Hybrid coherent control of magnons in a ferromagnetic phononic resonator excited by laser pulses

We propose and demonstrate the concept of hybrid coherent control (CC) whereby a quantum or classical harmonic oscillator is excited by two excitations: one is quasiharmonic (i.e., harmonic with a finite lifetime) and the other is a pulsed broadband excitation. Depending on the phase relation between the two excitations, controlled by the detuning of the oscillator eigenfrequencies and the wave forms of the quasiharmonic and broadband excitations, it is possible to observe Fano-like spectra of the harmonic oscillator due to the interference of the two responses to the simultaneously acting excitations. Experimentally, as an example, the hybrid CC is implemented for magnons in a ferromagnetic grating where GHz coherent phonons act as the quasiharmonic excitation and the broadband impact arises from pulsed optical excitation followed by spin dynamics in the ferromagnetic nanostructure

Giant photoelasticity of polaritons for detection of coherent phonons in a superlattice with quantum sensitivity

The functionality of phonon-based quantum devices largely depends on the efficiency of interaction of phonons with other excitations. For phonon frequencies above 20 GHz, generation and detection of the phonon quanta can be monitored through photons. The photon-phonon interaction can be enormously strengthened by involving an intermediate resonant quasiparticle, e.g. an exciton, with which a photon forms a polariton. In this work, we discover a giant photoelasticity of exciton-polaritons in a short-period superlattice and exploit it for detecting propagating acoustic phonons. We demonstrate that 42 GHz coherent phonons can be detected with extremely high sensitivity in the time domain Brillouin oscillations by probing with photons in the spectral vicinity of the polariton resonance.Comment: 6 pages, 3 figures, Supplemental Material

On-chip phonon-magnon reservoir for neuromorphic computing

Reservoir computing is a concept involving mapping signals onto a high-dimensional phase space of a dynamical system called “reservoir” for subsequent recognition by an artificial neural network. We implement this concept in a nanodevice consisting of a sandwich of a semiconductor phonon waveguide and a patterned ferromagnetic layer. A pulsed write-laser encodes input signals into propagating phonon wavepackets, interacting with ferromagnetic magnons. The second laser reads the output signal reflecting a phase-sensitive mix of phonon and magnon modes, whose content is highly sensitive to the write- and read-laser positions. The reservoir efficiently separates the visual shapes drawn by the write-laser beam on the nanodevice surface in an area with a size comparable to a single pixel of a modern digital camera. Our finding suggests the phonon-magnon interaction as a promising hardware basis for realizing on-chip reservoir computing in future neuromorphic architectures

Resonant thermal energy transfer to magnons in a ferromagnetic nanolayer

Energy harvesting is a concept which makes dissipated heat useful by transferring thermal energy to other excitations. Most of the existing principles are realized in systems which are heated continuously. We present the concept of high-frequency energy harvesting where the dissipated heat in a sample excites resonant magnons in a thin ferromagnetic metal layer. The sample is excited by femtosecond laser pulses with a repetition rate of 10 GHz which results in temperature modulation at the same frequency with amplitude ~0.1 K. The alternating temperature excites magnons in the ferromagnetic nanolayer which are detected by measuring the net magnetization precession. When the magnon frequency is brought onto resonance with the optical excitation, a 12-fold increase of the amplitude of precession indicates efficient resonant heat transfer from the lattice to coherent magnons. The demonstrated principle may be used for energy harvesting in various nanodevices operating at GHz and sub-THz frequency ranges

On-chip phonon-magnon reservoir for neuromorphic computing

Reservoir computing is a concept involving mapping signals onto a high-dimensional phase space of a dynamical system called "reservoir" for subsequent recognition by an artificial neural network. We implement this concept in a nanodevice consisting of a sandwich of a semiconductor phonon waveguide and a patterned ferromagnetic layer. A pulsed write-laser encodes input signals into propagating phonon wavepackets, interacting with ferro-magnetic magnons. The second laser reads the output signal reflecting a phase-sensitive mix of phonon and magnon modes, whose content is highly sensitive to the write-and read-laser positions. The reservoir efficiently separates the visual shapes drawn by the write-laser beam on the nanodevice surface in an area with a size comparable to a single pixel of a modern digital camera. Our finding suggests the phonon-magnon interaction as a promising hardware basis for realizing on-chip reservoir computing in future neuro-morphic architectures

Protected Long-Distance Guiding of Hypersound Underneath a Nanocorrugated Surface

In nanoscale communications, high-frequency surface acoustic waves are becoming effective data carriers and encoders. On-chip communications require acoustic wave propagation along nanocorrugated surfaces which strongly scatter traditional Rayleigh waves. Here, we propose the delivery of information using subsurface acoustic waves with hypersound frequencies of ∼20 GHz, which is a nanoscale analogue of subsurface sound waves in the ocean. A bunch of subsurface hypersound modes are generated by pulsed optical excitation in a multilayer semiconductor structure with a metallic nanograting on top. The guided hypersound modes propagate coherently beneath the nanograting, retaining the surface imprinted information, at a distance of more than 50 μm which essentially exceeds the propagation length of Rayleigh waves. The concept is suitable for interfacing single photon emitters, such as buried quantum dots, carrying coherent spin excitations in magnonic devices and encoding the signals for optical communications at the nanoscale

Hybrid coherent control of magnons in a ferromagnetic phononic resonator excited by laser pulses

