Cavity Quantum Electrodynamics Experiments Research Articles

Dynamic Fabry-Pérot cavity stabilization technique for atom-cavity experiments

We present a stabilization technique developed to lock and dynamically tune the resonant frequency of a moderate finesse Fabry-Pérot (FP) cavity used in precision atom-cavity quantum electrodynamics (QED) experiments. Most experimental setups with active stabilization either operate at one fixed resonant frequency or use transfer cavities to achieve the ability to tune the resonant frequency of the cavity. In this work, we present a simple and cost-effective solution to actively stabilize an optical cavity while achieving a dynamic tuning range of over 100 MHz with a precision under 1 MHz. Our unique scheme uses a reference laser locked to an electro-optic modulator (EOM) shifted saturation absorption spectroscopy (SAS) signal. The cavity is locked to the PDH error signal obtained from the dip in the reflected intensity of this reference laser. Our setup provides the feature to efficiently tune the resonant frequency of the cavity by only changing the EOM drive without unlocking and re-locking either the reference laser or the cavity. We present measurements of precision control of the resonant cavity frequency and vacuum Rabi splitting (VRS) to quantify the stability achieved and hence show that this technique is suitable for a variety of cavity QED experiments.

Vibration damping platform for cavity quantum-electrodynamics experiments.

We present a mechanical platform with enhanced vibration damping properties for cavity quantum-electrodynamics experiments. It is based on a composite design that combines a soft, vibration damping core with a rigid shell maintaining optical alignment. It passively damps the vibrations generated by piezoelectric actuators controlling the mirror positions. The mechanical resonances of the platform, which lead to a length change of the cavity, are efficiently suppressed up to 100kHz. Our platform is ultra-high vacuum compatible and can be used in most applications, in particular, where long cavities and optical access to the cavity center are required.

Fabrication, testing, and assembly of high-finesse optical fiber microcavity for molecule cavity QED experiment

The ultracold molecule is a promising candidate for versatile quantum tasks due to its long-range interaction and rich internal rovibrational states. With the help of the cavity quantum electrodynamics (QED) effects, an optical cavity can be employed to increase the efficiency of the formation of the photoassociated molecules and offers a non-demolition detection of the internal states of molecules. Here, we demonstrate the production of the high-finesse optical fiber microcavity for the Rb2 molecule cavity QED experiment, which includes the fabrication of fiber-based cavity mirrors, testing, and the assembly of ultra-high vacuum-compatible optical fiber microcavity. The optical fiber microcavity offers high cooperativity between cavity mode and ultracold molecule and paves the way for the study of molecule cavity QED experimental research.

Frustration-induced anomalous transport and strong photon decay in waveguide QED

We study the propagation of photons in a one-dimensional environment consisting of two non-interacting species of photons frustratingly coupled to a single spin-1/2. The ultrastrong frustrated coupling leads to an extreme mixing of the light and matter degrees of freedom, resulting in the disintegration of the spin and a breakdown of the "dressed-spin", or polaron, description. Using a combination of numerical and analytical methods, we show that the elastic response becomes increasingly weak at the effective spin frequency, showing instead an increasingly strong and broadband response at higher energies. We also show that the photons can decay into multiple photons of smaller energies. The total probability of these inelastic processes can be as large as the total elastic scattering rate, or half of the total scattering rate, which is as large as it can be. The frustrated spin induces strong anisotropic photon-photon interactions that are dominated by inter-species interactions. Our results are relevant to state-of-the-art circuit and cavity quantum electrodynamics experiments.

Universal pair polaritons in a strongly interacting Fermi gas.

Cavity quantum electrodynamics (QED) manipulates the coupling of light with matter, and allows several emitters to couple coherently with one light mode1. However, even in a many-body system, the light-matter coupling mechanism has so far been restricted to one-body processes. Leveraging cavity QED for the quantum simulation of complex, many-body systems has thus far relied on multi-photon processes, scaling down the light-matter interaction to the low energy and slow time scales of the many-body problem2-5. Here we report cavity QED experiments using molecular transitions in a strongly interacting Fermi gas, directly coupling cavity photons to pairs of atoms. The interplay of strong light-matter and strong interparticle interactions leads to well-resolved pair polaritons-hybrid excitations coherently mixing photons, atom pairs and molecules. The dependence of the pair-polariton spectrum on interatomic interactions is universal, independent of the transition used, demonstrating a direct mapping between pair correlations in the ground state and the optical spectrum. This represents a magnification of many-body effects by two orders of magnitude in energy. In the dispersive regime, it enables fast, minimally destructive measurements of pair correlations, and opens the way to their measurement at the quantum limit and their coherent manipulation using dynamical, quantized optical fields.

