# Paolo Zanardi
Paolo Zanardi is a physicist, Professor of Physics and [Mathematics](https://www.edgepedia.org/mathematics) at the [University of Southern California](https://www.edgepedia.org/university-of-southern-california) (USC), working in quantum information science and mathematical physics.[1](https://dornsife.usc.edu/profile/paolo-zanardi/) He is known for the 1997 [Physical Review Letters](https://www.edgepedia.org/physical-review-letters) paper "Noiseless Quantum Codes," for the 1999 proposal of holonomic quantum computation, and for a geometric, information-theoretic treatment of quantum phase transitions built on ground-state fidelity.[2](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.79.3306) • [3](https://arxiv.org/abs/quant-ph/9904011) • [4](https://doi.org/10.1103/physrevlett.99.100603)
| Key fact | Detail |
|---|---|
| Current position | Professor of Physics and Mathematics, USC Dornsife College[1](https://dornsife.usc.edu/profile/paolo-zanardi/) |
| Signature work | "Noiseless Quantum Codes," Physical Review Letters 79, 3306 (1997)[2](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.79.3306) |
| Holonomic quantum computation | Proposed 1999: gates from non-abelian holonomy on degenerate eigenspaces[3](https://arxiv.org/abs/quant-ph/9904011) |
| Recent activity | Publications through 2026, including Physical Review A 113, 042201 on mereological quantum phase transitions[5](https://inspirehep.net/authors/1969109) |
## Career record
His early papers carry Torino affiliations: Unità INFM at the Politecnico di Torino and the ISI Foundation.[2](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.79.3306) • [3](https://arxiv.org/abs/quant-ph/9904011)
According to *Operational Quantum Mereology and Minimal Scrambling* (Quantum, 2024), at USC he is affiliated with the Department of Physics and [Astronomy](https://www.edgepedia.org/astronomy), the Center for Quantum Information Science and Technology, and the Department of Mathematics.[6](https://doi.org/10.22331/q-2024-07-11-1406)
## Representative work
"Noiseless Quantum Codes," published in Physical Review Letters 79, 3306 on 27 October 1997, considers a quantum register of N replicas of a finite-dimensional system all coupled equally to a common environment. It shows that a linear subspace of this register is dynamically decoupled from the environment: states in that subspace evolve unitarily and are decoherence-dissipation free. The decoupled space realizes a noiseless quantum code in which information can, in principle, be stored for an arbitrarily long time without being affected by errors.[2](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.79.3306) The publisher records 1,071 citing articles for the paper.[2](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.79.3306)
## Holonomic quantum computation
In April 1999 Zanardi and Rasetti posted "Holonomic Quantum Computation," which proposes using non-abelian holonomy, the generalized [Berry phase](https://www.edgepedia.org/berry-phase), to enable quantum computation.[3](https://arxiv.org/abs/quant-ph/9904011) The computational space is an n-fold degenerate eigenspace of a family of Hamiltonians parametrized by a manifold of classical control fields; adiabatic loops in that manifold induce non-trivial unitary transformations on the eigenspace. For a generic system, composing a generic pair of loops allows universal quantum computation.[3](https://arxiv.org/abs/quant-ph/9904011) The gates are therefore geometric phases accumulated over closed paths in control space rather than dynamical phases of fixed Hamiltonians, which is the distinction from standard gate-based approaches. The topic entered the standard reference literature: the 2013 Cambridge volume *Quantum Error Correction* includes a chapter on holonomic quantum computation by Zanardi, alongside chapters on [decoherence-free subspaces](https://www.edgepedia.org/decoherence-free-subspace) and on fault tolerance for holonomic quantum computation.[7](http://ui.adsabs.harvard.edu/abs/2013qec..book.....L/abstract)
## Fidelity and quantum phase transitions
In the 2007 Physical Review Letters paper "Information-Theoretic Differential Geometry of Quantum Phase Transitions," the manifold of coupling constants parametrizing a quantum Hamiltonian is equipped with a natural [Riemannian metric](https://www.edgepedia.org/riemannian-metric) with an operational distinguishability content, and the singularities of this metric are argued to correspond to the quantum phase transitions of the system.[4](https://doi.org/10.1103/physrevlett.99.100603)
## Recent developments
Zanardi has remained active. In December 2023 he posted "Mutual averaged non-commutativity of quantum operator algebras" on arXiv (arXiv:2312.14019), which, according to the preprint, was published in [Journal of Mathematical Physics](https://www.edgepedia.org/journal-of-mathematical-physics) 65, 062202 (2024).[8](https://ar5iv.labs.arxiv.org/html/2312.14019) In July 2024 the journal Quantum published "Operational Quantum Mereology and Minimal Scrambling," from USC's physics and mathematics departments.[6](https://doi.org/10.22331/q-2024-07-11-1406)
This recent line of work treats subsystem structure itself as a variable. A paper dated 7 October 2025 introduces mereological quantum phase transitions (m-QPTs), based on a variational family of operator algebras defining generalized tensor product structures, a parameter-dependent Hamiltonian, and a [quantum scrambling](https://www.edgepedia.org/quantum-scrambling) functional; spin-chain simulations show sharp susceptibility responses at an integrability point and strong growth across disorder-induced localization, suggesting critical reorganizations of emergent subsystem structure. It was published in [Physical Review A](https://www.edgepedia.org/physical-review-a) 113, 042201 (2026).[9](https://arxiv.org/html/2510.06389) [INSPIRE-HEP](https://www.edgepedia.org/inspire-hep) lists further 2026 publications, including Physical Review A 113, 042429.[5](https://inspirehep.net/authors/1969109)
## References
1. Paolo Zanardi, USC Dornsife faculty profile. https://dornsife.usc.edu/profile/paolo-zanardi/
2. P. Zanardi and M. Rasetti, "Noiseless Quantum Codes," Phys. Rev. Lett. 79, 3306 (1997). https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.79.3306
3. P. Zanardi and M. Rasetti, "Holonomic Quantum Computation," arXiv:quant-ph/9904011 (1999). https://arxiv.org/abs/quant-ph/9904011
4. "Information-Theoretic Differential Geometry of Quantum Phase Transitions," Phys. Rev. Lett. 99, 100603 (2007). https://doi.org/10.1103/physrevlett.99.100603
5. Paolo Zanardi, INSPIRE-HEP author record. https://inspirehep.net/authors/1969109
6. "Operational Quantum Mereology and Minimal Scrambling," Quantum (2024). https://doi.org/10.22331/q-2024-07-11-1406
7. *Quantum Error Correction* (Cambridge, 2013), table of contents. http://ui.adsabs.harvard.edu/abs/2013qec..book.....L/abstract
8. "Mutual averaged non-commutativity of quantum operator algebras," arXiv:2312.14019. https://ar5iv.labs.arxiv.org/html/2312.14019
9. "Mereological Quantum Phase Transitions," arXiv:2510.06389. https://arxiv.org/html/2510.06389
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