Kitaev, toric code and linking theory to devices

In this episode of The New Quantum Era, your host Sebastian Hassinger is joined by Chetan Nayak, Technical Fellow at Microsoft, professor of physics at the University of California Santa Barbara, and driving force behind Microsoft's quantum hardware R&D program. They discuss a modality of qubit that has not been covered on the podcast before, based on Majorana fermonic behaviors, which have the promise of providing topological protection against the errors which are such a challenge to quantum computing.

Guest Bio

•  Chetan Nayak is a Technical Fellow at Microsoft and leads the company’s topological quantum hardware program, including the Majorana‑1 processor based on Majorana‑zero‑mode qubits. 
•  He is also a professor of physics at UCSB and a leading theorist in topological phases of matter, non‑Abelian anyons, and topological quantum computation. 
•  Chetan co‑founded Microsoft’s Station Q  in 2005, building a bridge from theoretical proposals for topological qubits to engineered semiconductor–superconductor devices. 

What we talk about

•  Chetan’s first exposure to quantum computing in Peter Shor’s lectures at the Institute for Advanced Study, and how that intersected with his PhD work with Frank Wilczek on non‑Abelian topological phases and Majorana zero modes. 
•  The early days of topological quantum computation: fractional quantum Hall states at , emergent quasiparticles, and the realization that braiding these excitations naturally implements Clifford gates. 
•  How Alexei Kitaev’s toric‑code and Majorana‑chain ideas connected abstract topology to concrete condensed‑matter systems, and led to Chetan’s collaboration with Michael Freedman and Sankar Das Sarma. 
•  The 2005 proposal for a gallium‑arsenide quantum Hall device realizing a topological qubit, and the founding of Station Q to turn such theoretical blueprints into experimental devices in partnership with academic labs. 
•  Why Microsoft pivoted from quantum Hall platforms to semiconductor–superconductor nanowires: leveraging the Fu–Kane proximity effect, spin–orbit‑coupled semiconductors, and a huge material design space—while wrestling with the challenges of interfaces and integration. 
•  The evolution of the tetron architecture: two parallel topological nanowires with four Majorana zero modes, connected by a trivial superconducting wire and coupled to quantum dots that enable native Z‑ and X‑parity loop measurements. 
•  How topological superconductivity allows a superconducting island to host even or odd total electron parity without a local signature, and why that nonlocal encoding provides hardware‑level protection for the qubit’s logical 0 and 1. 
•  Microsoft’s roadmap in a 2D “quality vs. complexity” space: improving topological gap, readout signal‑to‑noise, and measurement fidelity while scaling from single tetrons to error‑corrected logical qubits and, ultimately, utility‑scale systems. 
•  Error correction on top of topological qubits: using surface codes and Hastings–Haah Floquet codes with native two‑qubit parity measurements, and targeting hundreds of physical tetrons per logical qubit and thousands of logical qubits for applications like Shor’s algorithm and quantum chemistry. 
•  Engineering for scale: digital, on–off control of quantum‑dot couplings; cryogenic CMOS to fan out control lines inside the fridge; and why tetron size and microsecond‑scale operations sit in a sweet spot for both physics and classical feedback. 
•  Where things stand today: the Majorana‑1 chiplet, recent tetron loop‑measurement experiments, DARPA’s US2QC program, and how external users—starting with government and academic partners—will begin to access these devices before broader Azure Quantum integration. 

Papers and resources mentioned
These are representative papers and resources that align with topics and allusions in the conversation; they are good entry points if you want to go deeper.

• Non‑Abelian Anyons and Topological Quantum Computation – S. Das Sarma, M. Freedman, C. Nayak, Rev. Mod. Phys. 80, 1083 (2008); 
  Early device proposals

• Sankar Das Sarma, Michael Freedman, and Chetan Nayak, “Topological quantum computation,” Physics Today 59(7), 32–38 (July 2006).
• Roadmap to fault‑tolerant quantum computation using topological qubits – C. Nayak et al., arXiv:2502.12252. 
• Distinct lifetimes for X and Z loop measurements in a Majorana tetron - C. Nayaak et al., arXiv:2507.08795.
• Majorana qubit codes that also correct odd-weight errors - S. Kundu and B. Reichardt, arXiv:2311.01779. 
• Microsoft's Majorana 1 chip carves new path for quantum computing, Microsoft blog post