Summary form only given. The motion of a micromechanical resonator coupled simultaneously to a high-finesse optical cavity and a microwave resonator can be used to transduce the fragile quantum states generated in the realm of microwave superconducting circuits into optical photons that can transport quantum information over large distances in telecom optical fibers at room temperature. We have engineered the optical and mechanical properties of thin membranes patterned in a suspended high-stress Si3N4 film to realize such a hybrid opto-electro-mechanical system. An optical Fabry-Perot cavity with a finesse exceeding 12 000 was realized between a highly reflective photonic crystal patch realized on the suspended membrane and a conventional high-reflectivity mirror. The electromechanical coupling with a nearby planar superconducting circuit is achieved by approaching the membrane at a sub-micron distance from an on-chip interdigitated capacitor. By operating the hybrid opto-electro-mechanical system in a cryogenic environment, the photon-phonon swap rates between microwave, mechanical, and optical degrees of freedom is expected to overcome the mechanical decoherence rate. An artist view of the device envisioned is depicted on Figure 1.
Summary form only given. The motion of a micromechanical resonator coupled simultaneously to a high-finesse optical cavity and a microwave resonator can be used to transduce the fragile quantum states generated in the realm of microwave superconducting circuits into optical photons that can transport quantum information over large distances in telecom optical fibers at room temperature. We have engineered the optical and mechanical properties of thin membranes patterned in a suspended high-stress Si3N4 film to realize such a hybrid opto-electro-mechanical system. An optical Fabry-Perot cavity with a finesse exceeding 12 000 was realized between a highly reflective photonic crystal patch realized on the suspended membrane and a conventional high-reflectivity mirror. The electromechanical coupling with a nearby planar superconducting circuit is achieved by approaching the membrane at a sub-micron distance from an on-chip interdigitated capacitor. By operating the hybrid opto-electro-mechanical system in a cryogenic environment, the photon-phonon swap rates between microwave, mechanical, and optical degrees of freedom is expected to overcome the mechanical decoherence rate. An artist view of the device envisioned is depicted on Figure 1.
The motion of a micromechanical resonator coupled simultaneously to a high-finesse optical cavity and a microwave resonator can be used to transduce the fragile quantum states generated in the realm of microwave superconducting circuits into optical photons that can transport quantum information over large distances in telecom optical fibers at room temperature. We have engineered the optical and mechanical properties of thin membranes patterned in a suspended high-stress Si3N4 film to realize such a hybrid opto-electro-mechanical system. An optical Fabry-Perot cavity with a finesse exceeding 12 000 was realized between a highly reflective photonic crystal patch realized on the suspended membrane and a conventional high-reflectivity mirror. The electromechanical coupling with a nearby planar superconducting circuit is achieved by approaching the membrane at a sub-micron distance from an on-chip interdigitated capacitor. By operating the hybrid opto-electro-mechanical system in a cryogenic environment, the photon-phonon swap rates between microwave, mechanical, and optical degrees of freedom is expected to overcome the mechanical decoherence rate.
Microscale and nanoscale mechanical resonators have been used in advanced technological applications, from high precision time keeping and mass sensing, to processing high frequency signals in mobile communications. In the last few decades, they have been an important part of progress in the field of quantum information and metrology and have been proposed as quantum memories or transducers for measuring or connecting different types of quantum systems. The field of cavity optomechanics and electromechanics is concerned with coupling the electromagnetic field of a resonant optical cavity or electrical circuit to mechanical motion. These systems provide potential means to control and engineer the state of a mechanical object at the quantum level. This thesis contains the description of mechanical systems in megahertz to a few hundred megahertz frequency range formed by nano-fabricating photonic, phononic, and electrical circuits on a chip. These structures are designed to provide a large radiation pressure coupling between mechanical motion and electromagnetic fields to address and manipulate motional degrees of freedom. Qualitatively novel quantum effects are expected when one takes a step beyond linear coupling and exploits higher order interactions. To that end, we integrate electrical, mechanical and photonic structures in a multimode photonic crystal structure to observe "x2-coupling", where the optical cavity frequency is coupled to the square of the mechanical displacement. Moreover, we have developed two integrated on-chip platforms based on Si3N4 and Si nanomembranes capable of interfacing superconducting qubits and optical photons and realizing reversible microwave-to-optical conversion. We employ radiation pressure to cool these mechanical resonators to their quantum ground state. Finally, we demonstrate a form of electromechanical crystal for coupling microwave photons and hypersonic phonons of frequency ωm/2π = 0.425 GHz by capacitively coupling a phononic crystal acoustic cavity to a superconducting microwave resonator. Moving to higher frequency acoustic cavities not only facilitates the integration of electromechanical circuits and nanophotonic systems capable of operation in the resolved sideband limit of optomechanics for noise-free quantum signal conversion, but it opens up the possibility of using phonons as information carriers via phononic circuits. Utilizing a two-photon resonance condition for efficient microwave pumping and phononic bandgap shield to eliminate acoustic radiation, we achieve large cooperative electromechanical coupling (C ≈ 30) and intrinsic decay time of 2.3 ms. Moreover, electrical read-out of the phonon occupancy shows that the acoustic mode thermalizes close to its quantum ground-state of motion (phonon occupancy nm=1.5) at a fridge temperature of Tf = 10 mK. We conclude by considering several designs and fabrication improvements to the hypersonic electromechanical crystals that would enable them to perform quantum conversion between the electrical and acoustic domain.
