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Theoretical Physics  Group (TPG)

The TPG in the AIP is focused on all areas of theoretical physics, from elementary particles in the quantum realm to the universe, and everything in between. Many, if not all, of these areas have an overlap with the other AIP topical groups. Purely theoretical studies in physics have lead to amazing technological changes in society, including computers and satellite communication.

Who Can Join the TPG?

Any members of the AIP who are interested in theoretical physics can join the TP Group as part of their AIP membership at no extra charge. To sign up to the TP Group, login to the Membership portal, then click on Theoretical Physics (TPG) under Topical Groups in your Membership Profile. Please take the time to do this as it gives the AIP a gauge of how much interest there is in TPG across Australia and beyond.

TPG 2023 Committee 

  • Chair: Archil Kobakhidze (Sydney)
  • Vice-chair: Jacinda Ginges (UQ)
  • Secretary: Murray Batchelor (ANU)

Program Committee:

Murray Batchelor (ANU), Nicole Bell (Melbourne), Krzysztof Bolejko (Tasmania), Gavin Brennan (Macquarie), Eric Cavalcanti (Griffith), Susan Coppersmith (UNSW), Jacinda Ginges (UQ), Archil Kobakhidze (Sydney), Sergei Kuzenko (UWA), Karen Livesey (Newcastle), Meera Parish (Monash), Margaret Reid (Swinburne), David Tilbrook (ANU), James Zanotti (Adelaide)

News and Upcoming Events

Asia-Pacific Center for Theoretical Physics (APCTP) 

Who Are APCTP?

AIP TPG Seminar Series

Organisers: Murray Batchelor (ANU), Nicole Bell (Melbourne), Krzysztof Bolejko (Tasmania), Gavin Brennan (Macquarie), Eric Cavalcanti (Griffith), Susan Coppersmith (UNSW), Jacinda Ginges (UQ), Archil Kobakhidze (Sydney), Sergei Kuzenko (UWA), Karen Livesey (Newcastle), Meera Parish (Monash), Margaret Reid (Swinburne), David Tilbrook (ANU), James Zanotti (Adelaide)

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  • 17 Jul 2024 9:32 AM | Anonymous

    25 July 1pm AEST

    Zoom link    Webinar ID: 865 0628 2809  Passcode: theophys 

    Abstract: The spin-1/2 Heisenberg quantum spin chain is a paradigmatic model of theoretical physics. We consider the problem of preparing exact eigenstates of this model on a quantum computer. We begin by briefly reviewing the basics of coordinate Bethe ansatz and quantum computing. We then describe an efficient construction of Dicke states, and finally its generalization to Bethe states. The algorithm is explicit, deterministic, and does not use ancillary qubits. 

  • 17 Jun 2024 3:04 PM | Anonymous

    27 June 1pm AEST

    Click here  to watch the recording on the AIP YouTube channel.

    Abstract: Conical intersections occur between energy bands in certain two-dimensional periodic lattices. Wavepacket dynamics in the vicinity of a conical intersection mimics that of relativistic spinor particles, where the role of the particle spin is played by an internal spin-like "pseudospin" degree of freedom within the lattice. I will discuss intruiging relations between this pseudospin and other forms of angular momentum, focusing on the pseudospin-1/2 "Dirac cone" between two bands, which occurs in the electronic band structure of graphene. I will then show how Dirac cones can be generalised to pseudospin-1 and pseudospin-2 conical intersections using relatively simple and experimentally-feasible periodic lattice potentials. These findings are applicable to a variety of systems admitting mean field dynamics governed by Schrödinger-type equations, including photonic crystals, Bose-Einstein condensates in optical lattices, and exciton-polariton condensates in structured microcavities.

  • 29 Apr 2024 11:04 AM | Anonymous

    30 May 1pm AEST 

    Click here  to watch the recording on the AIP YouTube channel.

    AbstractAn accessible argument is given for why some correlations between quantum systems boggle our classical intuition.  The argument relies on simple properties of joint probabilities, and recovers the standard experimentally-testable Bell inequality in a form that applies equally well to correlations between six-sided dice and between photon polarizations. The observed violation of this inequality implies that the quantities measured on one system cannot have a joint probability distribution that is invariant with respect to the choice of measurement made on a distant system.   The possible but extraordinary physical mechanisms underlying this result -- intrinsically incompatible observables, faster-than-light influences and constrained experimental choice  -- are briefly discussed. The talk will be at a level suitable for a broad audience.

  • 3 Nov 2023 2:29 PM | Anonymous

    9 November 7pm AEDT 

    Click here  to watch the recording on the AIP YouTube channel.

    AbstractIn this talk I present our solution to the information paradox published in Phys. Rev. Lett. 128 (2022) 11, 111301 and Phys. Lett. B 827 (2022) 136995 (see EPL 139 (2022) 4, 49001 for a review). Long wavelength quantum gravitational effects allow the interior state of the black hole to influence Hawking radiation, leading to unitary evaporation. I explain why the Mathur theorem is evaded due to the complex nature of the Hawking radiation superposition state. 

  • 5 Oct 2023 11:28 AM | Anonymous

    12 October 11am AEDT 

    Click here  to watch the recording on the AIP YouTube channel.

    AbstractEverything in our Universe is virtually only made up of matter and not antimatter. This baryon asymmetry of the Universe cannot be explained within the Standard Model of particle physics. This asymmetry drives a lot of new physics models. I will explain how this asymmetry can be generated in a few different new physics models. I will then focus on particle-antiparticle oscillations in the early Universe as a source of the asymmetry. 

  • 9 Aug 2023 10:28 AM | Anonymous

    Thursday 17 Aug 1pm AEST 

    Click here  to watch the recording on the AIP YouTube channel.

    AbstractScattering is described in physics by the relations between asymptotically ingoing and outgoing states. The corresponding notions in Einstein’s theory of gravity are the past and future light-like infinities as introduced by Roger Penrose. They rely on the conformal structure of the Lorentz manifold describing the system. In this talk, we will discuss how conformal methods can be used to describe the scattering of gravitational waves geometrically and numerically.

  • 6 Jul 2023 10:16 AM | Anonymous

    Thursday 13 July 1pm AEST 

    Click here  to watch the recording on the AIP YouTube channel.

    AbstractDark matter is an elusive substance which, despite considerable effort, continues to evade detection. In this talk we will tour through the realms of particle, nuclear, atomic, and astro-physics, surveying the rich interdisciplinary research that propels our search for dark matter. The efforts of astrophysics and cosmology provide us with the necessary cosmic context, while the fields of nuclear and atomic physics ground us, informing and guiding the search for dark matter in the laboratory. We will explore the compelling evidence for the existence of dark matter and how we can best determine its true nature. 

  • 18 Apr 2023 12:48 PM | Anonymous

    Peter Drummond, Margaret Reid, Alex Dellios, Bogdan Opanchuk, Simon Kiesewetter, and Run-Yan Teh

    Thursday 27 April 1pm AEST

    Click here  to watch the recording on the AIP YouTube channel.

    Abstract:   There are experimental claims of computational advantage on quantum computers. This raises  theoretical questions of validation for the random-number generation tasks that are solved. How does one verify the output? Are the answers obtained even correct, and how can one test this in practise?

    Brute-force computational verification is not possible. No classical computer is large or fast enough for this, without taking billions of years. Even computing the distributions is exponentially hard, not just from time and memory, but also due to precision constraints, as there is insufficient precision.

    For Gaussian boson sampling tasks, we show that simulations in quantum phase-space can solve this, by generating any diagnostic that is measurable. This uses an FFT binning algorithm to obtain computable statistics, with up to 16,000 qubits in large test cases, far larger than in any experiment.

    The result is that recent experimental data from China and USA is significantly different from theory, with over 100 standard deviations of discrepancy for some measured output statistics. Possible explanations are explored, but this is a nontrivial physics problem, and we do not have a complete explanation.

    This does not disprove the computational advantage claims. These are very hard tasks, and we do not directly generate the required numbers. However, the outputs do not survive the chi-squared tests one would normally use to test validity of random numbers, as used in numerous cryptography applications.

    Finally, we point out how similar techniques may in future be useful in testing other quantum network and computer designs. The principle is to use scalable methods that generate probabilities, rather than trying to use naive algorithms on classical machines, which are now totally impractical.

  • 29 Mar 2023 11:35 AM | Anonymous

    Thursday 6 April 11am AEST

    Click here  to watch the recording on the AIP YouTube channel.

    Abstract:   Our understanding of the structure of matter, encapsulated in the Standard Model of particle physics, is that protons, neutrons, and nuclei emerge dynamically from the interactions of underlying quark and gluon degrees of freedom. I will describe how first-principles theory calculations have given us new insights into this structure, including recent predictions of the contributions of gluons to the pressure and shear distributions in the proton, which will be measurable at the planned Electron-Ion Collider. I will also discuss studies of light nuclei which provide insights relevant to dark matter direct detection experiments and to searches for evidence of the Majorana nature of neutrinos through neutrinoless double beta decay. Finally, I will explain how provably exact machine learning algorithms are providing new possibilities in this field.

  • 10 Nov 2022 3:25 PM | Anonymous

    Thursday 17 Nov 1pm AEDT

    Click here  to watch the recording on the AIP YouTube channel.

    Abstract:   The Rotating Wave Approximation (RWA) is one of the oldest and most successful approximations in quantum mechanics. It is often used for describing weak interactions between matter and electromagnetic radiation. In the semi-classical case, where the radiation is treated classically, it was introduced by Rabi in 1938. For the full quantum description of light-matter interactions it was introduced by Jaynes and Cummings in 1963. Despite its success, its presentation in the literature is often somewhat handwavy, which makes it hard to handle both for teaching purposes and for controlling the actual error that one gets by performing the RWA. Bounding the error is becoming increasingly important. Recent experimental advances in achieving strong light matter couplings and high photon numbers often reach regimes where the RWA is not great. At the same time, quantum technology creates growing demand for high-fidelity quantum devices, where even errors of a single percent might render a technology useless for error-corrected scalable quantum computation.

    I will give a gentle introduction to the history of the RWA and then report a conceptually simple way of explaining it. Finally, I will show how to tame it by providing non-perturbative error bounds, both for the semi-classical case and the full quantum case.

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