Photonic Spin Research Articles

Spin-orbit-enabled sorting of optical flows in plasmonic nanocircuits.

On-chip controlling of photon spin is essential in developing future integrated nanophotonics with complex functionalities. Here we propose and demonstrate a robust spin-sorting nanocircuit, which consists of a spin-orbit coupler (i.e., combined nanoring and nanodisk) and an L-shaped dielectric-loaded surface plasmon (DLSPs) waveguide. The nanocircuit with optimized geometric parameters is shown to be capable of unidirectionally exciting and routing a DLSP mode along an independent waveguide. We found experimentally that the proposed device possesses an average insertion loss (extinction ratio) of 0.13 dB (14.8 dB) under complete circularly polarized incidence with opposite spin, which is in good agreement with theoretical calculations. The proposed spin-selective scheme may pave the way for applications in the manipulation of chirality with a flexible degree of freedom.

Detection of photogenerated single electrons in a lateral quantum dot with a surface plasmon antenna

Electron spins in gate-defined lateral quantum dots (QDs) are a suitable platform for qubits and have the capacity for coherent coupling to free-space photons. Superposition state transfer from single photon polarizations to single spins has been realized using a GaAs gate-defined QD. However, its efficiency is limited by the small size of the QDs. Here, we use a surface plasmon antenna on a GaAs gate-defined QD and demonstrate that the photoelectron detection probability is enhanced by 5.3–9.2 times. This result contributes to the development of photon–spin quantum interface using gate-defined lateral QDs.

Limitations of the transmitted photonic spin Hall effect through layered structure

In this paper, we show theoretically that the spin-dependent transverse shift of the transmitted photonic spin Hall effect (SHE) through layered structure cannot exceed half of the incident beam waist. Exact conditions for obtaining the upper limit of the transmitted SHE are clarified in detail. In addition, different from the popular view in many investigations, we find that there is no positive correlation between the spin-dependent transverse displacement and the ratio between the Fresnel transmission coefficients (tp, ts). In contrast, the optimal transmission ratio is determined by the incident angle and the beam waist. Moreover, two conventional transmission structures are selected and studied in detail. The characteristics of the transverse displacements obtained are in very good agreement with our theoretical conclusions. These findings provide a deeper insight into the photonic spin Hall phenomena and offer a guide for future related research.

Generation of relativistic positrons carrying intrinsic orbital angular momentum

High energy positrons can be efficiently created through high-energy photons splitting into electron-positron pairs under the influence of the Coulomb field. Here we show that a new degree of freedom-the intrinsic orbital angular momentum (OAM) can be introduced into relativistic positrons when the incident photons are twisted. We developed the full-twisted scattering theory to describe the transfer of angular momentum before and after the interaction. It is found that the total angular momentum (TAM) of the photon is equally distributed among the positron and electron. For each photon TAM value, the generated leptons gain higher average OAM number when the photon spin is anti-parallel to its TAM. The impact of photon polarization on the OAM spectrum profile and the scattering probability is more significant at small photon TAM numbers, owing to the various interaction channels influenced by flipping the photon spin. Our work provides the theoretical basis to study OAM physics in particle scattering and to obtain copious relativistic vortex positrons through the Beth-Heitler process.

Spin photonics: from transverse spin to photonic skyrmions

Abstract Spin angular momentum associated with circular polarization is a fundamental and important aspect of photons both in classical and quantum optics. The interaction of this optical spin with matter and structures results in many intriguing optical effects and state-of-the-art applications covered under the emerging subject of spin optics. Distinct from longitudinal optical spin along the mean wavevector, transverse spin, the corresponding vector of which is perpendicular to the mean wavevector, prevails and plays a significant role in confined electromagnetic waves such as focused beams, guided waves, and evanescent waves. In the optical near-field, these transverse spins are generated owing to the spatial variation of the kinetic momentum of confined electromagnetic waves, where the spin and orbital angular momenta are strongly coupled, leading to many interesting topological spin structures and properties. Several reviews on optical transverse spins have been published in recent years in which their concepts and the various configurations producing them were introduced systematically. Here, we introduce in this review the underlying physics and dynamics of transverse spin and the resultant topological structures and properties such as the photonic skyrmions and merons. We term this sub-area ‘spin photonics’, its scope being to cover the design and research of spin structures in strongly confined electromagnetic fields with unique properties and applications. The concepts and framework reviewed have importance in optics, topological photonics, metrology, and quantum technologies and may be used to extend spin-dynamics concepts to fluidic, acoustic, and gravitational waves.

