Upcoming seminars

Digital quantum metrology

Seminar date and time: 
2017-05-29 16:00
Author: 
Lorenzo Maccone
Affiliation: 
Universita' di Pavia, Italy

Quantum Metrology calculates the ultimate precision of all estimation

strategies, measuring what is their root mean-square error (RMSE) and

their Fisher information. Here, instead, we ask how many bits of the

parameter we can recover, namely we derive an information-theoretic

quantum metrology. In this setting we redefine "Heisenberg bound" and

"standard quantum limit" (the usual benchmarks in quantum estimation

Location: 
GiQ's seminar room

Quantum transport in Non-Markovian, strong coupling settings: bath degrees of freedom

Seminar date and time: 
2017-05-15 14:30
Author: 
Javier Cerrillo
Affiliation: 
Technische Universität Berlin

The possibility to extract full counting statistics (FCS) of transport processes in experimental settings exposes the necessity to upgrade existing simulation methods to gain access to environmental degrees of freedom. The techniques stemming from the theory of generating functions make it possible to encode all cumulants of the outcome of a specific measurement scheme in the form of a generalized density matrix.

Location: 
GIQ - Seminar room
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Recent Results on Uncertainty Relations

Seminar date and time: 
2017-04-04 14:30
Author: 
Reinhard Werner
Affiliation: 
Institut für Theoretische Physik, Leibniz Universität Hannover

Uncertainty relations come in two kinds: The more familiar type, called preparation uncertainty, captures the impossibility of preparing states that are sharp for two given observables, whereas measurement uncertainty provides quantitative bounds to the errors in any attempt to jointly measure the two. The quantitative theory requires, for each observable involved, a cost function for errors, usually a power of a metric on the outcome space.

Location: 
GIQ - Seminar room

Metrics on quantum channels: issues, fixes, applications

Seminar date and time: 
2017-03-08 12:00
Author: 
Andreas Winter
Affiliation: 
GIQ

The diamond norm on superoperators (aka 'completely bounded norm' in the Heisenberg picture) provides a natural, operationally well-motivated, and computable metric on quantum channels (cptp maps). In particular, it quantifies the optimal bias in hypothesis testing between two channels, it is given by a semidefinite programme, and it enjoys a number of good mathematical properties. It furthermore provides the natural setting when discussing continuity of channel capacities.

Location: 
GIQ - Seminar room
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Fundamental limits for cooling of linear quantum refrigerators

Seminar date and time: 
2017-02-15 15:30
Author: 
Nahuel Freitas
Affiliation: 
Departamento de Fisica, UBA & Instituto de Fisica de Buenos Aires, UBA CONICET

I study the asymptotic dynamics of a network of oscillators whose frequencies and couplings are periodically driven while coupled with a number of bosonic reservoirs. I obtain exact results for the heat currents coming into the system from each reservoir (valid beyond the usual weak coupling, weak driving or Markovian approximations). I use these expressions to rigorously prove the validity of the dynamical version of the third law of thermodynamics (Nernst unattainability principle) in this context.

Location: 
GIQ - Seminar room
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Gaussian optimizers in quantum information

Seminar date and time: 
2017-02-15 14:30
Author: 
Giacomo De Palma
Affiliation: 
QMATH, Department of Mathematical Sciences, University of Copenhagen

We determine the p->q norms of the one-mode quantum-limited attenuator and amplifier, and prove that they are achieved by Gaussian states. The proof technique is completely new: it is based on a new logarithmic Sobolev inequality, and it can be used to determine the p->q norms of any quantum semigroup. Our result extends to noncommutative probability the seminal theorem "Gaussian kernels have only Gaussian maximizers" [Lieb, Invent. Math. 102, 179 (1990)], stating that Gaussian functions achieve the p->q norms of Gaussian integral kernels.

Location: 
GIQ - Seminar room
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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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