PsiQuantum Alpha System to lead the Quantum Computing Race
In 2027, PsiQuantum expects photons to power a million-qubit supercomputer.
The Alpha System
California startup PsiQuantum wants to develop a million-qubit fault-tolerant quantum computer by 2027. Quantum computing could transform chemistry and materials research if this aim is reached. Four British university researchers launched the company in 2016 to build a silicon photonics-based optical quantum computer. It has raised $1.7 billion. The “Alpha System,” PsiQuantum's first fully working prototype, is being assembled at its new Milpitas, California plant. By building on networking and photonics technology, the company may reach critical scale faster than competitors using “matter-based” solutions like superconducting qubits, trapped ions, or neutral atoms.
Scaling: Fault-Tolerance Required
From the start, PsiQuantum focused on building a full-scale, fault-tolerant quantum computer. While early industrial expectations focused on tiny, “noisy intermediate-scale quantum” (NISQ) computers performing significant work without error correction, comprehensive fault tolerance is now accepted for utility.
According to cofounder and chief scientific officer Pete Shadbolt, this fundamental premise drove the search for optical approaches. Cooling, control, communication, and manufacturability must be addressed to reach millions of qubits for error correction. Photonics may solve these difficulties better than competitors.
A New Cryogenics/Connectivity Method
Matter-based qubits are sensitive to radiation and temperature fluctuations because they must be chilled to almost absolute zero. Photons can act as qubits at ambient temperature since they resist radiation and heat.
Cryogenic temperatures are still needed because PsiQuantum's technology uses superconducting photon detectors between 2 and 4 kelvins. It's easier to achieve these temperatures. PsiQuantum's server-rack-sized cryogenic cabinets can hold 250 chips, unlike superconducting qubits' dilution freezers, which hold one or two chips. Linde's cryoplant will cool three of these huge cabinets in Milpitas.
The heat and radiation resistance of photons allows control electronics to be placed near qubits, simplifying system design. Communication is simplified by qubits' ability to be transported over telecom fiber. Recently, the company sent qubits over 250 meters of fiber with 99.7% fidelity.
Making Mass Production with Semiconductors
Manufacturing is one of the biggest obstacles to large-scale quantum computing because most systems are unique. For this, PsiQuantum created a commercial chip production method using silicon-photonics technology.
Shadbolt notes that the company was founded to manufacture millions of high-maturity devices using the trillions of dollars invested in the semiconductor industry over the past 50 years. Despite its superconducting photon detectors and ultrafast optical switches, Global Foundries is commercially producing thousands of PsiQuantum devices in Malta, New York.
“Flighty Photons” Technical Challenges
Despite these advantages, photonics has significant downsides. The linear optics technology makes photon generation nondeterministic, therefore quick fault tolerance is needed, according to Simon Devitt of the Center for Quantum Software and Information at the University of Technology, Sydney.
Gate operations in PsiQuantum fail 25–50% of the time. The business utilizes “multiplexing” to try many photon-generation methods and pick the best ones, but this only partially solves the problem. The remaining gate failures need error correction. Devitt believes that gate failures have taken up a large portion of the error-correction budget, leaving little room for other faults.
Laser loss is the second leading cause of errors after gate failures. This loss depends on waveguides, photon detectors, and optical switches. Despite data showing ready waveguides and detectors, the company's switches have high losses.
Shadbolt remains convinced that purity and manufacturing are the real issues, not material science in general. He believes thousands of little, gradual improvements in chip geometry, design, and manufacturing accuracy will lead to success.
Not Seeking Supremacy, Testing System
Building the Alpha System in Milpitas is the first major test of the business's design. Vice president of system architecture Mercedes Gimeno-Segovia said these exploratory testing will not involve quantum techniques. Unlike other companies who used NISQ prototypes to establish quantum supremacy on “toy problems,” PsiQuantum believes NISQ machines behave too differently from fault-tolerant ones to provide useful information.
The Alpha System is used to assess if the system's behavior matches the company's theoretical models, which is crucial for designing large-scale systems.
The Alpha System should cool by the end of the year, allowing testing to begin in early 2026 assuming PsiQuantum continues on its current path, according to Shadbolt. Although he warns that raising the necessary money beyond the enormous funds already secured may be the major challenge, analyst Paul Smith-Goodson believes the company may achieve its ambitious technical goals. Instead of security and cryptography, PsiQuantum aims to use its future utility-scale computer to address global challenges like pharmaceutical development, materials research, and climate change.
