Simone Severini


I am a Royal Society University Research Fellow and a Reader in Physics of Information.
I obtained my PhD from Bristol University, in the then newly created Quantum Computation and Information Group. My advisor was Richard Jozsa, whose advisor was Roger Penrose. I was a visiting student at UC Berkeley (and MSRI), and previously I studied Chemistry at the University of Siena and Philosophy (Logic) at the University of Florence. I was a Newton International Fellow at UCL, a PostDoctoral Research Fellow of the Institute for Quantum Computing and the Department of Combinatorics & Optimization at the University of Waterloo, mentored by Michele Mosca, and a PostDoctoral Research Assistant in the Department of Computer Science and the Department of Mathematics at the University of York. My long term scientific visits include CRI, CWI, MIT, Nankai, NUS and RISCLinz.
My links at UCL are Intelligent Systems Group, UCL Quantum, CoMPLEX Research Group, UCL Institute of Origins, and London Center for Nanotechnology.
I am currently interested on:
Combinatorial parameters in quantum information;
Zeroerror information and quantum communication;
Informationtheoretic analysis of complex systems.
My research papers can be found in arXiv, MathSciNet, MPRA, PubMed, and IRIS.
R. Duan, S. Severini, A. Winter, On zeroerror communication via quantum channels in the presence of noiseless feedback, February 2015. arXiv:1502.02987v1 [quantph]
A. E. Teschendorff, C. R. S. Banerji , S. Severini , R. Kuehn , P. Sollich, Increased signaling entropy in cancer requires the scalefree property of protein interaction networks, accepted for publication in Sci. Rep., 2015.
C. R. S. Banerji, S. Severini, C. Caldas, A. E. Teschendorff, Intratumour signalling entropy determines clinical outcome in breast and lung cancer, PLoS Comput Biol 11(3): e1004115 (2015).


M. Furer, WeisfeilerLehman Renement Requires at Least a Linear Number of Iterations, ICALP 2001.
Chris Banerji, MRes and PhD, UCL. Octavio Zapata, PhD, UCL. Nadish de Silva, visiting student, University of Oxford. Daniel Temko, PhD, UCL. Arthur Guerard, MRes, UCL. Sherman Ip, MRes, UCL. YuChing Yang, Mres, UCL. Andrea Casaccino, PhD, University of Siena / MIT (then at General Electrics). Alessandro Cosentino, Laurea Magistrale, University of Pisa (then PhD at University of Waterloo with John Watrous). James West, PhD, UCL (then at a hedge fund). Janos Hodsagi, MRes, UCL. Lourdes Sriraja, MRes, UCL. Tommaso Gagliardoni, Laura Magistrale, University of Perugia (then at the Center for Advanced Security Research Darmstadt). Soomin Kim and Emma Rahman (Nuffield Research Placement Scheme). [CPs CoMPLEX: Thomas Wyatt, Sophie Atkinson , Janos Hodsagi, Andrew Maher, Tim Lucas, Robert Bentham, Teresa Attenborough], Si Bing MSci, University of Bristol. Walter Vinci, postdoc, UCL (then postdoc at University of Southern California).
Research students applications: Computer Science: here (PRISM); Centre for Doctoral Training in Delivering Quantum Technologies: here; Centre for Mathematics, Physics and Engineering in the Life Sciences and Experimental Biology (CoMPLEX): here.
Strand 1: Quantum Cryptography (Fernando Brandao and Lluis Masanes); Strand 3: Quantum Error Correction and Fault Tolerance (Dan Browne); Strand 4: Lab: Quantum Key Distribution (Jeroen Elzerman). Notes: Strand 1, Quantum Information Theory, from “PHASGQ01 Physics and Foundations of Quantum Technologies” thought by Jonathan Oppenheim is useful.
Lecture 1 (24/02/15; Week 27). Recap and warmup: Historical background, Ket/bra notation, quantum registers, projective measurements in different bases, composite systems, unitary evolution, classical limit and doubly stochastic matrices vs. unitary matrices, qubits, superpositions, basic quantum gates (Hadamard, bit flip, phase flip, phase gate, CNOT), Nocloning theorem, diagrams and circuits, partial measurements, Hamiltonian dynamics. Exercise: SWAP test. [Exercise: Entanglement in a Bell pair.]
