Light Can Now Be Stored on Silicon Chips for over One Microsecond
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Researchers led by Stephan Rinner at the Technical University of Munich, alongside collaborators at the Max Planck Institute of Quantum Optics have demonstrated a new quantum memory integrated directly onto silicon chips, representing a significant step towards scalable photonic quantum computing.
The team successfully fabricated and tested a functional quantum memory utilising erbium-doped silicon waveguides, produced as part of a multi-wafer project by a nanophotonic foundry. The device achieves light storage with a 44.2MHz bandwidth and a programmable delay exceeding 1s within a compact footprint of 1.5x 10⁻² mm², substantially outperforming the capabilities of conventional on-chip delay lines. Critically, the research preserves the phase of the read-out light field with a high visibility of 91.3%, a strong advance in maintaining quantum information and opening new avenues for manipulating photons in integrated circuits. Millisecond-scale quantum memory realised via integrated nanophotonics A programmable delay exceeding 1μs has been achieved in an on-chip quantum memory, a substantial improvement over existing technology where conventional on-chip delay lines offer performance many orders of magnitude lower. This breakthrough crosses a vital threshold for practical quantum computing, as previous devices lacked the capacity to reliably store quantum information for the durations required for complex calculations. Light signals typically propagate too quickly for effective manipulation, hindering complex calculations and limiting the depth of quantum circuits that can be implemented. The ability to coherently store quantum information, even for relatively short periods, allows for the temporal ordering of operations, enabling more complex quantum algorithms. This is particularly important for applications such as quantum repeaters, where entanglement needs to be established and maintained over long distances, and for quantum simulations requiring precise timing of interactions. The device, fabricated using erbium-doped silicon waveguides within a nanophotonic foundry, maintains phase preservation with a high visibility of 91.3%, important for preserving the integrity of quantum states during storage and retrieval. Loss of phase information would destroy the quantum state, rendering the memory useless for quantum computation. A bandwidth of 44.2MHz has been demonstrated, enabling the storage of complex quantum signals. This bandwidth determines the range of frequencies that can be stored simultaneously, allowing for the encoding of more information within the stored light pulse. Measuring just 1.5x 10⁻² mm², the silicon waveguide incorporates erbium doping to enhance light interaction and enable quantum storage, a process important for building compact quantum devices. The small footprint is crucial for scaling up the number of quantum memories on a single chip, a key requirement for building larger and more powerful quantum computers. Erbium-doped silicon waveguide fabrication and quantum memory optimisation Erbium-doped silicon waveguides were fabricated using a commercial silicon-on-insulator chip, processed within a nanophotonic foundry. This approach allows for mass production using standard semiconductor techniques, paving the way for wider adoption and reducing the cost of quantum devices. The use of a foundry-based process is essential for scalability, as it allows for the fabrication of large numbers of identical devices with consistent performance. Erbium dopants were integrated into the silicon during fabrication, with concentration carefully controlled to balance storage time and efficiency; a lower concentration minimises unwanted spectral diffusion. Spectral diffusion refers to the random fluctuations in the frequency of the stored light, which can degrade the quality of the quantum information. Optimising the erbium concentration is therefore crucial for achieving long storage times and high fidelity. Precise control over material composition and waveguide geometry was fundamental to achieving the observed performance. The waveguides are designed to confine light within a small volume, enhancing the interaction with the erbium ions. The geometry of the waveguides also influences the propagation characteristics of the light, affecting the storage time and bandwidth. Current device efficiency stands at 1.89x 10⁻⁸, and resonator enhancements or increased doping could potentially improve this, although these solutions introduce their own complexities. Resonator enhancements involve creating structures that trap light, increasing the interaction with the erbium ions, while increased doping could lead to higher absorption and reduced signal strength. Experiments were conducted at temperatures below 1.4 Kelvin within a 0.75 Tesla magnetic field to preserve the quantum information. These cryogenic conditions are necessary to reduce thermal noise, which can disrupt the delicate quantum states. The magnetic field helps to align the erbium ions, further enhancing the storage time. Approximately 7.5x 10⁶ erbium ions are integrated into the device at a peak concentration of 1x 10¹⁵ cm⁻³. This figure does not yet reflect the scalability needed to connect many such memories into a functional quantum computer.
The team is exploring methods to enhance performance and integration, including optimising the waveguide design and increasing the density of erbium ions. Silicon chip integrates light storage exceeding microsecond timescales This demonstration of a functional, on-chip quantum memory fabricated within a standard nanophotonic foundry represents a key advance for integrated photonics. Utilising existing semiconductor manufacturing techniques, the successful integration of this memory onto a silicon chip offers a pathway towards scalable quantum technologies. The ability to leverage established fabrication processes is a significant advantage, as it reduces the development time and cost associated with building quantum devices. Achieving far greater light storage rates remains a significant hurdle, despite the current efficiency of 1.89x 10⁻⁸. Improvements are possible, but these solutions introduce their own complexities, requiring careful trade-offs between performance and practicality. The device compactly stores light for over a microsecond, far exceeding existing on-chip technologies. A programmable delay of light signals exceeding one microsecond was achieved by using tiny channels that amplify and control light, a duration previously unattainable with comparable on-chip devices. This delay allows for the precise timing of quantum operations, enabling more complex quantum algorithms. Maintaining a high visibility of 91.3% in the retrieved light field confirms the preservation of quantum information during storage, essential for reliable quantum computation. This high visibility indicates that the quantum state is largely unaffected by the storage and retrieval process, ensuring the accuracy of the computation. The development of such on-chip quantum memories is crucial for realising practical and scalable quantum computing systems. The researchers successfully demonstrated an on-chip quantum memory using erbium-doped silicon waveguides, achieving a programmable delay exceeding one microsecond. This represents a significant step towards scalable quantum technologies because it utilises standard semiconductor manufacturing techniques. The device, with a footprint of 1.5x 10⁻² mm², stored light with a bandwidth of 44.2MHz and preserved the phase of the light field with a visibility of 91.3%.
The team is currently exploring methods to enhance performance, including optimising waveguide design and increasing dopant concentrations. 👉 More information 🗞 Quantum memory on a nanophotonic silicon chip 🧠 ArXiv: https://arxiv.org/abs/2604.00138 Tags: