Abstract Quantum transduction, the process of converting quantum signals from one form of energy to another, is an important area of quantum science and technology. The present perspective article reviews quantum transduction between microwave and optical photons, an area that has recently seen a lot of activity and progress because of its relevance for connecting superconducting quantum processors over long distances, among other applications. Our review covers the leading approaches to achieving such transduction, with an emphasis on those based on atomic ensembles, opto-electro-mechanics, and electro-optics. We briefly discuss relevant metrics from the point of view of different applications, as well as challenges for the future.
Abstract Quantum transduction, the process of converting quantum signals from one form of energy to another, is an important area of quantum science and technology. The present perspective article reviews quantum transduction between microwave and optical photons, an area that has recently seen a lot of activity and progress because of its relevance for connecting superconducting quantum processors over long distances, among other applications. Our review covers the leading approaches to achieving such transduction, with an emphasis on those based on atomic ensembles, opto-electro-mechanics, and electro-optics. We briefly discuss relevant metrics from the point of view of different applications, as well as challenges for the future.
Quantum frequency conversion between superconducting (SC) microwave qubits and telecom optical photons is critical for long distance communication of networked SC quantum processors. While SC qubits operate at cryogenic temperatures to sustain their quantum coherence, converting them to the optical domain enables transferring the quantum states to room temperature and over long distances. For such a quantum state transduction process, several schemes have been investigated, including optomechanics, magnons, piezomechanics, and Pockels electro-optics (EO). The EO conversion approach is particularly attractive since it is broadband, low noise, mechanically and thermally stable (i.e., does not rely on freestanding structures), scalable (largescale integration of EO devices with superconducting circuits is possible), and tunable (e.g., using bias voltages). In this presentation we review our progress in an electro-optic based quantum transduction and discuss the promises and challenges.
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.
Optical photons play unique role in transmitting information over long distances. Photonic links by the optical fiber networks compose the backbone of today's global internet. Such fiber optics can also provide the most cost-effective quantum channels to distribute quantum information across distant stationary nodes in future large-scale quantum networks. This prospect motivates the recent emerging efforts in developing microwave-optical quantum transduction technology to interconnect microwave quantum processors. Various frequency conversion approaches are investigated to efficiently bridge the enormous electromagnetic frequency gap while preserving quantum coherence. Nonetheless, high-fidelity entanglement generation between remote quantum processing units has remained out of reach to date. Here, we summarize the state-of-the-art progresses in quantum transducer engineering and provide the perspectives on the key challenges and opportunities toward optically heralded quantum entanglement distributions.
The development of scalable quantum networks requires coherent interfaces capable of converting microwave photons used in superconducting quantum processors into optical photons suitable for long-distance fiber transmission. This review surveys recent progress in microwave-to-optical quantum transduction across optomechanical, electro-optic, and magneto-optic platforms, with emphasis on conversion efficiency, bandwidth, added noise, and operating temperature. In addition to standard metrics, we propose the internal efficiency eta_in and the magnon decay rate kappa_m/2pi as normalized parameters that enable fairer comparison across heterogeneous implementations. Optomechanical systems achieve internal phonon-to-photon efficiencies of 93% with sub-quantum added noise of 0.25 quanta at millikelvin temperatures. Electro-optic devices based on LiNbO3 and AlN have advanced from room-temperature efficiencies below 1% to millikelvin systems with internal efficiencies approaching 99.5%, added noise as low as 0.16 quanta at 60 mK, and bandwidths extending to several tens of megahertz. Magneto-optic (optomagnonic) platforms exhibit the lowest efficiencies (typically 10−10 to 10−8), but offer intrinsic non-reciprocity and broadband magnonic operation, with emerging approaches based on topological heterostructures and magnon squeezing predicting enhancements up to 10−4. Optomechanical systems appear promising for high-fidelity quantum state transfer, electro-optic transducers for high-bandwidth coherent links, and magneto-optic devices for non-reciprocal network components. We discuss the fundamental trade-off between efficiency and added noise across all three platforms, and argue that heterogeneous microwave-optical transduction is emerging as a key enabling technology for distributed quantum computing and large-scale quantum networks.
The complementary features of different qubit platforms for computing and communicating impose an intrinsic hardware heterogeneity in any quantum network, where nodes, while processing and storing quantum information, must also communicate through quantum links. Indeed, one of the most promising hardware platforms at quantum node scale for scalable and fast quantum computing is the superconducting technology, which operates at microwave frequencies. Whereas, for communicating at distances of practical interest beyond few meters, quantum links should operate at optical frequencies. Therefore, to allow the interaction between superconducting and photonic technologies, a quantum interface, known asquantum transducer, able to convert one type of qubit to another is required. This paper aims to provide a tutorial treatise on the fundamental research challenges of quantum transduction. The tutorial is structured around a communications engineering framework, thereby shedding light on its fundamental role in quantum network design and deployment—a perspective often overlooked in existing literature. This framework allows us to categorize different transduction modalities and to reveal an unorthodox one where the transducer itself can act as an entanglement source. From this standpoint, it is possible to conceive different source-destination link archetypes, where transduction plays a crucial role in the communication performances. The analysis also translates the quantum transduction process into a proper functional block within a new communication system model for a quantum network.
Quantum states encoded in microwave photons or qubits can be effectively manipulated, whereas optical photons can be coherently transferred via optical fibre and waveguide. The reversible conversion of quantum states between microwave and optical photons will hence enable the distribution of quantum information over long distance and significantly improve the scalability of hybrid quantum systems. Owning to technological advances, mechanical resonators couple to quantum devices in distinctly different spectral range with tunable coupling, and can serve as a powerful interface to connect those devices. In this review, recent theory and experimental progress in the coherent conversion between microwave and optical fields via optoelectromechanical transducers are summarized. The challenges and perspectives in achieving single‐photon‐level quantum state conversion are also discussed.