Photon Tunneling Research Articles

Dissipative Josephson effect in coupled nanolasers

Josephson effects are commonly studied in quantum systems in which dissipation or noise can be neglected or do not play a crucial role. In contrast, here we discuss a setup where dissipative interactions do amplify a photonic Josephson current, opening a doorway to dissipation-enhanced sensitivity of quantum-optical interferometry devices. In particular, we study two coupled nanolasers subjected to phase coherent drivings and coupled by a coherent photon tunneling process. We describe this system by means of a Fokker–Planck equation and show that it exhibits an interesting non-equilibrium phase diagram as a function of the coherent coupling between nanolasers. As we increase that coupling, we find a non-equilibrium phase transition between a phase-locked (PL) and a non-phase-locked (NPL) steady-state, in which phase coherence is destroyed by the photon tunneling process. In the coherent, PL regime, an imbalanced photon number population appears if there is a phase difference between the nanolasers, which appears in the steady-state as a result of the competition between competing local dissipative dynamics and the Josephson photo-current. The latter is amplified for large incoherent pumping rates and it is also enchanced close to the lasing phase transition. We show that the Josephson photocurrent can be used to measure optical phase differences. In the quantum limit, the accuracy of the two nanolaser interferometer grows with the square of the photon number and, thus, it can be enhanced by increasing the rate of incoherent pumping of photons into the nanolasers.

Whether or not the Maxwell theory works on the atomic level

In this paper, we have studied the Maxwell radiation from the electron orbiting the nucleus in an atom such as hydrogen atom. The orbiting electron is thought as two oscillating dipoles: one on [Formula: see text]-axis and the other on [Formula: see text]-axis with the same frequency. We have derived the electromagnetic wave and calculated powers of the radiation from these two oscillating dipoles, and then determined the time period it takes for the electron to change its energy levels from [Formula: see text] to [Formula: see text] due to the Maxwell radiation. Compared the time period due to the Maxwell radiation with the time period from the uncertainty principle, it is found that the two time periods are different from each other by about nine orders of magnitude. So, we are led to believe that the Maxwell theory could not be used in the quantum photo emission by the electron in an atom. Thus, we suggest that the quantum photo emission by the electron in an atom may be photon tunneling from the electron [Formula: see text] in an atom.

Enhancement of near-field thermal radiation of semiconductor vanadium dioxide covered by graphene

Near-field thermal radiation refers to the radiation produced by two radiators in a narrow gap that is smaller than the characteristic wavelength. The studies of near-field thermal radiation began in the 1960s and 1970s. Some researchers have reported that near-filed thermal radiation can be enhanced by orders of magnitude higher than that of far-field radiation by photon tunneling and surface polariton. With the development and application of nanotechnology, the near-field heat radiation has developed into a research hotspot in the field of heat radiation. Recent studies have shown that the properties of near-field thermal radiation can be enhanced by optimizing the structures of radiators (covered by two-dimensional (2D) materials, such as graphene and black phosphorus), choosing radiation materials (hexagonal boron nitride, silicon dioxide, vanadium dioxide), and selecting appropriate physical parameters (chemical potential, vacuum distance, film thickness) of the radiator materials. According to the fluctuation dissipation theory and by solving the Maxwell equation and the green's function, in this article we report the near-field thermal radiation of the two half-infinite flats, including vanadium dioxide V/V, vanadium dioxide covered by graphene GV/GV and vanadium dioxide film covered by graphene GV0/GV0. The near-field thermal radiations in these structures are influenced by physical parameters, such as vacuum spacing, thickness of vanadium dioxide film and chemical potential of graphene. The results show that near-field thermal radiation of GV0/GV0 (38088.43 W/m<sup>2</sup>) is 8.6 times stronger than that of GV/GV (4426.73 W/m<sup>2</sup>, vacuum distance is 10 nm, chemical potential is 0.1 eV), and near-field thermal radiation of GV/GV (4426.73 W/m<sup>2</sup>) is 35 times stronger than that of V/V (127.21 W/m<sup>2</sup>, vacuum distance is 10 nm, chemical potential is 0.1 eV). For these three structures, thermal radiation decreases gradually by widening the vacuum distance. Moreover, thermal radiation also decreases by thickening vanadium dioxide film. While thermal radiation of GV0/GV0 decreases 3.34 times as chemical potential of graphene increases from 0.1 (38088.43 W/m<sup>2</sup>) to 0.6 eV (11399.80 W/m<sup>2</sup>). In this paper, the near-field heat radiation between vanadium dioxide and graphene is systematically investigated, which will give the guidance in the relevant experiment and practical applications of near-field heat radiation between vanadium dioxide and graphene.

