Leaky Cavity Research Articles

Development of a wideband compact leaky wave cavity antenna

As operating frequencies decrease, the aperture size of leaky wave antennas increases significantly – rendering them unsuitable for many sophisticated applications requiring small-sized communication antennas. In this article, a compact leaky wave cavity antenna with wide impedance bandwidth, using tapered cavity with substrate integrated waveguide is proposed. The antenna consists of a substrate and a rectangular metallic cavity fed by an L-shaped feed element. The metallic strips are placed along the sides of the substrate to fabricate a substrate integrated waveguide. The cavity is tapered to steer the beam in the desired direction. The tapering of the cavity causes the placement of the L-shaped feed element near the back wall of the cavity, producing input impedance mismatching. This problem of input impedance mismatching is resolved by the substrate integrated waveguide. It is demonstrated that the proposed antenna is compact (2λ0), and is wideband with voltage standing wave ratio (VSWR) bandwidth of 24% for 2:1 VSWR and a gain of 8.4 dBi. The experimental results for the designed antenna are in close agreement with the simulation results. The proposed antenna can be utilized in different wireless applications such as mobile communications, road vehicle communications and other applications.

Few emitters in a cavity: from cooperative emission to individualization

We study the temporal correlations of the field emitted by an electromagnetic resonator coupled to a mesoscopic number of two-level emitters that are incoherently pumped by a weak external drive. We solve the master equation of the system for increasing number of emitters and as a function of the cavity quality factor, and we identify three main regimes characterized by well-distinguished statistical properties of the emitted radiation. For small cavity decay rates, the emission events are uncorrelated and the number of photons in the emitted field becomes larger than one, resembling the build-up of a laser field inside the cavity. At intermediate decay rates (as compared with the emitter–cavity coupling) and for a few emitters, the statistics of the emitted radiation is bunched and strikingly dependent on the parity of the number of emitters. The latter property is related to the cooperativity of the emitters mediated by their coupling to the cavity mode, and its connection with steady-state subradiance is discussed. Finally, in the bad cavity regime the typical situation of emission from a collection of individual emitters is recovered. We also analyze how the cooperative behavior evolves as a function of pure dephasing, which allows us to recover the case of a classical source made of an ensemble of independent emitters, similar to what is obtained for a very leaky cavity. State-of-the-art techniques of Q-switch of resonant cavities, allied with the recent capability of tuning single emitters in and out of resonance, suggest this system to be a versatile source of different quantum states of light.

Entanglement dynamics of three interacting two-level atoms within a common structured environment

We derive exact time evolution of three two-level atoms coupled to a common environment. The environment is structured and is modeled by a leaky cavity with Lorentzian spectral density. The atoms are initially prepared in a generalized W state and later on experience pairwise dipole-dipole interactions and couplings to the cavity. We study tripartite disentangling and entangling dynamics as well as protecting bipartite entanglement with both atom-atom interactions and atom-cavity couplings taken simultaneously into account.

Development of Fixed Frequency Beam Steering Wide Band Leaky Wave Cavity Antenna

A complete design of substrate integrated leaky wave cavity antenna for fixed frequency beam steering is presented. The antenna consists of a small rectangular metallic tapered cavity fed by hook-shaped element and covered by the substrate. The steering of the beam in the desired direction is achieved by controlling the taper of the cavity. The beam is scanned at fixed frequency by changing position of the microstrip lines on the substrate. The substrate placed on the cavity resolves the problem of input impedance mismatch. The pertinent features of the antenna are compactness, broadband, and fixed-frequency beam steering capability.

Quantum dissonance induced by a thermal field and its dynamics in dissipative systems

In this paper, we study quantum correlation in separable systems termed quantum dissonance [K. Modi, T. Paterek, W. Son, V. Vedral, M. Williamson, Phys. Rev. Lett. 104, 080501 (2010)]. Firstly, we study the emergence of quantum dissonance between two atoms prepared in uncorrelated states and coupled to a single-mode thermal field. We show that even for situations when the thermal field cannot entangle the two atoms, it can nevertheless induce quantum dissonance between them. Then, we investigate the dynamics including the transfer in both Markovian and non-Markovian regimes of quantum dissonance due to dissipation modeled by two independent subsystems each of which consists of a leaky cavity containing a two-level atom and surrounded by a reservoir. The two subsystems possess some amount of atomic quantum dissonance at the beginning but do not interact with each other by any means later on. We show that the quantum dissonance can be transferred among the composite subsystems, but the way it evolves and is transferred may be very different compared to that of entanglement. Finally, we present an efficient method to refrain the unwanted transfer of quantum dissonance from interested systems to reservoirs.

