Lectures will be held at ICFO’s Blue Lecture Room on Mondays and Wednesdays.


RESEARCH SEMINARS

Seminar 1
Wednesday March 10, 2010 from 11:00 to 12:00
Quantum control of atomic spin qudits.

Atomic spins are natural carriers of quantum information given their long coherence times and the wide variety of coherent fields available to control them. The multiplet of magnetic sublevels in the hyperfine manifold of the grounds state of alkali atoms provides a particularly attractive playground to explore methods of quantum control, extending techniques from simple two-level systems (qubits) to general d-level systems (qudits). In this seminar I will review recent work done in collaboration with Prof. Poul Jessen, University of Arizona, to design new protocols for quantum control and measurement of hyperfine qudits in Cesium-133, and implement them in the lab. Specifically, we will study conditions for controllability, protocols to design arbitrary quantum states, and efficiently reconstruct the density operator via continuous measurement. Extensions to arbitrary qudit gates will also be discussed.


Seminar 2
Monday March 15, 2010 from 11:00 to 12:00
Collective mesoscopic spin control.

Control of complex quantum systems has applications in many-body physics, quantum information processing, and high-precision metrology. Mesoscopic ensembles of cold atomic spins are an ideal testbed for such explorations, given the growing quantum-control toolbox. In a cigar-shaped trap, when the ensemble is optically thick on resonance, the spins coherently couple to the polarization state of a paraxial laser probe. The photons serve as a “quantum bus” that transfers quantum correlations between atoms and entangles them. Spin-squeezed states based on this mechanism have recently been produced, representing an important step toward more complex control. In this seminar I will discuss new approaches to achieving more sophisticated and general control, including unitary evolution through coherent optical feedback and quantum erasure, exponential squeezing via phase matching, and the production of Schroedinger kittens via heralded scattering of single photons.


Seminar 3
Tuesday May 25, 2010 from 10:00 to 11:00
Alkaline-earth atoms -- a new platform quantum information with nuclear spins.

Alkaline-earth-like atoms are the new kids on the block that provide a platform for quantum control with cold atoms, building on the tools for optical atomic clocks. Whereas most cold-atom experiments are done with alkali-like atoms, the Group-II atoms (and cousins) have some unique properties. In the electronic ground state, the closed s-shell has no electron angular momentum, and thus no hyperfine coupling. The nuclear spin is thus decoupled and provides a robust degree of freedom for quantum coherence. Nuclear spins also dictate the nature of atomic collisions via quantum statistics and act a quantum switch for two-atom quantum logic gates. Metastable excited states used for atom clocks provide long-lived coherence that can be used to transfer quantum information between electrons and nuclei, which allows for the cooling of atomic motion without decohering the spin state. Finally, the narrow intercombination lines are particularly attractive for exciting optical Feshbach resonances for further coherent control of the two-atom quantum state.


LECTURE SERIES IN QUANTUM INFORMATION WITH ATOMS AND PHOTONS

Lecture 1
Wednesday March 24, 2010 from 11:00 to 13:00
Introduction: Atomic and Photons – natural carriers of quantum information.

• The basic units of quantum information: qubits, qudits, continuous variables. Atomic and photonic encodings.
• Representations – density matrices and phase space distributions.

Lecture 2
Tuesday March 30, 2010 from 11:00 to 13:00
(Atomic spin)–(photon polarization) interactions

• Zeeman and light shift interaction.
• Tensor polarizability and irreducible decomposition.
• Faraday effect and birefringence.

Lecture 3
Wenesday April 7, 2010 from 11:00 to 13:00
Mean-field Dynamics

• Field Dynamics: Faraday effect and birefringence.
• Spin dynamics: Nonlinear evolution, master equation.

Lecture 4
Monday April 12, 2010 from 11:00 to 13:00
Control

• Controllability.
• Designing control waveforms.
• Quantum-state preparation.

Lecture 5
Wednesday April 21, 2010 from 11:00 to 13:00
Measurement

• Completely positive map – Kraus decomposition.
• Continuous measurement.
• Back action.

Lecture 6
Wednesday May 5, 2010 from 11:00 to 13:00
Quantum-state reconstruction

• Informationally complete measurements.
• Quantum tomography.
• Quantum state reconstruction in continuous measurement.

Lecture 7
Monday May 10, 2010 from 10:00 to 12:00
Dynamics beyond mean field

• Entangling action between atoms photons
• Continuous variable description of collective spin/photons
• Spin squeezed states, entanglement

Lecture 8
Monday May 17, 2010 from 11:00 to 13:00
Decoherence and the collective spin

• Covariance matrix description of Gaussian states
• Completely positive maps on Gaussians
• Master equation description