Enhancement of rotational vacuum friction by surface photon tunneling

AbstractWhen a neutral sphere is rotating near a surface in vacuum, it will experience a frictional torque due to quantum and thermal electromagnetic fluctuations. Such vacuum friction has attracted many interests but has been too weak to be observed. Here we investigate the vacuum frictional torque on a barium strontium titanate (BST) nanosphere near a BST surface. BST is a perovskite ferroelectric ceramic that can have large dielectric responses at GHz frequencies. At resonant rotating frequencies, the mechanical energy of motion can be converted to electromagnetic energy through resonant photon tunneling, leading to a large enhancement of the vacuum friction. The calculated vacuum frictional torques at resonances at sub-GHz and GHz frequencies are several orders larger than the minimum torque measured by an optically levitated nanorotor recently, and are thus promising to be observed experimentally. Moreover, we calculate the vacuum friction on a rotating sphere near a layered surface for the first time. By optimizing the thickness of the thin-film coating, the frictional torque can be further enhanced by several times.

Observation of energy transfer at optical frequency to an ultrathin silicon waveguide.

Energy transfer from a submonolayer of rhodamine 6G molecules to a 130 nm thick crystalline silicon (Si) waveguide is investigated. The dependence of the fluorescence lifetime of rhodamine on its distance to the Si waveguide is characterized and modeled successfully by a classical dipole model. The energy transfer process could be regarded as photon tunneling into the Si waveguide via the evanescent waves. The experimentally observed tunneling rate is well described by an analytical expression obtained via a complex variable analysis in the complex wavenumber plane.

Near-field negative electroluminescent cooling via nanoparticle doping

Modulating the photon tunneling probability is the key to control the near-field radiative heat transfer (NFRHT) between two objects. It has been found that nanoparticle doping technology can enable plentiful resonance modes which significantly adjust photon emission spectra. In this work, we theoretically analyze the performance of a near-field negative electroluminescent refrigeration (NFNELR) system consisting a Mie-metamaterial emitter and mercury cadmium telluride (MCT) receiver with spacing between them less than the thermal wavelength. The emitter consists of graphene/SiC core-shell (GSCS) nanoparticle-embedded thin film of Si deposited on bulk Si. We show that with the inclusion of GSCS nanoparticles, the thin layer of Mie-metamaterial acts like an effective medium that excites radiative heat transfer for the photons above the band gap of MCT. We analyze NFNELR performance for various bias voltages, various cryogenic temperatures, various volume fractions and various chemical potentials of GSCS nanoparticles. We also would like to emphasize that in order to improve the performance of the NFNELR system, the host matrix materials chosen are not necessarily stationary. These results provide a powerful way to rouse and regulate the NFRHT, meanwhile in turn, open up a way to explore actual development and present some guidance for optimal design of NFRHT.

Enhancement and Manipulation of Near-Field Radiative Heat Transfer Using an Intermediate Modulator

Many efforts have been dedicated to enhancing near-field radiative heat transfer by designing different kinds of geometric shapes or introducing new materials. Besides just improving the heat-transfer rate, active and convenient thermal management is also important in micro- and nanothermal systems. We show that the introduction of an intermediate modulator, based on the $\mathrm{graphene}/h$-BN/graphene heterostructure, can enhance and manipulate thermal radiative heat transfer without changing the distance or other parameters of the emitter and absorber. Such three-body systems can increase the radiatively exchanged power several times over corresponding two-body counterparts. The introduced modulator can be viewed as a midrepeater to effectively enhance photon tunneling through evanescent modes. Furthermore, the heat-transfer rate can be modulated over a large range and can even be lower than that in two-body systems through the application of bias voltages. The mechanism can be explained by the change of energy-transmission coefficients between bodies through adjustment of the optical properties of graphene. The presented scheme may open a promising avenue for the active control of near-field heat transfer at the micro- and nanoscales.

Resonant photon emission during relative sliding of two dielectric plates

The effect of resonances in the photon emission rate in radiative heat generation and transfer, and Casimir friction at the relative sliding of two plates of polar dielectrics is studied. Resonances are of a different origin in the frequency range of the normal (NED) and anomalous (AED) Doppler effect. In the NED domain, resonances are associated with resonant photon tunneling between surface phonon/plasmon polaritons. In the AED domain resonances are associated with the instantaneous generation of excitations in both plates. While in the NED domain the resonances are finite, in the ADE domain singular resonances are possible even in the presence of dissipation in the system.

Negative Group Velocity Plasmons Propagating in Waveguides Composed of Graphene Metamaterials

Fast light which demonstrates negative group velocity, is achieved by the anomalous dispersion or photon tunneling. However, many applications based on the fast light are limited due to the disadvantages of inferior tunability or nonlinear dispersion relationship of the fast light-carrying medium. In this paper, we propose the graphene plasmonic crystal waveguides whose guiding and claddings are composed of the graphene plasmonic metamaterials, where the backward propagating plasmonic modes corresponding to negative group velocity are observed. The dispersion relation and the group velocity of three types of graphene plasmonic crystal waveguides are investigated by varying the materials and the geometrical parameters of the graphene plasmonic crystal waveguides. Numerical experiments are designed to verify the authenticity of a fast plasmon in the graphene plasmonic crystal waveguides. Our proposed graphene plasmonic crystal waveguides might find significant applications in the fields of nanophotonics, on-chip electromagnetic field manipulation in deep nanoscale, and the technique of high density plasmonic integrated plasmonic circuit in the future.

Giant near-field radiative heat transfer between ultrathin metallic films.

Understanding energy transfer via near-field thermal radiation is essential for applications such as near-field imaging, thermophotovoltaics and thermal circuit devices. Evanescent waves and photon tunneling are responsible for the near-field energy transfer. In bulk noble metals, however, surface plasmons do not contribute efficiently to the near-field energy transfer because of the mismatch of wavelength. In this paper, a giant near-field radiative heat transfer rate that is orders-of-magnitude greater than the blackbody limit between two ultrathin metallic films is demonstrated at nanoscale separations. Moreover, different physical origins for near-field thermal radiation transfer for thick and thin metallic films are clarified, and the radiative heat transfer enhancement in ultrathin metallic films is proved to come from the excitation of surface plasmons. Meanwhile, because of the inevitable high sheet resistance of ultrathin metal films, the heat transfer coefficient is 4600 times greater than the Planckian limit for the separation of 10 nm in ultrathin metallic films, which is the same order or even greater than that in other 2D materials with low carrier density. Our work shows that ultrathin metallic films are excellent materials for radiative heat transfer, which may find promising applications in thermal nano-devices and thermal engineering.

Optically induced transparency in coupled micro-cavities: tunable Fano resonance

We theoretically investigate the phenomena of optically induced transparency for a weak probe field and tunable asymmetric Fano line shape in coupled micro-cavities. One of the cavities is passive, consists of optical Kerr medium and coupled via photon tunnelling to an active cavity. The forward transmission and backward reflection profile of the output fields are analyzed for both passive-passive and passive-active cavity system by varying different system parameters. The transmission spectra show tunable transparency window and sharp asymmetric Fano line shape structure. The sharpness of line shape profile is controlled via the gain-to-loss ratio, photon tunnelling strength, Kerr nonlinear strength and input power. The findings in this study have the potential to be used as a highly sensitive sensor and also useful for telecom system.

