RIKEN Succeeds in Generating World's Highest Quality Squeezed Light with Waveguide Optical Devices

The Breakthrough: RIKEN's Record-Breaking Squeezed Light Generation

In a landmark achievement announced on March 5, 2026, researchers from RIKEN, the University of Tokyo, NTT, and OptQC have generated the world's highest quality squeezed light using compact waveguide optical devices. This collaboration marks a pivotal step in photonic quantum technologies, demonstrating 12.1 dB of squeezing—a measure of quantum noise reduction that surpasses previous waveguide records. Led by Akira Furusawa, Team Director at RIKEN's Center for Quantum Computing and professor at the University of Tokyo, the team utilized a periodically poled lithium niobate (PPLN, where PPLN stands for periodically poled lithium niobate) waveguide optical parametric amplifier (OPA) enhanced by machine learning-optimized spatial mode matching.

The experiment achieved this by minimizing optical losses to just 4.4%, primarily through a novel double-reflection spatial light modulator (SLM) controlled via Bayesian optimization. This setup allowed for direct measurement of squeezing without corrections, confirming the record at frequencies around 10 MHz with terahertz (THz) bandwidth potential. For context, 12 dB squeezing reduces quantum noise by a factor of about 16 in one quadrature of the light field, beating the standard quantum limit essential for advanced quantum applications.

Understanding Squeezed Light: Quantum Optics Fundamentals

Squeezed light is a non-classical state of light where the uncertainty in one property, such as phase or amplitude quadrature, is reduced below the Heisenberg uncertainty principle's standard quantum limit, at the expense of increased uncertainty in the conjugate property. Full name: squeezed vacuum state or squeezed coherent state. This 'squeezing' redistributes quantum noise, enabling precision measurements beyond classical limits.

In practice, optical parametric amplification (OPA) generates squeezed light by parametrically down-converting a pump photon into signal and idler photons in a nonlinear medium like PPLN. Step-by-step process: 1) A strong pump laser at 772.66 nm is coupled with a weak probe at 1545.32 nm into the waveguide. 2) Nonlinear interaction amplifies quantum correlations, producing squeezed vacuum at the signal wavelength. 3) Balanced homodyne detection interferes the squeezed light with a local oscillator (LO) to measure noise spectra.

Waveguide OPAs offer advantages over bulk or cavity-based systems: compactness (cm-scale), high conversion efficiency, and ultra-broadband operation (THz vs. MHz-GHz), ideal for integrated photonic quantum circuits.

The Experimental Setup: Step-by-Step Innovation

The core device is a quasi-single-mode PPLN waveguide with propagation loss under 0.1 dB/cm, pumped at 585 mW. Key innovation: addressing spatial mode mismatch between the multimode squeezed output and single-mode LO, which previously caused ~4% loss limiting squeezing to 10 dB.

• Machine learning (Bayesian optimization) shapes the LO beam via SLM with 40 Zernike parameters, achieving 99.6% mode overlap (0.4% loss).
• Double-reflection SLM configuration doubles degrees of freedom for aberration correction.
• Differential homodyne detection subtracts shot noise for accurate squeezing amid LO fluctuations.
• High-quantum-efficiency (99%) InGaAs photodiodes and low-noise electronics ensure circuit noise clearance >28 dB.

This resulted in stable 12.1 ± 0.2 dB squeezing at 3 MHz, degrading slightly to 11.8 dB at 100 MHz post-correction, with potential for further gains by reducing waveguide loss or phase noise.

Earlier work by the same group hit 10.1 dB with improved phase locking, published in Optics Express.

Surpassing Previous Records: A Quantum Leap

Prior waveguide squeezing topped at ~10 dB due to mode mismatch; cavity OPAs reach similar levels but lack THz bandwidth. This 12 dB mark rivals top cavity systems while enabling scalable integration. Japan's ecosystem—RIKEN's quantum center, UTokyo's Furusawa lab, NTT's photonics expertise, OptQC's computing focus—positions it as a leader in photonic QC.

Statistics: Total system efficiency ~95.6%, vs. 92% previously; broadband nature supports million-qubit scales by 2030 per OptQC goals.OptQC announcement

Photo by Artyom Korshunov on Unsplash

Implications for Photonic Quantum Computing

Squeezed light is the resource for continuous-variable (CV) measurement-based quantum computing (MBQC), generating cluster states via Gaussian operations. Higher squeezing lowers error rates in fusion gates, crucial for fault-tolerance.

• Enables ultrafast (THz clock) universal QC, unlike superconducting qubits' MHz limits.
• Integrates with IOWN for telecom-wavelength, room-temperature operation.
• Neural network acceleration: Low-noise linear optics for AI beyond classical simulations.

RIKEN's role accelerates Japan's Moonshot R&D Goal 6: rack-mountable million-qubit QC by 2030.

Japan's Quantum Research Landscape in Higher Education

Japan invests heavily in quantum tech, with RIKEN's ¥100B+ quantum center hosting Furusawa's team. UTokyo's Applied Physics leads CV quantum info; NTT/OptQC bridge academia-industry.

Recent stats: Japan holds 20% global quantum optics papers; collaborations yield 30% citation impact boost. Universities like Tohoku, Osaka contribute materials (e.g., low-loss PPLN).Japanese higher ed opportunities

Cultural context: Government's Quantum Technology Innovation Strategy (2025) funds ¥300B, prioritizing photonic paths for energy-efficient QC amid global race.

Broader Applications: Sensing, Communication, and Beyond

Beyond QC, high-squeezing aids gravitational wave detectors (LIGO-like), atomic clocks, and secure comms (CV-QKD). THz bandwidth enables real-time quantum tomography.

Stakeholder views: Furusawa notes, "This minimizes losses for practical QC." NTT eyes IOWN integration for 6G quantum networks.

Challenges Overcome and Future Roadmap

Challenges: Waveguide loss, mode mismatch, phase stability. Solutions: ML optimization, low-noise detection. Future: Shorter waveguides, on-chip SLMs, non-Gaussian operations for full universality.

Timeline: 2027 demo 10k qubits (OptQC); 2030 million-qubit fault-tolerant machine. Impacts: Revolutionize drug discovery, materials sim, optimization.

Photo by Pawel Czerwinski on Unsplash

Careers in Quantum Optics: Opportunities in Japan

This breakthrough highlights demand for PhDs/postdocs in quantum photonics. RIKEN/UTokyo offer positions in CV-QC; NTT hires for industry apps.

• Skills: Nonlinear optics, ML for photonics, nanofab.
• Prospects: Salaries ¥6-10M, global collabs.

Japan's postdoc jobs, research assistant roles booming. Check Rate My Professor for insights on quantum faculty.

For career advice, visit higher ed career advice.

Conclusion: Japan's Quantum Photonics Leadership

RIKEN's squeezed light milestone underscores Japan's edge in scalable QC. Aspiring researchers, explore university jobs or higher ed jobs in quantum fields. Stay tuned for fault-tolerant era.