Phonon Manipulation Research Articles

Nonreciprocal Photon Transport in a Chiral Optomechanical System

AbstractChiral interaction between light and quantum emitters leads to emergence development of chiral quantum optics and stimulates a wide range of practical applications in quantum regime, such as single‐photon isolation and photon unidirectional emission. Cavity optomechanics studying the interaction between optical and mechanical resonators plays an important role in the field of quantum optics. However, how to achieve the chiral interaction between light and mechanical oscillators and explore the applications of the chiral optomechanical systems are still difficult encountered in cavity optomechanics. Here, a method is proposed to achieve chiral optomechanical interaction by exploiting directional squeezed light in a multimode optomechanical system. Based on the chiral interaction between photon and phonon, the nonreciprocal photon transport at a single‐photon level can be realized. An isolation ratio of and a negligible insertion loss for the photonic isolator are obtained. This method paves the way to realize chiral optomechanical interaction for conducting chiral optomechanics and opens up the prospect of exploring and utilizing chiral photon–phonon manipulation in the quantum regime.

Terahertz phonon engineering with van der Waals heterostructures.

Phonon engineering at gigahertz frequencies forms the foundation of microwave acoustic filters1, acousto-optic modulators2 and quantum transducers3,4. Terahertz phonon engineering could lead to acoustic filters and modulators at higher bandwidth and speed, as well as quantum circuits operating at higher temperatures. Despite their potential, methods for engineering terahertz phonons have been limited due to the challenges of achieving the required material control at subnanometre precision and efficient phonon coupling at terahertz frequencies. Here we demonstrate the efficient generation, detection and manipulation of terahertz phonons through precise integration of atomically thin layers in van der Waals heterostructures. We used few-layer graphene as an ultrabroadband phonon transducer that converts femtosecond near-infrared pulses to acoustic-phonon pulses with spectral content up to 3 THz. A monolayer WSe2 is used as a sensor. The high-fidelity readout was enabled by the exciton-phonon coupling and strong light-matter interactions. By combining these capabilities in a single heterostructure and detecting responses to incident mechanical waves, we performed terahertz phononic spectroscopy. Using this platform, we demonstrate high-Q terahertz phononic cavities and show that a WSe2 monolayer embedded in hexagonal boron nitride can efficiently block the transmission of terahertz phonons. By comparing our measurements to a nanomechanical model, we obtained the force constants at the heterointerfaces. Our results could enable terahertz phononic metamaterials for ultrabroadband acoustic filters and modulators and could open new routes for thermal engineering.

InAs–InP Superlattice Nanowires with Tunable Phonon Frequencies

AbstractThe control of heat conduction through the manipulation of phonons in solids is of fundamental interest and can be exploited in applications for thermoelectric conversion. In this context, the advent of novel semiconductor nanomaterials with high surface‐to‐volume ratio, e.g. nanowires, offer exciting perspectives, leading to significant leaps forwarding the efficiency of solid‐state thermoelectric converters after decades of stagnation. Beyond the high aspect ratio, the nanowire geometry offers unprecedented possibilities of materials combination and crystal phase engineering not achievable with 2D counterparts. In this work, the growth of long (up to 100 repetitions) wurtzite InAs/InP superlattice nanowires with homogeneous segment thicknesses is reported, with control down to the single digit of nanometer. By means of Raman scattering experiments, clear modifications of the phonon dispersion in superlattice nanowires are found, where both InAs‐like and InP‐like modes are present. The experimentally measured modes are well reproduced by density functional perturbation theory calculations. Remarkably, it is found that the phonon frequencies can be tuned by the superlattice periodicity, opening exciting perspectives for phonon engineering and thermoelectric applications.

Coherent Phonon Manipulation via Electron-Phonon Interaction for Facilitated Relaxation of Metastable Centers in ZnO.

