Cavity QED Effects Research Articles

Geometric phase assisted observation of noninertial cavity-QED effects

The state of a quantum system acquires a phase factor, called the geometric phase, when taken around a closed trajectory in the parameter space, which depends only on the geometry of the parameter space. Because of its sensitive nature, the geometric phase is instrumental in capturing weak effects such as the acceleration-induced noninertial quantum field theoretic effects. In this paper, we study the geometric phase response of a circularly rotating detector inside an electromagnetic cavity. Using the cavity, the noninertial contribution to the geometric phase can be isolated from or strengthened relative to the inertial contribution. We show that the accumulative nature of the geometric phase may facilitate the experimental observation of the resulting, otherwise feeble, noninertial contribution to the modified field correlations inside the cavity. Specifically, we show that the atom acquires an experimentally detectable geometric phase at accelerations of the order of $\ensuremath{\sim}{10}^{7}\text{ }\text{ }\mathrm{m}/{\mathrm{s}}^{2}$ which is experimentally feasible.

Quantized quasinormal-mode description of nonlinear cavity-QED effects from coupled resonators with a Fano-like resonance

We employ a recently developed quantization scheme for quasinormal modes (QNMs) to study a nonperturbative open cavity-QED system consisting of a hybrid metal-dielectric resonator coupled to a quantum emitter. This hybrid cavity system allows one to explore the complex coupling between a low $Q$ (quality factor) resonance and a high $Q$ resonance, manifesting in a striking Fano resonance, an effect that is not captured by traditional quantization schemes using normal modes or a Jaynes-Cummings (JC) type model. The QNM quantization approach rigorously includes dissipative coupling between the QNMs, and is supplemented with generalized input-output relations for the output electric field operator for multiple modes in the system, and correlation functions outside the system. The role of the dissipation-induced mode coupling is explored in the strong coupling regime between the photons and emitter beyond the first rung of the JC dressed-state ladder. Important differences in the quantum master equation and input-output relations between the QNM quantum model and phenomenological dissipative JC models are found. In a second step, numerical results for the Fock distributions and system as well as output correlation functions obtained from the quantized QNM model for the hybrid structure are compared with results from a phenomenological approach. We demonstrate explicitly how the quantized QNM model manifests in multiphoton quantum correlations beyond what is predicted by the usual JC models.

Figure of merit for single-photon generation based on cavity quantum electrodynamics

We analytically derive the upper bound on the overall efficiency of single-photon generation based on cavity quantum electrodynamics (QED), where cavity internal loss is treated explicitly. The internal loss leads to a tradeoff relation between the internal generation efficiency and the escape efficiency, which results in a fundamental limit on the overall efficiency. The corresponding lower bound on the failure probability is expressed only with an "internal cooperativity," introduced here as the cooperativity parameter with respect to the cavity internal loss rate. The lower bound is obtained by optimizing the cavity external loss rate, which can be experimentally controlled by designing or tuning the transmissivity of the output coupler. The model used here is general enough to treat various cavity-QED effects, such as the Purcell effect, on-resonant or off-resonant cavity-enhanced Raman scattering, and vacuum-stimulated Raman adiabatic passage. A repumping process, where the atom is reused after its decay to the initial ground state, is also discussed.

Room temperature continuous-wave nanolaser diode utilized by ultrahigh-Q few-cell photonic crystal nanocavities

