Phonon Source Research Articles

Dual-driving parametric locking of GHz phonon sources to sub-hertz linewidth in optomechanical systems

In the exploration of collective dynamics and advanced information processing, synchronization and frequency locking of mechanical oscillations are cornerstone phenomena. Traditional synchronization techniques, which typically involve a single mechanical mode, are limited by their inability to distinguish between intrinsic mechanical oscillations and external signals after locking. Addressing this challenge, we introduce a parametric approach that enables simultaneous frequency locking of two gigahertz mechanical modes within an optomechanical crystal cavity. By modulating the pump light to match the sum and difference frequencies of the mechanical modes, we significantly narrow their linewidths from tens of kilohertz to below 1 Hz at room temperature and ambient pressure. This dual-locking scheme also drastically reduces the phase noise of the mechanical modes by 76.6 dBc/Hz at a 100 Hz offset, while allowing flexible tuning of the locked modes’ frequencies via input signal adjustments. Our method not only facilitates direct observation of mechanical oscillations under the locking regime but also enriches the understanding of coherent phonons in multimode regimes, opening new avenues for optomechanical applications in signal processing.

Vibrational dynamics dictate heat transport in metal-organic frameworks with gas adsorbates

Understanding the thermal conductivity (κ) of metal-organic frameworks (MOFs) with adsorbates is critical for tailoring their heat dissipation in practical applications. However, a detailed description of how adsorbates influence the heat transport of MOFs is still lacking. In this work, we employ molecular dynamics simulations combined with lattice dynamics calculations to investigate the effect of gas adsorbates on κ of representative crystalline and glassy zeolitic imidazolate frameworks (ZIFs). We identify that the diffusive adsorbate motions in the crystalline ZIFs with large pores can enhance lattice anharmonicity, serving as a source of phonon scattering and significantly suppressing κ. Conversely, the adsorbates with restricted dynamics in limited space (i.e., in the dense ZIF crystals or glasses) behave more like a heat transfer medium and facilitate heat transport. Besides pore size, gas dynamics are also proved to vary upon gas-lattice interaction strength, and dictate if gas adsorbates serve as a heat conduction suppressor or promoter. We anticipate that this governing role of gas dynamics is applicable to a diverse range of MOF-adsorbate systems. As such, our work offers guidance for the practical thermal management of MOF porous materials to ensure their desired storage or separation performance.

Thermoelectric performance enhancement of Pb-doped α -MgAgSb near room temperature

α-MgAgSb is taken as the p-type leg material for recently focused Mg-based thermoelectric devices because of the high thermoelectric performance near room temperature. However, the thermoelectric performance of α-MgAgSb is inhibited by the existence of the Ag-rich second phase. The ordinary methods like carrier concentration optimization and minimizing lattice thermal conductivity were nearly invalid because of the extremely low doping level for heteroatoms and intrinsically low lattice thermal conductivity. The crystal structure of α-MgAgSb can be viewed as Ag atom filled in half distorted hexahedron in the distorted rock salt skeleton formed by the Mg–Sb sublattice. In this work, by replacing the smaller Mg in the sublattice with Pb, the volume of the distorted hexahedron is effectively expanded to accommodate Ag atoms and then lead to the re-dissolution of Ag-rich second phase in the matrix. In addition, as Ag is the main source of low-frequency phonons, the enhanced lattice anharmonicity by Pb doping leads to stronger scattering of phonons in the distorted hexahedron and results in 20% reduction of lattice thermal conductivity in the temperature range of 300–500 K. Finally, the figure of merit zT is enhanced by ∼40% in the whole temperature range, demonstrating that lattice management is a promising method for the optimization of α-MgAgSb materials.