Methods that allow versatile manipulation of metastable centers in semiconductors are highly important owing to their potential for quantum information processing and computations. In this study, we demonstrate that the electron-phonon interaction enables phonon participation to promote relaxation of metastable centers in ZnO, which is known for its persistent photoconductivity (PPC) effect. Experimentally, we show that continuous infrared (IR) radiation (1064 nm, ∼30 mW/cm2) promotes longitudinal optical phonons via the Fröhlich interaction and increases the PPC relaxation rate by ∼4 folds. More importantly, we discover that coherent phonons activated by an ultrashort pulse IR laser of the same power increased the relaxation rate by ∼1200-fold, as confirmed by ultrafast transient spectroscopy to be correlated to the excitation of coherent acoustic phonons via the inverse piezoelectric effect. We expect this study to provide valuable guidance for the development of novel quantum and photoactive devices.

Coherent phonon manipulation using single-mode circular electrostatic resonator

Coherent phonon manipulation is the mechanical analogy to photonic frequency combs while there is lack of a comprehensive evaluation system on the performance. In this paper, coherent phonon manipulation is demonstrated using a single-mode circular electrostatic resonator. Its manipulation mechanism for controlling phononic frequency comb (PFC) parameters is verified experimentally and also theoretically based on waveform derivation of the differential equations. The spacing of PFC system is regulated solely by the pump frequency and a spacing resolution of 0.1 Hz is achieved at room temperature. The amplitude modulation law is investigated and a complete PFC evolution process with a pump threshold of 2 mVpp is achieved. The sweeping experiment of electrostatic resonators is explained from the perspective of phonons. Additionally, feasibility of manipulating phonons using the electrostatic resonators is verified through nonlinearity modulation and damping loss experiments. This new methodology of phonon manipulation can be extended to other resonant energy carriers, with great potentials for frequency detection and phonon-quantum computing.

Mode Coupling in Electromechanical Systems: Recent Advances and Applications

AbstractMode interactions have recently become the focus of intense research in micro/nanoelectromechanical systems (M/NEMS) due to their ability to improve device performance and explore the frontiers of fundamental physics. Understanding and controlling coupling between vibrational modes are critical for the development of advanced M/NEMS devices. This review summarizes the recent advances in studies of coupling between multiple modes in M/NEMS resonators, focusing especially on experimental developments and practical applications. First, depending on spatial distribution of interacting modes, this review divides the coupled mechanism in three types: intermode, near‐neighbor, and long‐range coupling. Then, several fundamental physics approaches based on mechanical‐mode coupling, including linear and nonlinear coupling, modal localization, synchronization, and phonon manipulation are reviewed. This review also introduces sensing applications by using coupled mechanical modes. Finally, the state‐of‐the‐art open questions and challenges are reviewed.

Optomechanical Generation of Coherent GHz Vibrations in a Phononic Waveguide.

Nanophononics has the potential for information transfer, in an analogous manner to its photonic and electronic counterparts. The adoption of phononic systems has been limited, due to difficulties associated with the generation, manipulation, and detection of phonons, especially at GHz frequencies. Existing techniques often require piezoelectric materials with an external radiofrequency excitation that are not readily integrated into existing CMOS infrastructures, while nonpiezoelectric demonstrations have been inefficient. In this Letter, we explore the optomechanical generation of coherent phonons in a suspended 2D silicon phononic crystal cavity with a guided mode around 6.8GHz. By incorporating an air-slot into this cavity, we turn the phononic waveguide into an optomechanical platform that exploits localized photonic modes resulting from inherent fabrication imperfections for the transduction of mechanics. Such a platform exhibits very fine control of phonons using light, and is capable of coherent self-sustained phonon generation around 6.8GHz, operating at room temperature. The ability to generate high frequency coherent mechanical vibrations within such a simple 2D CMOS-compatible system could be a first step towards the development of sources in phononic circuitry and the coherent manipulation of other solid-state properties.

Coherent Phonon-Induced Gigahertz Optical Birefringence and Its Manipulation in SrTiO3.