Effect of Evanescent Waves on the Dark Current of Thermophotovoltaic Cells

ABSTRACTThe output power of thermophotovoltaic (TPV) cells may be greatly increased when the gap between the emitter and cell is reduced to submicron distances (near-field regime), at which photon tunneling due to evanescent waves becomes important. Accurate modeling of TPV cells in these conditions is crucial for the design and optimization of near-field TPV systems. The conventional or standard modeling method uses the summation of the dark current and the short-circuit current, while the direct method applies the photon chemical potential. It has been shown that the two methods are linked through a modification of the direct method using Wien’s approximation. By contrasting different modeling approaches, we quantitatively analyze the effects of evanescent waves on the TPV cell performance parameters, especially the dark current, for different emitter and cell materials in the near-field regime. Our results show that the saturation current by radiative recombination is strongly affected by evanescent waves and the bandgap energy. The current-voltage characteristics calculated by different modeling methods are displayed to demonstrate that a constant saturation current typically used in the standard method could cause substantial error in the near-field regime. For a TPV system with an emitter operating at relatively low temperatures, we show that it is necessary to include the photon chemical potential in the computation of the net radiative heat transfer between the emitter and receiver.

Controlled optical bistability in parity-time-symmetric coupled micro-cavities: Possibility of all-optical switching

Abstract We theoretically explored the optical bistability in parity-time-symmetric coupled micro-cavities, where two cavities are coupled by photon tunnelling; one of the cavities contains Kerr-nonlinearity. Using Heisenberg-Langevin equations of motion we obtained steady state mean cavity photon number for different photon tunnelling strength, nonlinear strength and gain-to-loss ratio. A high degree of coherent influence and tunability via Kerr-nonlinear strength and photon tunnelling strength over the bistable behaviour is discussed. The impact of the exceptional point on the characteristics of bistability is also reported. The model system exhibits switching behaviour and tunable zero intensity window. Our result may be useful to design efficient all-optical switch and optical sensor.

Effect of Resonant Photon Emission in Radiative Heat Transfer and Generation

The effect of resonances in the photon emission rate in the radiative heat generation and transfer and the Casimir friction at the sliding of two polar dielectric plates has been studied. The resonances have different origin in the frequency ranges of the normal and anomalous Doppler effects. In the frequency range of the normal Doppler effect, the resonances are due to resonant photon tunneling between surface phonon/plas-mon polaritons of plates. Such resonances exist only at a relative sliding velocity v = 0 for two identical plates. However, the resonances may occur at v ≠ 0 for different plates. In the frequency range of the anomalous Doppler effect, the resonances are due to the excitation generation in both plates. While the resonances are finite in the frequency range of the normal Doppler effect, singular resonances are possible even in the presence of dissipation in the system in the frequency range of the anomalous Doppler effect. The resonances for identical and different sliding plates have been considered.

Dynamically generated synthetic electric fields for photons

Static synthetic magnetic fields give rise to phenomena including the Lorentz force and the quantum Hall effect even for neutral particles, and they have by now been implemented in a variety of physical systems. Moving towards fully dynamical synthetic gauge fields allows, in addition, for backaction of the particles' motion onto the field. If this results in a time-dependent vector potential, conventional electromagnetism predicts the generation of an electric field. Here, we show how synthetic electric fields for photons arise self-consistently due to the nonlinear dynamics in a driven system. Our analysis is based on optomechanical arrays, where dynamical gauge fields arise naturally from phonon-assisted photon tunneling. We study open, one-dimensional arrays, where synthetic magnetic fields are absent. However, we show that synthetic electric fields can be generated dynamically, which, importantly, suppress photon transport in the array. The generation of these fields depends on the direction of photon propagation, leading to a novel mechanism for a photon diode, inducing nonlinear nonreciprocal transport via dynamical synthetic gauge fields.