High frequency amplification of acoustic phonons in fluorine-doped single-walled carbon nanotubes

Herein, we report on a strong high-frequency induced amplification of coherent acoustic phonons in a non-degenerate fluorine-doped single-walled carbon nanotubes (FSWCNTs) by utilising a tractable analytical approach in the hypersound regime, ql≫1 (where q is the acoustic wavenumber and l is the carrier mean free path). The acoustoelectric gain obtained is highly nonlinear and is due to stimulated Cerenkov phonon emission by electrically driven carriers undergoing intraminiband transport and capable of performing Bloch oscillations. The transport process causes the carriers to undergo population inversion leading to intraminiband phonon-assisted processes. The generation rate (phonon emission) is expansive and surpasses phonon losses. The threshold field (Eo), at which attenuation switches over to amplification (gain) depends on the FSWCNT parameters (Δs&Δz), carrier drift velocity (vd=μEo), sound velocity (vs) and the ratio ζs,z. This result has potential for intense sources of reasonable acoustic phonons in the sub-THz regime and is vital for the generation of SASER (sound amplification by stimulated emission of acoustic radiation). The amplified phonons also have THz frequencies with wavelengths in the nanometer range, and depends on high spatial parameters which has potential applications for phonon filters and spectrometers.

Nonreciprocal Phonon Laser in an Asymmetric Cavity with an Atomic Ensemble

Phonon lasers, as a novel kind of lasers for generating coherent sound oscillation, has attracted extensive attention. Here, we theoretically propose a nonreciprocal phonon laser in a hybrid optomechanical system, which is composed of an asymmetric Fabry–Pérot cavity, an ensemble of N identical two-level atoms, and a mechanical oscillator. The effective driving amplitude related to driving direction leads to an obvious difference in mechanical gain and threshold power, bringing about a nonreciprocal phonon laser. In addition, the dependence of the phonon laser on the atomic parameters is also discussed, including the decay rate of the atoms and the coupling strength between the atoms and the cavity field, which provides an additional degree of freedom to control the phonon laser action. Our work provides a path to realizing a phonon laser in an atoms-cavity optomechanical system and may aid the manufacture of directional coherent phonon sources.

Exceptional-point-engineered phonon laser in a cavity magnomechanical system

We propose a scheme to engineer phonon laser in a non-Hermitian cavity magnomechanical (CMM) system with dissipative magnon-photon coupling. The exceptional point (EP) (the analog of the -symmetric regime), emerging in the system and changing the properties of photons, magnons, and phonons, can be observed with a tunable dissipative magnon-photon coupling caused by the cavity Lenz’s law. At the EP, we find that a strong nonlinear relation appears between the mechanical amplification factor and the detuning parameter, which results in a dramatic enhancement of magnetostrictive force and mechanical gain, and leading to the highly efficient phonon laser and the ultralow threshold power. Furthermore, EP induced by dissipative coupling is flexible and tunable compared to the -symmetric regime, and the ultralow threshold power phonon laser is immune to the loss rates of the photon and magnon modes. Our scheme provides a theoretical basis for phonon laser in non-Hermitian systems and presents potential applications ranging from preparing coherent phonon sources to operating on-chip functional acoustic devices.

Optical noise-resistant nonreciprocal phonon blockade in a spinning optomechanical resonator.

A scheme of nonreciprocal conventional phonon blockade (PB) is proposed in a spinning optomechanical resonator coupled with a two-level atom. The coherent coupling between the atom and breathing mode is mediated by the optical mode with a large detuning. Due to the Fizeau shift caused by the spinning resonator, the PB can be implemented in a nonreciprocal way. Specifically, when the spinning resonator is driven from one direction, the single-phonon (1PB) and two-phonon blockade (2PB) can be achieved by adjusting both the amplitude and frequency of the mechanical drive field, while phonon-induced tunneling (PIT) occurs when the spinning resonator is driven from the opposite direction. The PB effects are insensitive to cavity decay because of the adiabatic elimination of the optical mode, thus making the scheme more robust to the optical noise and still feasible even in a low-Q cavity. Our scheme provides a flexible method for engineering a unidirectional phonon source with external control, which is expected to be used as a chiral quantum device in quantum computing networks.