Intensity interference characteristics of fractional Laguerre–Gaussian optical vortex

The paper reports the intensity characteristics of fractional vortex beam, and controls the coupling between photon orbital angular momentum and spin angular momentum by coherently manipulating Laguerre–Gaussian vortex beam with linearly polarized plane light and its conjugate beam. By comparing theory with experiment, fractional vortex beams with different topological charges are generated by using pure phase liquid crystal spatial light modulator, and their intensity characteristics and interference characteristics are observed. The results show that the radial notch size of the spot is related to the fractional part of the topological charge value, and the closer the fractional part of the topological charge value is to the half integer, the more obvious the radial notch is. With the increase of integer part of topological charge, the spot radius also increases. In addition, interference with linearly polarized plane light reveals that the number of branches is equal to the number of topological charges. Interfere with its conjugate beam, and judge the topological charge number of vortex beam by the relationship between petal number and topological charge number. The petal number of integer vortex beam is twice the topological charge number, and fractional order vortex beam destroys the ring structure of Laguerre–Gaussian beam.

Linear-polarized terahertz isolator by breaking the gyro-mirror symmetry in cascaded magneto-optical metagrating

Abstract To realize nonreciprocal transmission, it is necessary to break the time-reversal symmetry of the transmission system, but it is very challenging to keep the linear polarized (LP) input and output unchanged in the free space transmission system. Magnetized semiconductor InSb can realize terahertz (THz) nonreciprocal transmission for the two conjugated photonic spin states, but it cannot realize efficient one-way transmission of LP state due to gyro-mirror symmetry. In this work, by introducing a pair of orthogonal uniaxial anisotropies from the meta-gratings on both sides of InSb, both the gyro-mirror and time-reversal symmetries are broken for the LP state, thus making this cascaded grating–InSb–grating structure serves as a high-performance isolator for the LP light. The experiment results indicate isolation of 50 dB at 0.4 THz for the same LP input and output under a weak biased magnetic field of 0.17 T. Moreover, we further illustrate the factors affecting the isolation bandwidth of the device, also demonstrated another broadband structure with the 10 dB isolation bandwidth from 0.2–0.7 THz, and the relative bandwidth achieves 110%. The mechanisms of THz nonreciprocal transmission and polarization manipulation proposed in this work will contribute to the development of efficient THz magneto-optical devices.

Highly Sensitive Magnetic Field Detection in Infrared Region With Photonic Spin Hall Effect in Silicon Waveguide Plasmonic Sensor

In this work, we propose and analyze a plasmonic sensor with a three-layer waveguide structure. We consider the transverse spin-dependent shift (SDS) of the horizontal photonic spin Hall effect (PSHE) in the waveguide at a given wavelength (1557 nm) for a TM (transverse magnetic or p-polarized) mode. The sensor structure is analyzed in two ways. First, under the normal methods, that is, angular and intensity interrogation methods, for which the results indicate that the maximum figure of merit (FOM) of 4007.0 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> is attained for an optimum thickness ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d_{2}=51$ </tex-math></inline-formula> nm) of the gold layer and this FOM is significantly greater than the corresponding FOM (413.7 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ) reported earlier (for a 50 nm thick gold layer). Also, the average sensitivity increases from 0.0005 to 0.002°/Oe when the volume fraction of Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> particles ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$c$ </tex-math></inline-formula> ) in the magnetic fluid is increased from 1.48% to 1.93%. Correspondingly, a considerably finer value of the resolution (0.046 Oe) is obtained when the volume fraction is increased to 1.93% (compared to 0.199 Oe at 1.48%). Second way is the proposed method of PSHE, for which the analysis indicates that transverse SDS of the horizontal PSHE is the maximum for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d_{2} = 51$ </tex-math></inline-formula> nm leads to the maximum sensitivity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6.25 \times 10^{7}~\mu$ </tex-math></inline-formula> m/RIU for an amplified angle <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta = 0.1^{\circ}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.09 \times 10^{6}~\mu$ </tex-math></inline-formula> m/RIU for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta = 0.1$ </tex-math></inline-formula> rad in the conventional weak measurements. The corresponding finest possible resolution of magnetic field detection at 1.93% is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.5 \times 10^{-6}$ </tex-math></inline-formula> Oe in the conventional weak measurements for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta = 0.1^{\circ}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7.8 \times 10^{-8}$ </tex-math></inline-formula> Oe in the modified weak measurements for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta = 0.5$ </tex-math></inline-formula> rad, which are significantly finer than those existing in the related state of the art. The above resolution is also superior to those found under normal methods mentioned earlier. Furthermore, the effect of temperature (24.3 °C–60 °C) on PSHE-based magnetic field sensor’s performance is also analyzed which indicates that the proposed PSHE-based magnetic field sensor should be operated in a thermally controlled milieu.

Quantum sensing of photonic spin density using a single spin qubit

Photonic spin density (PSD) in the near-field gives rise to exotic phenomena such as photonic skyrmions, optical spin-momentum locking and unidirectional topological edge waves. Experimental investigation of these phenomena requires a nanoscale probe that directly interacts with PSD. Here, we propose and demonstrate that the nitrogen-vacancy (NV) center in diamond can be used as a quantum sensor for detecting the spinning nature of photons. This room temperature magnetometer can measure the local polarization of light in ultra-subwavelength volumes through photon-spin-induced virtual transitions. The direct detection of light's spin density at the nanoscale using NV centers in diamond opens a new frontier for studying exotic phases of photons as well as future on-chip applications in spin quantum electrodynamics (sQED).

Non-classical photonic spin texture of quantum structured light

Classical structured light with controlled polarization and orbital angular momentum (OAM) of electromagnetic waves has varied applications in optical trapping, bio-sensing, optical communications and quantum simulations. However, quantum noise and photon statistics of three-dimensional photonic angular momentum are relatively less explored. Here, we develop a quantum framework and put forth the concept of quantum structured light for space-time wavepackets at the single-photon level. Our work deals with three-dimensional angular momentum observables for twisted quantum pulses beyond scalar-field theory as well as the paraxial approximation. We show that the spin density generates modulated helical texture and exhibits distinct photon statistics for Fock-state vs. coherent-state twisted pulses. We introduce the quantum correlator of photon spin density to characterize nonlocal spin noise providing a rigorous parallel with electronic spin noise. Our work can lead to quantum spin-OAM physics in twisted single-photon pulses and opens explorations for phases of light with long-range spin order.

Enhanced photonic spin Hall effect via singularity induced by destructive interference.

In this work, we report a simple and effective method for enhancing the photonic spin Hall effect (SHE) via singularity induced by destructive interference in an ultrathin uniaxial slab. Deriving from anisotropy, the incident angles corresponding to destructive interference for p- and s-polarized waves will be deviated, leading to an enhancement peak in transverse spin shift. Interestingly, by adjusting the thickness of slab, the destructive interference and the Brewster effect can act together. At this point, the photonic SHE exhibits great singularity, and the maximum transverse spin shift can approach about three times more than that of the Brewster effect acting alone. This Letter reveals the influence of the interference effect on photonic SHE in layered media and provides a simple way to achieve enhanced photonic SHE.

Magnetically Induced Terahertz Birefringence and Chirality Manipulation in Transverse‐Magnetized Metasurface

AbstractActive manipulation of photonic spin state and optical chirality leads to some key applications, such as in multichannel communication, polarization‐sensitive imaging, chiral spectroscopy, and chiral sensing. Magneto‐optical materials have unique advantages in the intrinsic transmission and magnetic control of photonic chiral spin states. Here, a scheme for dynamic terahertz (THz) anisotropy and chirality manipulations in the transversely magnetized InSb and its hybrid magneto‐optical metasurface structure is presented. A special transverse photonic spin state in the InSb and a transverse−longitudinal spin coupling effect in the hybrid magneto‐optical metasurface are revealed by the eigenmode analysis and numerical simulations. The strong magnetic birefringence effect induced by this spin mode is demonstrated in the experiment. Moreover, the symmetry‐breaking mechanism in this magneto‐optical structure leads to strong intrinsic chirality and polarization conversion. The experimental results confirm the magnetically active manipulation of spin states and their asymmetric transmission in this hybrid magneto‐optical metasurface, which achieve a polarization conversion rate of near 100% and an induced intrinsic chirality of over 15 dB. This work opens a new development for active THz polarization control and chiral manipulation in the magneto‐optical microstructure.

Design of bull’s-eye optical cavity toward efficient quantum media conversion using gate-defined quantum dot

Gate-defined quantum dots (GQDs) are promising solid-state quantum structures for realizing spin–photon quantum interfaces that convert the arbitrary polarization state of a photon to the corresponding spin state of an electron. For an efficient conversion, the optical absorption of GQDs must be enhanced without polarization dependence. In this study, we design an optical cavity based on the bull’s-eye structure. The symmetry of the structure allows the cavity to support doubly degenerate modes. We numerically demonstrate that for an incident light of any polarization state, the optical absorption of a GQD embedded in a bull’s-eye cavity is equally enhanced. A 450× absorption enhancement is obtained in an experimentally feasible structure. We elucidate the physical origins of this significant enhancement by analyzing the light absorption of GQDs using coupled mode theory. Our results indicate the potential of the bull’s-eye cavity structure as a building block for efficient quantum media conversion using GQDs.

Unidirectional propagation of the Bloch surface wave excited by the spinning magnetic dipole in two-dimensional photonic crystal slab

The photonic spin Hall effect (PSHE) can be realized in a photonic crystal (PC) slab, that is, the unidirectional Bloch surface wave can propagate along the surface of the PC slab under the excitation of elliptical polarized magnetic dipole. It is further proved that PSHE is caused by the interference of the component surface waves excited by the different components of the incident light, which is the so called component wave interference (CWI) theory. In addition, we also find that the spin of the surface wave oscillates periodically in space, and the oscillation period is a unit cell. In a unit cell, the average spin keeps the spin orbit locked. The results show that the spin separation can also be modulated by the position and the polarization state of the magnetic dipole.

Spin Hall effect of light based on a surface plasmonic platform

Abstract In recent years, the spin Hall effect of light (SHE), also called the photonic spin Hall effect has received extensive research attention, and a series of interesting results have been achieved. This phenomenon has potential applications in nanooptics, quantum information, and optoelectronic devices. In contrast to the pure photon SHE, the photonic spin Hall effect in the surface plasmonic platform exhibits unique properties due to the surface plasmon resonance effect of noble metal material and establishes the connection between photons and electrons. Therefore, the SHE of light in a surface plasmonic platform is expected to be applied to integrated optical devices to create a novel means of developing communication devices. In this paper, we review the progress on the SHE of light based on the plasmonic platform in recent years, and we discuss the future directions of research and prospects for its applications.

Nonreciprocal photonic spin Hall effect of magnetic Weyl semimetals

Magnetic Weyl semimetals allow the unique opportunities for the realizations of nonreciprocal optical properties, thermal radiation, and anomalous photon thermal Hall effect without the requirement of an external magnetic field. Here, we theoretically investigate the photonic spin Hall effect in the magnetic Weyl semimetal-based multilayered structure and demonstrate that this effect is nontrivial and nonreciprocal. Its induced nontrivial photonic spin Hall effect originates from the large differences between the reflectances under different polarized waves. In addition, the generation of this kind of nonreciprocal photonic spin Hall effect is guaranteed by the simultaneously broken space inversion symmetry and time reversal symmetry of this specific structure. Specially, the responses of nonreciprocal photonic spin Hall effect can sustain within a certain range of incident angle and it can be effectively manipulated by varying the Fermi energy of magnetic Weyl semimetals. Our work expands the fields of the photonic spin Hall effects and suggests magnetic Weyl semimetals potential candidates in the next-generation nonreciprocal spin photonic devices.

