Quantum PhD Projects

Quantum PhD Projects

PhD Projects on Offer in the Department of Physics and Astronomy at Macquarie University focused on Quantum Science and Technology

Quantum Carlo Keith

The projects below are available for possible PhD projects. We encourage you to read them, follow the hyperlinks to read background information on the science related to the projects, and email the Chief Project scientist (bold font), for more information. If you are interested to apply to do a PhD on a particular project please submit your Expression of Interest application by the next deadline by clicking HERE.

Quantum Simulation of Quantum Chemistry

quantum simulation and quantum chemistry

Dominic W Berry,
dominic.berry@mq.edu.au – Macquarie University

Alán Aspuru-Guzik,
aspuru@chemistry.harvard.edu – Harvard University

There are an enormous variety of technological challenges, such as renewable energy and pharmaceutical design, that could be solved if one could rapidly simulate molecules.  The problem is that quantum systems are fundamentally difficult to simulate on normal “classical” computers.  This led Feynman to propose the idea of quantum computers [1].  Later Lloyd gave a general quantum simulation algorithm [2], but it was Aspuru-Guzik and co-workers who showed how to simulate quantum chemistry on a quantum computer [3].  Unfortunately, this algorithm was relatively slow [4]. 

The goal of this PhD project is to develop techniques for quantum computers to simulate quantum chemistry that are much faster, and could enable quantum computers to simulate much larger molecules.  The basic techniques to achieve this have been presented in a pair of papers by Berry and Aspuru-Guzik [5], and are based upon the ability to exponentially accelerate a numerical integral.  This project will fully develop these techniques and devise ways to further improve the complexity, for example by showing how to better choose integration grids, and tailoring the algorithms for real molecules.

For more details about the host group and research centre, click here or here.

[1] R. Feynman, International Journal of Theoretical Physics 21, 467 (1982). 
[2] S. Lloyd, Science 273, 1073 (1996).
[3] A. Aspuru-Guzik, A. D. Dutoi, P. J. Love, and M. Head-Gordon, Science 309, 1704 (2005).
[4] D. Wecker, B. Bauer, B. K. Clark, M. B. Hastings, and M. Troyer, Phys. Rev. A 90, 022305 (2014).
[5] R. Babbush, D. W. Berry, I. D. Kivlichan, A. Y. Wei, P. J. Love, and A. Aspuru-Guzik, arXiv:1506.01020; arXiv:1506.01029 (2015).

Optical Trapping and Levitation of Nanoparticles

Molina-Terriza Quantum Levitation PhD MSc Scholarship Project

A/Prof Gabriel Molina-Terriza
gabriel.molina-terriza@mq.edu.au - Macquarie University

A/Prof Thomas Volz - Macquarie University
Prof. Jason Twamley - Macquarie University
Prof. Oriol Romero-Isart - University of Innsbruck

In the Quantum Nanophotonics laboratories of Macquarie University, we have started a series of experiments showing that the the Physics of the Star Wars’ “tractor beam” was possible. Using electromagnetic radiation (an optical beam) we have managed to capture a small particle and move it around without physically touching the particle. This technique, which has led to a Nobel prize in physics and a whole new industry in biotechnology, could allow us to explore new physical regimes when we combine it with cooling the particle to the its quantum ground state. Nevertheless, the possibility of trapping small particles in vacuum (optical levitation) is still a battleground for physicists.

In this project we will set-up an experiment to trap and manipulate small particles in water, air and vacuum. We will use a continuous wave laser and a nanopositioner in order to beat the gravitation and van der Waal’s forces locking the particles to the substrates. We will explore different experimental techniques to increase the optical forces to levitate smaller and smaller dielectric particles.

This project is part of an ambitious project to observe quantum effects in dielectric particles, by isolating them from any decoherence due to the environment. Over a 3 year PhD program, the candidate will have the opportunity to use these techniques to cool the dielectric particle to ultralow temperatures and observe the quantum properties of a macroscopic object.

[1] Near-field Levitated Quantum Optomechanics with Nanodiamonds: Strong Single-Photon Coupling at Room Temperature arXiv:1505.03363

Quantum Control of Plasmonic Structures with Entangled Photon States

Molina-Terriza PhD Scholarship Project on quantum plasmonics

A/Prof Gabriel Molina-Terriza 
gabriel.molina-terriza@mq.edu.au -Macquarie University

Prof. Javier Aizpurua: EHU
Prof. Anton Zeilinger: University of Vienna

The group of Prof. Gabriel Molina-Terriza (Macquarie University, Australia) offer a Ph.D. position to work in the field of quantum nanophotonics. The successful candidate will study both experimentally and theoretically the interaction of quantum states of light with nanoplasmonic structures. This is an exciting new field of research where several groups in the world are working to control the quantum properties of small metallic nanostructures. The extreme sensitivity of these quantum devices make them suitable to become the next generation of biosensors or to perform very precise measurements of electric and magnetic fields.

There are several PhD positions available in this research line, some of them could be carried out as a co-tutelle with other Universities, including the University of the Vasque Country (EHU) and the University of Vienna. The experimental research activity will be mainly developed in Macquarie University, where the candidate will benefit from the facilities in the group of Molina-Terriza, including a fully equipped quantum optics laboratory and nanofabrications and characterization facilities.

[1] Measurement and shaping of biphoton spectral wavefunctions, arXiv:1503.08629 
[2] Angular momentum-induced circular dichroism in non-chiral nanostructures Nature Communications
[3] Twisted Photons Nature Physics

Quantum Logic in Colour

quantum logic in colour

A/Prof. Michael Steel
michael.steel@mq.edu.au - Macquarie University

Dr Luke Helt - Macquarie University

In quantum mechanics, interference occurs whenever a given experimental outcome can come about in two or more ways. This means for instance that two photons incident from opposite sides of an oblique two-way mirror always leave as a pair. Weirdly, the two photons need not even reach the mirror at the same time: the interference occurs as long as we can’t tell which one arrived first. This surprising phenomenon is at the heart of photonic approaches to quantum information processing, including including quantum metrology, boson sampling, and optical quantum computing. These operations have been thoroughly investigated in real space, but there are even stranger analogs which are much less studied: it should be possible to see interference of two photons of completely different colour.

In this project we will explore the description and design of quantum logic gates and processes in the frequency and time domains. We will design nonlinear optical devices that enable the quantum interference of photons of different frequencies, including the optimisation and suppression of competing frequency conversion processes. Connections to classical optics will be pursued to facilitate ease of laboratory characterisation and implementation. There will be close interaction with experimental teams working on these and similar ideas.

[1] Z. Chaboyer, T. Meany, L. G. Helt, M. J. Withford, and M. J. Steel, Tunable quantum interference in a 3D integrated circuit Scientific Reports 5, 9601:1–5 (2015) 
[2] L. G. Helt, J. E. Sipe, and M. J. Steel, Spontaneous parametric downconversion in waveguides: What’s loss got to do with it? New Journal of Physics 17, 013055:1–17 (2015)
[3] M. J. Collins, C. Xiong, I. H. Rey, T. D. Vo, J. He, S. Shahnia, C. Reardon, T. F. Krauss, M. J. Steel, A. S. Clark, and B. J. Eggleton, Integrated spatial multiplexing of heralded single photon sources Nature Communications 4, 2582:1–7 (2013)
[4] M. K. Dezfouli, M. J. Steel, J. E. Sipe and M. M. Dignam, Heisenberg treatment of pair-generation in lossy coupled-cavity systems Physical Review A 90, 043832:1–12 (2014)

Single Spin Sensing with Nano Diamonds

single spin sensing with nano diamonds

Dr Thomas Volz
thomas.volz@mq.edu.au - Macquarie University

Dr Carlo Bradac - Macquarie University

The Quantum Materials and Applications group at Macquarie University Sydney is looking for an interested and highly motivated individual to work on a PhD project on nanoscale single-spin sensing with defect centres in (nano-)diamonds. The technique of using single NV centres for magnetic field sensing down to the nT/sqrt(Hz) level in different contexts is well established in the field and has been applied to different scenarios including magnetic-field sensing in biological contexts [1]. This project aims at implementing a low-temperature single-spin sensing platform based on a closed-cycle cryostat and a commercially available AFM platform. The platform will be used for studying novel and exotic solid-state materials and for exploring their potential for real-world applications. The student should bring a strong interest in technology and a good understanding and working knowledge of quantum mechanics. Previous experience in the field is a plus but not absolutely necessary.

If you are interested in the project please contact Dr Thomas Volz (thomas.volz@mq.edu.au) and/or Dr Carlo Bradac (carlo.bradac@mq.edu.au).