Superconducting circuits are important technological tools that have found various applications, notably hypothetical future superconducting quantum computers. Scaling such systems further is, however, proving challenging because of thermal heat load and space constraints in cryostats. One way of improving the scalability of such systems would be to resort to optical fibers for controlling the circuits in cryostats, as well as mediating long-distance interaction between them while preserving quantum coherence. Such a strategy relies on building a coherent interface between GHz frequencies and optical frequencies. This interface, referred to as "microwave-optical transducer", would need to exhibit high photon conversion efficiencies and very low added noise, ideally less than a quantum, in a cryogenic environment. Since the prospects of weaving networks of optically connected superconducting quantum processors have now attracted the attention of the scientific community for more than a decade, very efficient transducers have already been proposed and realized. However, despite their impressive performances against selected metrics, often equivalent to optimizing the on-chip conversion efficiency alone, none of the approaches pursued so far really solved the qubit interconnection problems in ways that could be applied to large-scale systems in the near future. The aim of this thesis was to develop transduction approaches that would ultimately enable optical driving of superconducting circuits and quantum state transfer between microwave and optical frequencies, while at the same time ensuring good scalability, both in terms of wafer manufacturability and integration in cryogenic environments. Integrated photonic circuits based on silicon nitride appeared as a promising platform, as silicon nitride is a CMOS-certified material, has a transparency window compatible with optical fibers and lacks two photon absorption. Realizing the coupling between microwave and optical frequencies in a way similar to what is done in optomechanics is desirable, because the field of optomechanics has seen the establishement of techniques that enable control of the low frequency degree of freedom at the quantum mechanical level, including ground state cooling, control of the susceptibility by dynamical backaction, quantum state transfer and entanglement. The heterogeneous integration of nonlinear crystalline thin films, such as lithium niobate and lithium tantalate, onto silicon nitride photonic circuitry endows it with an electro-optic activity that emulates the optomechanical interaction, while offering an inherent access to the microwave degree of freedom. However, material nonlinearities, including photorefraction, charge screening, and hysteresis, introduce complications that motivate exploring alternative approaches. Here, alongside an electro-optic implementation, a transducer that leverages the interaction of bulk acoustic resonances excited by micro-electromechanical systems with whispering-gallery-like modes of microresonators is presented. Coherent transduction between microwave and optical fields is demonstrated, and optomechanical dynamical backaction is observed. The transducers fast bandwidth, compatibility with multiplexing and ability to down-convert microwaves suggest interesting prospects, particularly upon further improvements of the optomechanical coupling.
A transducer capable of faithfully converting single quanta between microwave and optical frequencies would enable an optical network of superconducting quantum computers. A primary challenge in the ongoing effort to bridge these frequency scales is the detrimental effect that optical photons have on superconducting circuits. This manuscript details the membrane-optomechanical Fabry-P´erot architecture we employ in a high-efficiency electrooptomechanical transducer. We use a chemical bonding process to create an integrated membrane-mirror etalon assembly that is robust against thermal misalignment upon cryogenic cooling. Our choice of input coupling mirror and cavity geometry allow flexible operation of the transducer in the presence of any additional nonidealities in the optical cavity, such as additional scattering loss associated with one mirror. Our transducer is unique in its ability to operate with continuous laser illumination without substantially impacting the superconducting circuitry of the transducer or a superconducting transmon qubit linked to its microwave input. We quantify the effect of laser light on the superconductor, measuring the effective occupancy of the transducer’s superconducting circuit with varying optical power to be less than 0.15 photons even at powers greatly exceeding that needed for transducer operation. We also measure the coherence time T2 of a qubit attached to the transducer for optical readout, and determine that continuous laser pumping of the transducer has no measurable effect.
Continued development of complementary capabilities in two quantum technologies—information processing with microwave-frequency superconducting circuits and networks based on optical-frequency photonic links—have motivated an effort to bridge the frequency gap between them with a transducer capable of preserving quantum signals. At the same time, mechanical resonators have been engineered to interact with electromagnetic waves across the spectrum in a variety of tailorable physical implementations. This thesis describes advances in a transducer using the mechanical mode of a silicon nitride membrane as an intermediary permitting coupling between a superconducting resonant LC circuit and a Fabry-Pérot optical cavity. With this choice of architecture, we have developed transducers of unparalleled efficiency and the unique capability to run continuously without appreciably degrading the performance of the superconductor from scattered optical photons. We have been able to laser-cool the mechanical mode to an occupation of less than one photon, and achieved transducer performance capable of converting a single microwave photon to optical frequencies with a signal-to-noise ratio of 1/3. Furthermore, operating the transducer does not cause appreciable heating of a superconducting transmon qubit linked to its microwave input port. With progress towards a quantum-enabled interface, we have started to develop capabilities towards implementing protocols that optically verify the quantum performance of the transducer.
Superconducting qubits, realized by incorporating Josephson junctions into superconducting circuits, behave as artificial atoms with anharmonic energy spectra and can be precisely controlled and measured using microwave cavities within the framework of circuit quantum electrodynamics (cQED). Since its emergence in the early 2000s, cQED has established superconducting qubits as leading candidates for scalable quantum devices and has enabled the exploration of hybrid quantum systems that integrate disparate physical platformsThis review surveys superconducting hybrid quantum electromechanical systems in which mechanical resonators are coupled to superconducting qubits, with a focus on two widely used qubit platforms: the transmon and the fluxonium. We provide an overview of the underlying coupling mechanisms arising from interactions through the phase and charge degrees of freedom of the qubit, and discuss how these mechanisms give rise to both longitudinal and transverse qubit-mechanical interactions. We further review extensions of electromechanical platforms to electro-optomechanical architectures, in which optical cavities are integrated to enable coherent interfacing between superconducting circuits and optical photons. This review aims to present a unified framework and perspective on qubit-mechanical and qubit-mechanical-optical hybrid systems in superconducting quantum technologies and applications related to sensors.