Current graduate students

Tight bounds for Pauli channel learning with and without entanglement

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

Quantum entanglement is a crucial resource for learning properties from nature, but a precise characterization of its advantage can be challenging. In this work, we consider learning algorithms without entanglement as those that only utilize separable states, measurements, and operations between the main system of interest and an ancillary system. Interestingly, these algorithms are equivalent to those that apply quantum circuits on the main system interleaved with mid-circuit measurements and classical feedforward. Within this setting, we prove a tight lower bound for Pauli channel learning without entanglement that closes the gap between the best-known upper bound. In particular, we show that Θ(n^2/ε^2) rounds of measurements are required to estimate each eigenvalue of an n-qubit Pauli channel to ε error with high probability when learning without entanglement. In contrast, a learning algorithm with entanglement only needs Θ(1/ε^2) copies of the Pauli channel. Our results strengthen the foundation for an entanglement-enabled advantage for Pauli noise characterization. We will talk about ongoing experimental progress in this direction.

Reference: Mainly based on [arXiv: 2309.13461]

IQC Colloquium - Sisi Zhou, The Perimeter Institute

Quantum-Nano Centre, 200 University Ave West, Room QNC 0101 Waterloo, ON CA N2L 3G1

 Quantum metrology studies estimation of unknown parameters in quantum systems. The Heisenberg limit of estimation precision 1/N, with N being the number of probes, is the ultimate sensing limit allowed by quantum mechanics that quadratically outperforms the classically-achievable standard quantum limit 1/√N. The Heisenberg limit is attainable using multi-probe entanglement in the ideal, noiseless case. However, in presence of noise, many quantum systems only allow a constant factor of improvement over the standard quantum limit. To elucidate the noise effect in quantum metrology, we prove a necessary and sufficient condition for achieving the Heisenberg limit using quantum controls. We show that when the condition is satisfied, there exist quantum error correction protocols to achieve the Heisenberg limit; when the condition is violated, no quantum controls can break the standard quantum limit (although quantum error correction can be used to maximize the constant-factor improvement). We will also discuss the modified sensing limits when only restricted types of quantum controls can be applied. 

Creating and probing laser-cooled atomic ensembles inside a hollow-core optical fibre

Quantum-Nano Centre, 200 University Ave West, Room QNC 2101
Waterloo, ON CA N2L 3G1

Supervisor: Michal Bajcsy

Optimization of the Optical Infrastructure and Trapping Potential for a Quantum Processor Based on Trapped Barium Ions

Quantum-Nano Centre, 200 University Ave West, Room QNC 2101
Waterloo, ON CA N2L 3G1

Supervisor: Kazi Rajibul Islam

CS/MATH Seminar - Dominic Verdon (University of Bristol)

University of Waterloo, 200 University Ave West, Waterloo ON QNC 1501 + ZOOM

The quantum Boolean satisfiability problem, quantum k-SAT for short, is the quantum analogue of the classical Boolean satisfiability problem. It is QMA_1-complete for k >2, and therefore appears very difficult to solve in general. In this talk I will discuss a property testing approach to quantum k-SAT which, given the promise that an instance of the problem is either (i) satisfiable or (ii) far from satisfiable by a product state, yields a polynomial-time algorithm for deciding which of the two mutually exclusive properties (i) or (ii) holds. To show this we apply some tools from combinatorics, entanglement theory and algebraic geometry. The talk is based on joint work with Ashley Montanaro and Changpeng Shao (https://arxiv.org/abs/2301.10699).

ETSI and the Institute for Quantum Computing are pleased to announce the 10th ETSI/IQC Quantum Safe Cryptography Conference, taking place in Singapore on May 14-16, 2024. The event will be hosted by the Centre for Quantum Technologies, National University of Singapore.

This event was designed for members of the business, government, and research communities with a stake in cryptographic standardization to facilitate the knowledge exchange and collaboration required to transition cyber infrastructures and business practices to make them safe in an era with quantum computers. It aims to showcase both the most recent developments from industry and government and cutting-edge potential solutions coming out of the most recent research.