Realization of Multifunctional Bosonic Magnon Transistor via Thermal Phonon Gating

AbstractMagnons have demonstrated enormous potential for next‐generation information technology, namely the ability to build quasiparticle low‐power integrated circuits without the moving of electrons. An experimental bosonic magnon transistor with multifunction, low‐loss, and full‐wavelength control of propagating spin waves (magnon current) is developed in this work. Using a monolayer of graphene as the high‐efficiency thermal phonon source and a low‐loss electrically insulating ferrimagnetic single‐crystalline yttrium iron garnet film as the propagating spin‐wave channel, the presented transistor has three functioning regions of spin‐wave modulation at full wavelength: prominent amplification, complete cut‐off, and linear phase shift. The magnon‐phonon‐mediated nonequilibrium state created by the temperature gradient in this transistor works in two ways: when the thermal phonon flow is small, the positive thermal spin‐torque induced by the longitudinal spin‐Seebeck effect amplifies spin waves; when the thermal phonon flow is large, the magnon–magnon interaction due to nonequilibrium thermal magnon injection greatly contributes to spin‐wave cut‐off. Furthermore, linear adjustment of the spin‐wave phase by creating a thermal phonon bath is demonstrated. These findings reveal that the numerous magnon–phonon coupling mechanisms in magnetic insulators offer a promising platform for the implementation of reconfigurable magnonic transistors.

Sensitive phonon detection using a single Cooper-pair transistor

We demonstrate that the supercurrent branch of a single Cooper-pair transistor (SCPT) can be used for sensitive phonon detection. We built a theoretical model of phonon detection based on quasiparticle poisoning and demonstrated its operation with an SCPT and a superconducting quantum interference device as a phonon source both composed of mesoscopic Al/AlO x /Al junctions. The sensitivity of the SCPT detector turned out to be approximately 103 times as high as that of the traditional superconducting-tunnel-junction detector.

Deconvolution of Phonon Scattering by Ferroelectric Domain Walls and Point Defects in a PbTiO3 Thin Film Deposited in a Composition-Spread Geometry.

We present a detailed analysis of the temperature dependence of the thermal conductivity of a ferroelectric PbTiO3 thin film deposited in a composition-spread geometry enabling a continuous range of compositions from ∼25% titanium deficient to ∼20% titanium rich to be studied. By fitting the experimental results to the Debye model we deconvolute and quantify the two main phonon-scattering sources in the system: ferroelectric domain walls (DWs) and point defects. Our results prove that ferroelectric DWs are the main agent limiting the thermal conductivity in this system, not only in the stoichiometric region of the thin film ([Pb]/[Ti] ≈ 1) but also when the concentration of the cation point defects is significant (up to ∼15%). Hence, DWs in ferroelectric materials are a source of phonon scattering at least as effective as point defects. Our results demonstrate the viability and effectiveness of using reconfigurable DWs to control the thermal conductivity in solid-state devices.

Phononic Thermal Transport along Graphene Grain Boundaries: A Hidden Vulnerability.

While graphene grain boundaries (GBs) are well characterized experimentally, their influence on transport properties is less understood. As revealed here, phononic thermal transport is vulnerable to GBs even when they are ultra‐narrow and aligned along the temperature gradient direction. Non‐equilibrium molecular dynamics simulations uncover large reductions in the phononic thermal conductivity (κ p) along linear GBs comprising periodically repeating pentagon‐heptagon dislocations. Green's function calculations and spectral energy density analysis indicate that the origin of the κ p reduction is hidden in the periodic GB strain field, which behaves as a reflective diffraction grating with either diffuse or specular phonon reflections, and represents a source of anharmonic phonon–phonon scattering. The non‐monotonic dependence with dislocation density of κ p uncovered here is unaccounted for by the classical Klemens theory. It can help identify GB structures that can best preserve the integrity of the phononic transport.

Theoretical study on composition‐dependent properties of ZnO·nAl2O3 spinels. Part II: Mechanical and thermophysical

