Connecting superconducting qubits to optical fiber necessitates the conversion of microwave photons to optical photons. Modern experimental demonstrations exhibit strong coupling between a microwave resonator and an optical cavity mediated through phononic modes in a mechanical oscillator. This paradigmatic transduction experiment is bounded by a theoretical efficiency with constant driving amplitudes on electromagnetic resonators. By adding a parametric drive to the microwave resonator and optical cavity, we discover the converted signal through the quantum transducer is amplified, while maintaining a lower level of the added noise. We propose a theoretical framework for time-dependent control of the driving lasers based on the input-output formalism of quantum optics and solve analytically the transduction efficiency and added noise when the control signals parametrically drive the system. Our results show better transduction efficiency and lower added noise in varying parameter regimes relevant to current transduction experiments.
Connecting superconducting qubits to optical fiber necessitates the conversion of microwave photons to optical photons. Modern experimental demonstrations exhibit strong coupling between a microwave resonator and an optical cavity mediated through phononic modes in a mechanical oscillator. This paradigmatic transduction experiment is bounded by a theoretical efficiency with constant driving amplitudes on electromagnetic resonators. By adding a parametric drive to the microwave resonator and optical cavity, we discover the converted signal through the quantum transducer is amplified, while maintaining a lower level of the added noise. We propose a theoretical framework for time-dependent control of the driving lasers based on the input-output formalism of quantum optics and solve analytically the transduction efficiency and added noise when the control signals parametrically drive the system. Our results show better transduction efficiency and lower added noise in varying parameter regimes relevant to current transduction experiments.
Abstract The quantum transduction, or equivalently quantum frequency conversion, is vital for realizing, e.g., quantum networks and distributed quantum computing. The microwave-to-optical quantum transduction is of interest in the field of superconducting quantum computing, since interconnecting dilution refrigerators is considered inevitable for realizing large-scale quantum computers with fault-tolerance. In this review, we overview recent theoretical and experimental studies on the quantum transduction between microwave and optical photons. We describe a generic theory for the quantum transduction employing the input-output formalism, from which the essential quantities characterizing the transduction, i.e., expressions for the transduction efficiency, added noise, and transduction bandwidth, are derived. We review major transduction methods that have been experimentally demonstrated, including the optomechanical, electro-optic, and ensemble-based transducers. We also briefly review recent experiments on the quantum transduction from superconducting qubit to optical photon, which is an important step toward quantum state transfer between distant superconducting qubits interconnected over optical fibers.
The successes of superconducting quantum circuits at local manipulation of quantum information and photonics technology at long-distance transmission of the same have spurred interest in the development of quantum transducers for efficient, low-noise, and bidirectional frequency conversion of photons between the microwave and optical domains. We propose to realize such functionality through the coupling of electrical, piezoelectric, and optomechanical resonators. The coupling of the mechanical subsystems enables formation of a resonant mechanical supermode that provides a mechanically mediated, efficient single interface to both the microwave and optical domains. The conversion process is analyzed by applying an equivalent circuit model that relates device-level parameters to overall figures of merit for conversion efficiency $\ensuremath{\eta}$ and added noise N. These can be further enhanced by proper impedance matching of the transducer to an input microwave transmission line. The performance of potential transducers is assessed through finite-element simulations, with a focus on geometries in GaAs, followed by considerations of the AlN, LiNbO3, and AlN-on-Si platforms. We present strategies for maximizing $\ensuremath{\eta}$ and minimizing N, and find that simultaneously achieving $\ensuremath{\eta}>50\mathrm{%}$ and N<0.5 should be possible with current technology. We find that the use of a mechanical supermode for mediating transduction is a key enabler for high-efficiency operation, particularly when paired with an appropriate microwave impedance-matching network. Our comprehensive analysis of the full transduction chain enables us to outline a development path for the realization of high-performance quantum transducers that will constitute a valuable resource for quantum information science.