Few-cell point-defect photonic crystal (PhC) nanocavities (such as LX and H1 type cavities), have several unique characteristics including an ultra-small mode volume (Vm), a small device footprint advantageous for dense integration, and a large mode spacing advantageous for high spontaneous-emission coupling coefficient (β), which are promising for energy-efficient densely-integratable on-chip laser light sources enhanced by the cavity QED effect. To achieve this goal, a high quality factor (Q) is essential, but conventional few-cell point-defect cavities do not have a sufficiently high Q. Here we adopt a series of modified designs of LX cavities with a buried heterostructure (BH) multi-quantum-well (MQW) active region that can achieve a high Q while maintaining their original advantages and fabricate current-injection laser devices. We have successfully observed continuous-wave (CW) lasing in InP-based L1, L2, L3 and L5 PhC nanocavities at 23°C with a DC current injection lower than 10 μA and a bias voltage lower than 0.9 V. The active volume is ultra-small while maintaining a sufficiently high confinement factor, which is as low as ~10-15 cm3 for a single-cell (L1) nanocavity. This is the first room-temperature current-injection CW lasing from any types of few-cell point-defect PhC nanocavities (LX or H1 types). Our report marks an important step towards realizing a nanolaser diode with a high cavity-QED effect, which is promising for use with on-chip densely integrated laser sources in photonic networks-on-chip combined with CMOS processors.

Delayed formation of coherence in the emission dynamics of high-Q nanolasers

In the realization of ultrasmall semiconductor lasers, cavity-QED effects are used to enhance spontaneous emission and enable the lasing threshold to be crossed with gain contributions from only a few solid-state emitters. Operation in this regime fosters correlation effects that leave their fingerprint especially in the emission dynamics of nanolasers. Using time-resolved photon-correlation spectroscopy, we show that in a quantum-dot photonic-crystal nanolaser emitting in the telecom band, second-order coherence associated with lasing is established on a different timescale than the emission itself. By combining measurements with a microscopic semiconductor laser theory, we attribute the origin to carrier-photon correlations that give rise to non-Markovian effects in the emission dynamics that are not captured by laser rate-equation theories. Our results have direct implications with respect to the modulation response, repetition rate, noise characteristics, and coherence properties of nanolasers for device applications.

Realization of controllable photonic molecule based on three ultrahigh‐Q microtoroid cavities (Laser Photonics Rev. 11(2)/2017)

Photonic molecules have been shown to be a very useful platform for studying fundamental physics and practical applications. In recent years, double-cavity photonic molecules have been used in many important applications. Here, an approach to realize the fully-controlled triple-cavity photonic molecules, based on three ultrahigh-Q microtoroids with two different configurations, is experimentally demonstrated. By controlling the coupling strengths and resonant frequencies of the high-Q microcavities, interesting phenomena, such as super-mode evolution, dark state, double anti-crossing, as well as transition from double-EIT to double-EIA, are observed. This fully-controllable triple-cavity photonic molecule sets a unique stage for future investigations of photonic devices and cavity-QED effects. (Picture: Chao Yang et al., article number 1600178, in this issue)

Optical properties of organic-silicon photonic crystal nanoslot cavity light source

We theoretically study a dielectric photonic crystal nanoslot cavity immersed in an organic fluid containing near-infrared dyes by means of a full rate equation model including the complete cavity QED effects. Based on the modeling results, we numerically design an organic-silicon cavity light source in which its mode volume, quality factor, and far-field emission pattern are optimized for energy-efficient, high-speed applications. Dye quantum efficiency improved by two orders of magnitude and 3dB modulation bandwidth of a few hundred GHz can be obtained.

Modelling defect cavities formed in inverse three-dimensional rod-connected diamond photonic crystals

Defect cavities in 3D photonic crystal can trap and store light in the smallest volumes allowable in dielectric materials, enhancing non-linearities and cavity QED effects. Here, we study inverse rod-connected diamond (RCD) crystals containing point defect cavities using plane-wave expansion and finite-difference time domain methods. By optimizing the dimensions of the crystal, wide photonic bandgaps are obtained. Mid-bandgap resonances can then be engineered by introducing point defects in the crystal. We investigate a variety of single spherical defects at different locations in the unit cell focusing on high-refractive-index-contrast (3.3:1) inverse RCD structures; quality factors (Q-factors) and mode volumes of the resonant cavity modes are calculated. By choosing a symmetric arrangement, consisting of a single sphere defect located at the center of a tetrahedral arrangement, mode volumes < 0.06 cubic wavelengths are obtained, a record for high-index cavities.