AbstractKnowledge on the mechanical and thermophysical properties of ZnO·nAl2O3 is essential for practical applications. Based on the first‐principles calculations and the bond valence method, the disordered spinel‐type structure of ZnO·nAl2O3 (n = 1–4) was constructed to investigate the composition‐dependent mechanical and thermophysical properties. The effects of cation substitution on the hardness, elastic modulus, thermal expansion, and thermal conductivity were revealed from the insights into the chemical bonds. At a higher n, the tetrahedral bond is stronger, manifested as its higher hardness and bulk modulus as well as smaller thermal expansion coefficient. Meanwhile, the octahedral bond is weaker, leading to the lower hardness and bulk modulus, along with the larger expansion coefficient. In consequence, the hardness and elastic moduli of ZnO·nAl2O3 are improved moderately while the expansion coefficient is decreased with the rise of n. Due to the different vibration characteristics of ZnIV and AlIV, the cation disorder in the 8a site provides the primary source of phonon scattering, resulting in the dramatic reduction of thermal conductivity as n increases. The understanding offers guidance on the application‐oriented design of new oxide spinels.

Injection locking in an optomechanical coherent phonon source

Abstract Spontaneous locking of the phase of a coherent phonon source to an external reference is demonstrated in a deeply sideband-unresolved optomechanical system. The high-amplitude mechanical oscillations are driven by the anharmonic modulation of the radiation pressure force that result from an absorption-mediated free-carrier/temperature limit cycle, i.e., self-pulsing. Synchronization is observed when the pump laser driving the mechanical oscillator to a self-sustained state is modulated by a radiofrequency tone. We employ a pump-probe phonon detection scheme based on an independent optical cavity to observe only the mechanical oscillator dynamics. The lock range of the oscillation frequency, i.e., the Arnold tongue, is experimentally determined over a range of external reference strengths, evidencing the possibility to tune the oscillator frequency for a range up to 350 kHz. The stability of the coherent phonon source is evaluated via its phase noise, with a maximum achieved suppression of 44 dBc/Hz at 1 kHz offset for a 100 MHz mechanical resonator. Introducing a weak modulation in the excitation laser reveals as a further knob to trigger, control and stabilize the dynamical solutions of self-pulsing based optomechanical oscillators, thus enhancing their potential as acoustic wave sources in a single-layer silicon platform.

Novel hermetically sealed device to realize unconventional phonon blockade at near-micron dimensions and milliKelvin temperatures

This paper proposes a novel design for a hermetically sealable device, consisting of charged linear and nonlinear membranes driven in the gigahertz range in vacuum setting, as a source of antibunched single phonons. Constraints for effecting phonon antibunching are found using the stationary Liouville–von Neumann master equation. Using analytical calculations and material and geometry optimization, we show that sizes of the proposed system can be upscaled to the near-micrometer range in a trade-off with the system operating temperature. The results are significant to realize quantum phononics, which has much promise as a modality for sensing and computing applications.

Structure and optical properties of porous SiC film grown by magnetron sputtering on porous anodic aluminium oxide template

Porous fluorescent SiC films were deposited by magnetron sputtering (MS) using porous anodic aluminium oxide (AAO) template. In the first step AAO was carefully placed on the Si substrate and then coated with SiC film using magnetron sputtering at the deposition temperature of 873K for different times. The pore diameter, pore spacing and thickness of the double pass porous AAO template were 300, 450 and 500 nm, respectively. The SiC film deposited for 60min showed macroporous structure with the pore size of 200 to 250 nm and pore spacing of 450 nm. The photoluminescence (PL) spectrum of the porous SiC film ranged from 400 to 700 nm. The band gap of SiC is 2.305 eV, and the phonon energy of phonon participating in PL of SiC is estimated at 0.075 eV. The source of phonon participating in PL of SiC may be from phonon scattering of silica/SiC interface in porous SiC film. The porous AAO template assisted magnetron sputtering is a promising technical processing for the fabrication of macroporous fluorescent SiC film.

Quantum Hamiltonian for the surface charge density on a ring torus and radiative decay of plasmons