Tunable Autler–Townes Splitting in Optical Fiber

Based on the theory of quantum optics, an analogue of the Autler–Townes splitting (ATS) system is realized by coupling a Fabry–Perot (FP) microcavity and a long-period fiber grating via the photonic tunneling effect. The stationary equations of the intracavity field amplitudes indicate that the splitting modes can be tuned by controlling the resonance frequency of the device. We demonstrated the feasibility of this theoretical result by adjusting the microcavity mirror offset Δ x in the experiments. Both the theoretical analysis and the experimental results show that the transmission spectrum is remarkably adjustable due to the tunable ATS effect. The splitting modes of the developed device allow for an extra degree of freedom to respond to the sensing signal, which is important for ultra-sensitive sensing. The refractive index is accurately adjustable, providing for potential phase matching applications. In addition, the device can serve as either an ATS system or an FP cavity.

Enhancement of squeezing effects in [formula omitted] -symmetric coupled microcavities

We analyze theoretically the squeezing effects in parity-time symmetry coupled cavities, one is passive with optical Kerr medium and another one is active. The Heisenberg equations of motion for different field modes are solved analytically. Temporal variations of the variance of the field quadratures are studied for different photon tunneling strength, Kerr nonlinear strength and gain-to-loss ratio via single mode, compound mode, principal and normal squeezing. We also have done a numerical solution using the master equation for both single and compound mode. Squeezing effects are observed for single mode passive cavity field mode and passive-active cavity compound mode. Degree of squeezing parameter is controlled by photon tunneling strength between the cavities. The degree of squeezing is enhanced for passive-active cavity system as compared to passive-passive cavity system. The results may be useful for the generation of a low-noise signal via squeezed states and also suitable for optical communications.

Modulation and splitting of three-body radiative heat flux via graphene/SiC core-shell nanoparticles

We theoretically demonstrate the modulation and splitting of radiative heat flux in a three-body system consisting of graphene/SiC core-shell (GSCS) nanoparticles on the basis of their highly tunable polarizabilities, which play a dominant role in the coupling of localized surface resonance. The excitation of multiple photon tunneling modes enables the radiative heat transfer to be controlled in different scenarios. Using the dependence of photon tunneling on the Fermi level and radius of the intermediate GSCS nanoparticle, such a many-body system not only holds the potential to be a near-field thermal modulator with a thermal modulation ratio greater than 40, but also allows the heat splitting effect with the ratio over 99 when the intermediate particle becomes the hot source. This work may facilitate dynamical thermal management in a many-body system, and can also benefit the plasmonics community in the near future.

Harvesting the Electromagnetic Energy Confined Close to a Hot Body

Abstract In the close vicinity of a hot body, at distances smaller than the thermal wavelength, a high electromagnetic energy density exists due to the presence of evanescent fields radiated by the partial charges in thermal motion around its surface. This energy density can surpass the energy density in vacuum by several orders of magnitude. By approaching a photovoltaic (PV) cell with a band gap in the infrared frequency range, this nonradiative energy can be transferred to it by photon tunnelling and surface mode coupling. Here we review the basic ideas and recent progress in near-field energy harvesting.

Strong Coupling of an Emitter with Absorbing Matter: A Regime for Enhancement of Light Emission

The authors show that, counterintuitively, adding extremely small, fully $a\phantom{\rule{0}{0ex}}b\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}b\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}g$ metal nanoparticles to a material can notably enhance its light emission. The cause of the unexpected, huge enhancement seen in surface-enhanced Raman spectroscopy (SERS) is the tunneling of photons out of the strongly absorbing metal surface. This quantum phenomenon imposes finite limits on the dissipation of emitted photons by proximal absorbing matter, and presents an interesting analogy to Hawking radiation near a black hole. The effect could be further exploited in light generation, optical sensing, and radiative heat transfer.