
THE
FIELDS INSTITUTE FOR RESEARCH IN MATHEMATICAL SCIENCES 
Toronto
Quantum Information Seminars
201415
Fields
Institute, 222
College St.



OVERVIEW
The Toronto Quantum Information Seminar is held roughly every two
weeks to discuss ongoing work and ideas about quantum computation,
cryptography, teleportation, et cetera. We hope to bring together
interested parties from a variety of different backgrounds, including
math, computer science, physics, chemistry, and engineering, to
share ideas as well as open questions.
Upcoming
Seminars 
Oct 3, 2014
11:00 a.m.
RM 210 
ManDuen Choi (University of Toronto)
The Principle of Locality made simple
In physics, the Principle of Locality states that an object is influenced
directly only by its immediate surroundings. This could be transformed
to a simple mathematical statement of NO wisdom at all. Nevertheless,
with extravagent assumption (on the obvious truth) and fascinating
explanation (of the ultimate nonsense), the Principle may become a
big Law/Theory/Theorem or a tremendous Paradox to shake your heart/body.
This is an expository talk of my own adventure in the quantum wonderland
(concerning the structure problems of direct sums and tensor products).
No working knowledge of quantum information is required in this talk.

Oct 10, 2014
11:00 a.m.
RM 210 
Paola Cappellaro (Massachusetts
Institute of Technology)
TBA 
Oct 17, 2014
11:00 a.m.
RM 210 
Josh Combes (Perimeter Institute for Theoretical Physics)
TBA

Nov 14, 2014
11:00am
RM 210

Nancy Makri
(University of Illinois)
TBA 
Nov 21, 2014
11:00am
RM 210

Yaoyun Shi (University of Michigan)
How to generate the first secret, then as many as you like
Secrecy is randomness. A perfect secret is one for which all the
alternatives are equally likely to the adversary. For secrecy to be
possible, we have to assume that the world is not deterministic. Here
we show how this necessary assumption, together with the validity
of
quantum mechanics and relativity, will allow us to generate the first
and almost perfect secret, and then to expand it to be arbitrarily
long. Unlike all existing solutions, the security of our construction
is provable, unconditional (as opposed to computational), and
verifiable. Our method can also be used for the important task of
distributing cryptographic keys.
Technically speaking, we formulate a precise model of extracting
randomness from quantum devices whose innerworkings may be imperfect
or even malicious. We then construct such a "physical extractor"
that
needs only a single and arbitrarily weak classical source, and the
output randomness can be arbitrarily long and almost optimally close
to uniform. This is impossible to achieve for classical randomness
extractors, which cannot increase entropy and requires two or more
*independent* sources.
Our construction also differs from quantumbased random number
generators in the market, as they all require that the users trust
their quantum innerworkings. Such a trust threatens security when
the
devices are defective or were procured from an untrusted vendor.
Several features of our construction, such as maximum noise tolerance
and unit quantum memory requirement, have fundamentally lowered the
implementation requirements.

Past Seminars 
Sept 19, 2014
12:30 p.m
Fields RM 210

Boris Braverman (Massachusetts Institute of Technology)
Progress toward a spin squeezed optical atomic clock beyond the standard
quantum limit
State of the art optical lattice atomic clocks have reached
a relative inaccuracy level of $10^{18}$, making them the most stable
time references in existence. One limitation to the precision of these
clocks is the projection noise caused by the measurement of the atomic
state. This limit, known as the standard quantum limit (SQL), can be
overcome by entangling the atoms. By performing spin squeezing, it is
possible to robustly generate such entanglement and therefore surpass
the SQL of precision in optical atomic clocks. I will report on recent
experimental progress toward realizing spin squeezing in an ${}^{171}$Yb
optical lattice clock. A highfinesse micromirrorbased optical cavity
mediates the atomatom interaction necessary for generating the entanglement.
By exceeding the SQL in this state of the art system, we are aiming
to advance precision time metrology and expand the boundaries of quantum
control and measurement.

