Next seminars
22/02/2024
h 12:00 – Aula Caianiello Dipartimento di Fisica Ettore Pancini
Online: Online participation via MS Teams link
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Giuseppe Falci
Università di Catania
Adiabatic manipulations of ultrastrongly coupled superconducting systems: from virtual photons to modular computing
Abstract
I review recent scientific work performed at the University of Catania on the dynamics of superconducting architectures in the ultrastrong coupling (USC) regime.
First, I will address the problem of the detection of virtual photons from the ground-state of a USC system. This is a long-standing problem which still awaits experimental demonstration. We show that combining an unconventional design of the device, state-of-the-art superinductor technology, and advanced control techniques one may convert virtual photons to real ones, which can be detected, with nearly 100% efficiency, very large fidelity. Out protocol being resilient to a strong measurement backaction, it allows to integrate a relatively simple measurement procedure allowing to discriminate virtual from thermal photons.
Then, I will highlight new results on Quantum operations for modular computing with USC systems. Solid-state systems made of artificial atoms (AA) and cavity modes in the strong coupling (SC) regime are a well-established architecture for quantum computing leveraging the ability of manipulating individual excitations. The clock rate is fixed by the interaction strength suggesting that in the USC regime ultrafast quantum operations may be performed. However, faster dynamics has a cost since USC breaks conservation of the number of excitations leading to a series of new fundamental effects which are unfortunately detrimental to quantum state processing.
We study strategies for suppressing the impact of such errors in a system of AAs USC-coupled to a quantized harmonic mode. We introduce a class of adiabatic protocols using the mode as a virtual quantum bus and show that substantial speedup together with high fidelity may be demonstrated for selected key operations, such as state transfer between remote units, state swapping, bi- and multi-partite entanglement generation and sharing. We derived a suitable low-energy description of the problem and found analytically a control strategy which suppresses errors down to ~10-6 for state transfer. These results were improved by optimal control numerical techniques and their robustness against parametric fluctuations and noise was shown.
Past seminars
24/11/2023
h 10:00 – Aula 2g26 Dipartimento di Fisica Ettore Pancini
Online: Online participation via MS Teams link
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Federica Mantegazzini
Fondazione Bruno Kessler (FBK) Trento
Development of superconducting quantum devices at FBK
Abstract
Superconducting quantum devices, such as qubits, parametric amplifiers, photon detectors and multiplexers, share the same elementary building blocks, namely Josephson junctions, high-Q resonators and high kinetic inductance components. At FBK, we are currently developing and optimising cross-type Al/AlOx/Al Josephson junctions, high-Q aluminium resonators and high kinetic inductance NbTiN thin-films. These components are combined to build Josephson Parametric Amplifiers (JPAs), Kinetic Inductance Travelling Wave Parametric Amplifiers (KI-TWPAs) and transmon qubits. The microfabrication processes and the preliminary characterisation results will be presented and an outlook on future applications for quantum sensing and cQED experiments will be discussed.
08/11/2023
h 11:30 – Aula Caianiello Dipartimento di Fisica Ettore Pancini
Online: Online participation via MS Teams link
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Alessandro Miano
(Yale University)
Engineering nonlinear Hamiltonians with flux-tunable Josephson circuits
Abstract
Flux-biased loops including one or more Josephson junctions are ubiquitous elements in quantum information experiments based on superconducting circuits. These quantum circuits can be tuned to implement a variety of Hamiltonians, with applications ranging from decoherence-protected qubits to quantum limited converters and amplifiers. In this talk, we will introduce a systematic method to analyze an arbitrary flux-biased superconducting circuit and compute the series expansion of its low-energy Hamiltonian. Remarkably, the expansion coefficients of such Hamiltonian can be expressed analytically as a function of the phase bias induced by the external flux on the smallest Josephson junction in the loop. The Hamiltonian-engineering capabilities empowered by this description will be discussed, with a focus on designing superconducting circuits implementing tailor-made nonlinear parametric processes.
27/10/2023
h 11:00 – Aula 2g26 del Dipartimento di Fisica Ettore Pancini
Online: Online participation via MS Teams link
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Marta De Luca
(Università La Sapienza di Roma)
Tailoring nanowires’ bandgap on demand: towards size-controlled and site- controlled single photon sources and quantum rings
Abstract
Quantum-confined structures, such as quantum dots, quantum disks, and quantum rings can be embedded in semiconductor nanowires (NWs) to introduce new functionalities or improve the performance of NW devices, such as nanolasers and solar cells. In particular, quantum dots (QDs) in NW waveguides can provide efficient single photon sources in quantum photonic circuits useful for implementing quantum computation and quantum communication protocols.
Quantum structures are typically created in NWs during the NW growth, by alternating regions with different bandgaps, which is usually achieved by changing NW chemical composition or crystal phase. This very powerful approach is characterized, however, by a limited control of the quantum structures’ size and, most importantly, emission energy. This makes it difficult to integrate the quantum structure within narrow-band micro-cavities in photonic circuits.