Cavity quantum electro-dynamics with solid-state emitters in aperiodic nano-photonic spiral devices

Integrated quantum devices are at the basis of the realization of scalable, high-performance quantum technology, including quantum computers and quantum communication schemes, where single photons are emitted, guided, manipulated, and detected on a chip. Engineered nano-devices enable the efficient confinement of light and, ultimately, the control of the spontaneous emission dynamics of single emitters, which is crucial for cavity quantum electrodynamics experiments and for the development of classical and quantum light sources. Here, we report on the demonstration of enhanced light-matter interaction and Purcell effects on a chip, based on bio-inspired aperiodic devices fabricated in gallium arsenide. Indium arsenide single quantum dots are used as internal light sources to image, by means of micro-photoluminescence spectroscopy, the optical modes supported by photonic membranes with Vogel-spiral geometry. These emitters are also used to probe the density of optical states, modified by the aperiodic devices, by means of time-resolved spectroscopy. Our results show cavity quantum electrodynamics effects providing strong modifications of the spontaneous emission decay of single optical transitions. In particular, thanks to the significant modification of the density of optical states demonstrated in Vogel-spiral photonic structures, we show control of the decay lifetime of single emitters with a dynamic range reaching 20, thus opening the path to the implementation of aperiodic geometries in active classical and quantum devices.

Dicke model.

The Dicke model is a fundamental model of quantum optics, which describes the interaction between light and matter. In the Dicke model, the light component is described as a single quantum mode, while the matter is described as a set of two-level systems. When the coupling between the light and matter crosses a critical value, the Dicke model shows a mean-field phase transition to a superradiant phase. This transition belongs to the Ising universality class and was realized experimentally in cavity quantum electrodynamics experiments. Although the superradiant transition bears some analogy with the lasing instability, these two transitions belong to different universality classes.

Coupling Hexagonal Boron Nitride Quantum Emitters to Photonic Crystal Cavities.

Quantum photonics technologies require a scalable approach for the integration of nonclassical light sources with photonic resonators to achieve strong light confinement and enhancement of quantum light emission. Point defects from hexagonal boron nitride (hBN) are among the front runners for single photon sources due to their ultra-bright emission; however, the coupling of hBN defects to photonic crystal cavities has so far remained elusive. Here we demonstrate on-chip integration of hBN quantum emitters with photonic crystal cavities from silicon nitride (Si3N4) and achieve an experimentally measured quality factor (Q-factor) of 3300 for hBN/Si3N4 hybrid cavities. We observed 6-fold photoluminescence enhancement of an hBN single photon emission at room temperature. Our work will be useful for further development of cavity quantum electrodynamic experiments and on-chip integration of two-dimensional (2D) materials.

Photothermal tuning and stabilization of a photonic crystal nanofiber cavity.

We report the photothermal properties of a photonic crystal nanofiber (PhCN) cavity, which is fabricated using a femtosecond laser ablation technique, under ultra-high vacuum conditions. The results show that by launching a non-resonant guided light, the stopband of the PhCN, along with the cavity modes, can be tuned at a rate of 250GHz (∼0.5 nm)/mW. Moreover, due to the thermal self-locking effect of a resonant light, a cavity mode with a finesse of 25 can be tuned over a few free spectral ranges using only a few μW of guided light. As an enabling step, we demonstrate a dual-mode locking scheme to thermally stabilize a cavity mode to the atomic line for single atom-based cavity quantum electrodynamics experiments.

Excitation of whispering gallery modes with a "point-and-play," fiber-based, optical nano-antenna.

We demonstrate the excitation and detection of whispering gallery modes in optical microresonators using a "point-and-play," fiber-based, optical nano-antenna. The coupling mechanism is based on cavity-enhanced Rayleigh scattering. Collected spectra exhibit Lorentzian dips, Fano shapes, or Lorentzian peaks, with a coupling efficiency around 13%. The spectra are characterized by the coupling gap, polarization, and fiber tip position. The coupling method is simple, low-cost and, most importantly, the Q-factor can be maintained at 108 over a wide coupling range, thereby making it suitable for metrology, sensing, or cavity quantum electrodynamics experiments.

Large thermal tuning of a polymer-embedded silicon nitride nanobeam cavity.