State transfer between light and microwaves is a key challenge in quantum networks. Promising transducers use a mechanical intermediary that couples to both fields via radiation pressure. Such electro-optomechanical devices have achieved high efficiencies, yet require resolved-sideband cavities, and generally compromise in scalability and noise performance. Here, we relax this constraint by extending the protocol of Navarathna et al. that transfers optical quantum information onto a mechanical resonator using a broadband, sideband-unresolved cavity and feedback. Combining this with parametric mechanical-to-microwave conversion, we show that continuous optical-to-microwave quantum state transfer is possible using measurement-based feedback, while all-optical coherent feedback enables bidirectional transfer. To assess the transfer, we introduce the quantum transfer witness WT, which -- though similar to the input-referred added noise -- also identifies whether a channel is capable of both preserving Gaussian entanglement and outperforming classical transduction schemes. Finally, we show that quantum-compatible noise performance is within reach of current experimental capabilities. Our results unlock a new design space for electro-optomechanical transducers and strengthens their candidacy as scalable quantum links between distant nodes.
The successes of superconducting quantum circuits at local manipulation of quantum information and photonics technology at long-distance transmission of the same have spurred interest in the development of quantum transducers for efficient, low-noise, and bidirectional frequency conversion of photons between the microwave and optical domains. We propose to realize such functionality through the coupling of electrical, piezoelectric, and optomechanical resonators. The coupling of the mechanical subsystems enables formation of a resonant mechanical supermode that provides a mechanically-mediated, efficient single interface to both the microwave and optical domains. The conversion process is analyzed by applying an equivalent circuit model that relates device-level parameters to overall figures of merit for conversion efficiency η and added noise N. These can be further enhanced by proper impedance matching of the transducer to an input microwave transmission line. The performance of potential transducers is assessed through finite-element simulations, with a focus on geometries in GaAs, followed by considerations of the AlN, LiNbO3, and AlN-on-Si platforms. We present strategies for maximizing η and minimizing N, and find that simultaneously achieving η>50% and N<0.5 should be possible with current technology. Our comprehensive analysis of the full transduction chain enables us to outline a development path for the realization of high-performance quantum transducers that will constitute a new resource for quantum information science.
A quantum interface between microwave and optical photons is essential for entangling remote superconducting quantum processors. To preserve fragile quantum states, a transducer must operate efficiently while generating less than one photon of noise referred to its input. Here, we present a platform that meets these criteria, utilizing a combination of electrostatic and optomechanical interactions in devices made entirely from crystalline silicon. This platform's small mechanical dissipation and low optical absorption enable ground-state radiative cooling, resulting in quantum-enabled operation with a continuous laser drive. Under the optimal settings for high efficiency (low noise), we measure an external efficiency of 2.2% (0.47%) and an input-referred added noise of 0.94 (0.58) in microwave-to-optics conversion. We quantify the transducer throughput using the efficiency-bandwidth product, finding it exceeds previous demonstrations with similar noise performance by approximately two orders of magnitude, thereby paving a practical path to interconnecting remote superconducting qubits.
Converting signals from the microwave to the optical domain has attracted great attention due to its potential applications in the field of quantum networks. Achieving efficient transduction is a significant yet challenging task, where a high efficiency at single photon level and low added noise are required. Electro-opto-mechanics have been proven to be efficient to convert microwave and optical photons bidirectionally. In this work, we propose and demonstrate an enhanced microwave-optical conversion in an electro-opto-mechanical system by introducing a mechanical ancilla attached the microwave resonator. Based on the ancillary electromechanical coupling, the damping rate of the microwave resonator is controlled and further leads to significant enhancement in conversion, such as the increase of conversion efficiency, broadening of conversion bandwidth and reduction of added noise. It provides a feasible approach to realize a broadband microwave-optical conversion with high efficiency. Moreover, the reduced added noise may break the limitation of quantum transduction due to the ancillary electromechanical coupling. Our scheme is also applicable and feasible for opto-mechanics and other systems to achieve practical quantum interface.