Physics

Schrodinger's thought experiment famously illustrates the dramatic effect of measuring a quantum state. The resulting wave function collapse is often thought to make states more classical and familiar. However, in this colloquium, we explore how measurements can be used as a chisel to efficiently build exotic forms of quantum entanglement. We focus on topological states of matter, whose quasiparticles exhibit generalized 'anyonic' exchange statistics with potential relevance to quantum computation. We use these ideas to experimentally realize the first controlled realization of non-Abelian anyons, which can remember the sequence in which they are exchanged. The smoking gun signature of this experiment is inspired by the coat of arms of the House of Borromeo.

Zoom Link: https://pitp.zoom.us/j/98167813390?pwd=aG5vcklVZzBWT1BRSjI4RVRtbDhBUT09

We explore how measurements and unitary feedback can generate distinct phases of matter from a given resource state, with a specific focus on the toric code in two dimensions. First, we map random Pauli measurements on the toric code to a classical loop model with crossings, and we show how measurement-induced entanglement exactly maps to watermelon correlators of the loop model.  Then, we consider measuring all but a 1d boundary of qubits, and we map this setup to hybrid circuits in 1+1 dimensions.  In particular, we find that varying the probabilities of different Pauli measurements can drive phase transitions in the unmeasured boundary between phases with different orders and entanglement scaling, corresponding to short and long loop phases in the classical model.  Finally, by utilizing single-site boundary unitaries conditioned on the bulk measurement outcomes, we generate mixed state ordered phases and transitions that can be experimentally diagnosed with linear observables. Our findings showcase the potential of measurement-based quantum computing setups in producing and manipulating phases of matter.

Zoom Link: https://pitp.zoom.us/j/99159680593?pwd=V29wRit6T3NlSjZGTDEvTnRFcTlrUT09

The classical spacetime manifold of general relativity disappears in quantum gravity, with different research programs suggesting a variety of alternatives in its place. As an illustration of how philosophers might contribute to an interdisciplinary project in quantum gravity, I will give an overview of recent philosophical debates regarding how classical spacetime "emerges."  I will criticize some philosophers as granting too much weight to the intuition that a coherent physical theory must describe objects as located in space and time.  I will further argue, based in part on historical episodes, that an account of emergence needs to recover the structural features of classical GR responsible for its empirical success.  This is more demanding than it might at first appear, although the details of recovery will differ significantly among different approaches to quantum gravity.

Zoom link:  https://pitp.zoom.us/j/98331676824?pwd=VTNOakMxWWUzT2ZFZFYwYzBRdWxBUT09

Polyaromatic hydrocarbons (PAHs) such as acenes have long been studied due to its interesting optical properties and low singlet triplet gaps. Earlier studies have already noticed that use of complete valence active space is imperative to the understanding of its qualitative and quantitative properties. Since complete active space based methods cannot be applied to such large active spaces, we have used density matrix renormalization group (DMRG) based approaches. Further small modification to the PAH topology shows interesting new phases of behaviour in its optical gaps. We have understood the effect of these effects based on spin frustration due to the presence of odd membered rings. In this talk, I will discuss these observations from molecular and model Hamiltonian perspectives.Further developments based on artificial neural network based configuration interaction for strongly correlated systems will also be discussed.5  The similarities between the ANNs and the MPS wavefunctions will be leveraged for 2D systems.

Zoom link:  https://pitp.zoom.us/j/92159136836?pwd=ZFJBcXZ3R3czSUcxcThOci9ueStBZz09

I will describe a construction that allows to understand spinors in an arbitrary number of dimensions, with arbitrary signature. I will describe what pure spinors are, and how in low dimensions all spinors are pure. The first impure spinors arise in 8 dimensions, and "purest" impure spinors are octonions. I will describe how a spinor in an arbitrary dimension defines a set of geometric structures. The easiest example of this is how a pure spinor defines a complex structure. As one increases the dimension, the types of geometric structures that are described by spinors become more and more exotic. If time permits, I will describe some examples in 14 and 16 dimensions. Almost nothing is known about spinors in dimension beyond 16.

Zoom link:  https://pitp.zoom.us/j/94776499052?pwd=RGVURlRnaEx6REJwVE10VXhqa1Q5Zz09

Nils Siemonsen, Perimeter Institute & University of Waterloo

Dark Photon Superradiance

Gravitational and electromagnetic signatures of black hole superradiance are a unique probe of ultralight particles that are weakly-coupled to ordinary matter. Considering the lowest-order interactions one can write down for spin-1 dark photons, the kinetic mixing, a dark photon superradiance cloud sources a rotating visible electromagnetic field. A pair production cascade ensues in the superradiance cloud, resulting a turbulent plasma with strong electromagnetic emissions. The emission is expected to have a significant X-ray component and to potentially be periodic, with period set by the dark photon mass. The luminosity is comparable to the brightest X-ray sources in the Universe, allowing for searches at distances of up to hundreds of Mpc with existing telescopes. Therefore, multi-messenger search campaigns are sensitive to large parts of unexplored beyond the Standard Model parameter space.

Bruno Torres, Perimeter Institute & University of Waterloo

Optimal coupling for local entanglement extraction from a quantum field

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.

The session is addressed to educating startups, SMEs, and researchers to acquire fundamental knowledge on IP within the quantum computing domain. This introductory session includes real-world examples to explain the patent process with a view to commercialization of quantum computing projects. Other forms of IP are also covered. The session is facilitated by Benjamin Mak and Marco Clementoni of Ridout & Maybee LLP. 

Zoom Link: TBD

The aim of the presentation is to review the beautiful geometry underlying the standard model of particle physics, as captured by the framework of "SO(10) grand unification." Some new observations related to how the Standard Model (SM) gauge group sits inside SO(10) will also be described. 

I will start by reviewing the SM fermion content, organising the description in terms of 2-component spinors, which give the cleanest picture. 

I will then explain a simple and concrete way to understand how spinors work in 2n dimensions, based on the algebra of differential forms in n dimensions.

This will be followed by an explanation of how a single generation of standard model fermions (including the right-handed neutrino) is perfectly described by a spinor in a 10 ("internal") dimensions. 

I will review how the two other most famous "unification" groups -- the SU(5) of Georgi-Glashow and the SO(6)xSO(4) of Pati-Salam -- sit inside SO(10), and how the SM symmetry group arises as the intersection of these two groups, when they are suitably aligned.

I will end by explaining the more recent observation that the choice of this alignment, and thus the choice of the SM symmetry group inside SO(10), is basically the choice of two Georgi-Glashow SU(5) such that the associated complex structures in R^{10} commute. This means that the SM gauge group arises from SO(10) once a "bihermitian" geometry in R^{10} is chosen. I will end with speculations as to what this geometric picture may be pointing to. 

Zoom link:  https://pitp.zoom.us/j/95984379422?pwd=SE1ybktzQzcreWREblhEUkZWWElMUT09

Hank Chen, Perimeter Institute and University of Waterloo

Drinfel’d double symmetry of the 4d Kitaev model

We construct the 2-Drinfel'd double associated to a finite 2-group G, and compute its braided 2-category of 2-representations, in order to characterize the topological excitations in the 4d toric code and its spin-Z_2 variant. This work relates the categorical and field theoretical approaches toward characterizing higher-dimensional topological phases in existing literature. In particular, we show that particular twists of the underlying 2-Drinfel'd double is responsible for much of the higher-structural properties that arise in gapped topological phases in 4d. We emphasize that this work also displays the first ever instance of higher Tannakian duality for 2-categories.

Jacob Barnett, Perimeter Institute

Locality and Exceptional Points in Pseudo-Hermitian Physics

This talk discusses the role of non-Hermitian operators in fundamental and effective theories of physics. An implicit assumption of the tensor product model of locality is that the inner product factorizes with the tensor product. Quasi-Hermitian quantum frameworks can be used to lift this assumption while preserving the reality of spectra and unitarity. After characterizing local observable algebras and expectation values, I will examine Bell's inequality and its generalizations, the nonlocal games, in the setting of quasi-Hermitian theories. Pseudo-Hermitian operators characterize systems with time-reversal symmetry. These operators exhibit rich perturbative and symmetry-breaking properties that are unparalleled in the Hermitian regime. I will convey some geometric and topological aspects of these features, with emphasis placed on non-interacting many-body systems.