Dynamics of cavity fields with dissipative and amplifying couplings through multiple quantum two-state systems

We consider simultaneous dissipative and amplifying coupling of cavity fields to multiple two-state systems. We derive a master equation for optical field in a leaky cavity coupled to a reservoir through multiple two-state systems. In our previous works we have limited our study to systems where the reservoir either solely absorbs energy (detector setup) or adds energy (amplifying setup) to the cavity through a single two-state system. In this work we allow both interactions simultaneously and derive a reduced dynamic model for the optical field. We also generalize our model to cover the coupling of the field to several two state systems and discuss its connection to macroscopic interaction, e.g., in semiconductors. Our model includes four physical parameters: the field two-state system coupling $\ensuremath{\gamma}$, the excitation and deexcitation couplings of the two-state system by the reservoir ${\ensuremath{\lambda}}_{A}$ and ${\ensuremath{\lambda}}_{D}$, respectively, and the mirror losses of the cavity $C$. We solve the steady-state fields at different regimes of these physical parameters. Furthermore, we show that, depending on the parameters, our model can describe the operation of a detector, a light emitting diode, or a laser.

Subwavelength metal-optic semiconductor nanopatch lasers

We report on near infrared semiconductor nanopatch lasers with subwavelength-scale physical dimensions (0.019 cubic wavelengths) and effective mode volumes (0.0017 cubic wavelengths). We observe lasing in the two most fundamental optical modes which resemble oscillating electrical and magnetic dipoles. The ultra-small laser volume is achieved with the presence of nanoscale metal patches which suppress electromagnetic radiation into free-space and convert a leaky cavity into a highly-confined subwavelength optical resonator. Such ultra-small lasers with metallodielectric cavities will enable broad applications in data storage, biological sensing, and on-chip optical communication.

Cavity-QED assisted attraction between a cavity mode and an exciton mode in a planar photonic-crystal cavity

The photoluminescence spectra from a quantum-dot exciton weakly-coupled to a planar photonic-crystal cavity is experimentally investigated by temperature tuning. Significant resonance shifts of the cavity mode are observed as the cavity mode spectrally approaches that of the exciton mode, showing the appearance of cavity-to-exciton attraction or mode pulling. Cavity-mode spectral shifts are also found theoretically using a master equation model that includes incoherent pump processes for the coupled exciton and cavity, pure dephasing, and allows for photon emission via radiation modes and the leaky cavity mode. Both experiments and theory show clear cavity mode spectral shifts in the photoluminescence spectra, when certain coupling parameters are met. However, discrepancies between the experimental data and theory, including more pronounced spectral shifts in the measurements, indicate that other unknown mode-pulling effects may also be occurring.

Efficient method for analyzing leaky cavities in two-dimensional photonic crystals

An efficient numerical method is developed for analyzing leaky cavities in two-dimensional photonic crystals, assuming that the cavities are located in the vicinity of a photonic crystal waveguide or close to a homogeneous medium. A leaky cavity mode is characterized by its complex eigenfrequency and by the outgoing wave behavior of the field in the nearby waveguide or homogeneous medium. In our method, the eigenfrequency of a leaky cavity mode is determined from a condition formulated on one single edge of a defect unit cell. Such a condition is obtained by using rigorous boundary conditions to terminate photonic crystal waveguides and homogeneous media, Dirichlet-to-Neumann maps of the unit cells to reduce the problem to the cell edges, and standard Gaussian elimination to further reduce the problem to one single edge. The reduction process can be performed efficiently. Accurate solutions can be obtained when a small number of discrete points are used on each edge of the unit cells.

Reversing the weak measurement of an arbitrary field with finite photon number

For an arbitrary field with finite photon number inside a leaky cavity, we show that the null-result measurement can be conditionally reversed, using either multiple atoms or a multilevel atom. Even with photons detected, a certain class of fields can still be probabilistically recovered. The state protection probability in such a system can be significantly high.

A solvable operator motion equation of an excited-atom coupled leaky cavity in single-photon generation

A model for an excited-atom coupled leaky cavity in single-photon generation is proposed based on universal modes. Solvable motion equations of the atomic operators are obtained under the single-photon condition by adopting the Lorentzian line type of the universal modes.

Cavity mode emission in weakly coupled quantum dot - cavity systems

We study the origin of bright leaky-cavity mode emission and its influence on photon statistics in weakly coupled quantum dot - semiconductor cavity systems, which consist of a planar photonic-crystal and several quantum dots. We present experimental measurements that show that when the system is excited above the barrier energy, then bright cavity mode emissions with nonzero detuning are dominated by radiative recombinations of deep-level defects in the barrier layers. Under this excitation condition, the second-order photon autocorrelation measurements reveal that the cavity mode emission at nonzero detuning exhibits classical photon-statistics, while the bare exciton emission shows a clear partial anti-bunching. As we enter a Purcell factor enhancement regime, signaling a clear cavity-exciton coupling, the relative weight of the background recombination contribution to the cavity emission decreases. Consequently, the anti-bunching behavior is more significant than the bare exciton case - indicating that the photon statistics becomes more non-classical. These measurements are qualitatively explained using a medium-dependent master equation model that accounts for several excitons and a leaky cavity mode.