[1] L. Rondin, J.-P. Tetienne, T. Hingant, J.-F. Roch, P. Maletinsky, and V. Jacques Magnetometry with nitrogen-vacancy defects in diamond Rep. Prog. Phys. 77, 056503 (2014)

Parity-Time Symmetry Phase Transitions in Quantum Opto-acoustic Systems


A/Prof Michael Steel
michael.steel@mq.edu.au - Macquarie University 
Prof. Jason Twamley - Macquarie University

Conventional quantum mechanics of isolated systems is built upon the assumption of a Hermitian Hamiltonian to ensure physical real-valued energy levels. Parity-Time symmetric (PT) quantum systems are attracting enormous interest in the community. PT systems, while not Hermitian, still exhibit real eigenenergies and display complex and interesting behaviors. In particular such systems support a discontinuous phase transition when a control parameter is varied and PT symmetry is broken. Surprisingly, PT-symmetry breaking enables potentially very useful properties for technologies eg. non-reciprocal optical devices [1], enhancement of optomechanical coupling [2], and phonon/photon enhanced couplings.

In this project, we will explore the novel phase transitions that appear in PT related materials and in particular in systems that couple light to elastic vibrations (phononics) [4,5], and also to spin (spintronics). Such systems will have many potential applications ranging from novel types of sensors through to the quenching of quantum phase transitions. During the project you will learn techniques (analytic and numeric), in advanced photonics and acoustics, techniques related to quantum spin physics and the design and simulation of ultra-precise sensors [3].

Nonlinear Optomechanics

nonlinear optomechanicsProf Jason Twamley
jason.twamley@mq.edu.au - Macquarie University

Dr Matt Woolley - University of New South Wales

Optomechanics is the science that examines how optical forces can move mechanical systems [1]. This topic has undergone a huge boost in interest in recent years as many types of experiments have begun explorations in optomechanics. One of the holy grails of such work is to reach the strong coupling regime where the impact of a single photon is enough to cause significant mechanical disturbance. To reach these regime currently one can use extremely light mechanical systems e.g. collections (millions), of cold atoms held in optical lattices [2], or – curiously – couple multiple mechanical objects to the same light field in a collective manner [3,4]. To achieve strong optomechanical coupling one typically drives the optical system to have a large power and this effectively linearises the dynamics. In contrast, in the single photon strong coupling limit the dynamics becomes highly nonlinear and many novel features eg. the generation of nonclassical quantum states, becomes possible [5].

In this project we will explore the general topic of nonlinear quantum optomechanics looking, in particular, at the prototypical membrane in the middle model for an optomechanical system. Nonlinear classical systems often display strange phenomena such as hysteresis, switching, locking, phase transitions and chaos. Non-linear systems are often used for designing sensors, memories and self-stabilizing oscillators. We will investigate the semi-classical and quantum formulations of non-linear optomechanics with such applications in mind.

[1] M. Aspelmeyer, T. J. Kippenberg, and F. Marquardt, Cavity Optomechanics, Rev Mod Phys, 86, 1391  (2014).
[2] F. Brennecke, S. Ritter, T. Donner, T. Esslinger, Cavity Optomechanics with a Bose-Einstein Condensate, Science 322, 235 (2008)
[3] Xuereb, A., Genes, C. & Dantan, A. Collectively enhanced optomechanical coupling in periodic arrays of scatterers. Phys. Rev. A 88, 053803 (2013)
[4] S. Chesi, Y.D. Wang and J. Twamley,  Diabolical points in multi-scatterer optomechanical systems, Sci. Reports 5, 7816 (2015).
[5] M. Yuan, V. Singh, Y. M. Blanter, and G. A. Steele, Large cooperativity and microkelvin cooling with a three-dimensional optomechanical cavity, Nature Comms, 6, 1 (2015).

Self-Modifying Tensor Network Algorithms

Pfeifer - Network AlgorithmsDr. Robert Pfeifer
robert.pfeifer@mq.edu.au - Macquarie University

A/Prof. Gavin Brennengavin.brennen@mq.edu.au - Macquarie University 

Tensor network algorithms are one of the most powerful techniques for the study of low-dimensional quantum systems. Indeed, one of the most successful numerical methods of all time, the Density Matrix Renormalisation Group algorithm [1], is a tensor network algorithm. However, the effectiveness of the algorithm depends very strongly on the extent to which its structure reflects the underlying (and possibly unknown) physics as well as the spatial structure of the system under study. The design of successful tensor network algorithms is very much a skilled art.

