**PUBLIC
LECTURE - Artur Ekert
- What have we learned from quantum computation?**

*Quantum
theory of computation gives us not only the key to a new technology but also,
more importantly, much deeper understanding of the foundations of quantum physics,
computer science and mathematics. I will revisit some conceptual issues in quantum
information science and try to outline possible future directions, challenges,
and potential impacts of this new field. *

**Christof
Wunderlich - ****Spin
resonance with trapped ions: experiments and new concepts**

* Recent
experimental results relevant for quantum information processing obtained with
electrodynamically trapped Yb+ ions are reported. In addition, novel ideas for
coherent manipulation of internal and external degrees of freedom of trapped
ions will be outlined. In a suitably modified trap a string of ions can be treated
like a molecule used for spin resonance experiments: The collection of trapped
ions can be viewed as a $N$-qubit molecule with adjustable spin-spin coupling.*

**Paolo
Mataloni- ****A
New High-Brilliant Optical Parametric Source of Polarization Entangled States**

*Recent
results concerning the realization of a high-brilliant source of polarization-entangled
photon pairs, based on a original scheme developed in our laboratory, will be
presented. By exciting the source with 15 mW of the 363.8 nm Ar+ line, we were
able to generate pairs of photons with a very high degree of polarization entanglement
over the entire cone of emission of a type I phase matching crystal, with a
production rate of 104 couples/(s×mW). A 213-s violation of Bell's inequalities
was obtained in these conditions. Possible applications of this source will
be presented.*

**Klaus
Moelmer - Quantum
computing with ions and atoms**

*A
review will be presented on recent theory proposals for quantum computing with
trapped ions and atoms. This will be supplemented with examples of the current
achievements and near-future plans for experiments. It is suggested that we
may soon spot landsight and find prosperity on flourishing islands, although
the working general purpose quantum computer is still far below the horizon.
*

**Vladimir
Buzek - Programmable
quantum processors: Implementation of quantum maps**

*To follow.*

**Geza
Giedke - The characterization
of Gaussian operations and distillation of Gaussian States**

*We characterize the class of
all physical operations that transform Gaussian states to Gaussian states. We
show that this class coincides with that of all operations which can be performed
on Gaussian states using linear optical elements and homodyne measurements.
This characterization provides a powerful formalism to describe general Gaussian
operations, which we apply to the question of entanglement distillation and
entanglement generation by Gaussian operations. First, we prove that Gaussian
states cannot be distilled by local Gaussian operations and classical communication.
Then we derive the optimal way to generate entanglement or squeezing in a Gaussian
two-mode system given one interaction Hamiltonian and one-mode passive linear
optics. This directly relates to recent experiments using atomic ensembles for
quantum information tasks.*

**Rainer
Blatt - Quantum
information processing experiments with trapped Ca+ ions**

*Single
trapped Ca+ ions, stored in a linear Paul trap and laser–cooled to the ground
state of their harmonic quantum motion are used for quantum information processing.
For a demonstration, we used composite laser pulse sequences to implement a
Deutsch-Josza algorithm. For this, Stark shifts on the qubit transitions had
to be precisely measured and compensated. *

**Ronald
de Wolf - Quantum
Communication Complexity**

*In th
s eetting
of communication complexity, Alice receives an input x, Bob receives an input
y, and together they want to compute some function f(x,y), while minimizing
the amount of communication between them. In recent years, it has been found
that quantum communication is much more efficient than classical communication
for computing various functions. In this talk we survey some recent results
in this area: (1) quantum fingerprinting, which gives rise to an exponential
quantum-classical improvement in a constrained communication model, due to Buhrman,
Cleve, Watrous, and de Wolf; (2) a precise algebraic characterization of a "non-deterministic"
variant of quantum communication complexity, due to Hoyer and de Wolf; (3) a
slightly improved upper bound for the complexity of the disjointness problem,
due to Hoyer and de Wolf, and Razborov's recent lower bound for disjointness
(which was a major breakthrough). *