Quantum dot nonlinearity through cavity-enhanced feedback with a charge memory

In an oxide apertured quantum dot (QD) micropillar cavity-QED system, we observe strong QD hysteresis effects and line-shape modifications even at very low intensities corresponding to $l{10}^{\ensuremath{-}3}$ intracavity photons. We attribute this to the excitation of charges by the intracavity field; they get trapped at the oxide aperture, where they screen the internal electric field and blueshift the QD transition. This in turn strongly modulates light absorption by cavity-QED effects, eventually leading to the observed hysteresis and line-shape modifications. The cavity also enables us to observe the QD dynamics in real time, and all experimental data agree well with a power-law charging model. The observed charging effect can serve as a tuning mechanism for quantum dots.

Cavity QED Effect in Thermal Radiation from a Microparticle(Research)

Cavity QED Effect in Thermal Radiation from a Microparticle(Research)

Distilling one, two and entangled pairs of photons from a quantum dot with cavity QED effects and spectral filtering

A quantum dot can be used as a source of one- and two-photon states and of polarization entangled photon pairs. The emission of such states is investigated here from the point of view of frequency-resolved two-photon correlations. These follow from a spectral filtering of the dot emission, which can be achieved either by using a cavity or by placing a number of interference filters before the detectors. A combination of these various options is used to iteratively refine the emission in a ‘distillation’ process and arrive at highly correlated states with a high purity. The so-called ‘leapfrog processes’, where the system undergoes a direct transition from the biexciton state to the ground state by direct emission of two photons, are shown to be central to the quantum features of such sources. Optimum configurations are singled out in a global theoretical picture that unifies the various regimes of operation.

Semiconductor cavity QED with squeezed light: Nonlinear regime

We present a study of semiconductor cavity QED effects with squeezed light. We investigate the effects of external squeezed light produced by a subthreshold optical parametric down conversion on the quantum features of the cavity as well as output radiation in the presence of exciton-exciton scattering. It turns out that the width of the spectrum of the cavity field strongly depends on the degree of squeezing. This effect is observed both in weak- and strong-coupling regimes. Moreover, we show that the external squeezed light has a profound effect on the amount of squeezing of the output field.

Cavity QED effects with single quantum dots

A single quantum dot embedded in a photonic crystal defect cavity allows for the investigation of cavity quantum electrodynamics effects in a solid-state environment. We present experiments demonstrating the quantum nature of this fundamental system in the strong coupling regime. Photon correlation measurements are used to characterize the fundamental properties of this unique system: through these experiments, we identify an unexpected, efficient sustaining mechanism that ensures strong cavity emission and is quantum correlated with the exciton resonance, even when all the quantum dot resonances are far detuned from the cavity mode. To cite this article: A. Badolato et al., C. R. Physique 9 (2008).

Neutrino pair emission from excited atoms

We explore a possibility of measuring the absolute magnitude and the nature (Majorana vs Dirac) of neutrino masses, by using a novel process of neutrino pair emission from metastable excited atoms. Except lepton number nonconserving processes, the neutrino pair ($\ensuremath{\nu}\overline{\ensuremath{\nu}}$) emission is the unique process to directly distinguish the Majorana neutrino from the Dirac neutrino, using the interference effect of identical fermions. The small energy difference between atomic levels makes it easier to measure small neutrino masses as indicated by neutrino oscillation experiments. The crucial point is how to enhance the rate of pair emission without enhancing the radiative decay. We discuss two particular cases; (1) laser irradiated pair emission from metastable atoms, and (2) microwave irradiated emission from circular Rydberg states. A new mechanism of the parametric amplification to enhance the neutrino pair emission is pointed out when Rydberg atoms are irradiated by microwave, while the radiative process may be inhibited by the cavity QED effect. A great variety of measurable neutrino parameters and a variety of experimental methods make this investigation attractive.

