First CeFEMA-IT Workshop on Quantum Technologies
09:30 – Optimal Control, Lattice Gauge Theories, and Quantum Annealing, Simone Montangero (Padova University)
Quantum optima l control allows finding the optimal strategy to drive a quantum system in a target state. We review an efficient algorithm to optimally control many-body quantum dynamics and apply it to quantum annealing, going beyond the adiabatic strategy. We present an information theoretical analysis of quantum optimal control processes and its implications.
We review some recent advancements we have obtained in tensor network algorithms that enable such investigations, and that can be exploited to support the development of quantum technologies via classical numerical simulations: novel approaches to study abelian and non-abelian lattice gauge theories, open many-body quantum systems and systems with long-range interactions or periodic boundary conditions.
Finally, we report some theoretical and experimental applications of these approaches to relevant scenarios, such as Rydberg atoms in optical lattices and the gauge theory resulting from the mapping of classical hard problems to short-range quantum Hamiltonians.
10:15 – Quantized Angular Momentum in Topological Optical Systems, Mário Silveirinha (IT & IST)
It is shown that the photonic Chern number ca n be understood as a quantum of the (thermal or quantum) fluctuation-induced light-angular momentum in a "photonic insulator" cavity. The nontrivial expectation of the angular momentum is due to a circulation of heat in closed orbits. Our findings can be extended to systems without a topological classification, and in such a case the “quantum” of the angular momentum density is determined by the net number of unidirectional edge states supported by the cavity walls.
11:15 – Thermodynamically Unbalanced Steady-states - A Route to Novel Ordered Phases, Pedro Ribeiro (CeFEMA & IST)
In this talk I will argue that novel ordered phases can be expected for interacting quantum systems away from thermal equilibrium. I will start by reporting a set of mean-field results concerning the effects of large bias voltages applied across an half-filled Hubbard chain. As a function of the applied voltage and temperature a rich set of phases can be found that is induced by the interplay between electron-electron interactions and non-equilibrium conditions. Taking a step back, I try to explain why such phases are possible (at least at the mean field level). This will motivate the characterization of the current-carrying steady-state that arises in the middle of a non-interacting metallic wire connected to macroscopic leads. Finally, I will comment on some ongoing work regarding the fate of the Peierls transition in a similar non-equilibrium setup.
11:45 – Topological Insulating Phases from Nodal Loop Semimetals, Miguel Araújo (University of Évora)
A three-dimensional nodal-loop semimetal phase is exploited to engineer a number of intriguing phases featuring different peculiar topological surface states. In particular, by introducing various two-dimensional gap terms to a 3D tight-binding model of a nodal-loop semimetal, we obtain a rich variety of topological phases of great interest to ongoing theoretical and experimental studies, including a chiral insulator, degenerate-surface-loop insulator, and second-order topological insulator, as well as a Weyl semimetal with tunable Fermi arc profiles.
The unique concept underlying our approach is to engineer topological surface states that inherit their dispersion relations from a gap term. The results provide one rather unified principle for the creation of novel topological phases and can guide the search for new topological materials.
14:00 – Electrically-readout NV Solid State Spin Qubits in Diamond: Physics and Applications, Milos Nesladek (Hasselt University)
Scalable principles for quantum state readout belong to the category of open questions in quantum technology. Building on the recent results of photoelectric detection of magnetic resonances (PDMR) [1,2] we discuss the prospect of PDMR technique for solid-state qubit devices in diamond. One of the key PDMR advantages over the optical detected magnetic resonance (ODMR) technique is the high detection rate ~ 5 x 108 s-1, exceeding orders of magnitude ODMR. Consequently, this opens prospects towards using electrical readout in wide range of quantum application and potentially to achieve single-shot readout. Here we discuss physics of NV centres and photoelectric gain used to obtain high detection rates on small NV spin qubit ensembles. The optical transitions on NV centre are reviewed and scenarios for obtaining highest single/noise ratio are presented. We demonstrate pulsed PDMR measurements, compatible with coherent manipulation of the spin states realised on quantum chips. Finally, we demonstrate a single NV qubit read electrically. We discuss other defects as potential candidates for electrically-read spin qubits in diamond.
 E. Bourgeois et al Nat. Comm. 6, 8577 (2015).
 M. Gulka et al, Phys. Rev. Applied 7, 044032, (2017)
14:45 – Free Space Optical Comms Towards Quantum, Rui Semide (LusoSpace)
Be it to relay earth generated data from one side of the earth to the other or for space generated data to be downloaded to earth, satellites are indi spensable assets in worldwide communications today. Although the currently deployed infrastructure relies on radio comms, radio spectrum management is becoming overcrowded and extremely complex to manage. With increased security and throughput, free space optical comms are posed to be the next step in space segment based commercial communications. Sharing several technological building blocks, Optical comms could also prove to be the foundations of unconditionally secure communication: Quantum Comms.
15:45 – Enabling Quantum Communications over Optical Fiber, Paulo André (IT & IST)
The presentation will focus on the relevant experimental work done at IT during the last years focus the quantum communication or the technologies enabling the quantum communication.
The perspective for the near future activities will be also attained.
16:15 – Information Geometry in the Analysis of Dynamical Phase Transitions, Bruno Mera (CEFEMA, IT & IST)
The Uhlmann connection is a mixed state generalization of the Berry connection. The latter has a very important role in the study of topological phases at zero temperature. Closely related, the quantum fidelity is an information theoretical quantity which is a measure of distinguishability of quantum states. Moreover, it has been extensively used in the analysis of quantum phase transitions.
We study finite-temperature Dynamical Phase Transitions by means of the fidelity and the Interferometric Loschmidt Echoes. These phase transitions occur in systems out of equilibrium upon performing a quench, i.e., when one suddenly changes the Hamiltonian to that of a different phase. We explain the physical and mathematical origin of the different behaviour seen in the two Loschmidt Echoes by means of the associated dynamical susceptibilities.
16:45 – Anomalous Heat Exchanges between 1D Bose-Einstein Condensates, Marco Pezzutto (IT & IST)
In this work we present an analyti c and numerical study of the dynamics and thermodynamics of two interacting 1D Bose-Einstein Condensates (BECs), with the main goal of investigating the thermodynamic implications and manifestations of quantum correlations, in particular entanglement. We consider two bosonic modes at different initial temperatures prepared in a correlated state. We investigate whether initial correlations may cause anomalies in the heat flow between the two parts, up to the point of causing reversion, i.e. a net heat flow from the colder to the hotter system. We look at the experimental scenario of a split BEC in an atom chip in the Tomonaga-Luttinger liquid regime, which allows us to model the BEC in terms of two single-mode thermal states of phononic excitations. These bosonic modes and their interactions can be described with the formalism of Gaussian states and operations. We are thus able to derive a relation between the change of the mutual information between the two modes, and the hea t exchanged by them. We consider two different types of interaction and identify a range of the relevant physical parameters in which a reversed heat flow may be detected in an experiment.
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