Events

CS/Math Seminar - Avantika Agarwal IQC

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

The Polynomial-Time Hierarchy (PH) is a staple of classical complexity theory, with applications spanning randomized computation to circuit lower bounds to ''quantum advantage'' analyses for near-term quantum computers. Quantumly, however, even though at least four definitions of quantum PH exist, it has been challenging to prove analogues for these or even basic facts from PH. This work studies three quantum-verifier based generalizations of PH, two of which are from [Gharibian, Santha, Sikora, Sundaram, Yirka, 2022] and use classical strings (QCPH) and quantum mixed states (QPH) as proofs, and one of which is new to this work, utilizing quantum pure states (pureQPH) as proofs. We first talk about solutions to open problems from GSSSY22 which include a collapse theorem for QCPH and a quantum-classical Karp-Lipton. We then talk about our results for pureQPH, including lower bounds relating QCPH to pureQPH, and finally discuss some interesting open problems related to QCPH. This talk is based on https://arxiv.org/abs/2401.01633, a joint work with Sevag Gharibian, Venkata Koppula and Dorian Rudolph.

CS/MATH Seminar - Kieran Mastel from IQC ZOOM + IN PERSON

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

The recent MIP*=RE theorem of Ji, Natarajan, Vidick, Wright, and Yuen shows that the complexity class MIP* of multiprover proof systems with entangled provers contains all recursively enumerable languages. In prior work Grilo, Slofstra, and Yuen showed (via a technique called simulatable codes) that every language in MIP* has a perfect zero knowledge (PZK) MIP* protocol.  The MIP*=RE theorem uses two-prover one-round proof systems, and hence such systems are complete for MIP*. However, the construction in Grilo, Slofstra, and Yuen uses six provers, and there is no obvious way to get perfect zero knowledge with two provers via simulatable codes. This leads to a natural question: are there two-prover PZK-MIP* protocols for all of MIP*?

In this talk we answer the question in the affirmative. For the proof, we use a new method based on a key consequence of the MIP*=RE theorem, which is that every MIP* protocol can be turned into a family of boolean constraint system (BCS) nonlocal games. This makes it possible to work with MIP* protocols as boolean constraint systems, and in particular allows us to use a variant of a construction due to Dwork, Feige, Kilian, Naor, and Safra which gives a classical MIP protocol for 3SAT with perfect zero knowledge. To show quantum soundness of this classical construction, we develop a toolkit for analyzing quantum soundness of reductions between BCS games, which we expect to be useful more broadly. This talk is based on joint work with William Slofstra

Join us for Quantum Connections May 1-2, 2024. This year we’re highlighting Quantum Perspectives: the impacts and outlooks driving our future.

Fermionic encodings: BK Superfast, ternary trees, and even fermionic encodings

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

We give an introduction to fermionic encoding schemes applicable in the context of quantum simulation of fermionic systems in condensed matter physics, lattice gauge theories, and in quantum chemistry.
 
For this we will focus on the circuit depth overhead for a variety of constructions of fermionic encodings, more precisely in terms of their weight given by the choice of encoding within the Pauli group, and as such also in terms of their circuit depth due to multi-qubit rotation gates.
 
In particular we will introduce the Fenwick tree encoding due to Bravyi and Kitaev, as well as an optimal all-to-all encoding scheme in terms of ternary trees due to Jiang et al, and put those in perspective with the well-known fermionic encoding given by the Jordan-Wigner transformation. Such encoding schemes of fermionic systems with all-to-all connectivity become relevant especially in the context of molecular simulation in quantum chemistry.
 
We then further discuss the encoding of the algebra of even fermionic operators, which becomes particularly handy in the estimation of ground state energies for complex materials and their phase transitions in condensed matter physics.
 
In particular, we will introduce here the so-called Bravyi--Kitaev superfast encoding for the algebra of even fermionic operators, as well as the compact encoding due to Klassen and Derby as a particular variant thereof. These encoding schemes require the further use of stabilizer subspaces and so of fault-tolerant encoding schemes for their practical implementation for the purpose of quantum simulation. We then finish with a further improvement, the so-called supercompact encoding, due to Chen and Xu. In particular, we will focus here on its code parameters (more precisely its encoding rate and code distance) and put those in perspective with the previous compact encoding due to Klassen and Derby.
 
This talk is meant as an expository talk on available encoding schemes for fermionic systems, together with their best practices for the purpose of quantum simulations.

This workshop is centred around quantum computer science and brings together researchers in Canada and France, especially from IQC and the Paris Centre for Quantum Technologies. It aims to review the latest developments in the field while strengthening existing ties between the two communities and fostering new ones.

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

Clifford gates are ubiquitous in quantum computing. We consider the multiqudit analog for arbitrary d>1, which for example, includes the qudit Fourier transform. In this talk, we discuss the structure of the multiqudit projective Clifford group and give a high-level overview of a Clifford-based functional programming language whose underlying type system incorporates the resulting encoding scheme for projective Cliffords. This is joint work with Jennifer Paykin.

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.

IQC Seminar - Universty of Maryland

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

 In the realm of quantum computing,non-equilibrium quasiparticle tunneling may be a significant loss mechanism in transmon qubits. Understanding the behavior of these quasiparticles across junctions may lead to improved qubit devices . One approach involves the fabrication of asymmetric transmons through gap-engineering techniques aimed at mitigating quasiparticle tunneling and subsequent loss. In our research, we have conducted repeated measurements of the relaxation time (T1) in Al/AlOx/Al transmons featuring electrodes with varying superconducting gap values. Specifically, one device utilized a first-layer electrode formed via thermal evaporation of nominally pure Al, while the counter-electrode incorporated oxygen-doped Al. This device exhibited notable fluctuations in T1, ranging from approximately 100 μs to slightly over 300 μs at 20 mK. Additionally, we explored different configurations of junction layouts in an effort to enhance device performance.

IQC CS/Math Seminar - Amolak Ratan Kalra, University of Waterloo

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

In this talk I will discuss qutrit circuit synthesis over various families of universal gate sets. I will describe a method which relates the question of exact synthesis for both single qubits and single qutrits to the problem of solving a system of polynomial equations mod p.
 

Entangled photon source for a long-distance quantum key distribution

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