- CQT Lecture Series by Serge Haroche, College de France and Ecole Normale Superieure, Paris, France — Wed 08 Feb, 10:00 AM
CQT Lecture Series by Serge Haroche, College de France and Ecole Normale Superieure, Paris, France
Date/Time: Wednesday, 08 Feb at 10:00 am
Venue: CQT Seminar Room, S15-03-15
Title: Quantum information with real or artificial atoms and photons in cavities
Abstract: Manipulating states of simple quantum systems has become an important field in quantum optics and in mesoscopic physics, in the context of quantum information science. Various methods for state preparation, reconstruction and control have been recently demonstrated. Two-level systems (qubits) and quantum harmonic oscillators play an important role in this physics. The qubits are information carriers and the oscillators act as memories or quantum bus linking the qubits together. Coupling qubits to oscillators is the domain of Cavity Quantum Electrodynamics (CQED) and Circuit Quantum Electrodynamics (Circuit-QED). In microwave CQED, the qubits are Rydberg atoms and the oscillator is a mode of a high Q cavity while in Circuit QED, Josephson junctions act as artificial atoms playing the role of qubits and the oscillator is a mode of an LC radiofrequency resonator. The goal of these lectures is to analyze various ways to synthesise non-classical states of qubits or quantum oscillators, to reconstruct these states and to protect them against decoherence using quantum feedback methods. Experiments demonstrating these procedures will be described, with examples from both CQED and Circuit-QED physics. These lectures will give us an opportunity to review basic concepts of measurement theory in quantum physics and their links with classical estimation theory.
Lecture 1 Introduction to Cavity QED with Rydberg atoms interacting with microwave fields stored in a high- Q superconducting resonator.
Lecture 2 Review of measurement theory illustrated by the description of Quantum non-demolition (QND) photon counting in Cavity QED.
Lecture 3 Estimation and reconstruction of quantum states in Cavity QED experiments: the cases of Fock and Schrödinger cat states.
Lecture 4 Quantum feedback experiments in Cavity QED preparing and protecting against decoherence nonclassical states of a radiation field.
Lecture 5 An introduction to Circuit QED describing Josephson junctions as qubits and radiofrequency resonators as quantum oscillators.
Lecture 6 Description of Circuit QED experiments synthesing arbitrary states of quantum oscillators.
Lecture Dates: 6 , 8 , 10 , 13 , 15 , 17 Feb 2012 (Mon, Wed, Fri)
Time: 10am – 12pm - CQT Talk by Loïck Magnin, CQT — Wed 08 Feb, 2:00 PM
CQT Talk by Loïck Magnin, CQT
Date/Time: Wednesday, 08 Feb at 2:00 pm
Venue: CQT Seminar Room, S15-03-15
Title: A simpler proof of existence of quantum weak coin flipping with arbitrarily small bias
Abstract: Mochon’s result on the existence of quantum weak coin flipping with arbitrarily small bias [arXiv:quant-ph/0711:4114] is a fundamental result in quantum cryptography (No kidding, have a look at [arXiv:0904.1511] and [arXiv:1102.1678]) but at the same time one of the least understood. In this talk I'll explain the main ideas behind a simplified proof (no Green functions and no perturbation theory!). Compared to the original proof, ours contain simplifications from a technical point of view and also conceptually. We believe that our proof is an important step towards exhibiting a simple weak coin flipping protocol with arbitrarily small bias and provides new insight on the power of quantum cryptography. If you like convoluted proofs and semidefinite programming, you should appreciate this talk. This is joint work with D. Aharonov, A. Chailloux, M. Ganz and I. Kerenidis - CQT Lecture Series by Iacopo Carusotto, Universita' di Trento — Wed 08 Feb, 4:00 PM
CQT Lecture Series by Iacopo Carusotto, Universita' di Trento
Date/Time: Wednesday, 08 Feb at 4:00 pm
Venue: CQT Seminar Room, S15-03-15
Title: Quantum fluids of light
Abstract: In these lectures I will give an introduction to nonlinear and quantum optics of planar microcavity devices. The discussion will be carried out from an interdisciplinary perspective, trying to emphasize the conceptual links between optics and many-body physics and illustrate the general concept of fluid of light. After a general introduction about microcavities and strong light-matter coupling effects, I will review the most fascinating features of the fluid of light, e.g. Bose-Einstein condensation effects, superfluidity, topological excitations, as well as their recent experimental observations. I will conclude the cycle of lectures with an overview on future developments in the direction of strongly correlated photon states such as Tonks- Girardeau gases of fermionized photons or quantum Hall liquids of light.
Lecture Dates: 6 , 8 , 10 , 13 , 15 , 16 Feb 2012
(Mon, Wed, Fri – except for 16 Feb is Thurs)
Time: 4 – 6pm, except for 6 Feb is at 5.15pm – 6.50pm - CQT Colloquium by Guido Burkard, Department of Physics, University of Konstanz, Germany — Thu 09 Feb, 4:00 PM
CQT Colloquium by Guido Burkard, Department of Physics, University of Konstanz, Germany
Date/Time: Thursday, 09 Feb at 4:00 pm
Venue: CQT Seminar Room, S15-03-15
Title: Carbon Spintronics
Abstract:
Carbon, in the form of graphene and carbon nanotubes, has recently emerged as an interesting alternative material for electronics. Here, we argue that carbon is also a unique material for a new type of electronics that is based on the electron spin rather than its charge, known as spintronics, and in particular for spin-based quantum computing [1]. Due to the low concentration of nuclear spins and relatively weak spin-orbit coupling, carbon-based structures allow for long coherence times, which is the primary figure of merit for the quality of a spin quantum bit (qubit). We discuss the formation of quantum dots, acting as electron “traps’’, in graphene and their potential use for quantum information processing. In diamond, the spin coherence of defect centers can persist even at ambient temperatures. After introducing this fascinating quantum system, we briefly present a particular mechanism for storing and retrieving quantum information in an atomic nucleus in diamond [2].
[1] B. Trauzettel, D. Bulaev, D. Loss, and G. Burkard, Nature Phys. 3, 192 (2007).
[2] G. D. Fuchs, G. Burkard, P. V. Klimov, and D. D. Awschalom, Nature Phys. 7, 789 (2011). - CQT Talk by Martin Kiffner, CQT — Mon 13 Feb, 4:00 PM
CQT Talk by Martin Kiffner, CQT
Date/Time: Monday, 13 Feb at 4:00 pm
Venue: CQT Level 3 Conference Room, S15-03-18
Title: "Quantum coherence created by spontaneous emission"
Abstract:
In spontaneous emission an atom in an excited state undergoes a transition to the ground state and emits a single photon. This process usually leads to decoherence. On the contrary, a recent experiment [J. Tomkovic, M. Schreiber, J. Welte, M. Kiffner, J. Schmiedmayer and M. K. Oberthaler, Nature Physics 7, 379 (2011)] demonstrates that spontaneous emission of a single photon in front of a mirror can create a coherent superposition of two centre-of-mass states of the emitting atom.
In my talk I will describe the experiment and present a theoretical analysis of the results.
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