**Serge
Massar - Quantum
Non-Locality and Bell Inequalities **

*Recent
results concerning tests of quantum non locality generally (often called Bell
inequalities) will be presented. Applications of Bell inequalities will be discussed
and a connexion between Bell inequalities and the field of computer science
called "communication complexity" will be presented. Recently discovered Bell
inequalities resistant to noise and to detector inefficiency will be presented,
both for the case of small systems and in the asymptotic case of large dimensionality
or of many parties. *

**Markus
Grassl - Quantum
Error-Correcting Codes**

* Methods
for both active and passive stabilisation of quantum systems play a central
role on the way towards quantum information processing. Since the presentation
of the first scheme for quantum error-correction by Peter Shor in 1995, a general
theory of quantum error-correcting has been established, showing that fault
tolerant quantum computation is possible. This talk will give a survey on different
methods of quantum error-correction, concentrating on algorithmic aspects.*

**Chiara
Macchiavello - Communication
and detection of entanglement over noisy channels**

* The
ability of exploiting entanglement to achieve more efficient communication protocols
and of detecting entanglement are central issues in quantum information. In
this talk the role of entanglement in transmission of classical information
over noisy channels is analysed. It is shown in particular that entanglement
is a useful resource to increase the mutual information when the noisy transmission
channel is not memoryless. Moreover, the problem of experimental detection of
entanglement is addressed and some cases where entanglement can be detected
by performing a few local measurements are presented. *

**Eugene
Polzik - Light-Atoms
Quantum Interface for Continuous Variables**

*Off-resonant
interaction of light with an atomic ensemble followed by a suitable quantum
projection measurement is sufficient to form a continuous variable quantum interface.
Phase-amplitude or polarization state of light can be recorded in atomic ground
state coherences. Two protocols are feasible: teleportation-like transfer, which
requires two entangled atomic ensembles and another protocol, which requires
one atomic ensemble only. In the first experiment we have demonstrated recording
of light in a long-lived atomic state with quantum sensitivity. *

**Dieter
Suter - A
scalable architecture for spin-based quantum computers**

*Endohedral
fullerenes like N@C60 can be considered as nanometer-sized atom traps. The long
decoherence times of the electronic and nuclear spins qualify these molecules
as interesting candidates for a solid-state spin-based quantum computer. One-
and two-qubit gates may be implemented by sequences of radio-frequency and microwave
pulses in an inhomogeneous magnetic field.*

**Seigo
Tarucha - ****Spin
effects in quantum dots and technical approach for implementing spin qu-bits
**

*Electron
spin is a natural candidate for a spin-qubit since every spin 1/2 encodes exactly
one qubit. It is theoretically predicted that the spin-qubit located in quantum-confined
systems satisfies all requirements necessary for a scalable quantum computer.
There are, however, quite a few issues left for understanding the spin physics
in quantum dots. I will first review experimental studies on spin-related properties
of single and double quantum dot structures such as spin lifetime, exchange
coupling, and Pauli effect. Then I will discuss technical approaches for spin-rotation,
manipulation of exchange coupling, initialization and read-out.*

**Daniel
Esteve - Operation
of a solid state quantum bit circuit **

*We
have designed and operated a quantum bit circuit based on the Cooper pair box,
a superconducting device for which quantum coherence has already been demonstrated.
In this new circuit, the box Josephson junction is replaced by two junctions
in parallel forming a loop. The advantage of this design is to provide separate
ports for qubit manipulation and readout, and to efficiently decouple the qubit
from its external environment when readout is off. The qubit manipulation is
performed by applying microwave pulses to the box gate, and the readout by measuring
the current in the loop, which is different for both qubit states. This measurement
is performed by monitoring the switching of an extra large Josephson junction
inserted in the loop when a bias current pulse is applied to it. We show that
this readout strategy approaches single-shot resolution, and we demonstrate
that all qubit manipulations can be performed using Rabi precession of the qubit
state when resonant microwave pulses are applied to the gate. Using a two-pulse
sequence analogous to the Ramsey sequence in atomic physics, we have determined
the coherence time of the qubit. This coherence time, which corresponds to about
8000 periods of the qubit transition, is sufficiently long to envision coupled
qubit circuits. *

