Academic year 2024/2025
19/06/2025
h 14:00 Room 0M03 – Physics Department
Online: Online participation via MS Teams link
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Speaker: Giulio Campanaro (Alice&Bob, Paris, France)
Dissipative cat qubits for quantum computing
Abstract
The hardware overhead of quantum error correction (QEC) is a major
obstacle to building fault-tolerant quantum computers. Bosonic codes
offer a solution by implementing error correction directly at the
physical qubit level, significantly reducing hardware demands.
Dissipative cat qubits exponentially suppress bit-flip errors over
orders of magnitude, leaving only phase-flip errors needing active
correction. This approach could enable Shor’s algorithm to run with 60
times fewer physical qubits than required by the surface code.
In
this talk, I will summarise basic concepts of QEC, and introduce cat
states as a promising encoding for hardware-efficient QEC. Finally, I
will focus on the physical implementation of dissipative cat qubits and
their built-in bit-flip error suppression.
Short Bio: Giulio Campanaro studied in the Universtiy of Milan for his master. He got his PhD in the university of Oxford, where he studied transmon devices in the group of Peter Leek. He joined Alice & Bob in 2022, with his
focus on the development and realization of two-qubit gates for dissipatively stabilized cat states. Beyond that, he contributed to the development and refinement of transom-free techniques for quantum tomography.
21/03/2025
h 11:30
Online: Online participation via MS Teams link
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Speaker: Gianluca Esposito
Entanglement and Stabilizer entropies of random pure states
Abstract
The interplay between non-stabilizerness and entanglement in random states is a very rich arena of study for the understanding of quantum advantage and complexity. In this work, we tackle the problem of such interplay in random pure quantum states. We show that while there is a strong dependence between entanglement and magic, they are, surprisingly, perfectly uncorrelated. We compute the expectation value of non-stabilizerness given the Schmidt spectrum (and thus entanglement). At a first approximation, entanglement determines the average magic on the Schmidt orbit. However, there is a finer structure in the average magic distinguishing different orbits where the flatness of entanglement spectrum is involved.
13/03/2025
h 15:30
Online: Online participation via MS Teams link
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Speaker: Emanuele Tirrito
(postdoc ICTP/unina)
Magic in many-body systems
Abstract
Quantum resources have played a crucial role in our understanding of many-body systems over the past two decades. While entanglement has been extensively studied, the role of other quantum resources—such as magic, which is essential for quantum computational advantage—remains less explored. Understanding the emergence and dynamics of magic is key to advancing quantum
simulators and quantum computing architectures.
In this talk, I will show how magic serves as a fundamental bridge between quantum information theory and many-body physics. I will begin by reviewing stabilizer Rényi entropies as a powerful measure of magic and its utility in characterizing complex quantum states. Building on this framework, I will explore three key aspects of magic in many-body systems:
(a) Magic Growth in Many-Body Dynamics: I will discuss how generic many-body evolution—whether governed by random circuits or Hamiltonian dynamics—rapidly generates magic, highlighting its connections to thermalization and quantum chaos [1-2].
(b) Classical Simulability of Quantum Many-Body Systems: I will examine the feasibility of classical simulations that leverage tensor network methods and the stabilizer formalism. Specifically, I will show that Pauli expectation values can be efficiently computed even for deep Clifford circuits doped with T-gates or general phase gates, provided the number of non-Clifford operations remains comparable to the system size [3].
(c) Complexity Transitions in Monitored Quantum Circuits: I will present recent insights into complexity transitions in monitored quantum dynamics, where measurement-induced phase transitions sharply delineate regimes of classical simulability and quantum advantage [4-5].
I will conclude by discussing experimental implications, outlining potential avenues for realizing these phenomena in near-term quantum devices, and addressing the challenges in probing and controlling magic in many-body settings.
[1] X. Turkeshi, E. Tirrito, P. Sierant, Magic spreading in random quantum circuits
arXiv:2407.03929 (2024)
[2] E. Tirrito, X. Turkeshi, P. Sierant, Anticoncentration and magic spreading under ergodic quantum dynamics, arXiv:2412.10229
[3] G. Fux, B. Beri, R. Fazio, E. Tirrito, Disentangling unitary dynamics with classically simulable quantum circuits, arXiv:2410.09001
[4] G. Fux, E. Tirrito, M. Dalmonte, R. Fazio, Measurement-induced phase transition in magic, Phys. Rev. Research 6, L042030 (2024)
[5] P.S. Tarabunga, E. Tirrito, Magic transition in measurement-only circuits arXiv:2407.15939
27/02/2025
h 15:00 – Aula Caianiello Dipartimento di Fisica Ettore Pancini
Online: Online participation via MS Teams link
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Dr. Javier Navarro Montilla
National Quantum Computing Centre (NQCC) , UK
Development of microwave and W-band superconducting Josephson Travelling Wave Parametric Amplifiers for quantum computing and beyond
Abstract
Quantum-limited amplifiers are crucial for the readout of weak signals in applications such as quantum computing and fundamental physics. Josephson Travelling Wave Parametric Amplifiers (JTWPAs) have emerged as a promising quantum-limited amplification technology for the readout of superconducting qubit arrays, significantly improving readout fidelity across several gigahertz of bandwidth.
In this seminar, I will delve into the research conducted during my PhD with the Superconducting Quantum Detectors (SQD) group at the University of Oxford. This work focused on the design, fabrication, and characterisation of JTWPAs. I will also discuss our efforts to push the operational frequency range of JTWPAs to the W-band (75–110 GHz). This range aligns with emerging superconducting qubit architectures that operate at 4 K temperatures, alleviating the cryogenic bottleneck and paving the way for scalable quantum computing.
Finally, I will conclude with an update on the scientific work currently developed at the Superconducting Circuits group from the National Quantum Computing Centre (NQCC) in the United Kingdom, which I have recently joined following my PhD.
Short Bio
Javier was a PhD student at the Superconducting Quantum Detectors (SQD) group, led by Dr. Boon-Kok Tan, from the University of Oxford. After completing his PhD in December 2024, he has recently joined the National Quantum Computing Centre (NQCC) in the United Kingdom as a Superconducting Qubit Physicist.
30/10/2024
h 12:00 – Aula Caianiello Dipartimento di Fisica Ettore Pancini
Online: Online participation via MS Teams link
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Prof. Sergey Kubatkin
Chalmers University, Sweden
National Quantum Computing Centre (NQCC) , UK
Learning about decoherence sources in superconducting circuits from the measurements on high-Q superconducting resonators
Abstract
Quantum-limited amplifiers are crucial for the readout of weak signals in applications such as quantum computing and fundamental physics. Josephson Travelling Wave Parametric Amplifiers (JTWPAs) have emerged as a promising quantum-limited amplification technology for the readout of superconducting qubit arrays, significantly improving readout fidelity across several gigahertz of bandwidth.
In this seminar, I will delve into the research conducted during my PhD with the Superconducting Quantum Detectors (SQD) group at the University of Oxford. This work focused on the design, fabrication, and characterisation of JTWPAs. I will also discuss our efforts to push the operational frequency range of JTWPAs to the W-band (75–110 GHz). This range aligns with emerging superconducting qubit architectures that operate at 4 K temperatures, alleviating the cryogenic bottleneck and paving the way for scalable quantum computing.
Finally, I will conclude with an update on the scientific work currently developed at the Superconducting Circuits group from the National Quantum Computing Centre (NQCC) in the United Kingdom, which I have recently joined following my PhD.
Short Bio
Sergey Kubatkin is full Professor at Quantum Device Physics, Chalmers.