Lecture 2 (26/02/15; Week 27). From classical to quantum computation: Entanglement (measuring entanglement), classical gates, Boolean functions, Boolean circuits, recognizability, Thermodynamics of computation: Landauer's principle, CCNOT, universal sets, SolovayKitaev's theorem, function evaluation, parallelism, the notion of query complexity, Deutsch's algorithm, DeutschJozsa's algorithm, Exercise: measuring interference.
Lecture 3 (03/03/15; Week 28). The Fourier transform and its applications: Simon's algorithm, Fourier transform (classical, quantum), FFT algorithm, efficiency, quantum phase estimation (see also Aram Harrow's lecture in December 2014), the Hidden Subgroup Problem. Exercise: Fourier transform.
Lecture 4 (05/03/15; Week 28). Shor's factoring algorithm: factoring, reduction to period finding, Shor's method for period finding, continued fractions and postprocessing, Grouptheoretic setting for the Fourier transform (representations, abelian vs. nonabelian case). Exercise: Factoring.
Lecture 5 (09/03/15; Week 29). Walks: Graphs 101. Matrices representing graphs. Spectrum. Random walks. Mixing. Quantum approaches and physical intuition. Coined quantum walks. Grover walks. Example: line. Average mixing (cycle and hypercube). Continuous walks. State transfer on spin systems (perfect state transfer, distance). Ambainis' Element Distinctness algorithm (mention).
Lecture 6 (12/03/15; Week 29). Quantum complexity theory: P, NP, Pcomplete, PSPACE, NPcompleteness, Notion of polynomial reductions, P vs NP question, BPP, BQP, QMA, inclusion diagrams (classical and quantum classes). Reference: J. Watrous, Quantum Computational Complexity, arXiv:0804.3401 [quantph]
Lecture 7 (17/03/15; Week 30). Hamiltonian complexity [Guest lecturer: Toby Cubitt]: Quantum computation aims to engineer complex manybody systems to process information in ways that would not be possible classically. Manybody physics aims to understand the complex behaviour of naturallyoccurring manybody systems. In a sense, they are two sides of the same coin. We will investigate the computational complexity of quantum manybody systems, culminating in Kitaev's seminal proof of QMAhardness of the ground state problem for local Hamiltonians.
Lecture 8 (18/03/15; Week 30). Grover's search: Unstructured database search, Grover's algorithm, Grover's iterate, Geometric argument, Search via continuous walks.
Lecture 9 (20/03/15; Week 30). Adiabatic computation [Guest lecturer: Andrew Green]: Amongst the many remarkable changes in viewpoint that have occurred in condensed matter in recent years, notions of quantum information and entanglement are perhaps the most prominent. Adiabatic quantum computation provides an arena where the overlap between condensed matter physics and quantum information is most direct. Ideas and analytical methods from quantum phase transitions, manybody localization, outofequilibrium dynamics and the dynamics of decoherence may all be used to assess its power and limitations and provide a complementary view to those of the quantum information theorists. I will review some of the basic ideas of adiabatic computation  from the performance of an ideal computation, to the limiting effects of the environment and how one might hope to mitigate them. To do this, I will use tools of Langevin equations, matrix product states and tensor networks. I will spend half an hour or so at the blackboard introducing these ideas as appropriate during the talk.
General references:
J. Watrous, CPSC 519/619, University of Waterloo: Quantum Computation, 2006.
J. Preskill, Ph219/CS219, Caltech, Quantum Computation, 201314. Chapter 6
P. Kaye, R. Laflamme, and M. Mosca, An Introduction to Quantum Computing, Oxford University Press (2007).
M. A. Nielsen and I. L. Chuang, Quantum Computation and Quantum Information, Cambridge University Press (2000).
S. Aaronson, PHYS771, University of Waterloo, Quantum Computing Since Democritus, 2006.
S. Arora and B. Barak, Complexity theory: a modern approach, (free pdf draft), Cambridge University Press (2007).