Perimeter Institute Quantum Discussions

This series consists of weekly discussion sessions on foundations of quantum Theory and quantum information theory. The sessions start with an informal exposition of an interesting topic, research result or important question in the field. Everyone is strongly encouraged to participate with questions and comments.

Seminar Series Events/Videos

Currently there are no upcoming talks in this series.


Monday Jun 17, 2013

We introduce two relative entropy quantities called the min- and max-relative 
entropies and discuss their properties and operational meanings.

These relative entropies act as parent quantities for tasks such as data compression, information
transmission and entanglement manipulation in one-shot information theory. Moreover, they lead us to define entanglement monotones which have interesting operational interpretations.

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Monday May 27, 2013

Expressions of several information theoretic quantities involve an optimization over auxiliary quantum registers. Entanglement-assisted version of some classical communication problems provides examples of such expressions. Evaluating these expressions requires bounds on the dimension of these auxiliary registers. In the classical case such a bound can usually be obtained based on the

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Monday May 13, 2013

show that particle detectors, such as 2-level atoms, in non-inertial motion (or
in gravitational fields) could be used to build quantum gates for the
processing of quantum information. Concretely, we show that through
suitably chosen non-inertial trajectories of the detectors the interaction
Hamiltonian's time dependence can be modulated to yield arbitrary rotations in the
Bloch sphere due to relativistic quantum effects.


Ref. Phys.
Rev. Lett. 110, 160501 (2013)

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Monday Apr 29, 2013

A recent development in
information theory is the generalisation of quantum Shannon information theory
to the operationally motivated smooth entropy information theory, which
originates in quantum cryptography research. In a series of papers the first
steps have been taken towards creating a statistical mechanics based on smooth
entropy information theory. This approach turns out to allow us to answer
questions one might not have thought were possible in statistical mechanics,

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Monday Apr 22, 2013

I will discuss a
path-integral representation of continuum tensor networks that extends the
continuous MPS class for 1-D quantum fields to arbitrary spatial dimensions
while encoding desirable symmetries. The physical states can be interpreted as
arising through a continuous measurement process by a lower dimensional virtual
field with Lorentz symmetry. The resultant physical states naturally obey
entropy area laws, with the expectation values of observables determined by the

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Monday Apr 15, 2013

Entanglement distillation
transforms weakly entangled noisy states into highly entangled states, a
primitive to be used in quantum repeater schemes and other protocols designed
for quantum communication and key distribution. In this work, we present a comprehensive
framework for continuous-variable entanglement distillation schemes that
convert noisy non-Gaussian states into Gaussian ones in many iterations of the
protocol. Instances of these protocols include the recursive Gaussifier

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Monday Apr 08, 2013

A circuit obfuscator is an algorithm that translates
logic circuits into functionally-equivalent similarly-sized logic circuits that
are hard to understand. While ad hoc obfuscators have been implemented, theoretical
progress has mainly been limited to no-go results. In this work, we propose a
new notion of circuit obfuscation, which we call partial indistinguishability.
We then prove that, in contrast to previous definitions of obfuscation, partial
indistinguishability obfuscation can be achieved by a polynomial-time

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Monday Mar 25, 2013

Matrix product states and
their continuous analogues are variational classes of states that capture
quantum many-body systems or quantum fields with low entanglement; they are at
the basis of the density-matrix renormalization group method and continuous
variants thereof. In this talk we show that, generically, N-point functions of
arbitrary operators in discrete and continuous translation invariant matrix
product states are completely characterized by the corresponding two- and

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Monday Mar 11, 2013

I will explain how to simulate arbitrary quantum circuits on a distributed quantum computer (DQC), in which the pairs of qubits that are allowed to interact are restricted to the edges of some (connected) graph G.  Even for graphs with only a modest number of long-range qubit interactions, such as the hypercube, this simulation is, in fact, efficient.  Furthermore, for all graphs, the emulation scheme is very close to being optimal. 

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Monday Feb 25, 2013

A mixed state can be expressed as a sum of D tensor product matrices, where D is its operator Schmidt rank, or as the result of a purification with a purifying state of Schmidt rank D', where D' is its purification rank. The question whether D' can be upper bounded by D is important theoretically (to establish a description of mixed states with tensor networks), as well as numerically (as the first decomposition is more efficient, but the second one guarantees positive-semidefiniteness after truncation).

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