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News

Monday, June 17, 2024

Taking quantum to the community

New quantum-nano fabrication and characterization facility lab advances research and enhances community innovation and collaboration.

The University of Waterloo has officially opened its state-of-the-art Inert Atmosphere Fabrication Lab (IAFL) as part of the Quantum-Nano Fabrication and Characterization Facility (QNFCF).

This year, the Institute for Quantum Computing (IQC) celebrates our members Albie Chan, a PhD student at IQC who won the Dean of Science Award from the Department of Physics and Astronomy, and Nicki Shaw, senior facility microscopist at the Quantum-Nano Fabrication and Characterization Facility (QNFCF) who was awarded the Department of Chemistry’s award.

Events

Tuesday, June 18, 2024 3:00 pm - 4:00 pm EDT (GMT -04:00)

Circuit-to-Hamiltonian from tensor networks and fault tolerance

CS Math Seminar - Quynh Nguyen, Harvard University

Quantum-Nano Centre, 200 University Ave West, Room QNC 1201 + ZOOM Waterloo, ON CA N2L 3G1

We define a map from an arbitrary quantum circuit to a local Hamiltonian whose ground state encodes the quantum computation. All previous maps relied on the Feynman-Kitaev construction, which introduces an ancillary ‘clock register’ to track the computational steps. Our construction, on the other hand, relies on injective tensor networks with associated parent Hamiltonians, avoiding the introduction of a clock register. This comes at the cost of the ground state containing only a noisy version of the quantum computation, with independent stochastic noise. We can remedy this - making our construction robust - by using quantum fault tolerance. In addition to the stochastic noise, we show that any state with energy density exponentially small in the circuit depth encodes a noisy version of the quantum computation with adversarial noise. We also show that any ‘combinatorial state’ with energy density polynomially small in depth encodes the quantum computation with adversarial noise. This serves as evidence that any state with energy density polynomially small in depth has a similar property. As an application, we give a new proof of the QMA-completeness of the local Hamiltonian problem (with logarithmic locality) and show that contracting injective tensor networks to additive error is BQP- hard. We also discuss the implication of our construction to the quantum PCP conjecture, combining with an observation that QMA verification can be done in logarithmic depth.

Based on joint work with Anurag Anshu and Nikolas P. Breuckmann. (https://arxiv.org/abs/2309.16475)

Wednesday, June 19, 2024 12:00 pm - 1:00 pm EDT (GMT -04:00)

IQC Student Seminar Featuring Bruno De Souza Leao Torres

Optimal coupling for local entanglement extraction from a quantum field

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

The entanglement structure of quantum fields is of central importance in various aspects of the connection between spacetime geometry and quantum field theory.  However, it is challenging to quantify entanglement between complementary regions of a quantum field theory due to the formally infinite amount of entanglement present at short distances. We present an operationally motivated way of analyzing entanglement in a QFT by considering the entanglement which can be transferred to a set of local probes coupled to the field. In particular, using a lattice approximation to the field theory, we show how to optimize the coupling of the local probes with the field in a given region to most accurately capture the original entanglement present between that region and its complement. This coupling prescription establishes a bound on the entanglement between complementary regions that can be extracted to probes with finitely many degrees of freedom.

Based on: J. High Energ. Phys. 2023, 58 (2023), arXiv:2301.08775

Wednesday, July 10, 2024 11:45 am - 12:45 pm EDT (GMT -04:00)

Security implications of device imperfections in quantum key distribution

IQC Special Seminar, Jerome Wiesemann, Fraunhofer Heinrich Hertz Institute HHI

Quantum key distribution (QKD) is on the verge of becoming a robust security solution, backed by security proofs that closely model practical implementations.  As QKD matures, a crucial requirement for its widespread adoption is establishing standards for evaluating and certifying practical implementations, particularly against side-channel attacks resulting from device imperfections that can undermine security claims. Today, QKD is at a stage where the development of such standards is increasingly prioritized. This works aims to address some of the challenges associated with this task by focusing on the process of preparing an in-house QKD system for evaluation. We first present a consolidated and accessible baseline security proof for the one-decoy state BB84 protocol with finite-keys, expressed in a unified language. Building upon this security proof, we identify and tackle some of the most critical side-channel attacks by characterizing and implementing countermeasures both in the QKD system and within the security proof. In this process, we iteratively evaluate the risk of the individual attacks and re-assess the security of the system. Evaluating the security of QKD systems additionally involves performing attacks to potentially identify new loopholes. Thus, we also aim to perform the first real-time Trojan horse attack on a decoy state BB84 system, further highlighting the need for robust countermeasures. By providing a critical evaluation of our QKD system and incorporating robust countermeasures against side-channel attacks, our research contributes to advancing the practical implementation and evaluation of QKD as a trusted security solution.