Spring 2021

Fermionic Linear Optics (FLO) is a restricted model of quantum computation which in its original form is known to be efficiently classically simulable. We show that, when initialized with suitable input states, FLO circuits can be used to demonstrate quantum computational advantage with strong hardness guarantees. Based on this, we propose a quantum advantage scheme which is a fermionic analogue of Boson Sampling: Fermion Sampling with magic input states.

Hyperbolic lattices are tessellations of the hyperbolic plane using, for instance, heptagons or octagons. They are relevant for quantum error correcting codes and experimental simulations of curved space quantum physics in circuit quantum electrodynamics. Underneath their perplexing beauty lies a hidden and, perhaps, unexpected periodicity that allows us to identify the unit cell and Bravais lattice for a given hyperbolic lattice.

Marcus is recognised as a principal contributor to the emergence of diamond-based quantum technologies, including quantum microscopy, quantum computing and quantum communications. These technologies represent new paradigms of microscopy, computing and communications that have the potential to revolutionise many disciplines of science and technology. During this seminar Marcus will share more about how the industry can expand the vision for quantum computing.

In many natural situations where the input consists of n quantum systems, each associated with a state space C^d, we are interested in problems that are symmetric under the permutation of the n systems as well as the application of the same unitary U to all n systems. Under these circumstances, the optimal algorithm often involves a basis transformation, known as (quantum) Schur transform, which simultaneously block-diagonalizes the said actions of the permutation and the unitary groups.

Competition between unitary dynamics that scrambles quantum information non-locally and local measurements that probe and collapse the quantum state can result in a measurement induced entanglement phase transition. Here we study this phenomenon in an all-to-all Brownian hybrid circuit model of qubits that is analytically tractable. A part of the system is initially entangled with a reference which remains mixed at low measurement rates but is purified at high measurement rates.

Analog quantum algorithms are formulated in terms of Hamiltonians rather than unitary gates and include quantum adiabatic computing, quantum annealing, and the quantum approximate optimization algorithm (QAOA).  These algorithms are promising candidates for near-term quantum applications, but they often require fine tuning via the annealing schedule or variational parameters.  In this work we connect all these algorithms to the optimal analog procedure.  Notably, we explore how the optimal procedure approaches a smooth adiabatic procedure but with a superposed oscillato

Recently, works such as the landmark MIP*=RE paper by Ji et. al. have established deep connections between computability theory and the power of nonlocal games with entangled provers. Many of these works start by establishing compression procedures for nonlocal games, which exponentially reduce the verifier's computational task during a game. These compression procedures are then used to construct reductions from uncomputable languages to nonlocal games, by a technique known as iterated compression.

Commuting projector models (CPMs) have provided microscopic theories for a host of gauge theories and are the venue for Kitaev’s toric code. An immediate question that arises is whether there exist CPMs for the Hall effect, the discovery of which ignited a revolution in modern condensed matter physics. In fact, a no-go theorem has recently appeared suggesting that no CPM can host a nonzero Hall conductance. In this talk, we present a CPM for just that: U(1) states with nonzero Hall conductance.

Please note that this is a special industry speaker seminar.

We finally made it to what seemed like sci-fi wishful thinking. Quantum computers are real and available on the cloud, and their power is growing at a greater-than-Moore’s-Law pace. What does this mean for those entering the job market soon? What will we be using these qubit-loaded behemoths for? Join us for some informal Q&A about this post-quantum era we find ourselves within.

For non-interacting fermions at zero temperature, it is well established that charge transport is quantized whenever the chemical potential lies in a gap of the single-body Hamiltonian. Proving the same result with interactions was an open problem for nearly 30 years until it was solved a few years ago by Hastings and Michalakis.  The solution uses new tools originally developed in the context of the classification of exotic phases of matter, and was used before in the proof of the many-dimensional Lieb-Schultz-Mattis theorem.