Birefringence, which modulates the polarization of electromagnetic wave, has been commercially developed and widely used in modern photonics. Fostered by high-frequency signal processing and communications, feasible birefringence technologies operating in gigahertz (GHz) range are highly desired. Here, a coherent phonon-induced GHz optical birefringence and its manipulation in SrTiO3 (STO) crystals are demonsrated. With ultrafast laser pumping, the coherent acoustic phonons with low damping are created in the transducer/STO structures. A series of transducer layers are examined and the optimized one with relatively high photon-phonon conversion efficiency, i.e., semiconducting LaRhO3 film, is obtained. The most intriguing finding here is that, by virtue of high sensitivity to strain perturbation of STO, GHz optical birefringence can be induced by the coherent acoustic phonons and the birefringent amplitudes possess crystal orientation dependence. Optical manipulation of both coherent phonons and its induced GHz birefringence by double pump technique are also realized. These findings reveal an alternative mechanism of ultrafast optical birefringence control, and offer prospects for applications in high-frequency acoustic-optics devices.

Effective interface engineering for phonon manipulation in an Al/ErAs/GaAs system

Interface, an effective means of phonon manipulation, is an important concept to be clarified in the study of interfacial thermal transport. In this work, we have used semi-metallic ErAs in a variety of forms to modify the morphology of an Al/GaAs interface so is the interfacial thermal resistance. Using the time-domain thermoreflectance technique, we have measured the interfacial thermal conductance and demonstrated effective phonon manipulation in this Al/ErAs/GaAs system. As the ErAs thickness changes, we have observed clear transitions of phonon behaviors from ballistic to diffusive. The ErAs thickness for ballistic transport is determined to be up to 30 nm in this material system. The thickness dependent thermal conductivity of ErAs is also determined and the electron contribution is estimated to be about 50–60% in the total thermal conductivity.

Strong tunable phonon-phonon interactions induced by silicon-vacancy centers in one-dimensional chiral phononic waveguides

In solid quantum systems, strong phonon-phonon repulsive or attractive interactions are difficult to achieve. The highly adjustable phonon-phonon interactions created by silicon-vacancy (SiV) centers in a one-dimensional chiral phononic waveguide are investigated in this paper. Under specific situations, phonon-phonon attractive or repulsive interactions between the chiral transport phonons are created when they are scattered by two-level or three-level structural SiV centers. Furthermore, by modulating the laser Rabi frequencies and detunings, the resultant attractive or repulsive interactions between phonons can be adjusted over a large frequency range. Single-phonon creation and phonon manipulation in solid acoustic quantum information processing could benefit from the tunable phonon-phonon interactions.

Engineering nanoscale hypersonic phonon transport.

Controlling vibrations in solids is crucial to tailor their elastic properties and interaction with light. Thermal vibrations represent a source of noise and dephasing for many physical processes at the quantum level. One strategy to avoid these vibrations is to structure a solid such that it possesses a phononic stop band, that is, a frequency range over which there are no available elastic waves. Here we demonstrate the complete absence of thermal vibrations in a nanostructured silicon membrane at room temperature over a broad spectral window, with a 5.3-GHz-wide bandgap centred at 8.4 GHz. By constructing a line-defect waveguide, we directly measure gigahertz guided modes without any external excitation using Brillouin light scattering spectroscopy. Our experimental results show that the shamrock crystal geometry can be used as an efficient platform for phonon manipulation with possible applications in optomechanics and signal processing transduction.

Nonlinearity-mediated digitization and amplification in electromechanical phonon-cavity systems

Electromechanical phonon-cavity systems are man-made micro-structures, in which vibrational energy can be coherently transferred between different degrees of freedom. In such devices, the energy transfer direction and coupling strength can be parametrically controlled, offering great opportunities for both fundamental studies and practical applications such as phonon manipulation and sensing. However, to date the investigation of such systems has largely been limited to linear vibrations, while their responses in the nonlinear regime remain yet to be explored. Here, we demonstrate nonlinear operation of electromechanical phonon-cavity systems, and show that the resonant response differs drastically from that in the linear regime. We further demonstrate that by controlling the parametric pump, one can achieve nonlinearity-mediated digitization and amplification in the frequency domain, which can be exploited to build high-performance MEMS sensing devices based on phonon-cavity systems. Our findings offer intriguing opportunities for creating frequency-shift-based sensors and transducers.