**Gennady
Berman - Perturbation
theory for scalable solid-state quantum computation and single-spin measurement
using magnetic resonance force microscopy**

*We developed
a perturbation theory for solid-state quantum computation with many qubits.
Using this theory, we discuss how to simulate simple quantum logic operations
with a large number of qubits (more than 1000) in a solid-state quantum computer
based on a nuclear spin chain. These simulations are needed for experimental
testing of scalable solid-state quantum computer devices. Quantum logic for
remote qubits is simulated. Analytical estimates are presented for possible
correlated errors caused by non-resonant transitions. A range of parameters
is given in which non-resonant effects can be minimized. *

**Daniel
Loss - Electron
spins in quantum dots as qubits for quantum information processing **

*Coherent
manipulation, filtering, and measurement of electronic spin in quantum dots
and other nanostructures are new technologies which have promising applications
both in conventional and in quantum information processing and transmission.
I review the spintronics proposal for quantum computing, in which electron spins
in quantum confined structures play the role of the quantum bits (qubits), and
discuss the essential requirements for such an implementation. I describe several
realizations of one- and two-qubit quantum gates and of state preparation and
measurement, based on an all-electrical scheme to control the dynamics of spin,
including spin-orbit effects. I discuss recently proposed schemes for using
a single quantum dot as a spin filter and spin read-out device, and show how
the decoherence time can be measured in a transport set-up. I address the issue
of spin decoherence due to non-uniform hyperfine interactions with nuclei and
show that for electrons confined to dots the spin decay is non-exponential.
Finally, I discuss methods for producing and detecting the spin-entanglement
of electronic EPR pairs, being an important resource for quantum communication.
*

**Martin
Plenio - The
entanglement cost under operations respecting the partial transpose **

*We
study the entanglement cost under quantum operations preserving the positivity
of the partial transpose (PPT-operations). We demonstrate that this cost is
directly related to the logarithmic negativity, thereby providing the operational
interpretation for this easily computable entanglement measure. As examples
we discuss general Werner states and arbitrary bi-partite Gaussian states. Equipped
with this result we then prove that for the anti-symmetric Werner state PPT-cost
and PPT-entanglement of distillation coincide giving the first example of a
truly mixed state for which entanglement manipulation is asymptotically reversible.
*

**Pranab
Sen - Relative
entropy and a substate theorem about quantum states**

* The
von Neumann relative entropy of two quantum states is an important function
in quantum information theory. The relative entropy satisfies some powerful
properties, which makes it a useful tool to work with. In this talk, we discuss
a new theorem about relative entropy. It roughly states that if the relative
entropy of two quantum states is small, then the first state "sits inside"
the second state as a "substate". We also discuss two applications
of this theorem to privacy and interaction in quantum communication. *

**Mauro
D'Ariano - Quantum
information encoded on CP-maps**

*Encoding
quantum information on completely positive (CP) maps---instead of quantum states---is
a powerful point of view, which allows also to include cryptographic issues
in the analysis of a communication protocol. For example, the optimal discrimination
between maps automatically includes the possibility of EPR cheating in either
concealing or binding issues in a quantum commitment. In this talk a review
of recent work of the Quantum Optics & Information Group in Pavia will be presented,
discussing discrimination schemes for CP-maps, the use of entanglement for reconstructing
the unknown CP map of a device, the definition of "disturbance" and
tradeoff with information, a complete classification of protocols and cheating
strategies for quantum bit commitment, and a classification of unitary transformations
corresponding to a CP maps.*

**Steffen
Glaser - Time-Optimal
Control of Quantum Dynamics and NMR Quantum Computing**

*"What
is the minimum time to realize a desired unitary transformation in a given quantum
system?" This simple question is not only of fundamental theoretical interest,
but also is of great relevance for practical realizations of quantum computing
algorithms. Based on principles of optimal control theory, this question will
be addressed and examples will be given where time-optimal pulse sequences yield
significant gains compared to conventional implementations of quantum gates.
Furthermore, a scalable NMR quantum computing algorithm will be discussed. *