Insider Brief:
- Quantum Source released a comprehensive technical report, developed with The Quantum Insider, that compares all major qubit modalities and outlines engineering pathways toward fault-tolerant quantum computing.
- The report highlights that the field has moved from theoretical exploration to practical engineering, with recent demonstrations from Google and Quantinuum showing logical qubits outperforming physical ones.
- It introduces a unified framework comparing qubit systems by qubit carrier and computational model, showing that while no modality currently dominates, hybrid approaches may have the potential to overcome key scalability limits.
- A case study on Quantum Source’s deterministic atom–photon platform shows how their design replaces probabilistic photonic entanglement with efficient, repeatable atom-mediated processes, reducing hardware overhead and enabling scalable, modular architectures for future fault-tolerant systems.
Quantum Source, a pioneering company developing scalable photonic quantum computing systems, has released a new industry report, From Qubits to Logic: Engineering Fault-Tolerant Quantum Systems, offering one of the most comprehensive technical assessments to date of the global push toward fault-tolerant quantum computing.
The report, developed in partnership with The Quantum Insider, synthesizes progress across all major qubit modalities and introduces a comparative framework linking physical qubit performance, quantum-error-correction (QEC) strategies, and scalability. The report emphasizes that the path to fault tolerance has shifted from a theoretical goal to an engineering challenge, defined by how well systems scale, and integrate control, architecture, and error-correction design.
The Transition from Theory to Demonstration
The report defines fault tolerance as the capability of a quantum computer to perform arbitrarily long computations reliably, even when each underlying physical gate or measurement is prone to error. Achieving this requires encoding logical qubits across many physical qubits and applying continuous error detection and correction.
As explained in the report, recent milestones such as Google’s Willow processor achieving error suppression below the surface-code threshold and Quantinuum’s demonstration of logical gates outperforming physical ones confirm that the field has entered a new phase. Logical qubits are now capable of surpassing physical fidelity, which is an essential crucial step toward scalable, useful quantum machines
“For more than two decades, the theoretical foundations of quantum error correction have matured,” said Michael Slutsky, Head of Theory at Quantum Source. “In recent years, the first functional logical elements have been experimentally demonstrated across a broad range of hardware platforms, showing steadily improving performance and marking real progress toward the fault-tolerant era. We’re not there yet—but the future is coming into focus.”
A Unified Framework for Comparing Qubit Modalities
The report organizes today’s quantum hardware landscape along two fundamental axes:
- The physical nature of the qubit carrier (matter-based vs. photon-based), and
- The computational model (circuit-based vs. measurement-based quantum computing, MBQC).
This two-axis perspective clarifies both the constraints and opportunities inherent to each modality:
- Superconducting qubits – Fast gate speeds and mature fabrication, but cryogenic wiring and variability limit scaling.
- Trapped-ion qubits – Record-setting fidelities and all-to-all connectivity, yet scaling is constrained by mode crowding and control complexity.
- Neutral-atom qubits – Large, reconfigurable arrays with second-scale coherence, but two-qubit fidelities must exceed 99.9 %.
- Semiconductor spin qubits – CMOS compatibility and density advantages offset by device variability and cryogenic control challenges.
- Photonic qubits – Operate at room temperature and excel at networking, but photon loss and probabilistic entanglement limit scalability.
The comparative framework reveals that no modality yet leads the path to fault tolerance. Each platform carries its own engineering trade-offs, from coherence limits to fabrication challenges, making progress uneven and interdependent. While hybrid approaches remain unproven, they represent a promising area of exploration, particularly for addressing bottlenecks that no single technology can overcome alone. It is within this emerging space that Quantum Source is positioning its deterministic atom–photon architecture.
Quantum Source’s Deterministic Atom–Photon Architecture
At the center of the report there is a case study on Quantum Source’s hybrid atom–photon platform, which replaces probabilistic two-photon fusion with deterministic atom-mediated entanglement.
In conventional measurement-based photonic computing, millions of synchronized photon sources and switches are needed to compensate for low entangling-gate success rates. Quantum Source’s design solves this by using single trapped atoms as reusable entanglement mediators:
- A photon is first entangled with an atom inside a high-finesse optical cavity.
- The atomic state is then mapped onto a second photon, entangling the two photons deterministically through the shared atomic state.
- The same atom can repeat this process, efficiently generating large photonic cluster states.
This deterministic atom–photon mechanism reduces hardware overhead, requiring fewer photon sources, switches, and detectors. It also maintains full compatibility with room-temperature photonic systems.
“By harnessing deterministic photon–atom interactions on a chip, we can generate entangled photonic states with unprecedented efficiency, at room temperature, in a compact and scalable architecture,” said Oded Melamed, CEO of Quantum Source.
The report concludes that this hybrid approach “directly addresses the primary photonic bottleneck of two-photon entanglement” and could enable modular, distributed FTQC architectures where matter qubits handle deterministic logic and photons manage long-distance communication
Implications for Industry and Policy
The paper frames FTQC as both a technological and strategic inflection point.
For industry, success will depend on co-optimizing hardware, software, and error-correction stacks to minimize overhead. For investors and policymakers, diversification across hardware modalities is essential: each contributes unique value to the developing ecosystem.
The report forecasts that within the next decade, logical qubits will likely outperform physical ones and million-qubit systems will become a realistic engineering target. Hybrid innovations such as Quantum Source’s atom–photon platform may play an essential role in achieving those goals.
About the Report
From Qubits to Logic: Engineering Fault-Tolerant Quantum Systems is a 2025 technical white paper by Quantum Source, developed in partnership with The Quantum Insider.
The report presents a comprehensive comparative analysis of major qubit modalities and introduces a framework for evaluating fault-tolerant scalability across hardware classes. It includes expert commentary from leading researchers and references to recent experimental breakthroughs spanning superconducting, ion-trap, neutral-atom, spin, and photonic platforms.
For more information or to access the full report, visit this link.
