high-Q Cavity Research Articles

Damping of Vacuum Rabi Oscillations in a Two-Qubit Structure in a High-Q Cavity

The article studies the attenuation of vacuum Rabi oscillations for a system of two superconducting solid-state qubits placed in a high-Q microwave cavity. Two different cases are considered in which: 1) the first qubit is excited at the initial time and 2) the initial state comprises an entangled symmetric and antisymmetric pair of states. The dependence of the attenuation on various parameters, primarily on the coupling constant between qubits and the field and on the distance between qubits, is studied in detail. It is shown that, for some parameters, the relaxation time of the excited state of a qubit in such a system is significantly longer than that of a single qubit in the cavity.

Joints and shape imperfections in high-Q 3D SRF cavities for RF optomechanics

In this paper, we report on simulations of two types of high-Q 3-dimensional cavities: cylindrical TE011 and coaxial quarter-wave stub. We investigate the dependence of Q on the practical implementation tolerances of gaps between components, shape imperfections, and frequency tuning strategies. We find that cylindrical cavities can maintain high Q for designs that include frequency tuning and mechanical elements, provided extraordinary care is taken with shape and gap tolerance during construction and assembly. Coaxial stub cavities can be made with variable frequency while maintaining high Q, but they require more creativity to include a mechanical element. Finally, we report on a coaxial stub cavity, incorporating a conically shaped stub that confines the electric field near the stub’s tip, thus enhancing field–matter interactions near the tip.

Lithium niobate photonic-crystal electro-optic modulator

Modern advanced photonic integrated circuits require dense integration of high-speed electro-optic functional elements on a compact chip that consumes only moderate power. Energy efficiency, operation speed, and device dimension are thus crucial metrics underlying almost all current developments of photonic signal processing units. Recently, thin-film lithium niobate (LN) emerges as a promising platform for photonic integrated circuits. Here, we make an important step towards miniaturizing functional components on this platform, reporting high-speed LN electro-optic modulators, based upon photonic crystal nanobeam resonators. The devices exhibit a significant tuning efficiency up to 1.98 GHz V−1, a broad modulation bandwidth of 17.5 GHz, while with a tiny electro-optic modal volume of only 0.58 μm3. The modulators enable efficient electro-optic driving of high-Q photonic cavity modes in both adiabatic and non-adiabatic regimes, and allow us to achieve electro-optic switching at 11 Gb s−1 with a bit-switching energy as low as 22 fJ. The demonstration of energy efficient and high-speed electro-optic modulation at the wavelength scale paves a crucial foundation for realizing large-scale LN photonic integrated circuits that are of immense importance for broad applications in data communication, microwave photonics, and quantum photonics.

Optimization of Laser Stabilization via Self-Injection Locking to a Whispering-Gallery-Mode Microresonator

Self-injection locking is a dynamic phenomenon representing stabilization of the emission frequency of an oscillator with a passive cavity enabling frequency filtered coherent feedback to the oscillator cavity. For instance, self-injection locking of a semiconductor laser to a high-quality-factor (high-Q) whispering gallery mode (WGM) microresonator can result in multiple orders of magnitude reduction of the laser linewidth. The phenomenon was broadly studied in experiments, but its detailed theoretical model allowing improving the stabilization performance does not exist. In this paper we develop such a theory. We introduce five parameters identifying efficiency of the self-injection locking in an experiment, comprising back-scattering efficiency, phase delay between the laser and the high-Q cavities, frequency detuning between the laser and the high-Q cavities, the pump coupling efficiency, the optical path length between the laser and the microresonator. Our calculations show that the laser linewidth can be improved by two orders of magnitude compared with the case of not optimal self-injection locking. We present recommendations on the experimental realization of the optimal self-injection locking regime. The theoretical model provides deeper understanding of the self-injection locking and benefits multiple practical applications of self-injection locked oscillators.

Decay suppression of spontaneous emission of a single emitter in a high- Q cavity at exceptional points

The authors show that the peculiar spectral response of the electromagnetic field of a high-Q cavity operating at an exceptional point modifies the spontaneous emission of a single emitter in the strong coupling regime. The theory, based on macroscopic QED in dispersing and absorbing media, demonstrates much longer effective decay times in the exceptional point case in comparison to the single-mode case

Large-volume centimeter-wave cavities for axion searches

The scan rate of an axion haloscope is proportional to the square of the cavity volume. In this paper, a new class of thin-shell cavities are proposed to search for axionic dark matter. These cavities feature active volume much larger (>20×) than that of a conventional cylindrical haloscope, comparable quality factor Q, and a similar frequency tuning range. Full 3D numerical finite-element analyses have been used to show that the TM010 eigenmodes are singly polarized throughout the volume of the cavity and can facilitate axion-photon conversion in uniform magnetic field produced by a superconducting solenoid. To mitigate spurious mode crowding and volume losses due to localization, a pre-amplification binary summing network will be used for coupling. Because of the favorable frequency-scaling, the new cavities are most suitable for centimeter-wavelength (∼ 10–100 GHz), corresponding to the promising post-inflation axion production window. In this frequency range, the tight machining tolerances required for high-Q thin-shell cavities are achievable with standard machining techniques for near-infrared mirrors.