Interband chiral phonon transfer in a magnetic field

Chiral phonons, which offer a possibility for information processing and storing, have been theoretically proposed and experimentally observed in two-dimensional hexagonal lattices. Here, we theoretically predict and study the interband chiral phonon transfer in a honeycomb lattice with an external magnetic field. The interband chiral phonon transfer induced by the magnetic field is accompanied by band inversions and the opening or closing of bandgaps. This can be attributed to the abrupt change of phonon band topology from the calculations of Berry curvature and Chern number. Moreover, the signs of phonon magnetic moments contributed by two optical or acoustic bands tend to be the same when a magnetic field is applied, which leads to the increasing phonon magnetic moment with the increasing strength of the magnetic field. The transfer of phonon pseudoangular momentum is also obtained due to the interband chiral phonon transfer in magnetic fields. Our findings enrich the exploration of chiral phonons and may offer theoretical guidance on the potential manipulation of chiral phonons by the external magnetic field.

Excitation and detection of acoustic phonons in nanoscale systems.

Phonons play a key role in the physical properties of materials, and have long been a topic of study in physics. While the effects of phonons had historically been considered to be a hindrance, modern research has shown that phonons can be exploited due to their ability to couple to other excitations and consequently affect the thermal, dielectric, and electronic properties of solid state systems, greatly motivating the engineering of phononic structures. Advances in nanofabrication have allowed for structuring and phonon confinement even down to the nanoscale, drastically changing material properties. Despite developments in fabricating such nanoscale devices, the proper manipulation and characterization of phonons continues to be challenging. However, a fundamental understanding of these processes could enable the realization of key applications in diverse fields such as topological phononics, information technologies, sensing, and quantum electrodynamics, especially when integrated with existing electronic and photonic devices. Here, we highlight seven of the available methods for the excitation and detection of acoustic phonons and vibrations in solid materials, as well as advantages, disadvantages, and additional considerations related to their application. We then provide perspectives towards open challenges in nanophononics and how the additional understanding granted by these techniques could serve to enable the next generation of phononic technological applications.

Optomechanical dynamics in the PT - and broken- PT -symmetric regimes

We theoretically study the dynamics of typical optomechanical systems, consisting of a passive optical mode and an active mechanical mode, in the $\mathcal{PT}$- and broken-$\mathcal{PT}$-symmetric regimes. By fully analytical treatments for the dynamics of the average displacement and particle numbers, we reveal the phase diagram under different conditions and the various regimes of both $\mathcal{PT}$-symmetry and stability of the system. We find that by appropriately tuning either mechanical gain or optomechanical coupling, both phase transitions of the $\mathcal{PT}$-symmetry and stability of the system can be flexibly controlled. As a result, the dynamical behaviors of the average displacement, photons, and phonons are radically changed in different regimes. Our study shows that $\mathcal{PT}$-symmetric optomechanical devices can serve as a powerful tool for the manipulation of mechanical motion, photons, and phonons.

Graphene-Based Nanoelectromechanical Periodic Array with Tunable Frequency.

Phononic crystals (PnCs) have attracted much attention due to their great potential for dissipation engineering and propagation manipulation of phonons. Notably, the excellent electrical and mechanical properties of graphene make it a promising material for nanoelectromechanical resonators. Transferring a graphene flake to a prepatterned periodic mechanical structure enables the realization of a PnC with on-chip scale. Here, we demonstrate a nanoelectromechanical periodic array by anchoring a graphene membrane to a 9 × 9 array of standing nanopillars. The device exhibits a quasi-continuous frequency spectrum with resonance modes distributed from ∼120 MHz to ∼980 MHz. Moreover, the resonant frequencies of these modes can be electrically tuned by varying the voltage applied to the gate electrode sitting underneath. Simulations suggest that the observed band-like spectrum provides an experimental evidence for PnC formation. Our architecture has large fabrication flexibility, offering a promising platform for investigations on PnCs with electrical accessibility and tunability.