Tunable silicon nitride nanophotonic resonators are a critical building block for integrated photonic systems in the visible wavelength range. We experimentally demonstrate a thermally tunable polymer-embedded silicon nitride nanobeam cavity with a tuning efficiency of 44pm/°C and 0.13nm/mW in the near-visible wavelength range. The large tuning efficiency comes from the high thermo-optic coefficient of the SU-8 polymer and the "air-mode" cavity design, where a large portion of the cavity field is confined inside the polymer region. The demonstrated resonator will enable locally tunable cavity quantum electrodynamic experiments in the silicon nitride platform.

Applying electric and magnetic field bias in a 3D superconducting waveguide cavity with high quality factor

Three-dimensional microwave waveguide cavities are essential tools for many cavity quantum electrodynamics experiments. However, the need to control quantum emitters with dc magnetic fields inside the cavity often limits such experiments to normal-conducting cavities with relatively low quality factors of about 104. Similarly, controlling quantum emitters with dc electric fields in normal- and superconducting waveguide cavities has so far been difficult, because the insertion of dc electrodes has strongly limited the quality factor. Here, we present a method to apply dc electric fields within a superconducting waveguide cavity, which is based on the insertion of dc electrodes at the nodes of the microwave electric field. Moreover, we present a method to apply dc magnetic fields within the same cavity by trapping the magnetic flux in holes positioned in facing walls of the cavity. We demonstrate that the TE301 mode of such a superconducting, rectangular cavity made from niobium maintains a high internal quality factor of at the few photon level and a base temperature of 3 K. A cloud of Rydberg atoms coupled to the microwave electric field of the cavity is used to probe the applied dc electric and magnetic fields via the quadratic Stark effect and the Zeeman effect, respectively.

Photonic crystal cavities from hexagonal boron nitride

Development of scalable quantum photonic technologies requires on-chip integration of photonic components. Recently, hexagonal boron nitride (hBN) has emerged as a promising platform, following reports of hyperbolic phonon-polaritons and optically stable, ultra-bright quantum emitters. However, exploitation of hBN in scalable, on-chip nanophotonic circuits and cavity quantum electrodynamics (QED) experiments requires robust techniques for the fabrication of high-quality optical resonators. In this letter, we design and engineer suspended photonic crystal cavities from hBN and demonstrate quality (Q) factors in excess of 2000. Subsequently, we show deterministic, iterative tuning of individual cavities by direct-write EBIE without significant degradation of the Q-factor. The demonstration of tunable cavities made from hBN is an unprecedented advance in nanophotonics based on van der Waals materials. Our results and hBN processing methods open up promising avenues for solid-state systems with applications in integrated quantum photonics, polaritonics and cavity QED experiments.

High quality factor GaAs microcavity with buried bullseye defects

The development of high quality factor solid-state microcavities with low mode volumes has paved the way towards on-chip cavity quantum electrodynamics experiments and the development of high-performance nanophotonic devices. Here, we report on the implementation of a new kind of solid-state vertical microcavity, which allows for confinement of the electromagnetic field in the lateral direction without deep etching. The confinement originates from a local elongation of the cavity layer imprinted in a shallow etch and epitaxial overgrowth technique. We show that it is possible to improve the quality factor of such microcavities by a specific in-plane bullseye geometry consisting of a set of concentric rings with subwavelength dimensions. This design results in a smooth effective lateral photonic potential and therefore in a reduction of lateral scattering losses, which makes it highly appealing for experiments in the framework of exciton-polariton physics demanding tight spatial confinement.

Nanomechanical control of optical field and quality factor in photonic crystal structures

Actively controlling the properties of localized optical modes is crucial for cavity quantum electrodynamics experiments. While several methods to tune the optical frequency have been demonstrated, the possibility of controlling the shape of the modes has scarcely been investigated. Yet an active manipulation of the mode pattern would allow direct control of the mode volume and the quality factor and therefore of the radiative processes. In this work, we propose and demonstrate a nano-optoelectromechanical device in which a mechanical displacement affects the spatial pattern of the electromagnetic field. The device is based on a double-membrane photonic crystal waveguide which, upon bending, creates a spatial modulation of the effective refractive index, resulting in an effective potential well or antiwell for the optical modes. The change in the field pattern drastically affects the optical losses: large modulations of the quality factors and dissipative coupling rates larger than 1 GHz/nm are predicted by calculations and confirmed by experiments. This concept opens new avenues in solid-state cavity quantum electrodynamics in which the field, instead of the frequency, is coupled to the mechanical motion.