Theory of quantum light emission from a strongly-coupled single quantum dot photonic-crystal cavity system

We present a rigorous medium-dependent theory for describing the quantum field emitted and detected from a single quantum dot exciton, strongly coupled to a planar photonic crystal nanocavity, from which the exact spectrum is derived. By using simple mode decomposition techniques, this exact spectrum is subsequently reduced to two separate user-friendly forms, in terms of the leaky cavity mode emission and the radiation mode emission. On application to study exciton-cavity coupling in the strong coupling regime, besides a pronounced modification of the usual vacuum Rabi spectral doublet, we predict several new effects associated with the leaky cavity mode emission, including the appearance of an off-resonance cavity mode and a loss-induced on-resonance spectral triplet. The cavity mode emission is shown to completely dominate the emitted spectrum, even for large cavity-exciton detunings, whereby the usual cavity-QED formulas developed for radiation-mode emission drastically fail. These predictions are in qualitative agreement with several "mystery observations" reported in recent experiments, and apply to a wide range of semiconductor cavities.

Singular Perturbation of Quantum Stochastic Differential Equations with Coupling Through an Oscillator Mode

We consider a physical system which is coupled indirectly to a Markovian resevoir through an oscillator mode. This is the case, for example, in the usual model of an atomic sample in a leaky optical cavity which is ubiquitous in quantum optics. In the strong coupling limit the oscillator can be eliminated entirely from the model, leaving an effective direct coupling between the system an the resevoir. Here we provide a mathematically rigorous treatment of this limit as a weak limit of the time evolution and observables on a suitably chosen exponential domain in Fock space. The resulting effective model may contain emission and absorption as well as scattering interactions.

The spatial focusing of a leaky time reversal chaotic cavity

Elastic waves propagating inside a solid chaotic cavity create a diffusive random field that contains both longitudinal and shear waves. In the current paper, we are interested in the field radiated in a fluid in contact with such cavity. The goal of this paper is to predict the spatial focusing properties that can be obtained in the fluid using a time-reversal piezoelectric transducer in contact with the cavity. We present a statistical approach that supposes a fully diffused wavefield inside the cavity with an equipartition of energy between longitudinal and shear waves. We show that the critical angles of transmission in the solid–fluid interface generate a cut-off of the spatial frequencies and then a degradation in the spatial focusing. This limitation can be overcome using a rough surface. A set of experiments conducted in the MHz range confirm the theoretical model.

Control of atomic decay rates via manipulation of reservoir mode frequencies

We analyse the problem of a two-level atom interacting with a time-dependent dissipative environment modelled by a bath of reservoir modes. In the model of this paper the principal features of the reservoir structure remain constant in time, but the microscopic structure does not. In the context of an atom in a leaky cavity this corresponds to a fixed cavity and a time-dependent external bath. In this situation we show that by chirping the reservoir modes sufficiently fast it is possible to inhibit, or dramatically enhance the decay of the atomic system, even though the gross reservoir structure is fixed. Thus, it is possible to extract energy from a cavity–atom system faster than the empty cavity rate. Similar, but less dramatic effects are possible for moderate chirps where partial trapping of atomic population is also possible.

Generation of Werner states via collective decay of coherently driven atoms

We show deterministic generation of Werner states as a steady state of the collective decay dynamics of a pair of neutral atoms coupled to a leaky cavity and strong coherent drive. We also show how the scheme can be extended to generate a $2N$-particle analogue of the bipartite Werner states.

Production of large-area surface-wave plasmas with an internally mounted planar cylindrical launcher

We studied the characteristics of two different types of planar cylindrical microwave launchers installed inside the vacuum chamber for the production of a large-area processing plasma. The microwave launcher consisted of a coaxial waveguide and a cylindrical planar cavity, inside which a large-area thin quartz plate was inserted. We tested two configurations of microwave launchers; one was a closed cylindrical cavity structure and the other was a leaky open cavity structure. With a 1.5 kW microwave source, we demonstrated the production of large-area, surface-wave plasma (SWP) using Ar gas. Using the microwave launcher with a leaky open cavity structure, a spatial uniformity of SWP within ±3.5% over 160 mm in radius was achieved at a pressure of 20 ∼ 30 Pa. Numerical analyses using the electromagnetic wave simulator, MAFIA, were also carried out to study the electric field distribution radiated from the microwave launcher and to explain the experimental results.

Coherent Single Photon Transport in a One-Dimensional Waveguide Coupled with Superconducting Quantum Bits

A recent theoretical analysis and experimental results show that interesting transport properties of a single microwave photon emerge when a quantum bit in a cavity is coupled to a one-dimensional waveguide. Here we adopt a real-space model Hamiltonian to give a unified approach which accounts for the experimental results, and make new predictions on the properties of single photon transport, such as the general Fano line shape, symmetric vacuum Rabi splitting for a leaky cavity at resonance, and a one-photon switching capability.

Cooling many particles to very low temperatures

In a recent paper [Beige, Knight, and Vitiello, quant-ph/0404160], we showed that a large number N of particles can be cooled very efficiently. The particles should be excited by red-detuned laser fields while coupling to the quantized field mode inside a resonant and leaky optical cavity. When the coupling constants are for all particles the same, a collective behavior can be generated and the cooling rate can be as large as << times the single-particle coupling constants. Here we study the algebraic structure of the dynamics and the origin of the collective cooling process in detail.