Using some of the latest developments in tensor network design [2,3], this project will investigate whether it is possible to make the networks design themselves, detecting both the spatial and entanglement structure of a physical system and organizing themselves appropriately.

For more details about the host group and research centre, please follow these links:

Research centre: (1) Host group: (1) (2)

[1] U. Schöllwock, Ann. Phys. 326, 96–192 (2011).
[2] G. Evenbly and R. N. C. Pfeifer, Phys. Rev. B 89, 245118 (2014).
[3] R. N. C. Pfeifer, J. Haegeman, and F. Verstraete, Phys. Rev. E 90, 033315 (2014).

Exploring Phase Diagrams of Anyonic Systems

Pfeifer - Anyonic SystemsDr. Robert Pfeifer robert.pfeifer@mq.edu.au - Macquarie University

A/Prof. Gavin Brennen
gavin.brennen@mq.edu.au - Macquarie University

When you exchange a pair of identical bosons, you can’t tell the difference. When you exchange a pair of fermions once you can tell, but exchange them twice, and you’re back to where you started. Exchange a pair of anyons, and almost anything could happen. Anyons are a kind of exotic particle (or excitation) found in two-dimensional systems, and are defined as any particle showing non-bosonic, non-fermionic exchange behaviours [1]. For some of the simplest, you might need to swap a pair three, four, or more times to get back to your original state.

Very little is known about the behaviours of large numbers of anyons, but recent developments in the simulation techniques known as tensor network algorithms are finally permitting us to start to explore their properties. In this project you will further develop and apply these techniques [2,3] to study unexplored anyonic systems on a variety of manifold topologies and characterise their behaviours [4].

For more details about the host group and research centre, please follow these links:

Research centre: (1) Host group: (1) (2)

[1] A. Kitaev, Ann. Phys. 321, 2 (2006). 
[2] R. N. C. Pfeifer et al., Phys. Rev. B 82, 115126 (2010).
[3] R. N. C. Pfeifer and S. Singh, Phys. Rev. B 92, 115135 (2015).
[4] R. N. C. Pfeifer, arXiv:1505.06928 [cond-mat.str-el] (2015).

Numerical Techniques for Long-Range Hamiltonians 

PfeiferDr. Robert Pfeifer,
robert.pfeifer@mq.edu.au - Macquarie University

Prof. Jason Twamley
jason.twamley@mq.edu.au - Macquarie University

Tensor network algorithms are some of the most powerful general techniques ever developed for the study of low-dimensional quantum systems. However, the study of systems with long-range (polynomial) interactions remains challenging, and existing algorithms either specialise to short-range interactions (e.g. MERA [1]) or introduce an effective cut-off (e.g. DMRG with MPO [2]). Almost all physical systems exhibit polynomial interactions and to explore novel quantum correlations mediated by such long range interactions has so far proved feasible only in relatively small systems. In quantum computers, many types of quantum error correction typically do not correct errors due to long range interactions and so its important to be able to gauge how such interactions can build up large correlations in the various quantum systems upon which quantum computers are based.

In this project, you will work to develop a real-space tensor network algorithm for large spin systems with polynomial interactions. You will acquire skills and experience in the design and implementation of tensor network algorithms, and in the application of ideas in real-space renormalisation group theory to lattice systems [3]. You will then take these powerful methods and apply them to various detailed physical systems relevant to quantum information processing [4,5]. There is also the potential to collaborate with experimental groups to probe the accuracy of the simulations from an experimental point of view. Subject to interest, there may also be opportunities to work with anyonic systems, and to investigate the role of self-organisation in the design of tensor network algorithms.

For more details about the host group and research centre, please follow these links:

Research centre: (1) Host group: (1) (2)

[1] G. Vidal, Phys. Rev. Lett. 101, 110501 (2008).
[2] U. Schöllwock, Ann. Phys. 326, 96 (2011).
[3] R. N. C. Pfeifer, G. Evenbly, and G. Vidal, Phys. Rev. A 79, 040301(R) (2009).
[4] M. Feng, Y.P. Zhong, T. Liu, L.L. Yan, W.L. Yang, J. Twamley, and H. Wang, Nat. Comms. 6, 7111 (2015).
[5] G. Waldherr, J. Beck, P. Neumann, R. S. Said, M. Nitsche, M. L. Markham, D. J. Twitchen, J. Twamley, F. Jelezko, and J. Wrachtrup, Nat. Nanotech 7, 105 (2012)

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