Atomic microwave-to-optical signal transduction via magnetic-field coupling in a resonant microwave cavity

Atomic vapors offer many opportunities for manipulating electromagnetic signals across a broad range of electromagnetic spectra. Here, a microwave signal with an audio frequency modulation encodes information in an optical signal by exploiting an atomic microwave-to-optical double resonance and magnetic-field coupling that is amplified by a resonant high-Q microwave cavity. Using this approach, audio signals are encoded as amplitude or frequency modulations in a GHz carrier, transmitted through a cable or over free space, demodulated through cavity-enhanced atom-microwave interactions, and, finally, optically detected to extract the original information. This atom-cavity signal transduction technique provides a powerful means by which to transfer information between microwave and optical fields, all using a relatively simple experimental setup without active electronics.

A tunable high-Q millimeter wave cavity for hybrid circuit and cavity QED experiments

The millimeter wave (mm-wave) frequency band provides exciting prospects for quantum science and devices since many high-fidelity quantum emitters, including Rydberg atoms, molecules, and silicon vacancies, exhibit resonances near 100 GHz. High-Q resonators at these frequencies would give access to strong interactions between emitters and single photons, leading to rich and unexplored quantum phenomena at temperatures above 1 K. We report a 3D mm-wave cavity with a measured single-photon internal quality factor of 3×107 and mode volume of 0.14×λ3 at 98.2 GHz, sufficient to reach strong coupling in a Rydberg cavity quantum electrodynamics system. An in situ piezotunability of 18 MHz facilitates coupling to specific atomic transitions. Our unique, seamless, and optically accessible resonator design is enabled by the realization that intersections of 3D waveguides support tightly confined bound states below the waveguide cutoff frequency. Harnessing the features of our cavity design, we realize a hybrid mm-wave and optical cavity, designed for interconversion and entanglement of mm-wave and optical photons using Rydberg atoms.

Fractional population transfer among three-level systems in a cavity by Stark-shift-chirped rapid adiabatic passage

We show that the technique of Stark-chirped rapid adiabatic passage (SCRAP), hitherto used for complete population transfer among three states in atoms and molecules, offers a simple and robust method for creating coherent superpositions of states in the interaction of a three-level atom with cavity and laser fields. We also use this technique to generate maximally atom–photon entangled states. SCRAP in three-level systems uses three laser pulses: a strong far-off-resonant pulse modifies the transition frequencies by inducing dynamic Stark shifts and thereby creating time-dependent level crossings among the three diabatic states, while near-resonant and moderately strong pump and Stokes pulses, appropriately offset in time, drive the population between the initial and final states via adiabatic passage. In our method, the atom falls through a high-Q cavity and encounters the cavity mode and the laser beams such that the populations are transferred fractionally between two ground states (f-SCRAP). The populations of the created superposition are controlled by the detunings of the pump and cavity fields from the transition frequencies. Unlike the technique of fractional stimulated Raman adiabatic passage (f-STIRAP), f-SCRAP can be applied to one-photon as well as multiphoton transitions and it is a powerful alternative tool for f-STIRAP in the media exhibiting inhomogeneous broadening. This technique is robust against moderate variations in peak Rabi frequencies, in distance between the center of the cavity and axis of the pump and Stark laser beams and in the velocity of the atom.

All-optical control of exciton flow in a colloidal quantum well complex

Excitonics, an alternative to romising for processing information since semiconductor electronics is rapidly approaching the end of Moore’s law. Currently, the development of excitonic devices, where exciton flow is controlled, is mainly focused on electric-field modulation or exciton polaritons in high-Q cavities. Here, we show an all-optical strategy to manipulate the exciton flow in a binary colloidal quantum well complex through mediation of the Förster resonance energy transfer (FRET) by stimulated emission. In the spontaneous emission regime, FRET naturally occurs between a donor and an acceptor. In contrast, upon stronger excitation, the ultrafast consumption of excitons by stimulated emission effectively engineers the excitonic flow from the donors to the acceptors. Specifically, the acceptors’ stimulated emission significantly accelerates the exciton flow, while the donors’ stimulated emission almost stops this process. On this basis, a FRET-coupled rate equation model is derived to understand the controllable exciton flow using the density of the excited donors and the unexcited acceptors. The results will provide an effective all-optical route for realizing excitonic devices under room temperature operation.