Photon scattering and the ensuing excitation of surface plasmons in single rings, single composite rings, and many-ring systems was recently shown to provide dispersion and field distributions [K. V. Garapati et al., J. Phys. Commun. 2, 015031 (2018)] of potential for specific applications in particle and molecular trapping [R. Alaee et al., Appl. Phys. Lett. 109, 141102 (2016); M. Salhi et al., Phys. Rev. A 92, 033416 (2015)], in addition to metamaterials and sensing. Following photon or electron interactions with metallic nanorings, both radiative and nonradiative decay channels are important in the consideration of the nanoparticle as a photon or phonon source, and in related applications. Here, we quantize the electronic normal modes of the ring torus and obtain the radiative decay of plasmons. Due to a geometry-related complexity, we employ a perturbation approach to obtain analytical expressions for the radiative decay channel for a vacuum bounded single solid nanoring. In quantizing the fields, the frequency spectrum of the charge density normal modes of the nanoring is obtained and shown to agree with the exact quasistatic plasmon dispersion relations. Higher-order corrections beyond the presented zero- and first-order calculations may be obtained following the presented results. The results are of potential interest in quantum sensing such as entangling photons and plasmons, or plasmons and trapped molecules.

Epitaxial bulk acoustic wave resonators as highly coherent multi-phonon sources for quantum acoustodynamics

Solid-state quantum acoustodynamic (QAD) systems provide a compact platform for quantum information storage and processing by coupling acoustic phonon sources with superconducting or spin qubits. The multi-mode composite high-overtone bulk acoustic wave resonator (HBAR) is a popular phonon source well suited for QAD. However, scattering from defects, grain boundaries, and interfacial/surface roughness in the composite transducer severely limits the phonon relaxation time in sputter-deposited devices. Here, we grow an epitaxial-HBAR, consisting of a metallic NbN bottom electrode and a piezoelectric GaN film on a SiC substrate. The acoustic impedance-matched epi-HBAR has a power injection efficiency >99% from transducer to phonon cavity. The smooth interfaces and low defect density reduce phonon losses, yielding (f × Q) and phonon lifetimes up to 1.36 × 1017 Hz and 500 µs respectively. The GaN/NbN/SiC epi-HBAR is an electrically actuated, multi-mode phonon source that can be directly interfaced with NbN-based superconducting qubits or SiC-based spin qubits.

Detecting a phonon flux in superfluid He4 by a nanomechanical resonator

Nanoscale mechanical resonators are widely utilized to provide high sensitivity force detectors. Here we demonstrate that such high quality factor resonators immersed in superfluid \(^4\mathrm{He}\) can be excited by a modulated flux of phonons. A nanosized heater immersed in superfluid \(^4\mathrm{He}\) acts as a source of ballistic phonons in the liquid -- "phonon wind". When the modulation frequency of the phonon flux matches the resonance frequency of the mechanical resonator, the motion of the latter can be excited. This ballistic thermomechanical effect can potentially open up new types of experiments in quantum fluids.

Cu Interstitials Enable Carriers and Dislocations for Thermoelectric Enhancements in n-PbTe0.75Se0.25

Summary Aliovalent defects are extremely effective in manipulating charge transport and atomic vibrational properties for thermoelectric enhancements. Electronic performance of thermoelectrics is optimized at a reduced Fermi level of ∼0.3, which causes the optimal carrier concentration (nopt) to be strongly temperature dependent. This motivates a dynamic doping approach for electronic enhancements through an increase with temperature of solubility of aliovalent dopants. In addition, the defects could simultaneously act as scattering sources of phonons for reducing the lattice thermal conductivity. These effects are illustrated in this work by the temperature-dependent excess Cu solubility in n-PbTe0.75Se0.25 thermoelectrics, in which both carriers and dislocations are induced for regulating the electronic and phononic transport properties for a realization of an extraordinary thermoelectric figure of merit. The resultant defect structures and temperature gradient doping effects (for aliovalent solutes) could in principle open extra possibilities for optimizing charge and phonon transport properties in thermoelectrics.

Squeezed states of coupled photons and phonons in nanoscale waveguides

We investigate the generation of photon–phonon entangled states by exploiting stimulated Brillouin scattering in nanoscale waveguides. The squeezing type Hamiltonian that represents creation and annihilation of photon–phonon pairs is obtained out of the multimode photon–phonon interaction Hamiltonian in the presence of a pump field. The Bogoliubov eigenstates of the Hamiltonian, which are a coherent mix of propagating photons and phonons, show squeezing properties in the uncertainties of the collective quadrature operators. The measurement of the photonic component can provide a controllable source of single phonons in demand.