2017

 

 

 

 

Corey Jones
Home institution:
Australian National University

SEMINAR

Time: 3pm-4pm, Thursday, 19 October 2017
Venue: 4020 SNH
Topic: The Modular Data Machine

Abstract:

In this talk, we will describe the methods of Gannon-Morrison for computing the S and T matrices of the Drinfeld center of a fusion category from just its fusion ring.

 

 

Tomohiro Hashizume
Home institution:
University of Queensland

SEMINAR

Time: 4pm-5pm, Thursday, 28 September 2017
Venue: 4020 SNH
Topic: Numerical study of the prethermalization of quasi-two-dimensional spin 1/2 lattice.

Abstract: The dynamical behavior of a spin 1/2 triangular lattice with long range interactions is studied numerically. It is an approximate model of an ion trap, which is experimentally realized.  To simulate the system, a new algorithm for evolving infinite matrix product states is developed. Algorithm is first verified with an analytical model and a previously studied system. It is then used to simulate quenching on the ground states of the lattice.

 

 

Peter S. Turner, with Stasja Stanisic
Home institution:
University of Bristol

SEMINAR

Time: 3pm-4pm, Thursday, 28 September 2017
Venue: 4020 SNH
Topic: On the quantum information of quantum interference

Abstract:

Recent advances in scaling photonics for universal quantum computation, and the race to demonstrate quantum `supremacy' via analog computations that
sample the scattering amplitudes of multipartite states, spotlight the need for a thorough understanding of practicalities such as distinguishability in multimode quantum interference.  Rather than the usual second quantized approach to such situations, we can gain insight by bringing quantum information concepts to bear in first quantization.  Distinguishability can then be modelled as entanglement between degrees of freedom, where loss of interference is caused by decoherence due to correlations with an environment carried by the particles themselves.  This is formalized by observing that Fock states can be Schmidt decomposed, corresponding to what has been called unitary-unitary duality in the representation theory of many-body physics. An example of a pertinent idea from quantum information is state discrimination; we start by showing how this reproduces the well known Hong-Ou-Mandel test for distinguishability, and apply it to a new analysis of quantum interference for three photon scattering in three modes.  We also show that completely distinguishable particles can be postselectively filtered so as to become completely indistinguishable without operating on, or indeed having any knowledge of, the distinguishing degree of freedom, a result inspired by the quantum information concept of decoupling.  In principle the formalism accommodates any number of particles and modes, and we discuss the extension of these techniques to large scale photonic information processing.

 

 

Zhengfeng Ji
Home institution:
University of Technology

SEMINAR

Time: 11am-12pm, Monday 25 September 2017
Venue: CB10.02.410,UTS
Topic: Nonlocal Games for Quantum Codes

Abstract:

The code space of a quantum error correcting code exhibits strong entanglement properties. Nonlocal games are important ways to reveal the nonlocal nature of entangled systems. These are two well-known facts and, in this talk, we attempt to combine them in one topic by motivating and analyzing several natural definitions of nonlocal games for quantum error correcting codes. We will discuss the techniques for analyzing the rigidity properties of the games and introduce their applications in the study of quantum multi-prover interactive proofs.

 

 

Prahald Warzawski
Home institution:
University of Sydney

SEMINAR

Time: 3-4pm, Thursday 14 September 2017
Venue: 4020 SNH
Topic: Tomography of an Optomechanical Oscillator

Abstract:

Optomechanical systems provide an attractive testbed for the creation and manipulation of nonclassical states of mechanical motion. A key experimental challenge is demonstrating that the desired quantum state has actually been prepared. We propose a new, realistic, experimental protocol for quantum state tomography of nonclassical states in optomechanical systems. Using a parametric drive, the procedure overcomes the challenges of weak optomechanical coupling and thermal noise to provide high efficiency homodyne measurement. Our analysis is based on the theoretical description of the generalised measurement that is performed when optomechanical position measurement competes with thermal noise and the parametric drive. The proposed experimental procedure is numerically simulated in realistic parameter regimes, which allows us to show that tomographic reconstruction of otherwise unverifiable nonclassical states is made possible.

 

 

Dominic Williamson
Home institution:
University of Vienna

SEMINAR

Time: 3-4pm, Thursday 7 September 2017
Venue: 4020 SNH
Topic: Topological Symmetries in Tensor Networks

Abstract:

Tensor network descriptions of topologically ordered states possess hidden symmetries. I will describe the algebraic structure of these symmetries and how to extract the emergent topological order of a state from them. Time permitting, I will also explain how breaking these symmetries leads to extrinsic defects and anyon condensation.

 

 

Robin Harper
Home institution:
University of Sydney

SEMINAR

Time: 3-4pm, Thursday 31 August 2017
Venue: 4020 SNH
Topic: Quantum Nescimus

Abstract:

We are currently approaching the point where quantum systems with 15 or more qubits will be controllable with high levels of coherence over long timescales. One of the fundamental problems that has been identified is that, as the number of qubits increases to these levels, there is currently no clear way to use efficiently the information that can be obtained from such a system to make diagnostic inferences and to enable improvements in the underlying quantum gates. Even with systems of only a few bits the exponential scaling in resources required by techniques such as quantum tomography or gate-set tomography will render these techniques impractical. Randomized benchmarking (RB) is a technique that will scale in a practical way with these increased system sizes. Although RB provides only a partial characterization of the quantum system, recent advances in the protocol and the interpretation of the results of such experiments confirm the information obtained as helpful in improving the control and verification of such processes. This thesis examines and extends the techniques of RB including practical analysis of systems affected by low frequency noise, extending techniques to allow the anisotropy of noise to be isolated, and showing how additional gates required for universal computation can be added to the protocol and thus benchmarked. Finally, it begins to explore the use of machine learning to aid in the ability to characterize, verify and validate noise in such systems, demonstrating by way of example how machine learning can be used to explore the edge between quantum non-locality and realism.

 



Event contact: Wicky West/ Fran Vega
Email: