SCIENTIFIC PROGRAMS AND ACTIVITIES

September 16, 2014
THE FIELDS INSTITUTE FOR RESEARCH IN MATHEMATICAL SCIENCES
Toronto Quantum Information Seminars
2014-15
The Fields Institute,
Fridays, 11:10 a.m.

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

September 19, 2014
12:30 p.m 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 high-finesse micromirror-based optical cavity mediates the atom-atom 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.
October 3, 2014
11:00 a.m.

Man-Duen 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.

October 10, 2014
11:00 a.m. RM 210
Paola Cappellaro (Massachusetts Institute of Technology)
TBA
Past Seminars
September 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 Bose-Einstein 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 sub-shot-noise 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 two-slit 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 fair-sampling 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 non-Markovian 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 24-mode 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 ion-trap based quantum computer. The presented experimental data illustrates how we can detect all physical single-qubit 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 surface-patterned chip as a strong source of ultra-cold 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 P-Q partitioning technique to derive a closed one- component integro-differential 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 fast-changing 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 system-bath 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 two-level 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 N-level systems, appropriate state preparation allows for N-fold 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, axially-guided modes of the bath, may drastically enhance the range of entanglement mediated by the bath, or lead to giant enhancement of bath-induced 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 non-linear 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 multi-particle 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 non-Markovian 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 space-time, 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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