High-performance photonic spin Hall effect in anisotropic epsilon-near-zero metamaterials.

A high-performance photonic spin Hall effect is demonstrated in an anisotropic epsilon-near-zero (ENZ) metamaterial based on the wave-vector-varying Pancharatnam-Berry phase. The giant out-of-plane anisotropy of ENZ metamaterial induces strong spin-orbit coupling. With a small incident angle, photons with opposite spins move along opposite transverse directions gradually. After transmitting through a submicrometer thick ENZ metamaterial, the spin photons are fully separated with a spin separation of 2.7 times beam waist and transmittance of 70.1%, allowing a figure of merit F up to 1.9. A practical ENZ metamaterial consisting of an Ag nanorod array is proposed, whose figure of merit is still up to 0.006. This high-performance photonic spin Hall effect provides an integrated and practical way for the development of spin-photonic devices.

Quantum networks based on color centers in diamond

With the ability to transfer and process quantum information, large-scale quantum networks will enable a suite of fundamentally new applications, from quantum communications to distributed sensing, metrology, and computing. This Perspective reviews requirements for quantum network nodes and color centers in diamond as suitable node candidates. We give a brief overview of state-of-the-art quantum network experiments employing color centers in diamond and discuss future research directions, focusing, in particular, on the control and coherence of qubits that distribute and store entangled states, and on efficient spin–photon interfaces. We discuss a route toward large-scale integrated devices combining color centers in diamond with other photonic materials and give an outlook toward realistic future quantum network protocol implementations and applications.

Broadband photonic spin Hall metalens based metal nanohole array metasurface

In this paper, we propose a method to construct geometric-phase-based spin Hall metalens, which consists of identical metal nanoholes with spatially variant orientations. It is demonstrated that the metalens can realize simultaneous focusing for different spin states in the broad spectral range of 550–900 nm due to the extremely similar hyperbolic phase profiles at different optimized values of wavelength and focal length. The transverse and longitudinal positions of spin-dependent focal spots can be arbitrarily manipulated by adjusting the orientation angles of metal nanoholes. The intensities of the spin-dependent focal spots can be effectively controlled by the proportion of the phase profile associated with right- or left-hand circularly polarized component. In addition, our designed metalens enables the focusing beyond the optical diffraction limit across the above wavelength coverage as the phase profile only contains right or left-hand circularly polarized component. It is expected that our simple and novel metalens would be applied in polarimetric imaging, optical sensing, and photon spin splitting.

Active terahertz spin state and optical chirality in liquid crystal chiral metasurface

Dynamic control of photonic spin state and chirality plays a vital role in various applications, such as polarization control, polarization-sensitive imaging, and biosensing. Here, we present a scheme for the flexible and dynamic manipulation of terahertz spin state conversion and optical chirality by combining two achiral structures: an asymmetric metasurface and a layer of anisotropic liquid crystal. The proposed asymmetric metasurface can realize the polarization conversion effect. For the circularly polarized incidence, it exhibits the asymmetric transmission of the spin-flipped states but no spin-locked optical chirality since its geometry is mirror symmetric along with the wave propagation. The introduction of the liquid crystal makes the composite metasurface not only exhibit the spin state conversion but also spin-locked chirality and spin-flipped chirality on account of breaking mirror symmetry, which realizes an electrically active terahertz chiral device. The experimental results show that the asymmetric transmission of the terahertz spin states can be dynamically manipulated, resulting in a large controllable range 83.8% to \ensuremath{-}30.7% of spin-locked circular dichroism at 0.76 THz and \ensuremath{-}98.2% to 44.7% of spin-flipped circular dichroism at 0.73 THz. This work paves the way for the development of terahertz meta devices capable of enabling active photonic spin state and chirality manipulation.