Moreover, this conventional approach does not allow to obtain high-quality QDs in every desired spectral range, tailor-made to a specific application. Here, we investigate dilute nitride NWs and InN NWs, and we report for the first time in NWs a post-growth bandgap engineering by mere exposition to low-energy ionized hydrogen gas. This new method allows fine-tuning on demand and over a wide range the bandgap of grown NWs and, when implemented at the nanoscale, can result in quantum structures as quantum dots and quantum rings with deterministic energy, position, and size.
Finally, we investigate excitonic lines in thin dilute nitride nanowires and find a g2 value of 0.05, thus proving the potential of GaAsN nanowires to act as single photon emitters.
Short Bio
Marta De Luca is Associate Professor in the Physics Department of Sapienza University of Rome (Italy). She has recently received an ERC starting grant on the topic of photonic circuits with nanowires. She is currently building a new lab and a new research group (NANO-SPECTROSCOPY group). She is expert in advanced optical spectroscopy of low-dimensional materials, with special focus on nanowires and 2D materials. In the last 3 years, she has been research scientist in the Physics Department of the University of Basel (Switzerland) under an Ambizione grant. Previously, she was post-doc in the Nano-phononics group in the University of Basel. M. De Luca obtained the PhD in Materials Science in Sapienza University.
M. De Luca has been awarded with the Laura Bassi prize by the Italian Society of Physics for being the best female physicist in 2021 and with the Rita Levi Montalcini grant allowing selected Italian scientists to set up a new research group in an Italian University.
12/10/2023
h 11:15 – Aula 2g26 del Dipartimento di Fisica Ettore Pancini
Online: Online participation via MS Teams link
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Patrick Cameron
(University of Glasgow and Sorbonne University)
Entanglement-enabled Adaptive Optics
Abstract
Adaptive optics (AO) has revolutionized imaging in applications ranging from astronomy to microscopy by enabling the correction of optical aberrations. In label-free microscopes, however, conventional AO methods are limited due to the absence of guidestar and the need to select an optimization metric specific to the type of sample and imaging process being used. Here, we propose an AO approach that exploits entanglement between photons to directly access and correct the point spread function (PSF) of the imaging system. This guidestar-free method is independent of the specimen and imaging modality. We demonstrate the imaging of biological samples in the presence of aberrations using a bright-field imaging setup operating with a source of spatially-entangled photon pairs. We show that our approach performs better than conventional AO in correcting certain types of aberrations, particularly in cases involving significant defocus. Our work improves AO for label-free microscopy, and could play a major role in the development of quantum microscopes, in which optical aberrations can counteract the advantages of using entangled photons and undermine their practical use.
25/09/2023
h 14:30 – Aula Caianiello del Dipartimento di Fisica Ettore Pancini
Online: Online participation via MS Teams link
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Farzad Ghafari
(Griffith University)
Simulating stochastic processes using quantum simulators
Abstract
Since its inception, quantum information processing (QIP) has been branched into many new directions. As well as well-known applications such as teleportation and metrology, researchers are beginning to investigate interdisciplinary areas such as quantum machine learning. One of the interesting areas is where quantum information science meets stochastic modelling, from the field of complexity science. Recently, it has been shown theoretically that, for simulating classical systems, quantum-assisted models and simulators are more efficient in terms of memory storage they require to do simulations, compared with classical computers. That is, for most systems, classical simulators demand an excessive amount of memory storage, while quantum simulators can do the same simulation with less memory. The main focus of this talk is on the experimental realisation of quantum simulators that are capable of simulating stochastic processes with a reduced amount of memory. To implement the (nearly) exact simulation of stochastic processes using quantum simulators, it is essential to have low-noise state preparation, robust unitary operations, and high-precision read-out. These requirements, and the flexibility and precision of photonic quantum optics, make photonics the ideal system for developing the science of this new quantum advantage and for making strides towards its technological realisation.
12/09/2023
h 11:00 – Aula Caianiello del Dipartimento di Fisica Ettore Pancini
Online: Online participation via MS Teams link
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Alessio D’Errico
(University of Ottawa)
Imaging the quantum state of bi-photons
Abstract
Reconstructing the quantum state of two-photon wave functions in high dimensional degrees of freedom is a challenging task that in general requires time-consuming and efficiency-limited projective approaches [1]. Here we show how recent imaging technologies allow for new efficient and reliable ways to characterize the quantum state of two photons entangled in the spatial degrees of freedom. We introduce a new technique that exploits classical digital holography applied to images extracted from postselected coincidence patterns [2]. The technique is based on superimposing an unknown biphoton state with a reference that exhibits the same spatial correlations.
By coincidence imaging the quantum state with a time-stamping camera, we reconstruct the amplitude and phase of the biphoton wave function when preparing the pump beam in different spatial modes [3] (e.g. Laguerre-Gauss and Hermite-Gauss). The results allow observing, to a high level of accuracy, high dimensional Bell states, Orbital Angular Momentum anti-correlations, parity conservation, and correlations in radial modes.
References
- A. D’Errico, F. Hufnagel, F. Miatto, M. Rezaee, and E. Karimi, Optics Letters 46, 2388 (2021).
- Zia, D., Dehghan, N., D’Errico, A. et al. Interferometric imaging of amplitude and phase of spatial biphoton states. Nat. Photon. (2023)
- A. D’Errico and E. Karimi, Electromagnetic Vortices: Wave Phenomena and Engineering Applications , 423 (2021).