Quantum networks and large-scale quantum computers demand efficient ways to transfer quantum information between distant components, and a crucial element in achieving this is the conversion of quantum signals between different frequencies, a process known as quantum transduction. Akihiko Sekine, Ryo Murakami, and Yoshiyasu Doi, all from Fujitsu Research, Fujitsu Limited, investigate methods for converting microwave signals, commonly used within quantum processors, into optical signals suitable for transmission over long distances via optical fibre. Their work represents a significant step towards building practical quantum interconnects, as it explores both the theoretical underpinnings and experimental progress in various transduction techniques, including those leveraging optomechanical, electro-optic, magneto-optic, and atomic ensemble effects. By establishing a comprehensive understanding of transduction efficiency, noise, and bandwidth, this research paves the way for scalable and robust quantum communication systems.
Mathematical Derivations For Quantum Transduction Models
This supplementary material provides detailed mathematical derivations supporting research on quantum transduction, a process for converting quantum information between different frequencies. It explains the calculations and assumptions behind the presented results, offering a deeper understanding of the model’s efficiency and noise characteristics. The document begins with mathematical formulations establishing a foundation for understanding the transduction process. The core of this material focuses on zero-stage transduction, a method where conversion occurs in a single step, often utilizing the electro-optic effect, changing optical properties with an electric field.
Researchers define vectors representing the cavity modes, microwave and optical, and input noise operators to model the system. The scattering matrix describes how input noise transforms into output noise, while matrices define the system’s dynamics and coupling between microwave and optical cavities. The team calculates transduction efficiency, the probability of converting a microwave photon into an optical photon, which depends on geometric coupling strength, cavity parameters, and the cooperativity, a measure of the interaction strength between cavities. They also quantify added noise, an unavoidable consequence of the transduction process, crucial for evaluating performance. This section provides the mathematical framework for optimizing transducer design to minimize noise and maximize efficiency.
Efficient Microwave-to-Optical Quantum Transduction Methods
Scientists are developing quantum transduction techniques to connect quantum devices, a crucial step towards building large-scale quantum computers and networks. This work focuses on efficiently converting quantum information between microwave and optical frequencies, addressing the significant challenge of the large frequency difference between these ranges. The team employs a theoretical model to analyze quantum transduction, deriving expressions for efficiency, added noise, and bandwidth, essential parameters for characterizing performance. Researchers investigate several transduction methods, including those utilizing optomechanical, electro-optic, magneto-optic, and atomic ensemble effects.
A key goal is developing systems capable of transferring quantum states between superconducting qubits via optical fibers, a necessary architecture for scaling quantum computation beyond the limitations of single dilution refrigerators. The study establishes a method for defining transduction efficiency as the ratio of outgoing to incoming photons, providing a benchmark for evaluating system performance. Experiments aim to achieve transduction efficiency exceeding 99% with minimal added noise, critical for reliable quantum state transfer. The team investigates systems where optical fibers at telecom frequencies enable long-range communication, while superconducting qubits operate at microwave frequencies in the millikelvin regime. This research demonstrates a pathway towards building scalable quantum computers by interconnecting dilution refrigerators, overcoming current limitations in qubit density and thermal load.
Efficient Quantum Transduction with Minimal Added Noise
Scientists are developing quantum transducers, devices essential for connecting quantum systems and realizing large-scale quantum computers. This work focuses on efficiently converting quantum information between microwave and optical frequencies, a critical step for linking distant quantum processors. The research demonstrates that a transduction efficiency exceeding 1/2, combined with minimal added noise, is necessary to enable reliable quantum state transfer. Specifically, achieving low added noise, below 1, opens pathways for quantum communication even with less-than-ideal transduction efficiency, supplemented by heralded entanglement generation techniques.
The team modeled quantum transduction as a beam splitter mixing input signals with thermal noise, allowing precise quantification of efficiency and noise. Their analysis reveals that transduction efficiency directly represents the ratio of outgoing to incoming photons, and is fundamentally linked to the ability to transmit quantum information faithfully. Researchers established that a channel’s performance is governed by transmissivity, which defines the relationship between input and output photons, and is crucial for maintaining the integrity of quantum states. Measurements confirm that minimizing added noise during transduction is key to successful quantum communication. The study demonstrates that even with transduction efficiency below 1/2, quantum communication remains viable if the added noise is sufficiently low, paving the way for more flexible and robust quantum networks. This research establishes a clear threshold for both efficiency and noise, providing a roadmap for developing practical quantum interconnects and realizing the full potential of distributed quantum computing.
Microwave to Optical Transduction Advances Significantly
Recent research has significantly advanced quantum transduction, specifically the conversion of signals between microwave and optical frequencies, a crucial step towards scalable quantum technologies. Academics have developed a comprehensive theoretical framework for understanding transduction processes, defining key metrics such as efficiency, added noise, and bandwidth. This work has facilitated progress across several experimental approaches, including optomechanical, electro-optic, and atomic ensemble methods, each demonstrating unique strengths in achieving efficient and low-noise conversion. Notably, researchers have demonstrated transduction from superconducting qubits to optical photons, a vital capability for building quantum networks and distributed computing systems.
The most efficient transduction achieved to date reaches 47% using optomechanical techniques, while recent experiments employing electro-optic methods have simultaneously achieved high efficiency and exceptionally low added noise, entering the quantum-enabled regime. Although current systems have limitations in bandwidth and operating temperature, ongoing research focuses on improving these parameters and exploring novel materials and designs. Future work will likely concentrate on increasing bandwidth, reducing operating temperatures, and further optimizing transduction efficiency and noise characteristics to realize practical quantum communication and computation platforms.