Cavity-QED effects on entangled photon generation from a quantum dot

We theoretically study polarization-entangled photon generation due to the resonant hyper-parametric scattering in a single quantum dot embedded in a microcavity. In contrast to the entangled photon generation from semiconductor until now, a biexciton does not play an important role because of the characteristic excitation states in the cavity QED. Although co-polarized non-entangled photon pairs are also emitted, the rate of entangled photon pairs becomes high in the strong-coupling limit due to the photon blockade effect.

Whispering gallery modes in silicon-nanocrystal-coated silica microspheres

Silica microspheres were deposited into two-dimensional periodic arrays and coated with a thin layer of silicon nanocrystals. The luminescence from the silicon nanocrystals coupled into the whispering gallery modes of the spheres, with Q factors that depended on a range of parameters including sphere size, position on the sphere, viewing direction, and thickness of the nanocrystal coating. Scattering from the film–sphere and/or the sphere–substrate contacts resulted in a lower Q for modes that intersect these regions. The highest Q factors obtained in this work were ∼1500. The results suggest that silica microspheres may be promising candidates for high- Q cavities that incorporate silicon nanocrystals for cavity QED or nonlinear optical effects.

Enhanced photostability of photoluminescent dye-doped solutions and polymers with the addition of dielectric-oxide micro-particles

Organic dye molecules in both solid polymethyl methacrylate and in solution have been found to display greatly enhanced photostability with the addition of micro-particles. Micro-particle doped poly(methyl methacrylate) samples and solutions were prepared doped with the laser dye pyrromethene 567 and rhodamine 6G. Study of the composite dye material as a gain medium in a laser provided a controlled and sensitive test of the photostability. The micro-particle doped samples used as the active laser medium demonstrated a doubling in service life to 0.4 million pulses compared with undoped samples before the output intensity was reduced to one-half. Further addition of a singlet oxygen quencher (DABCO) enhanced the photostability to 0.6 million pulses. Possible explanations discussed include cavity QED effects, surface photophysical and photochemical interactions and thermo-mechanical effects. These observations are relevant to photoluminescent devices and in general to the photostability of organic molecules.

Cavity-induced damping and level shifts in a wide aperture spherical resonator

We calculate explicitly the space dependence of the radiative relaxation rates and associated level shifts for a dipole placed in the vicinity of the center of a spherical cavity with a large numerical aperture and a relatively low finesse. In particular, we give simple and useful analytic formulas for these quantities, that can be used with arbitrary mirrors transmissions. The vacuum field in the vicinity of the center of the cavity is actually equivalent to the one obtained in a microcavity, and this scheme allows one to predict significant cavity QED effects.

On cavity modification of stimulated Raman scattering

We study theoretically stimulated Raman scattering (SRS) in a nonlinear dielectric microcavity and compare SRS thresholds for the cavity and the bulk material it is made of. We show that cavity SRS enhancement results solely from the intensity build up in the cavity and from the differences of the SRS dynamics in free and confined space. There is no significant modification of the Raman gain due to cavity QED effects. We show that the SRS threshold depends significantly on the nature of the dominating cavity decay as well as on the coupling technique with the cavity used for SRS measurements.

Single trapped ions interacting with low‐ and high‐finesse optical cavities

AbstractThe presence of mirrors modifies both the coherent coupling of an atom to a light mode and its spontaneous emission into the mode [1]. We study such cavity QED effects experimentally with single ions and optical cavities. We focus on two examples which are equally interesting as fundamental systems and for application in quantum information processing. (i) By retroreflecting the fluorescence of a single trapped Ba+ ion with a mirror 25 cm away, we observe inhibition and enhancement of the atom's spontaneous emission. When two ions are trapped, the distant mirror creates super‐ and subradiance. (ii) With a single trapped Ca+ ion we demonstrate coherent coupling of its narrow S1/2 – D5/2 “qubit” transition to a mode of a high‐finesse optical cavity. We also achieve deterministic coupling of the cavity standing wave to the ion's vibrational state by controlling the ion's position with nanometer‐precision and selectively exciting vibrational state‐changing transitions.