Cavity Detuning Research Articles

Understanding cavity resonances with intracavity dispersion properties

We experimentally study the strongly coupled three-level atom-cavity system at both cavity and coupling frequency detuning cases. Side peak splitting and anti-crossing-like phenomena are observed under different experimental conditions. Intracavity dispersion properties are used to explain qualitatively the complicated cavity resonance structures in the composite system of inhomogeneously broadened three-level atoms inside an optical ring cavity with relatively strong driving intensities.

Characteristics of exciton-polaritons in ZnO- based hybrid microcavities

Wide bandgap semiconductors are promising materials for the development of polariton-based optoelectronic devices operating at room temperature (RT). We report the characteristics of ZnO-based microcavities (MCs) in the strong coupling regime at RT with a vacuum Rabi splitting of 72 meV. The impact of scattering states of excitons on polariton dispersion is investigated. Only the lower polariton branches (LPBs) can be clearly observed in ZnO MCs since the large vacuum Rabi splitting pushes the upper polariton branches (UPBs) into the scattering absorption states in the ZnO bulk active region. In addition, we systematically investigate the polariton relaxation bottleneck in bulk ZnO-based MCs. Angle-resolved photoluminescence measurements are performed from 100 to 300 K for different cavity-exciton detunings. A clear polariton relaxation bottleneck is observed at low temperature and large negative cavity detuning conditions. The bottleneck is suppressed with increasing temperature and decreasing detuning, due to more efficient phonon-assisted relaxation and a longer radiative lifetime of the polaritons.

Many-body and nonequilibrium effects on relaxation oscillations in a quantum-dot microcavity laser

We investigate many-body and nonequilibrium effects on the dynamical behavior of a quantum-dot laser diode. Simulations, based on the Maxwell-semiconductor-Bloch equations, show strong dependence of the turn-on delay on initial cavity detuning, because of a dynamical shift in the quantum-dot distribution caused by band gap renormalization. Gain switch behavior is found to be insensitive to inhomogeneous broadening, because the balancing between many-body and free-carrier effects inhibits a cavity resonance walk-off. Both the relaxation oscillation damping and frequency are found to increase with decreasing inhomogeneous broadening widths. However, in contrast to bulk and quantum-well lasers, oscillation damping increases less than the frequency.

Evaluating and minimizing distributed cavity phase errors in atomic clocks

We perform 3D finite element calculations of the fields in microwave cavities and analyse the distributed cavity phase (DCP) errors of atomic clocks that they produce. The fields of cylindrical cavities are treated as an azimuthal Fourier series. Each of the lowest components produces clock errors with unique characteristics that must be assessed to establish a clock's accuracy. We describe the errors and how to evaluate them. We prove that sharp structures in the cavity do not produce large frequency errors, even at moderately high powers, provided the atomic density varies slowly. We model the amplitude and phase imbalances of the feeds. For larger couplings, these can lead to increased phase errors. We show that phase imbalances produce a novel DCP error that depends on the cavity detuning. We also design improved cavities by optimizing the geometry and tuning the mode spectrum so that there are negligible phase variations, allowing this source of systematic error to be dramatically reduced.

Strong and tunable nonlinear optomechanical coupling in a low-loss system

A major goal in optomechanics is to observe and control quantum behavior in a system consisting of a mechanical resonator coupled to an optical cavity. Work towards this goal has focused on increasing the strength of the coupling between the mechanical and optical degrees of freedom; however, the form of this coupling is crucial in determining which phenomena can be observed in such a system. Here we demonstrate that avoided crossings in the spectrum of an optical cavity containing a flexible dielectric membrane allow us to realize several different forms of the optomechanical coupling. These include cavity detunings that are (to lowest order) linear, quadratic, or quartic in the membrane's displacement, and a cavity finesse that is linear in (or independent of) the membrane's displacement. All these couplings are realized in a single device with extremely low optical loss and can be tuned over a wide range in situ; in particular, we find that the quadratic coupling can be increased three orders of magnitude beyond previous devices. As a result of these advances, the device presented here should be capable of demonstrating the quantization of the membrane's mechanical energy.

Chaotic control and synchronization in optical second-harmonic generation with parameter modulating by delay feedback

Chaotic behaviors can be controlled and converted into periodic behaviors by modulating the cavity detuning parameters using delay feedback signal from itself in optical second-harmonic generation (OSHG) system. Numerical simulations show that the period orbit differs on the account of the modulating coefficient and delay time. When the modulating coefficient and delay time are matching, many OSHG systems, whether or not they are in chaos initially, can reach chaotic synchronization if they are driven by a master system and their cavity detuning parameters are varied with the time-delay feedback chaotic signal. Different modulating coefficients with the corresponding minimum delay time are calculated.