Superradiance with local phase-breaking effects

We study the superradiant evolution of a set of $N$ two-level systems spontaneously radiating under the effect of phase-breaking mechanisms. We investigate the dynamics generated by non-radiative losses and pure dephasing, and their interplay with spontaneous emission. Our results show that in the parameter region relevant to many solid-state cavity quantum electrodynamics experiments, even with a dephasing rate much faster than the radiative lifetime of a single two-level system, a sub-optimal collective superfluorescent burst is still observable. We also apply our theory to the dilute excitation regime, often used to describe optical excitations in solid-state systems. In this regime, excitations can be described in terms of bright and dark bosonic quasiparticles. We show how the effect of dephasing and losses in this regime translates into inter-mode scattering rates and quasiparticle lifetimes.

Cavity quantum electrodynamics with quantum interference in a three-level atomic system

Spontaneously generated coherence and enhanced dispersion in a V-type, three-level atomic system interacting with a single mode field can considerably reduce the radiative and cavity decay rates. This may eliminate the use of high finesse, miniaturized cavities in optical cavity quantum electrodynamics experiments under strong atom-field coupling conditions.

A 3D printed superconducting aluminium microwave cavity

3D printing of plastics, ceramics, and metals has existed for several decades and has revolutionized many areas of manufacturing and science. Printing of metals, in particular, has found a number of applications in fields as diverse as customized medical implants, jet engine bearings, and rapid prototyping in the automotive industry. Although many techniques are used for 3D printing metals, they commonly rely on computer controlled melting or sintering of a metal alloy powder using a laser or electron beam. The mechanical properties of parts produced in such a way have been well studied, but little attention has been paid to their electrical properties. Here we show that a microwave cavity (resonant frequencies 9.9 and 11.2 GHz) 3D printed using an Al-12Si alloy exhibits superconductivity when cooled below the critical temperature of aluminium (1.2 K), with a performance comparable with the common 6061 alloy of aluminium. Superconducting cavities find application in numerous areas of physics, from particle accelerators to cavity quantum electrodynamics experiments. The result is achieved even with a very large concentration of non-superconducting silicon in the alloy of 12.18%, compared with Al-6061, which has between 0.4% and 0.8%. Our results may pave the way for the possibility of 3D printing superconducting cavity configurations that are otherwise impossible to machine.

Coupling of Whispering-Gallery Modes in the Graphene Nanodisk Plasmonic Dimers

In this paper, we proposed plasmonic dimers consisted of two evanescent field coupled graphene monolayer nanodisks. The electromagnetic properties including the split modes with non-degenerate wavelengths, enhancement of the quality factors (Q factors) and mode areas, and the coupling between the fundamental and the first-order whispering-gallery modes are numerically predicted and analyzed systematically. Compared with the single graphene nanodisk, the Q factor of TM4,1 reaches 356 in a dimer with a radius of 5 nm of each nanodisk and an inter-disk gap of 0.4 nm, where the corresponding mode area is as small as 6.88 × 10‐ 5(λ 0)2. In addition, the enhanced performances of size-mismatched coupled graphene plasmonic dimers are investigated. This graphene monolayer plasmonic dimer could be one of the fundamental components in the future ultra-high density plasmonic circuit technique, on-chip plasmonic interconnect, and transformation plasmonics. It also could be used as the test-beds for added explorations of cavity quantum electrodynamic experiments.

High-finesse fiber Fabry–Perot cavities: stabilization and mode matching analysis

Fiber Fabry-Perot cavities, formed by micro-machined mirrors on the end-facets of optical fibers, are used in an increasing number of technical and scientific applications, where they typically require precise stabilization of their optical resonances. Here, we study two different approaches to construct fiber Fabry-Perot resonators and stabilize their length for experiments in cavity quantum electrodynamics with neutral atoms. A piezo-mechanically actuated cavity with feedback based on the Pound-Drever-Hall locking technique is compared to a novel rigid cavity design that makes use of the high passive stability of a monolithic cavity spacer and employs thermal self-locking and external temperature tuning. Furthermore, we present a general analysis of the mode matching problem in fiber Fabry-Perot cavities, which explains the asymmetry in their reflective line shapes and has important implications for the optimal alignment of the fiber resonators. Finally, we discuss the issue of fiber-generated background photons. We expect that our results contribute towards the integration of high-finesse fiber Fabry-Perot cavities into compact and robust quantum-enabled devices in the future.