photons; for unpolarized light, the major merit of high SDE would get compromised, which could be detrimental for photon-starved applications. Here, we create SNSPDs with an arced fractal geometry that almost completely eliminates this polarization dependence of the SDE, and we experimentally demonstrate 84$\pm$3$\%$ SDE, 1.02$^{+0.06}_{-0.02}$ polarization sensitivity at the wavelength of 1575 nm, and 20.8 ps timing jitter in a 0.1-W closed-cycle Gifford-McMahon cryocooler, at the base temperature of 2.0 K. This demonstration provides a novel, practical device structure of SNSPDs, allowing for operation in the visible, near-, and mid-infrared spectral ranges, and paves the way for polarization-insensitive single-photon detection with high SDE and high timing resolution

Topology-Abstraction-Based Protection Scheme in Quantum Key Distribution Networks with Partially Trusted Relays

Quantum key distribution (QKD) can protect the exchange process of confidential information between communicating parties. By using the basic principles of quantum mechanics and combined with “one-time pad” cipher encryption, information can be unconditionally secure. The BB84 protocol first describes the method of transmitting information by photon polarization state, and it expounds the transmission process of services between trusted relays. However, due to the defects of real experimental devices, there are security vulnerabilities in QKD in a real system. The birth of measurement-device-independent quantum key distribution (MDI-QKD) protocol solves the problem, providing immunity to hacker attacks at the end of the detector. It can enable both sides of the transmission service to establish a connection and generate secret keys through an untrusted relay node to ensure information security. However, the types and properties of link nodes in quantum key distribution network (QKDN) based on partially trusted relay are more complex, which can easily result in network fault. Therefore, how to prevent the impact of failure on QKDN has become an urgent problem. In this paper, we propose a protection scheme for QKDN with partially trusted relays. The method deals with trusted and untrusted relays differently and constructs the working and protection paths of the secret key for each service. It reduces resource conflict between the protection and working paths by establishing a key protection threshold, which realizes the resource trade-off between the two factors. Simulation results show that the scheme provides effective protection to the services, and it improves the stability and reliability of QKDN based on partially trusted relay.

Quantum ghost polarimetry with entangled photons.

The theory of the formation of polarization ghost images in biphoton light of spontaneous parametric scattering is developed. On the basis of the developed theory, the quantum ghost polarimetry concept has been suggested, which makes it possible to obtain two-dimensional maps of the polarization properties of objects by measuring a set of correlation functions obtained in various polarization states of photons. For objects with linear dichroism, a complete set of measurement states is found, which allows for obtaining the maps of the distributions of absorption, value, and azimuth of anisotropy.

Spectral and polarization properties of reflected X-ray emission from black hole accretion discs

ABSTRACTX-ray polarimetric missions planned for this decade will significantly enhance our knowledge of compact accreting sources. Observations of the X-ray polarization signal from active galactic nuclei (AGNs) or X-ray binary systems (XRBs) will bring new means to study inner accretion flow in these objects that, together with currently used spectroscopic and timing techniques, will help us to determine better their properties, such as their inclination, orientation, shape, and size of their corona as well as the black hole spin. In this work, we present a yet missing piece in the global polarization models of black hole accretion discs. We compute the reflected X-ray emission from the disc in a local co-moving frame using (1) the radiative transfer code titan to obtain the ionization structure of the disc and (2) the Monte Carlo code stokes that incorporates the physics of absorption, re-emission, and Compton scattering to produce a complete spectropolarimetric output. We present the final Stokes parameters I, Q, and U for a set of photon-indices of the incident primary power-law radiation, the disc ionization parameters, incident and emission angles, for three independent polarization states of the incident coronal X-ray photons with a sufficient resolution in energy to allow for sharp discussion of spectral and polarization properties. We show that the spectral component matches well literature predictions. The polarization degree and angle are in agreement with analytical approximations previously appearing in reflection models and we demonstrate that the polarized reflected X-ray emission can be, locally, quite large in the $2{\!-\!}12\,$ keV band.

Theory and experiment for resource-efficient joint weak-measurement

Incompatible observables underlie pillars of quantum physics such as contextuality and entanglement. The Heisenberg uncertainty principle is a fundamental limitation on the measurement of the product of incompatible observables, a 'joint' measurement. However, recently a method using weak measurement has experimentally demonstrated joint measurement. This method [Lundeen, J. S., and Bamber, C. Phys. Rev. Lett. 108, 070402, 2012] delivers the standard expectation value of the product of observables, even if they are incompatible. A drawback of this method is that it requires coupling each observable to a distinct degree of freedom (DOF), i.e., a disjoint Hilbert space. Typically, this 'read-out' system is an unused internal DOF of the measured particle. Unfortunately, one quickly runs out of internal DOFs, which limits the number of observables and types of measurements one can make. To address this limitation, we propose and experimentally demonstrate a technique to perform a joint weak-measurement of two incompatible observables using only one DOF as a read-out system. We apply our scheme to directly measure the density matrix of photon polarization states.