Optomechanical correlations and signal self-amplification in interferometric measurements

Radiation pressure exerted by light in interferometric measurements is responsible for displacements of mirrors which appear as an additional back-action noise and limit the sensitivity of the measurement. We experimentally study these effects by monitoring in a very high-finesse optical cavity the displacements of a mirror with a sensitivity at the 10−20 m/ level. This very high sensitivity is a step towards the observation of fundamental quantum effects of radiation pressure such as the standard quantum limit in interferometric measurements. We report the observation of optomechanical correlations between two optical beams sent into the same moving mirror cavity. We also observed a self-amplification of a signal, which is a consequence of dynamical back-action of radiation pressure in a detuned cavity, and may improve the interferometric measurement sensitivity beyond the standard quantum limit.

Scheme for Generating a χ-Type Four-Atom Entangled State in Cavity QED

We propose a scheme for generating a χ-type four-atom entangled state in cavity QED. In the present scheme, the atoms interact simultaneously with a highly detuned cavity mode with the assistance of a strong classical field. The scheme is insensitive to the cavity decay and the thermal field, which is of importance from the experimental point of view.

Backaction Amplification and Quantum Limits in Optomechanical Measurements

Optical interferometry is by far the most sensitive displacement measurement technique available, with sensitivities at the 10(-20) m/square root(Hz) level in the large-scale gravitational-wave interferometers currently in operation. Second-generation interferometers will experience a tenfold improvement in sensitivity and be mainly limited by quantum noise, close to the standard quantum limit (SQL), once considered as the ultimate displacement sensitivity achievable by interferometry. In this Letter, we experimentally demonstrate one of the techniques envisioned to go beyond the SQL: amplification of a signal by radiation-pressure backaction in a detuned cavity.

Non-Gaussian states produced by close-to-threshold optical parametric oscillators: Role of classical and quantum fluctuations

Quantum states with non-Gaussian statistics generated by optical parametric oscillators (OPO) with fluctuating parameters are studied by means of the kurtosis excess of the external field quadratures. The field generated is viewed as the response of a nonlinear device to the fluctuations of pump laser amplitude and frequency, crystal temperature, and cavity detuning, in addition to quantum noise sources. The kurtosis excess has been evaluated perturbatively up to the third order in the strength of the crystal nonlinear coupling factor and the second order in the classical fluctuating parameters. Applied to the device described in Opt. Expr. 13, 948 (2005), the model has given values of the kurtosis excess in good agreement with the measured ones.

Experimental demonstration of a displacement noise free interferometry scheme for gravitational wave detectors showing displacement noise reduction at low frequencies

This paper reports an experimental demonstration of partial displacement noise free laser interferometry in the gravitational wave detection band. The used detuned Fabry-Perot cavity allows the isolation of the mimicked gravitational wave signal from the displacement noise on the cavities input mirror. By properly combining the reflected and transmitted signals from the cavity a reduction of the displacement noise was achieved. Our results represent the first experimental demonstration of this recently proposed displacement noise free laser interferometry scheme. Overall, we show that the rejection ratio of the displacement noise to the gravitational wave signal was improved in the frequency range of 10 Hz to 10 kHz with a typical factor of $\ensuremath{\sim}60$.

Modulational instability of two-component Bose–Einstein condensates in an optical lattice formed inside a cavity

We investigate the modulational instability (MI) of two-component Bose–Einstein condensates (BECs) in an optical lattice formed inside a cavity. By adjusting the pump–cavity detuning and the pump amplitude, the optical potentials are modified, and then the hopping parameters are altered. The relevant MI scenarios due to these changes are analysed and numerically confirmed. Our results show that the driven cavity can be utilized as a possible tool to control the MI of the BECs.

Resonant Excitation of a Quantum Dot Strongly Coupled to a Photonic Crystal Nanocavity

We describe the resonant excitation of a single quantum dot that is strongly coupled to a photonic crystal nanocavity. The cavity represents a spectral window for resonantly probing the optical transitions of the quantum dot. We observe narrow absorption lines attributed to the single and biexcition quantum dot transitions and measure antibunched population of the detuned cavity mode [g{(2)}(0)=0.19].

A SCHEME FOR REALIZATION OF TWO-QUBIT LOGIC GATES IN CAVITY QED

We propose a simple scheme for realizing two-qubit logic gate in cavity QED. In our scheme, the quantum controlled-not gate, phase gate and swap gate can be implemented without the ancillary level. The quantum controlled-not gate and phase gate can be realized easily by only one interaction between atoms and a highly detuned cavity mode with the assistance of a strong classical field. Thus, the scheme is insensitive to both the cavity decay and the thermal field.

Multimode squeezed light generation in a three-plane-mirror confocal cavity

In this paper, we propose a kind of degenerate optical parametric oscillator below threshold and use the thin crystal approximation to analyze the quantum noise reduction of the spectrum emitted from this cavity, and get the relation between the squeezing level and the pump field or the cavity detuning. We found that better squeezing level could be obtained only by properly choosing the phase of the local field, the amplitude of the pump field and the cavity detuning of the confocal cavity.

