Upcoming seminars

Quantum Channel Parameter Estimation with Noisy Initial States

Seminar date and time: 
2017-01-24 14:30
Author: 
David Collins
Affiliation: 
Department of Physical and Environmental Sciences, Colorado Mesa University

We consider estimating the parameters governing the strengths of the phase-flip and qubit depolarizing channels. Quantifying the accuracy of any protocol via the quantum Fisher information per channel invocation, it is known that the optimal protocols use pure input states. For the phase-flip channel the optimal uses unentangled single qubits and, for the depolarizing channel, pairs of entangled qubits.

Location: 
GIQ - Seminar room
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Quantum states cannot be transmitted efficiently classically

Seminar date and time: 
2017-01-17 14:30
Author: 
Ashley Montanaro
Affiliation: 
University of Bristol

In this talk I will discuss recent work showing that any classical communication protocol that can approximately simulate the result of applying an arbitrary measurement (held by one party) to a quantum state of n qubits (held by another) must transmit at least 2^n bits, up to constant factors. The argument is based on a lower bound on the classical communication complexity of a distributed variant of the Fourier sampling problem. Two optimal quantum-classical separations follow as corollaries.

Location: 
GIQ Seminar Room

The quantum information of quantum interference.

Seminar date and time: 
2016-11-30 15:30
Author: 
Peter Turner
Affiliation: 
University of Bristol

We show how one can understand the Hong-Ou-Mandel (HOM) effect from a first quantised perspective, connecting it with the quantum information concept of Schmidt decompositions that are core to entanglement theory.  This gives a general approach to distinguishability between particles’ “System” and “Label” degrees of freedom, corresponding to what has been called unitary-unitary duality in many-body physics.

Location: 
GIQ - Seminar room
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Holonomic Quantum Computation In a Chain of Three Level Systems

Seminar date and time: 
2016-11-30 14:30
Author: 
Nilhan Gurkan
Affiliation: 

Holonomic quantum computation is the idea to use non-Abelian geometric phases to implement universal quantum gates that are robust to fluctuations in control parameters. In this talk, I will explain demonstration of non-adiabatic universal holonomic quantum computation in a linear chain of interacting three-level systems. The scheme does not require adiabatic evolution and can be implemented in arrays of atoms or ions trapped in standing wave potentials.

 

Location: 
GIQ - Seminar room
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Bell Tests: investigating ``spooky action at a distance’’ in the laboratory

Seminar date and time: 
2016-11-28 13:00
Author: 
Morgan Mitchell
Affiliation: 
ICFO

I will describe briefly the nature and status of Bell tests, from their origins in the discussions between Niels Bohr and Albert Einstein, to 2015’s three loophole-free Bell tests, to the current efforts to incorporate Bell tests in communications technologies.

Location: 
Sala d'actes Edifici C

Special geometric configurations in the state space and the extremal points of the entropy of quantum measurement

Seminar date and time: 
2016-11-23 14:30
Author: 
Anna Szymusiak
Affiliation: 
Jagiellonian University, Kraków

One of the many differences between classical and quantum world is that in the classical setup we can always perform a measurement that gives certain outcomes for all pure states. Thus one can interprete the randomness of the probability distribution of the measurement outcomes as a measure of 'quantumness' (with respect to given measurement) of the initial pure state. In the talk I would like to present some special geometric configurations in the state space corresponding to the states of minimal and maximal 'quantumness' and discuss possible relations between them.
 

Location: 
GIQ - Seminar room
Contact: 

Flexible resources for quantum metrology

Seminar date and time: 
2016-11-18 14:30
Author: 
Davide Orsucci
Affiliation: 
University of Innsbruck

Quantum metrology grants a quadratic advantage over classical approaches to parameter estimation exploiting entanglement and nonclassicality. Customarily, however, the hurdle of actually implementing the necessary quantum probe states and quantum measurements is usually not taken into account, and moreover in different metrological scenarios the required states and measurements vary.

Location: 
GIQ - Seminar room

Quantifying identical-particle entanglement

Seminar date and time: 
2016-10-24 15:30
Author: 
Enrico Sindici
Affiliation: 
University of Strathclyde

Indistinguishability of particles is a counterintuitive and highly non-classical feature of quantum systems which has proven challenging to relate to standard distinguishable-particle entanglement. Inter-particle entanglement of bosons and fermions, however, plays an important role in systems with particle number superselection rules, such as atom interferometers and cold atom systems. We introduce an entanglement measure aimed at quantifying inter-particle correlations in systems with a given symmetry with respect to particle exchange.

Location: 
GIQ - Seminar Room

Fundamental limitation on quantum broadcast networks

Seminar date and time: 
2016-10-24 14:30
Author: 
Stefan Bäuml
Affiliation: 
NTT Basic Research Laboratories, NTT Corporation,

The ability to distribute entanglement over complex quantum networks is an important step towards a quantum Internet. Recently, there has been significant theoretical effort by mainly focusing on the distribution of bipartite entanglement via a simple quantum network composed only of bipartite quantum channels. There are, however, a number of quantum information processing protocols based on multipartite entanglement, rather than bipartite one, which should be served more naturally by a quantum broadcast network, rather than such a simple network.

Location: 
GIQ - Seminar Room

A histories framework for contextuality and quantum computation

Seminar date and time: 
2016-10-18 14:30
Author: 
Leonardo Disilvestro
Affiliation: 
Univ Paris-Saclay, Telecom ParisTech

In this work, we use the sum-over-histories formulation of quantum theory (a generalisation of the idea of path integrals) in order to provide two frameworks: one framework for contextuality scenarios and one framework for a specific model of quantum computation known as Measurement-Based Quantum Computation (MBQC). Using both frameworks, we re-examine the role of contextuality in the speed-up that quantum computation offers.

Location: 
GIQ Seminar room

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