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.

Universal fault-tolerant quantum computation with only transversal gates and error correction

Wednesday Sep 25, 2013
Speaker(s):

Transversal
implementations of encoded unitary gates are highly desirable for
fault-tolerant quantum computation.  It is known, however, that
transversal gates alone cannot be computationally universal.  I will show
that the limitation on universality can be circumvented using only
fault-tolerant error correction, which is already required anyway.  This
result applies to triorthogonal'' stabilizer codes, which were recently
introduced by Bravyi and Haah for state distillation.  I will show that

Scientific Areas:

Generalized Relative Entropies, Entanglement Monotones and One-Shot Information Theory

Monday Jun 17, 2013
Speaker(s):

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.

Scientific Areas:

Information Theoretic Benefit of Entanglement in Classical Communication Settings

Monday May 27, 2013
Speaker(s):

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

Scientific Areas:

Processing quantum information with relativistic motion of atoms

Monday May 13, 2013

We
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)

Scientific Areas:

Laws of thermodynamics beyond the von Neumann regime

Monday Apr 29, 2013
Speaker(s):

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,

Scientific Areas:

The continuum limit of tensor networks: a path integral representation

Monday Apr 22, 2013
Speaker(s):

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

Scientific Areas:

Continuous-variable entanglement distillation and non-commutative central limit theorems

Monday Apr 15, 2013
Speaker(s):

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

Scientific Areas:

Classical and quantum circuit obfuscation with braids

Monday Apr 08, 2013
Speaker(s):

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

Scientific Areas:

Wick's theorem for Matrix Product states

Monday Mar 25, 2013
Speaker(s):

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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Efficient Distributed Quantum Computing

Monday Mar 11, 2013
Speaker(s):

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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