Scalable Quantum Interferometers with SiN and Liquid Crystal Integration: Towards Low-Power, Reconfigurable Quantum Photonic Circuits

arXiv (学術論文プレプリント) そ 他

Overview

Compact, efficient, and low-power phase modulators are essential for integrated quantum photonics. This research developed a Mach-Zehnder interferometer (MZI) integrating liquid crystal (LC) on a silicon nitride (SiN) platform, demonstrating CMOS-compatible performance and high-visibility quantum interference (approx. 98.5%). LC offers an attractive alternative to existing SiN modulators’ high power consumption and thermal crosstalk issues, due to its large refractive index change and industrial maturity. This study establishes LC-integrated SiN photonics as a scalable, reconfigurable, and energy-efficient platform for quantum photonic circuits.

In Depth

The Importance of Phase Modulators in Quantum Photonic Circuits

In the fields of quantum computing and quantum communication, integrated quantum photonic circuits play a crucial role in encoding and manipulating quantum information using photons. One of the central components of these circuits is the phase modulator, which precisely controls the phase of photons to enable qubit operations and quantum interference. However, existing phase modulators have faced challenges in terms of miniaturization, efficiency, low power consumption, and scalability.

Innovative Integration of Silicon Nitride (SiN) and Liquid Crystal (LC)

To address these challenges, this research developed an innovative Mach-Zehnder interferometer (MZI) that integrates Liquid Crystal (LC) on a Silicon Nitride (SiN) platform. SiN is an excellent photonic material known for its ultra-low loss and broad transparency window, but existing SiN-based thermo-optic modulators have struggled with high power consumption and thermal crosstalk. In contrast, LC offers an attractive alternative due to the following advantages:

• Large Refractive Index Change: Enables a significant refractive index change with applied voltage, allowing for efficient phase modulation.
• Low Power Consumption: Requires significantly less power for operation compared to traditional thermo-optic modulators, offering superior energy efficiency. This research achieved CMOS-compatible performance (Vpi * L < 1 V-mm).
• Reduced Thermal Crosstalk: Since LC is not thermally dependent, it minimizes the impact of thermal crosstalk in highly integrated circuits.
• Industrial Maturity: Benefits from industrial maturity gained in liquid crystal displays, offering a relatively clear path to mass production.

Demonstration of High-Visibility Quantum Interference and Scalability

The research team conducted a two-photon interference experiment using this LC-integrated SiN MZI, demonstrating quantum interference with an extremely high visibility of approximately 98.5%. This signifies that high-fidelity quantum operations are possible with this new platform in optical quantum computing. This technology establishes the potential of SiN-LC integration as a scalable, electrically reconfigurable, and energy-efficient platform for quantum photonic circuits.

Contribution to the Future of Quantum Technology

This SiN and LC integration technology is expected to significantly contribute to the chip-level implementation and scalability of quantum computing, potentially influencing the commercialization roadmap for future quantum computers. As NTT aims for a 1 million-qubit optical quantum computer by 2030, such low-power and reconfigurable phase modulators will be indispensable for realizing large-scale quantum circuits. Moving forward, challenges include establishing stable integration processes for LC materials and SiN platforms, and further validating the long-term reliability of devices, but this marks a crucial step in accelerating the development of quantum technology.