Synthetic gauge fields for phonon transport in a nano-optomechanical system

Abstract

Gauge fields play important roles in condensed matter, explaining for example nonreciprocal and topological transport phenomena. Establishing gauge potentials for phonon transport in nanomechanical systems would bring quantum Hall physics to a new domain, which offers broad applications in sensing and signal processing, and is naturally associated with strong nonlinearities and thermodynamics. In this work, we demonstrate a magnetic gauge field for nanomechanical vibrations in a scalable, on-chip optomechanical system. We exploit multimode optomechanical interactions, which provide a useful resource for the necessary breaking of time-reversal symmetry. In a dynamically modulated nanophotonic system, we observe how radiation pressure forces mediate phonon transport between resonators of different frequencies, with a high rate and a characteristic nonreciprocal phase mimicking the Aharonov-Bohm effect. We show that the introduced scheme does not require high-quality cavities, such that it can be straightforwardly extended to explore topological acoustic phases in many-mode systems resilient to realistic disorder.Recent years have seen the emergence of theoretical and experimental efforts exploring exotic transport phenomena in bosonic systems exploiting broken structural and temporal symmetries [1][2][3]. Magnetic gauge potentials play a particularly important role in those efforts. They can break time-reversal symmetry for transport, imparting a nonreciprocal, direction-dependent phase on a particle's wavefunction. For electrons, this leads to the celebrated Aharonov-Bohm effect [4] as well as the integer quantum Hall effect, which offers topologically protected transport in extended systems. Periodic modulation has been proposed to create synthetic gauge fields to achieve similarly rich phenomena: It allows to effectively break time-reversal symmetry and explore emergent phases for electrons [5], but importantly also for chargeless excitations of cold atoms and ions [6,7], light [8,9] and mechanics [10]. Cavity optomechanics provides a natural platform to realize time-varying potentials for either light or sound, and has been used to demonstrate nonreciprocal control of photons and phonons recently [11][12][13][14][15][16][17]. In manymode optomechanical lattices, the phase and amplitude of interactions could be controlled with optical fields to induce exotic topological phases of light and sound at the nanoscale [18][19][20]. These inspiring proposals, however, require high quality factors and put extreme demands on fabrication tolerances and control intensities to achieve sufficiently strong interactions.Here we introduce a new mechanism to establish a magnetic gauge potential for sound at the nanoscale to overcome those challenges. It relies on optically-mediated mechanical mode transfer, which arises naturally in a system that dispersively couples two mechanical modes to a single optical cavity driven with a detuned laser [21]: A displacement of one mechanical mode then shifts the cavity resonance, modifying...

Generating synthetic magnetism via Floquet engineering auxiliary qubits in phonon-cavity-based lattice

“…Inspired by these studies, we propose a novel method to realize synthetic magnetism in the phonon systems by Floquet engineering qubits coupled to phonons. Different from previous methods based on optomechanical systems [15,20,27], we find that the Floquet driving can be effectively realized in an opposite way, i.e. via the unconventional cavity optomechanics (UOM) discussed in [52], where the mechanical frequency is effectively modulated by an electromagnetic field via an auxiliary qubit.…”

“…These include exploring topological photonics and phononics in circuit-QED-based photon lattices, optomechanical arrays and microwave cavity systems [15,[22][23][24][25][26]. For example, as discussed in [17,27], one can artificially generate synthetic magnetism for photons in an optomechanical systems via site-dependent modulated laser fields.…”

“…Analog to quantum controls with photons, many acoustic devices, such as circulators, switches and routers, are also needed for generating, controlling, and detecting SAW phonons in QAD experiment [10,35,[41][42][43][44][45][46][47]. However, it is still challenging to realize these nonreciprocal acoustic quantum devices in the artificial nano-and micro-scale SAW systems [27,48].By applying an external time periodic drive on a static system, the effective Hamiltonian of the whole system for the longtime evolution can be tailed freely, which allows one to observe topological band properties. This approach is referred as Floquet engineering [49][50][51], and has been exploited to simulate the topological toy models such as Haldane and Harper-Hofstadter lattices in artificial systems [21].…”

“…Analog to quantum controls with photons, many acoustic devices, such as circulators, switches and routers, are also needed for generating, controlling, and detecting SAW phonons in QAD experiment [10,35,[41][42][43][44][45][46][47]. However, it is still challenging to realize these nonreciprocal acoustic quantum devices in the artificial nano-and micro-scale SAW systems [27,48].…”

“…Therefore, we just need to consider the zero-and first-order terms in equation (27). Consequently, we obtain the following effective Hamiltonian where we find that the relative phase f is successfully encoded into the coupling between cavity 1 and 2.…”