Quantum technologies

Invited speaker: Prof. Fabrice Debbasch
Affiliation: Université Paris 6
Title: Discrete time quantum walks in (1 + 1) dimensions: wave propagation and
diffusive transport
Time and room: 17:15 lecture hall IAP

Abstract: I will focus on discrete time quantum walks defined in one space dimension with a quantum coin acting on a two-dimensional Hilbert space. The quantum coin is then an operator in U(2) and depends on 4 angles, which are allowed to depend on both time and space.
I will first revisit the continuous limits of these walks. A new systematic and mathematically rigorous limiting procedure will be introduced. It will be shown that the continuous limit, in most cases where it exists, is represented by a Dirac equation in (1 + 1) dimensional space-time. The space-time dependence of the angles defining the walks transcribes into a coupling between the Dirac fermion and both an electric and a relativistic gravitational field. This new result opens up the possibility of performing laboratory experiments simulating relativistic charged spin 1/2 particles in arbitrary electromagnetic and gravitational fields.
The second part of the talk will be devoted to quantum walks loosing quantum coherence because at least one of the angles defining the walk is chosen randomly at each time step. I will present numerical evidence that these walks, as they loose their coherence, are best approximated in classical terms by relativistic stochastic or diffusion processes.
The seminar will end by my listing several open problems suggested by these results, highlighting in particular connections between quantum walks and geometry.

Invited speaker: Prof. Thierry Giamarchi
Affiliation: Universität Genf
Title: Deconstructing the Electron: Quantum Physics in One Dimension
Time and room: 17:30 lecture hall IAP

Abstract: The effect of interactions on quantum particles is a long standing question, with important consequences for most realistic systems. In one dimension interactions lead to a radically new type of physics, very different from the one we know for higher dimensional systems. Once a pure theoretical game, such one dimensional physics has forcefully entered reality with the progress in miniaturization of electronic devices, and the appearance of novel physical system such as cold atoms in optical lattices.
I will present the main concepts underlying this physics, known as  Tomonaga-Luttinger liquid, and show the various realizations of such systems that recent progress in material science, nanotechnology and cold atomic physics have provided.
I will discuss where the field is standing now, and what are today's challenges.

Invited speaker: Dr.  Hendrik Ulbricht
Affiliation: University of Southampton
Title:Centre Of Mass Motion Interferometry Of Molecules And Nanoparticles
Time and room: 17:15 lecture hall IAP
Abstract:
The motivation for de Broglie interference of heavy particles is manifold, for example, to address the foundations of physics by investigating the quantum to classical transition, the use of interferometric techniques for applications such as: molecule metrology, molecule sorting, molecule quantum interference lithography and investigations of van der Walls/Casimir-Polder interactions, and to study the coherent manipulation of complex partciles for instance  to reconstruct the Wigner function of the motional quantum state of the diffracted molecules.  The centre of mass interferometry is not affected by internal excitation of the molecules as impressively demonstrated by our experiments. If however internal state dynamics is coupled to the centre of mass motion by electric or optical fields, the interference pattern is changed. I will explain our experiment on mapping the dynamics of the change of conformation of hot molecules onto its centre of mass motion while measuring the interference pattern.I will further emphasise the status of the develpoment of the Southampton molecule interferometer, where we recently achieved 27% of quantum contrast.
 
In the last part of my talk I shall illustrate our ideas for de Broglie interference of polystyrene or glass spheres (beads) of up to 100nm in diameter. Our approach considers the use of optical tweezing and position stabilisation as a launch pad for Talbot-Lau interferometry. We have very recently started the first experiments.

Invited speaker: Prof. Enrique Solano
Affiliation: Universidad del País Vasco UPV/EHU & Ikerbasque)
Title: Quantum Simulations As Our Quantum Theatre For Atoms And Photons
Time and room: 17:15 lecture hall IAP
Abstract: I will introduce the field of quantum simulations from a wide scientific perspective. Then, I will discuss the relevance of quantum simulations for reproducing different aspects of quantum physics: nonrelativistic and relativistic quantum dynamics, physical and unphysical quantum operations, as well as strong and ultrastrong light-matter interactions.
Finally, I will give examples in the context of trapped-ion and circuit QED technologies.

Invited speaker: Dr. Fabio Sciarrino
Affiliation: Università Sapienza di Roma
Title: Quantum Simulation With Integrated Photonics
Time and room: 17:15 lecture hall IAP
Abstract: Integrated photonic circuits have a strong potential to perform quantum information processing [1, 2]. Indeed, the ability to manipulate quantums states of light by integrated devices may open new perspectives both for fundamental tests of quantum mechanics and for novel technological applications [3,4]. Within this framework we have developed a directional coupler, fabricated by femtosecond laser waveguide writing, acting as an integrated beam splitter able to support polarization-encoded qubits [5]. As following step we addressed the implementation of quantum walk. This represents one of the most promising resources for the simulation of physical quantum systems, and has also emerged as an alternative to the standard circuit model for quantum computing. Up to now the experimental implementations have been restricted to single particle quantum walk, while very recently the quantum walks of two identical photons have been reported. For the first time, we investigated how the particle statistics, either bosonic or fermionic, influences a two-particle discrete quantum walk [6]. Such experiment has been realized by adopting two-photon entangled states and integrated photonic circuits. As following step we have exploited this technology to simulate the evolution for disordered quantum systems observing how the particle statistics influences Anderson localization. Finally we will discuss the perspectives of optical quantum simulation: the implementation of the boson sampling to demonstrate the computational capability of quantum systems [7] and the development of integrated architecture with three-dimensional geometries [8,9].

References
[1] T. D. Ladd, et al, “Quantum computers”, Nature 464, 45–53 (2010).
[2] J. L. O’Brien, A. Furusawa, and J. Vuckovic, “Photonic quantum technologies”, Nature Photonics 3, 687 (2009).
[3] P. Kok, et al, “Linear optical quantum computing with photonic qubits”, Rev. Mod. Phys. 79, 135 (2007).
[4] A. Politi, J. Matthews, M. Thompson, and J.O’Brien, “Integrated quantum photonics”, Selected Topics in Quantum Electronics, IEEE Journal of QE 1673, 15 (2009).
[5] L. Sansoni, F. Sciarrino, G. Vallone, P. Mataloni, A. Crespi, R. Ramponi, R. Osellame, “Polarization entangled state measurement on a chip”, Phys. Rev. Lett. 105, 200503 (2010).
[6] L. Sansoni, F. Sciarrino, G. Vallone, P. Mataloni, A. Crespi, R. Ramponi, R. Osellame, “Two-particle bosonic-fermionic quantum walk via 3D integrated photonics”, Phys. Rev. Lett. 108, 010502 (2012).
[7] A. Crespi, R. Osellame, R. Ramponi, D. J. Brod, E. F. Galvao, N. Spagnolo, C. Vitelli, E. Maiorino, P. Mataloni, and F. Sciarrino, “Experimental boson sampling in arbitrary integrated photonic circuits”, [arXiv:1212.2783]
[8] N. Spagnolo, C. Vitelli, L. Aparo, P. Mataloni, F. Sciarrino, A. Crespi, R. Ramponi, and R. Osellame, “Three-photon bosonic coalescence in an integrated tritter”, [arXiv:1210.6935]
[9] N. Spagnolo, L. Aparo, C. Vitelli, A. Crespi, R. Ramponi, R. Osellame, P. Mataloni, and F. Sciarrino, Quantum interferometry with three-dimensional geometry, Sci. Rep. 2, 862 (2012).