Entanglement sudden death of two atoms interacting with a cavity via the two-photon process in a strong-driving-assisted system

We examine the entanglement dynamics between two strongly driven atoms off-resonantly coupled with a single-mode cavity via the two-photon process with the help of negativity in two different types of initial states. The results show that entanglement sudden death may occur under both the above conditions and the sudden death effect can be monitored by modulating the atom–cavity detunings. Furthermore, we also find an atomic decoherence-free subspace so that the initial entanglement between two atoms remains invariable in application.

Superpositions and Entanglement of Mesoscopic High-order Squeezed Vacuum States in Cavity QED

We propose a scheme for generating the superpositions and the entanglement between the mesoscopic high-order squeezed vacuum states by considering the multi-photon interaction of N two-level atoms in a cavity with high quality factor, assisted by a strong driving field. In terms of specific choices of the cavity detuning, many multiparty entangled states between the atoms and the mesoscopic high-order squeezed vacuum states and among the high-order squeezed vacuum states of the cavity modes can be generated, including the macroscopic “Schrodinger cats” of the mesoscopic high-order squeezed vacuum states, the entanged states of the macroscopic “Schrodinger cats”, and so on. Our scheme is achievable within the current techniques in the cavity QED.

Oscillation dependence of two-wave mixing gain for unidirectional ring resonator in photorefractive materials

Dependence of the coupling strength of two-wave mixing gain in photorefractive materials for the single unidirectional ring resonator on oscillation conditions has been analyzed in the strong nonlinear regime. In this regime, difference between the frequency of the pump beam and oscillating beam is proportional to the cavity-length detuning, which can be explained in terms of the photorefractive phase-shift. This phase-shift results due to slightly non-degenerate two-wave mixing that compensates for cavity detuning and satisfies the round-trip phase condition for the steady-state oscillation. The presence of such a phase-shift allows the possibility of the nonreciprocal steady-state energy transfer between the pump and oscillating beams. If the gain due to the beam coupling is large enough to overcome the cavity losses then the signal beam is amplified in the presence of material absorption. Such amplification is responsible for the oscillations. For the single unidirectional ring resonator, the effects of cavity-length detuning, energy coupling coefficient, crystal thickness of the material, reflectivity of the cavity mirrors and material's absorption coefficient on the frequency and intensity of oscillations have also been studied in detail. It has been found that for the smaller value of absorption coefficient ( α) of the photorefractive crystal, the unidirectional ring resonator can oscillate at almost any cavity-length detuning (Δ Γ) whereas for the larger value of α oscillation occurs only when the cavity-length detuning is limited to small region (around Δ Γ=0). But reverse of the case is found for energy coupling coefficient ( γ 0).

Beam Energy Compensation in a Thermionic RF Gun by Cavity Detuning

A thermionic RF gun usually suffers from a rapid decrease of electron beam energy caused by a rapid increase of beam current due to the back-bombardment effect. The authors propose a new method named ldquocavity detuningrdquo to keep the electron beam energy constant. This method detunes the resonant frequency of the gun cavity to a frequency that is lower (by several hundred kilohertz) than the driving frequency. A proof-of-principle experiment was carried out using a 4.5 cell S-band RF gun. The beam energy was successfully kept constant during a macro-pulse duration of 7.5 mus using a cavity detuning of -590 kHz, even with a significant current increase from 240 to 660 mA. A numerical simulation was also conducted to evaluate the cathode temperature, the current density on the cathode surface, and the phase stability of the output beam. All results demonstrated that cavity detuning provides an easy and simple way to compensate for the energy decrease in thermionic RF guns.

Spatial mode dynamics in wide-aperture quantum-dot lasers

We present a systematic theoretical study of spatial mode dynamics in wide-aperture semiconductor quantum-dot lasers within the Maxwell-Bloch formalism. Our opto-electro-thermal model self-consistently captures the essential dynamical coupling between field, polarization, and carrier density in both thermal and nonthermal regimes, providing detailed description of the complex spatiotemporal modal intensity structure and spectra in these novel devices and broad area edge-emitting lasers in general. Using linear stability analysis and high resolution adaptive-grid finite element numerical simulation, we show that in the nonthermal regime, the presence of inhomogeneous broadening in quantum-dot active media leads to suppressed filamentation and enhanced spatial coherence compared to conventional quantum well devices with comparable phase-amplitude coupling (alpha parameter). Increasing the degree of inhomogeneous broadening in the active medium leads to further improvement in spatial coherence. In the thermal regime, there is further suppression of filamentation in the inhomogeneously broadened quantum-dot active medium; however, the spatial coherence aided by inhomogeneous broadening is partly lost due to the effect of temperature on cavity detuning. We propose that device designs based on optimized inhomogeneous broadening of quantum-dot gain medium could ultimately lead to diffraction-limited outputs in the quasi-cw regime which are still very difficult to achieve in conventional wide-aperture designs.