Events

Quantum Nano Centre (QNC) Room 0101, 200 University Avenue West, Waterloo, ON

IQC Colloquium, Harry Buhrman - QuSoft

One of the major challenges in computer science is to establish lower bounds on the resources, usually time, that are needed to solve computational problems. This holds in particular for computational problems that appear in practise. One way towards dealing with this situation is the study of fine- grained complexity where we use special reductions to prove time lower bounds for many diverse problems based on the conjectured hardness of some key problems.

Quantum Nano Centre (QNC) Room 1201, 200 University Avenue West, Waterloo, ON

IQC Seminar Featuring Jasminder Sidhu, University of Strathclyde, Glasgow

A network of quantum technologies will herald improvements to applications ranging from communications, sensing, and computing. Finite resources available in practical implementations and losses are two prominent limitations to the global scale-up of distributed quantum technologies. This can lead to a significant departure in the expected performance of these applications and limits their range. In this talk, I will highlight recent work that looks into the impact of finite resources to determine practical performances in satellite-based quantum communications. I will also introduce recent proposals that leverage space-based quantum repeaters to extend the range of quantum networks.

IQC Seminar - Stefanie Haeusler, Department of Optical Satellite Links, Institute of Communications and Navigation, Germany

Quantum Nano Centre, 200 University Ave W, Room QNC 1201 Waterloo, ON, CA N2L 3G1

Quantum Key Distribution (QKD) is a promising method to guarantee future-proof, information theoretic security. Since optical fibers have an exponential loss with distance, satellite-based QKD solutions are being developed in order to realize long-distance links. Therefore, Optical Ground Stations for QKD (QKD-OGS) need to be designed to enable quantum communication with satellites. Different link configurations will result in different integration options of the QKD-OGS in the terrestrial fiber network and therefore impact its performance. Applicable integration options are identified and discussed.

Kim de Laat, University of Waterloo

Quantum Nano Centre (QNC) Room 0101, 200 University Avenue West, Waterloo, ON

The field of quantum computing has a unique opportunity to pre-empt many of the inequities that have riddled AI and computer science. But radical technologies require new, radical solutions. In this talk, I take issue with the leaky pipeline metaphor as a way of structuring policy interventions concerning inequality in STEM fields. I outline three reasons why overreliance on the leaky pipeline metaphor is problematic: (1) it does not accurately represent the phenomenon it is meant to describe; (2) it is incomplete; and (3) it does not capture the full heterogeneity of experiences with inequality in STEM disciplines. I conclude the talk by sharing feedback from the quantum technology community concerning potential pitfalls in the pursuit of equity in quantum, and what we can do about it.

Impromptu Whiteboard Poster Session

Quantum Nano Centre (QNC) Room 1201, 200 University Avenue West, Waterloo, ON

This week’s student seminar will take place in the form of an impromptu whiteboard poster session, where attendees will be divided into groups and will discuss each other's current work using the whiteboard. This is to encourage students to talk about their work in progress, and practice communication skills by talking to non-experts (quantum is a big field!). As always, pizza will be provided for attendees after the seminar.

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IQC Colloquium - Alex May, Perimeter Institute

Quantum Nano Centre (QNC) Room 0101 200 University Ave West, Waterloo Ontario

The subject of quantum gravity seeks to understand gravitational physics within the framework of quantum mechanics. Increasingly, tools from quantum information, complexity, and cryptography have been brought into this challenging area. Here, I describe a set of connections between quantum gravity, specifically the AdS/CFT correspondence, and a set of cryptographic primitives studied in information theoretic cryptography and position-verification. The cryptographic perspective provides new insights into how gravitational physics can be recorded into quantum mechanics, and led to new gravitational conjectures in AdS space. These conjectures were then proven gravitationally. Conversely, the gravitational perspective has suggested new relationships among these cryptographic primitives, and these relationships were then proven within quantum cryptography. I comment on some directions this cryptography-gravity relationship may lead in the future.  

IQC Colloquium - Mio Murao, The University of Tokyo

Quantum Nano Centre (QNC) Room 0101 200 University Ave West, Waterloo Ontario

Please note start time 3:00 PM

Efficiently learning properties of unknown quantum objects is a fundamental task in quantum mechanics and quantum information. When there are two unknown quantum objects, and if we want to learn just the relationship between the objects, a method to directly compare the two objects without identifying their descriptions is preferable, especially when the number of available copies of each target object is limited. In this work, we investigate the comparison of unknown unitary channels with multiple uses of the unitary channels based on the quantum tester formalism.  We obtain the optimal minimum-error strategy and the optimal unambiguous strategy of unitary comparison of two unknown d-dimensional unitary channels when the number of uses of the channels satisfies a certain condition. These optimal strategies are implemented by parallel uses of the unitary channels, even though all sequential and adaptive strategies implementable by the quantum circuit model are considered. When the number of the smaller uses of the unitary channels is fixed, the optimal averaged success probability is achieved by a certain number of uses of the other channel. This feature contrasts with the case of pure-state comparison, where adding more copies of the unknown pure states always improves the optimal averaged success probability. It highlights the difference between corresponding tasks for states and channels, which has been previously shown for quantum discrimination tasks.  