Multiple reflection assisted Laser Doppler Vibrometer setup for high resolution displacement measurement

An experimental design of high resolution non-intrusive displacement sensor working on the principle of basic LDV is being presented. Resolution enhancement has been achieved through phase multiplication using multiple reflections within a high-Q cavity created by a vibrating surface and a high reflection mirror placed parallel to each other. Displacement of 72 nm has been measured with an error range of ±14 nm through direct counting of characteristic peaks in “half cycle” of a interferogram. A linear relationship between displacement and number of reflections has been obtained which offers a straightforward route to measure displacements up to sub-nanometer scale and the resolution is essentially dictated by the reflectivity and physical dimension of moving source.

Temporal dynamics of zero-delay second order correlation function and spectral entanglement of two photons emitted from ladder-type atomic three-level systems.

We theoretically investigate temporal dynamics of the second order cross correlation function at zero delay time (G12(2)(t)) and spectral entanglement of two photons emitted from an atomic three-level cascade. In Heisenberg's picture, a closed set of quantum kinetic equations of motion for G12(2)(t) is derived within density matrix formalism with cluster expansion rule. G12(2)(t) shows qualitatively distinctive features depending on the spectral entanglement of two photons. Although incoherent photon pairs generated from spontaneous radiation of the excited electron are not entangled, their correlation and anti-correlation properties can be found in G12(2)(t) depending on the radiative decay rates. In the coherent excitation regime where the light emitter is located in a high Q-cavity, and its atomic polarizations are predominantly initialized, spectral entanglement between two coherent photons is established. We show that G12(2)(t) is well fitted by the entanglement criterion by Duan-Giedke-Cirac-Zoller and explain the close relationship between them by means of the optically forbidden transition in the three-level cascade.

High-Q factor photonic crystal cavities with cut air holes [Invited

Planar photonic crystal (PPC) cavities with high quality (Q) factors were currently designed by missing or moving air holes. Here, we propose that cutting air holes in PPC into semicircles could be considered as another strategy to realize and optimize cavities, presenting superiorities over cavities with missed or moved air holes in a higher Q factor and a smaller mode volume (Vmode). Examples are demonstrated: (1) in a PPC lattice, cutting two adjacent air holes promises a cavity mode with a Q exceeding 200,500 and an ultrasmall mode volume Vmode < 0.329(λ/2 n)3; (2) in a PPC waveguide, cutting two air holes on opposite sides of the waveguide supports a cavity mode with a Q exceeding 104,600 and a Vmode < 1.22(λ/2 n)3; (3) cutting the two air holes at the edges of an L3-type PPC cavity, the Q factor is optimized from 5500 to 124,700, with an almost constant Vmode. The concept of cutting air holes to introduce defects in PPC also promises the design of PPC also waveguides with an engineered transmission loss and dispersion.

Cooperative interactions between nano-antennas in a high-Q cavity for unidirectional light sources

We analyse the resonant mode structure and local density of states in high-Q hybrid plasmonic-photonic resonators composed of dielectric microdisks hybridized with pairs of plasmon antennas that are systematically swept in position through the cavity mode. On the one hand, this system is a classical realization of the cooperative resonant dipole–dipole interaction through a cavity mode, as is evident through predicted and measured resonance linewidths and shifts. At the same time, our work introduces the notion of ‘phased array’ antenna physics into plasmonic-photonic resonators. We predict that one may construct large local density of states (LDOS) enhancements exceeding those given by a single antenna, which are ‘chiral’ in the sense of correlating with the unidirectional injection of fluorescence into the cavity. We report an experiment probing the resonances of silicon nitride microdisks decorated with aluminium antenna dimers. Measurements directly confirm the predicted cooperative effects of the coupled dipole antennas as a function of the antenna spacing on the hybrid mode quality factors and resonance conditions.

ANALYSIS OF THE DIODE GENERATOR FREQUENCY STABILIZATION METHOD

This article presents the results of a theoretical analysis of the parameters of a synchronizing diode oscillator, the frequency of which is stabilized by a high-quality cylindrical resonator of passage type. An LPD generator with a frequency-stabilizing high-Q pass-through cavity resonator in frequency was used as a source of a synchronizing signal. Frequency stabilization in a generator on a caseless avalanche-span diode is carried out by a high-quality cylindrical pass-through cavity resonator. As a result of a theoretical analysis, the parameters of the open-frame diode are established on the basis of an equivalent circuit, the coupling value of a high-quality cylindrical resonator with the waveguide system of the generator and its design parameters are determined. It is proved that obtaining relative frequency instability of the generator frequency within the range of 10-6-10-7 degrees is possible by synchronizing the frequency of the power adder with a signal from an external highly stable generator, for which frequency-stability a cylindrical resonator of the through type on a wave of type TE011 with parameters is used: R = 32mm, h = 7.5mm.