We propose and demonstrate the concept of hybrid coherent control (CC) whereby a quantum or classical harmonic oscillator is excited by two excitations: one is quasi-harmonic (i.e. harmonic with a finite lifetime) and the other is a pulsed broadband excitation. Depending on the phase relation between the two excitations, controlled by the detuning of the oscillator eigenfrequencies and the waveforms of the quasi-harmonic and broadband excitations, it is possible to observe Fano-like spectra of the harmonic oscillator due to the interference of the two responses to the simultaneously acting excitations. Experimentally, as an example, the hybrid CC is implemented for magnons in a ferromagnetic grating where GHz coherent phonons act as the quasi-harmonic excitation and the broadband impact arises from pulsed optical excitation followed by spin dynamics in the ferromag-netic nanostructure. Coherent control (CC) is well established as a powerful method to manipulate the amplitude and phase of quantum states. First used for chemical reactions [1, 2], CC has been demonstrated for single electrons [3], spins [4, 5], nanoelectromechanical oscillators [6], magnons [7, 8] and other systems [9]. The basic phenomenon governing CC is the interference of the responses of a quantum system to specific excitations, which determine the phase of the wavefunction. One of the common technical solutions for realizing CC is to use two optical pulses from ultrafast lasers with adjustable time separation or more sophisticated laser pulse shaping [10]. For CC of magnons, two microwave pulses may be used [11]. Traditionally , the excitations that lead to the interfering responses have the same origin, e.g. transitions between the ground and an excited quantum state are induced by a resonant electromagnetic field. However, there are quantum systems that may be excited by a pair of exci-tations of different origins. For example, one excitation may be broad-band and the other harmonic. Exploiting a combination of various types of excitations for hybrid CC would broaden a diversity of CC applications for quantum computing and communications. The idea of hybrid CC in the spectral domain is illustrated in Figs. 1(a) and 1(b) for a linear tunable quantum or classical oscillator with eigenfrequency ω 0 and finite lifetime. Figures 1(a) and 1(b) show the amplitude spectra of the oscillator's responses to two types of excitation: (1) quasi-harmonic (i.e. harmonic with finite lifetime) excitation with central frequency ω R detuned relative to ω 0 ; and (2) broad band excitation. Two cases of detun-ing are considered: negative (ω 0 ω R) in Fig. 1(b). The top blue curves show the spectra when only quasi-harmonic excitation is present. In this case the phase ϕ of the oscillator at ω = ω 0 changes by π when the oscillator eigenfrequency is tuned through the resonance ω = ω R , say from −π/2 to π/2 as demonstrated in the comparison of the blue spectra in Figs. 1(a) and 1(b). The middle red curves are spectral responses when the oscillator is excited by a broadband excitation (2). The oscillator's phase ϕ, e.g. ϕ = π/2, at ω = ω 0 in this case does not depend on ω 0. The lower black curves are the spectra when the two ex-citations, (1) and (2), operate together. Clearly, we get destructive [ Fig. 1(a)] or constructive [Fig. 1(b)] interference of the oscillator's responses at ω = ω 0 depending on the detuning of the oscillator eigenfrequency relative to the central frequency of the quasi-harmonic excitation, ω 0 ω R respectively. For negative detuning (ω 0 ω R) the spectral amplitude at ω = ω 0 increases by a factor of two. The interference effects represent an example of hybrid CC where two excitations have different spectra and are of different nature, for example (1) could be a coherent phonon wavepacket and (2) could be a short microwave or laser pulse. By varying the detuning, amplitudes and phases of excitations (1) and (2), it is possible to model various Fano-like spectral shapes similar to Fano spectra which appear as a result of interference of broad-and narrow-band eigenstates [12]. In the present Letter we demonstrate an example where CC is realized for the case of magnons. Magnons are a typical example for which a diversity of quantum excitations exists [13]. The quasi-harmonic excitation of magnons is coming from quasi-monochromatic surface phonons. They drive the spectrally isolated magnon mode at the frequency ω R. The broadband excitation is based on ultrafast modulation of the ferromagnet mag-netization. Both excitations are triggered optically by a femtosecond laser pulse. The magnon eigenfrequency ω 0 is tuned by the external magnetic field B. Monitoring the magnon spectrum, we observe destructive or constru

On-chip phonon-magnon reservoir for neuromorphic computing

Reservoir computing is a concept involving mapping signals onto a high-dimensional phase space of a dynamical system called “reservoir” for subsequent recognition by an artificial neural network. We implement this concept in a nanodevice consisting of a sandwich of a semiconductor phonon waveguide and a patterned ferromagnetic layer. A pulsed write-laser encodes input signals into propagating phonon wavepackets, interacting with ferromagnetic magnons. The second laser reads the output signal reflecting a phase-sensitive mix of phonon and magnon modes, whose content is highly sensitive to the write- and read-laser positions. The reservoir efficiently separates the visual shapes drawn by the write-laser beam on the nanodevice surface in an area with a size comparable to a single pixel of a modern digital camera. Our finding suggests the phonon-magnon interaction as a promising hardware basis for realizing on-chip reservoir computing in future neuromorphic architectures.</p

Supplementary information files for On-chip phonon-magnon reservoir for neuromorphic computing

© the authors, CC-BY 4.0Supplementary files for article On-chip phonon-magnon reservoir for neuromorphic computingReservoir computing is a concept involving mapping signals onto a high-dimensional phase space of a dynamical system called “reservoir” for subsequent recognition by an artificial neural network. We implement this concept in a nanodevice consisting of a sandwich of a semiconductor phonon waveguide and a patterned ferromagnetic layer. A pulsed write-laser encodes input signals into propagating phonon wavepackets, interacting with ferromagnetic magnons. The second laser reads the output signal reflecting a phase-sensitive mix of phonon and magnon modes, whose content is highly sensitive to the write- and read-laser positions. The reservoir efficiently separates the visual shapes drawn by the write-laser beam on the nanodevice surface in an area with a size comparable to a single pixel of a modern digital camera. Our finding suggests the phonon-magnon interaction as a promising hardware basis for realizing on-chip reservoir computing in future neuromorphic architectures.</p