Dr. Charles Tahan

"Quantum Information Technology and Society from 2000 to 2040,” Charles Tahan, Partner at Microsoft Quantum and Visiting Research Professor at the University of Maryland; formerly Assistant Director for Quantum Information Science at the White House Office of Science and Technology Policy

In December 2025, the Science, Technology, and Social Values Lab at the Institute for Advanced Study (IAS) hosted the third event in the: Quantum, Broadly Considered lecture series. The series explores how unresolved questions in physics and mathematics, alongside government investments, market dynamics, and social imaginaries have shaped, and continue to shape, the possibilities of quantum research.

In this lecture, Dr. Charles Tahan, a partner at Microsoft Quantum and a physicist, reflected on his 25 years working in academia, government, and industry. During his career he has led the US National Security Agency’s Laboratory for Physical Sciences, and shaped US quantum strategy at The White House Office of Science and Technology Policy. His work has spanned fundamental research on quantum dots and superconducting qubits, science policy coordination across multiple federal agencies, and scaling quantum computers for commercial applications. Today, he heads a technical team at Microsoft Quantum.

Looking back, Tahan cited key milestones in quantum technology, including the 2024 error correction demonstrations across multiple platforms. Illustrating the scale of the challenge ahead, he noted that building a practical quantum computer requires that a vast gap is bridged between current c.1,000-qubit systems with imperfect error rates, and the hundreds of thousands to millions of nearly perfect (stable) qubits needed for useful applications.

Realizing Quantum Computing Requires a Collective Effort
That building a quantum computer remains so intensely difficult after more than two decades of effort speaks volumes about the field’s complexity, according to Tahan. In his view, quantum computing dates back to 2000 when, motivated by Shor’s algorithm, the field first attracted real government attention and funding. The algorithm was developed by US mathematician Peter Shor in the 1990s and made it possible to factor large numbers exponentially faster than classical algorithms. This triggered serious quantum computing investment, because of the associated threat to RSA encryption used for secure data transmission and digital signatures.

Some of Tahan’s own breakthrough moments came during his time as a program manager at the Defense Advanced Research Projects Agency (DARPA), developing quantum research programs. Here, he said, he began to “see the whole clock,” not just “one gear,” giving him new perspective on how to strategically accelerate science and engineering. When he issued a funding announcement for quantum benchmarking, for instance, he received no proposals because there was no established field. Tahan addressed this by organizing workshops, bringing the right people together, and convincing them of the subject’s value, then reissuing the call. The result was a thriving quantum characterization community that now provides standards for comparing technologies.

But challenges remained, not least the cost of pursuing next quantum breakthroughs. The solution Tahan found was to fund MIT Lincoln Laboratory and companies to fabricate qubits for the community, so that researchers could experiment in this research area without massive capital investment. This democratized research access beyond a few elite universities, Tahan noted, remarking that quantum efforts were otherwise concentrated in four main US states. Greater equity in science, he suggested, would bring more minds to complex problems, accelerating progress.

Making Impossible Trade-offs Manageable
In the meantime, considerable engineering challenges remain. A common thread, Tahan suggested, is the need to make impossible trade-offs manageable. One example he cited was “dual-rail encoding.” This doubles the qubit count but eliminates expensive microwave generators, because it uses simple voltage pulses, compatible with standard CMOS technology. The net result is a simpler system, despite more qubits. Another illustration he offered was making superconducting qubits 1,000 times smaller with better materials (e.g., parallel-plate design rather than sprawling planar structures). “Instead of a football-field-sized quantum computer, now you can make it in a single wafer,” he explained.

His point here was that quantum computing doesn’t need brute force, but rather architectural intellect: the discovery of designs that help reduce overall system complexity even as individual component counts increase. So, what about quantum computing’s “wiring problem”? This is the physical challenge of connecting the increasing number of qubits to individual control and readout lines. It results in an unmanageable density of wires, heat, and crosstalk as systems scale, making large-scale, practical quantum computers difficult to build.

When Tahan led the National Security Agency’s Laboratory for Physical Sciences (he worked there between 2009 and 2020, becoming Technical Director in 2015), he came to appreciate the magnitude of the wiring challenge in scaling quantum computing. Where classical computers work because of digital logic’s noise tolerance and massive multiplexing (billions of transistors, thousands of wires), quantum needs at least one wire per qubit, representing a fundamentally different architecture. In other words, quantum wiring is a physical constraint to design around, he explained.

Policy Matters
Returning to the theme of applying more minds (and wallets) to solving the quantum computing challenge, Tahan talked about policy, funding, and his takeaways from his three years at The White House Office of Science and Technology Policy earlier this decade, where he was a colleague of Professor Nelson. Explaining that the US National Quantum Initiative takes a coordinated approach across some 20 federal agencies, he highlighted the US’s federated approach to science and technology. His role was to encourage multi-agency co-operation, despite those agencies competing for resources.

He highlighted three policy achievements from that time:

mandating that government agencies upgrade to post-quantum encryption
promoting investment in home-grown science and technology skills
remaining open to international collaboration despite security concerns. (“Quantum has always been a global field,” Tahan noted.)

Quantum in Context: Microsoft’s Roadmap
Tahan concluded with a roundup of his current work at Microsoft, which includes testing error correction with partner companies (currently at a scale of hundreds of qubits); developing topological qubits with better scalability properties; and promoting neutral-atom systems to international partners.

Microsoft approaches quantum as an accelerator within a massive cloud infrastructure, Tahan said. That is, it sees quantum as one tool in a heterogeneous computing environment —along with other specialized hardware accelerators, including graphics processing units and field-programmable gate arrays.

On AI and quantum, Tahan emphasized genuine progress (including Microsoft using AI to discover new battery electrolytes and coolants, “compressing times from years to weeks”) as an example of where the technology offers tangible value. This is in contrast to more speculative presumptions about quantum-AI synergy (given that AI needs big data, while quantum excels at working with small, high-quality data). He proffered a hybrid framework in which quantum generates data and AI learns patterns.

Microsoft’s ambition is to build “the world’s computer”—one combining a high-performance computing foundational infrastructure, AI, and quantum, by 2040, Tahan said. He also highlighted his own role in creating a “crucible for acceleration” (in Maryland), made up of Microsoft scientists, partner companies, and academia.

During the Q&A session, Tahan told scholars he believed fault-tolerant quantum computers were “not imminent, but inevitable,” requiring perhaps at least another decade of disciplined engineering. But serious progress will need not only theorists, but also materials scientists, device engineers, cryogenic specialists, and systems engineers, he warned—so quantum-oriented education curricula must become more interdisciplinary.