Sept 12, 2014
11:00 a.m.
RM 210 
Raphael Pooser (Oak Ridge National Labs)
Quantum Sensors: Data at the information frontier of physics
Quantum information processing has a host of applications, including
quantum key distribution and quantum computing as some of the most
prominent. In all of these applications, sensing and control are needed
in order to maintain the fidelity of quantum information. In quantum
sensors, information stored in quantum mechanical systems is extracted
and put to use, either in subsequent control signals, or in general
information processing applications. Some famous examples of quantum
sensors include atomic clocks, cold atom interferometers, or BoseEinstein
condensates used in gravitometers, accelerometers, etc. Some of the
original proposals for quantum sensors involved optical fields. In
particular, sensors that exploit continuously variable degrees of
freedom have been of interest since the discovery of quantum noise
reduction. One of the first examples proposed by Caves is the use
quantum noise reduction to achieve interferometric sensitivity in
the quantum regime. Advanced LIGO is an example of an upcoming application.
In addition to LIGO, in recent years continuous variables have seen
renewed interest. In this talk we will discuss quantum sensors and
their applications with a focus on the sensors developed at ORNL.
We use quantum noise reduction to produce subshotnoise limited sensing
devices, particularly in quantum plasmonic sensors and displacement
sensors using MEMS cantilevers. Some applications for these devices
include trace detection or quantum information applications, such
as removing bias from QRNGs through adaptive control. We will also
discuss other sensing types that use both discrete and continuous
variables, such as quantum compressive imaging, and single photon
detection applications.

Aug 29, 2014
11:00 a.m. RM 210 
Robert Boyd (University of Ottawa)
Menzel's Experiment: Violation of Complementarity?
In 2012, the group of Ralf Menzel in Potsdam, Germany published an
article in PNAS that appeared to violate the accepted quantum mechanical
notion of complementarity. Specifically, they observed interference
with good fringe visibility in a Young's twoslit experiment, even
though, through use of a quantum protocol, they were able to deduce
through which slit each photon had passed. Our group has recently
articulated an explanation for these unexpected results (Bolduc et
al., PNAS 2014). Our explanation is that the Potsdam group had inadvertently
violated a fairsampling assumption by means of the manner in which
they collected and analyzed their data.

Aug 8, 2014
11:00 a.m. 
Ioannis Thanapoulos (National Hellenic Research Foundation)
Quantum dynamics by the Effective Modes Differential Equations method
We show that the nonMarkovian quantum dynamics of a system comprised
of a subspace Q coupled to a much larger subspace P can be described
by a set of Effective Modes Differential Equations (EMDE). The computational
efficiency of the method is demonstrated by investigating the 24mode
decay dynamics and laser control of the radiationless transitions
from the second to the first singlet electronic excited state of the
pyrazine molecule.

Aug 7, 2014
11:00 a.m. 
Thomas Monz (University of Innsbruck)
Topological qubits
Arbitrarily long quantum computation requires techniques to overcome
errors accumulated during the operation. Here, different approaches
have been proposed, with topological quantum computation yielding
one of the highest thresholds against errors. In this talk I will
first provide a brief introduction into topological quantum computation,
in particular the color code. Subsequently I will show how, for the
first time, a qubit has been topologically encoded using an iontrap
based quantum computer. The presented experimental data illustrates
how we can detect all physical singlequbit errors, perform the entire
set of Clifford operations on this logical qubit and investigate its
coherence properties. The presentation is concluded by an outline
on upcoming milestones and their experimental as well as theoretical
challenges.

Aug 7, 2014
2:00 p.m. 
Prof. Charlie Ironside (Curtin University)
A surfacepatterned chip as a strong source of ultracold atoms for
quantum technologies

Aug 1, 2014
11:00 am

Prof. Lianao Wu (University of Basque Country)
One Component Dynamical Equation and a Universal Control Theory
We use a Feshbach PQ partitioning technique to derive a closed one
component integrodifferential equation. The resultant equation properly
traces the footprint of the target state in quantum control theory.
The physical significance of the derived dynamical equation is illustrated
by both general analysis and concrete examples. We show that control
can be realized by fastchanging external fields, even fast noises.
We illustrate the results by quantum memory and controlled adiabatic
paths.