Reference: Y. Hashimoto, A. Soeda and M. Murao, Comparison of unknown unitary channels with multiple uses, arXiv:2208.12519

IQC Seminar - Johannes Prell, Institute of Communication and Navigation, OSL German Aerospace Center (DLR) Oberpfaffenhofen, Germany

Quantum Nano Centre (QNC) Room 0101 200 University Ave West, Waterloo Ontario

Satellite based laser communication technology both classical and QKD (Q uantum K ey D istribution is gaining popularity and being increasingly commercial i zed . Optical ground stations serve as the receiv ing station in satellite to ground scenarios. The DLR institute of Communications and Navigation hosts an experimental optical ground station for research and demonstration purpose. Supporting increasingly demanding technical requirements from current and futu re missions and technology demonstrations, it was decided to replace the 40cm Cassegrain telescope an equip the new one with Nasmyth Ports for direct experiments, a Coudé Path to the lab and an Adaptive Optics System . This new 80cm (31.5inch) main apertur e diameter i nstrument is a Nasmyth Design Ritchey Chretien telescope The special feature is the C oudé P ath which is guiding the received light onto an optical table in a lab oratory room below the telescope mount (see figure 1 The usage of the Coudé Path is new implemented at DLR and offers a wide possibility for several different experiments with the same setup The optical propaga tion through a custom designed lens system inside the coudé path is optimized for wavelength s used for optical communication, like 589nm, 850nm, 1064nm and 1550nm. It is possible to use the setup as a receiving station and also as a transmitting facility f or beacon lasers . The transmitt ing system ca n be installed either beside the telescope as a side installation or even launched from the optical table through coudé path and telescope directly

The optical Experiment table in the lab is equipped with an Adaptive Optics ( System including fibe r coupling. This system uses a Shack Hartmann Wave front sensor, designed to match a deformable mirror in the “ f ried g eometry”. The system couples the light into a single mode fibe r , which can be con nected to a coherent or Quantum encrypted communications system. [ The telescope itself has four usable Nasmyth ports The first one is reserved for the coudé pa th, t wo others are equipped with optical benches directly on the telescope, and on the last one has a fixed classical laser communication receiving setup including two cameras one visible light and one infra red and a signal receiving united is installed References

[1] Andrew Paul Reeves, Ilija R. Hristovski, Alexandru Octavian Duliu, Stefanie H äu sler, Hela Friew Kelemu, Pia Lützen, Florian Moll, Eltimir Peev, Juraj Poliak, Amita Shrestha, Joana Sul Torres; Adaptive Optics Corrected Bi Directional Links with a Geo Stationary Satellite from the DLR KN Optical Ground Station Figure 1 OGSOP System Overvi ew

Computational Entanglement Theory

Quantum Nano Centre, 200 University Ave W, Room QNC 1201
Waterloo, ON, CA N2L 3G1

Quantum entanglement is an important resource that contributes to the potential of quantum computers over classical computers. It turns out to be an interesting idea to quantify entanglement in states, and there are different approaches to this. We can, for example, consider the number of Bell states that are required to approximately produce a given state or the number of Bell states that can be produced from the state - these correspond to the 'entanglement cost’ and ‘distillable entanglement' respectively. Throughout this, we bear in mind a picture where Alice (A) and Bob (B) own a shared state, and are only able to perform LOCC operations on their respective systems. In practice, however, computational complexity must be taken into account. I will explain some recent developments towards taking computational complexity into account for these operational measures, as well as introducing pseudo-entanglement, and hopefully some quantum cryptography.

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Neutron Scattering Investigations of Three-Dimensional Topological States

Physics, 200 University Ave West, Room PHY 352
Waterloo, ON, CA N2L 3G1

Magnetic skyrmions represent a unique class of topological magnet characterized by nanometric swirling spin-textures which possess a non-trivial Berry curvature. The combination of their topological stability, unique transport properties, and emergent dynamics has made skyrmions the forerunner for novel spintronic high-density memory and ultra-low power logic device applications. In this thesis, we explore the development and application of various neutron scattering tomography and structured neutron beam techniques for three-dimensional investigations of bulk magnetic topological materials and their defect-mediated dynamical phenomena. Characterization of the disordered multi-phase bulk skyrmion material, Co8Zn8Mn4, was performed through detailed SANS measurements over the entire temperature-magnetic field phase diagram of the material as a function of a dynamic skyrmion ordering sequence. 2D SANS images in combination with micromagnetic simulations reveal a novel disordered-to-ordered skyrmion square lattice transition pathway which represents a new type of non-charge conserving topological transition. In the metastable skyrmion triangular lattice phase, dynamical field-dependent skyrmion responses showed an exotic memory phase in spite of hysteresis protocols involving field-induced saturation into the ferromagnetic phase. Three-dimensional examinations of skyrmion stabilization mechanisms and their dynamical defect pathways were explored using a novel SANS tomography technique which processes multi-projection neutron scattering images as its input. Application of the technique to the ordered thermal equilibrium skyrmion triangular lattice phase yielded the first three-dimensional visualizations of a bulk skyrmion lattice. The reconstructions unveiled a host of exotic skyrmion features, such as branching, segmented, twisting, and filament structures, mediated by three-dimensional topological transitions through two different emergent monopole (MP)-antimonopole (AMP) defect pathways. Finally, the direct identification and determination of topological features and defects in bulk micromagnetic materials, without a priori knowledge of the sample, was explored using holographic approaches for the generation of neutron helical waves. Linear neutron waves in a conventional SANS setup were input on microfabricated gratings which consist of arrays of various q-fold fork-dislocation phase-gratings with nanometric spatial dimensions. Far-field scattering images exhibited doughnut intensity profiles centered on the first diffraction orders, thereby demonstrating the tunable generation of topological neutron states for phase- and topology-matched studies of quantum materials. The amalgamation of these works demonstrates the development and application of novel tools for direct investigations of bulk topological magnetic materials, while uncovering a diverse collection of skyrmion energetics, disorder-dependent dynamics, and three-dimensional topological transition defect pathways. These methods and results open the door to a new generation of neutron scattering techniques for the probing of exotic topological interactions and the complete standalone characterization of quantum materials and their topological phenomena.