Multiphoton process in cavity QED photons for implementing a three-qubit quantum gate operation

Based on cavity QED of free atoms, we theoretically investigate the implementation of a three-qubit quantum phase gate in which the three qubits are represented by the photons in modes of the cavity. A single four-level atom in double-V type passing through the high-Q cavity is used to implement the gate. We apply the theory of multiphoton resonance and use two-level effective Hamiltonians to predict the proper values for detunings, coupling constants, and interaction times. By the use of both the density matrix approach and wave function method, the influence of the decoherence processes is theoretically and numerically analyzed. Further, we address the effects of deviation in detunings and coupling coefficients and find that the gate operation is substantially insensitive to such variations. Finally, we show that the proposed scheme here can be extended for the implementation of multiqubit quantum phase gates.

Normal-mode splitting in coupled high-Q microwave cavities

Three-dimensional radio frequency cavities demonstrate excellent frequency selectivity and, as such, are known for their use in RF filters. These cavities have potential applications in quantum information science, precision displacement metrology, and quantum electrodynamics. Additionally, coupled cavities that form a spectral doublet allow for parametric gain when incorporating mechanical elements. Here, we investigate normal-mode splitting in a pair of quarter-wave stub microwave cavities at room temperature and cryogenic environments in order to identify coupling mechanics for normal and superconducting systems. Superconducting quarter-wave stub cavities with a resonant frequency of 10 GHz are made from reactor-grade niobium and exhibit Q ranging from 105 to 109. We varied cavity-to-cavity coupling to observe several normal-mode splittings of increasing peak separation until we observed a mode crossing. The minimum observed peak separation was 7 MHz for room temperature tests and 200 kHz for cryogenic tests. We also report on values of an intrinsic quality factor for the tuning cavity as a dielectric rod is translated along its symmetry axis. The realization of coupled superconducting radio frequency (SRF) cavities of this type is a necessary step toward implementation of parametric SRF-mechanical gain.

Creation of superposition of arbitrary states encoded in two high-Q cavities.

The principle of superposition is a key ingredient for quantum mechanics. A recent work [Phys. Rev. Lett.116, 110403 (2016)10.1103/PhysRevLett.116.110403] has shown that a quantum adder that deterministically generates a superposition of two unknown states is forbidden. Here we consider the implementation of the probabilistic quantum adder in the 3D cavity-transmon system. Our implementation is based on a three-level superconducting transmon qubit dispersively coupled to two cavities. Numerical simulations show that high-fidelity generation of the superposition of two coherent states is feasible with current circuit QED technology. Our method also works for other physical systems such as two optical cavities coupled to a three-level atom or two nitrogen-vacancy center ensembles interacted with one three-level superconducting flux qubit.

Flattop output extra-wide tuning range tunable laser design technique

The laser oscillator design principle, which provides extended tunability together with a flattop output in the wide spectral range, is proposed and demonstrated on the examples of the dye laser. It is realized by using an high-reflecting (HR) moving intracavity mirror (scraper) with the sharp edge partially overlapping the laser radiation in the high-Q cavity and extracting it out. The technique provides the output laser beam with M2 < 1.2 and can be applied to any type of lasers operating from the far-IR to the VUV spectral ranges. Besides, wide-band HR cavity mirrors are only used, and there are no special demands to the material of the mirror substrate.

Microwave Losses in a DC Magnetic Field in Superconducting Cavities for Axion Studies

The hypothetical axion particle is an excellent cold dark matter candidate. Models predict an axion mass of tens of μeV (GHz frequency range). In principle, it is possible to convert galactic axions into a monochromatic microwave signal or to detect them with an electron-spin flip. In both cases, to measure the resulting vanishing signal (P ≈ 10 -23 W), a high-Q cavity is needed, with Q ~ 10 6 . Superconducting RF technology can satisfy the requirement of operation in moderate-to-high dc magnetic fields. In this paper, we present an experimental study of the behavior of superconducting cavities in the vortex state. This study has been realized using 14 GHz Cu-NbTi and Cu-NbTiNx film cavities. A new cavity geometry is presented. We measured the magnetic field dependence of the Q-factor and Δf res /f res , where f res is the resonant frequency in the range B = 0-6 T at 4.2 K. Also, Q versus temperature at fixed B in zero-field-cooling and field-cooling setups has been considered. A comparison was made with Cu and Nb cylindrical bulk cavities. The data for Q(B) were analyzed in terms of the elastic and dissipative motion of flux lines, thus including flux flow and flux pinning. We discuss whether the field-induced quasiparticle contribution is relevant in our field and temperature range.