Motional n-phonon bundle states of a trapped atom with clock transitions

Quantum manipulation of individual phonons could offer new resources for studying fundamental physics and creating an innovative platform in quantum information science. Here, we propose to generate quantum states of strongly correlated phonon bundles associated with the motion of a trapped atom. Our scheme operates in the atom–phonon resonance regime where the energy spectrum exhibits strong anharmonicity such that energy eigenstates with different phonon numbers can be well-resolved in the parameter space. Compared to earlier schemes operating in the far dispersive regime, the bundle states generated here contain a large steady-state phonon number. Therefore, the proposed system can be used as a high-quality multiphonon source. Our results open up the possibility of using long-lived motional phonons as quantum resources, which could provide a broad physics community for applications in quantum metrology.

Direct Imaging of Resonant Phonon-Magnon Coupling

Direct detection of phonons is important for the investigation of information interconversion between the resonantly coupled magnons and phonons. Here we report resonant coupling of magnons and phonons, which can be directly visualized by using micro focused Brillouin light scattering in Ni/LiNbO3 hybrid heterostructures. The patterns of surface acoustic wave phonons, originating from the interference between the original wave {\psi}0(A_0,k) and reflected wave {\psi}1(A_1,-k), can be modulated by magnetic field due to the magnon-phonon coupling. By analyzing the information of phonons obtained from Brillouin spectroscopy, the properties of the magnon system (Ni film), e.g., ferromagnetic resonance field and resonance linewidth can be determined. The results provide spatially resolved information about phonon manipulation and detection in a coupled magnon-phonon system.

Controlling Light, Heat, and Vibrations in Plasmonics and Phononics

AbstractPlasmonic nanostructures have attracted considerable attention for their ability to couple with light and provide strong electromagnetic energy confinement at subwavelength dimensions. The absorbed portion of the captured electromagnetic energy can lead to significant heating of both the nanostructure and its surroundings, resulting in a rich set of nanoscale thermal processes that defines the subfield of thermoplasmonics with applications ranging from nanochemistry and nanobiology to optoelectronics. Recently, phononic nanostructures have started to attract attention as a platform for manipulation of phonons, enabling control over heat propagation and/or mechanical vibrations. The complex interaction phenomena between photons, electrons, and phonons require appropriate modelling strategies to design nanodevices that simultaneously explore and exploit the optical, thermal, and mechanical degrees of freedom. Examples of such devices are micro‐ and nanoscale opto‐thermo‐mechanical systems for sensing, imaging, energy conversion, and harvesting applications. Here, an overview of the fundamental theory and concepts crucial to the modelling of plasmo‐phonon devices is provided. Particular attention is given to micro‐ and nanoscale modelling frameworks, highlighting their validity ranges and the experimental works that contributed to their validation and led to compelling applications. Finally, an open‐ended outlook focused on emerging applications at the intersection between plasmonics and phononics is presented.

Phonon manipulation with valley-Hall junctions

In this work, we investigate experimentally the existence of in-plane valley Hall edge states in hexagonal lattices with relaxed space inversion symmetry and we exploit them to realize non-trivial backscattering-free interfaces. We propose special tessellations of lattice domains in which multiple non-trivial domain walls coalesce to form junctions, and we study how guided waves behave when they impinge on such junctions. We show that, through a proper selection of the interface types and orientations, it is possible to achieve junctions with different and exotic wave manipulation capabilities. Specifically, we discuss two applications. The first is a direction-selective splitter, which endows its host lattice with asymmetric wave transport characteristics. The second is a signal delayer that is realized by embedding in the lattice a non-trivial waveguide loop, along which the energy can be temporarily trapped and periodically released. These junctions can serve as building blocks for a new structural logic paradigm enabled by topological mechanics.