Amir Youssefi

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Cavity optomechanics enables the control of mechanical motion through the radiation-pressure interaction(1), and has contributed to the quantum control of engineered mechanical systems ranging from kilogramme-scale Laser Interferometer Gravitational-wave Observatory (LIGO) mirrors to nanomechanical systems, enabling ground-state preparation(2,3), entanglement(4,5), squeezing of mechanical objects(6), position measurements at the standard quantum limit(7) and quantum transduction(8). Yet nearly all previous schemes have used single- or few-mode optomechanical systems. By contrast, new dynamics and applications are expected when using optomechanical lattices(9), which enable the synthesis of non-trivial band structures, and these lattices have been actively studied in the field of circuit quantum electrodynamics(10). Superconducting microwave optomechanical circuits(2) are a promising platform to implement such lattices, but have been compounded by strict scaling limitations. Here we overcome this challenge and demonstrate topological microwave modes in one-dimensional circuit optomechanical chains realizing the Su-Schrieffer-Heeger model(11,12). Furthermore, we realize the strained graphene model(13,14) in a two-dimensional optomechanical honeycomb lattice. Exploiting the embedded optomechanical interaction, we show that it is possible to directly measure the mode functions of the hybridized modes without using any local probe(15,16). This enables us to reconstruct the full underlying lattice Hamiltonian and directly measure the existing residual disorder. Such optomechanical lattices, accompanied by the measurement techniques introduced, offer an avenue to explore collective(17,18), quantum many-body(19) and quench(20) dynamics, topological properties(9,21) and, more broadly, emergent nonlinear dynamics in complex optomechanical systems with a large number of degrees of freedom(22-24).

NATURE PORTFOLIO2022

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A cryogenic electro-optic interconnect for superconducting devices

Nathan Rafaël Bernier, Tobias Kippenberg, Anton Lukashchuk, Liu Qiu, Itay Shomroni, Amir Youssefi

A major challenge to the scalability of cryogenic computing platforms is the heat load associated with the growing number of electrical cable connections between the superconducting circuitry and the room-temperature environment. Compared with electrical cables, optical fibres have significantly lower thermal conductivity and are widely used in modern telecommunications. However, optical modulation at cryogenic temperatures remains relatively unexplored. Here we report the cryogenic electro-optical readout of a superconducting electromechanical circuit using a commercial titanium-doped lithium niobate modulator. We demonstrate coherent spectroscopy by measuring optomechanically induced transparency and incoherent thermometry by encoding the mechanical sidebands in an optical signal. We also show that our modulators can maintain their room-temperature Pockels coefficient at 800 mK. Further optimization of the modulator design-for example, by using longer waveguides and materials with a higher Pockels coefficient-could reduce the added noise of our setup to similar levels as current semiconductor microwave amplifiers. A commercial titanium-doped lithium niobate phase modulator can be employed at temperatures as low as 800 mK for the electro-optical readout of a superconducting electromechanical circuit at 15 mK.

2021

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Two-Tone Optomechanical Instability and Its Fundamental Implications for Backaction-Evading Measurements

Tobias Kippenberg, Liu Qiu, Itay Shomroni, Amir Youssefi

While quantum mechanics imposes a fundamental limit on the precision of interferometric measurementsof mechanical motion due to measurement backaction, the nonlinear nature of the coupling also leads toparametric instabilities that place practical limits on the sensitivity by limiting the power in theinterferometer. Such instabilities have been extensively studied in the context of gravitational wavedetectors, and their presence has recently been reported in Advanced LIGO. Here, we observeexperimentally and describe theoretically a new type of optomechanical instability that arises in two-tone backaction-evading (BAE) measurements, a protocol designed to overcome the standard quantumlimit. We demonstrate the effect in the optical domain with a photonic crystal nanobeam cavity and in themicrowave domain with a micromechanical oscillator coupled to a microwave resonator. In contrast to thewell-known parametric oscillatory instability that occurs in single-tone, blue-detuned pumping, and resultsfrom a two-mode squeezing interaction between the optical and mechanical modes, the parametricinstability in balanced two-tone optomechanics results from single-mode squeezing of the mechanical modein the presence of small detuning errors in the two pump frequencies. Counterintuitively, the instabilityoccurs even in the presence of perfectly balanced intracavity fields and can occur for both signs of detuningerrors. We find excellent quantitative agreement with our theoretical predictions. Since the constraints ontuning accuracy become stricter with increasing probe power, the instability imposes a fundamentallimitation on BAE measurements as well as other two-tone schemes, such as dissipative squeezing of opticaland microwave fields or of mechanical motion. In addition to identifying a new limitation in two-tone BAEmeasurements, the results also introduce a new type of nonlinear dynamics in cavity optomechanics.

2019

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