July 25, 2014
Room 210 
Prof. Gershon Kurizki, Weizmann Institute of Science
A thermal bath: more friend than foe?
Traditionally, the interaction of quantum systems with a thermal
bath is viewed as detrimental to their quantumness. Yet this is not
always the case, as the bath may actually promote quantumness, particularly
when systembath interactions are subject to control. I will review
our recent results concerning different types of control capable of
generating or enhancing quantum processes via the bath:
1. Control by modulation: By periodically modulating the energy of
twolevel or multilevel systems we may purify the state of the systems
or the bath they couple to, upon tailoring the modulation to the bath
spectrum. An intriguing consequence of such purification is the possibility
to cool a bath consisting of coupled spins down to absolute zero,
in apparent violation of Nernst's third law of thermodynamics. The
thermal bath may also mediate the transfer of quantum information
between distant systems, at a rate and fidelity controllable by the
modulation.
2. Control by state preparation: The quantum state of an oscillator
coupled to a thermalized qubit determines the amount and efficiency
of work extractable from the thermal bath, thereby retaining its quantum
features over surprisingly long time scales. Remarkably, certain quantum
states yield higher efficiency than allowed by the Carnot bound, yet
in full compliance with the second law of thermodynamics. In Nlevel
systems, appropriate state preparation allows for Nfold enhancement
of work extractable from the bath at steady state.
3. Control by bath engineering: The ability to control the coupling
of quantum systems to appropriately designed, axiallyguided modes
of the bath, may drastically enhance the range of entanglement mediated
by the bath, or lead to giant enhancement of bathinduced dispersion
forces, colloquially known as van der Waals and Casimir forces.

July 11, 2014
Stewart Library

Matthew Broome, University of New South Wales
My Quantum Optics Show and Tell: Topology, complexity and biology
Progress in optical quantum computation has started to slow in recent
times due to the problems associated with probabilistic quantum gates,
lack of good single photon sources and poor nonlinear optical materials.
However, by looking at other applications besides a fully scalable
quantum computer, we see that linear optics alone (beam splitters
and phase shifters) is a powerful tool for simulation or emulation
of interesting physical systems. In this talk I will discuss some
recent results from the University of Queensland's Quantum Technology
Lab that employ purely linear optical schemes for this purpose. In
particular, I will focus the talk around single and multiparticle
quantum walks for investigating areas from condensed matter science
to complexity theory.

July 4, 2014
Room 210 
Katja Ried, Perimeter Institute, Waterloo
How drug trials are simpler if your subjects are quantum (and other
applications of quantum causal models)
A fundamental question in trying to understand the world  be it
classical or quantum  is why things happen. We seek a causal account
of events, and merely noting correlations between them does not provide
a satisfactory answer. In classical statistics, a better alternative
exists: the framework of causal models has proven useful for studying
causal relations in a range of disciplines. We try to adapt this formalism
to allow for quantum variables, and in the process discover a new
perspective on how causality is different in the quantum world. One
of the peculiarities that arise in this context can be harnessed to
solve a task of causal inference  inferring the causal relation
between variables based on observed statistics  that is impossible
for classical variables. I will report on a recent experimental realization
of this scheme.
Time permitting, I will also discuss a more realistic approach to
the problem of characterizing quantum processes in the presence of
initial
correlations with an environment, viz nonMarkovian dynamics. Another
application of quantum causal inference arises in the context of quantum
field theory: if one couples two detectors to a quantum field at different
points throughout spacetime, this may allow one of them to causally
influence the other, via the field. We explore how different variables
of the model, such as the acceleration of the detectors and the ultraviolet
cutoff of the field theory, are reflected in the strength and quality
of the causal influence.

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