Quantum simulations and algorithms
Our research is in the areas of quantum information and quantum optics. In quantum information, we are performing research into the most efficient ways of simulating physical quantum systems on a quantum computer. Such simulations are a very promising application for quantum computers, because simulating quantum systems is extremely important in areas such as design of molecules, and it is natural for quantum computers to give exponential speedups.
Our research has shown how to perform simulations far more efficiently than the traditional product formula approach, and we are now researching the specific application of these techniques to quantum chemistry.
In the area of quantum optics, we are researching the most accurate ways to perform phase measurements. Phase measurements are needed for precision measurement, for example in gravitational wave detection. While coherent states as produced by a laser give one level of precision, special nonclassical states such as squeezed states or “NOON” states can potentially give much higher precision. Our research shows how to best perform measurements optimised for loss, how to resolve ambiguities in phase measurements arising from use of nonclassical states, and how to best use nonclassical states for tracking of a varying phase.
D. W. Berry, A. M. Childs, R. Cleve, R. Kothari, and R. D. Somma, Simulating Hamiltonian dynamics with a truncated Taylor series , Physical Review Letters 114, 090502 (2015)
D. W. Berry, A. M. Childs, R. Cleve, R. Kothari, and R. D. Somma, Exponential improvement in precision for simulating sparse Hamiltonians, In Proceedings of the 46th Annual ACM Symposium on Theory of Computing, pages 283-292 (2014)
D. W. Berry, M. J. W. Hall, and H. M. Wiseman, Stochastic Heisenberg Limit: Optimal Estimation of a Fluctuating Phase, Physical Review Letters 111, 113601 (2013)
H. Yonezawa, D. Nakane, T. A. Wheatley, K. Iwasawa, S. Takeda, H. Arao, K. Ohki, K. Tsumura, D. W. Berry, T. C. Ralph, H. M. Wiseman, E. H. Huntington, and A. Furusawa, Quantum-enhanced optical-phase tracking, Science 337, 1514 (2012)
G. Y. Xiang, B. L. Higgins, D. W. Berry, H. M. Wiseman, and G. J. Pryde, Entanglement-enhanced measurement of a completely unknown phase, Nature Photonics 5, 43 (2011)
D. W. Berry and A. I. Lvovsky, Linear-Optical Processing Cannot Increase Photon Efficiency, Physical Review Letters 105, 203601 (2010)
Scientific Reports 4, 6955 (2014) DOI:http://dx.doi.org/10.1038/srep06955
Quantum Many Body science
Nature is a wondrous place and it’s not a finished product. I grew up in Alaska and received my PhD in theoretical physics from the University of New Mexico under the advisement of Prof. Ivan Deutsch. Following post-doc positions at NIST Gaithersburg/UMaryland, and the Institute for Quantum Optics and Quantum Information in Austria I assumed an Assoc. Prof. position at Macquarie in 2007.
My main interests are how to use physical laws we know, particularly quantum mechanics, to probe in ever more exquisite detail the manifestations of nature — from elementary interactions to the collective behaviour of complex many particle systems. With new engineered quantum systems we can build quantum enhanced sensors like magnetometers and gravimeters to full bore quantum computers that open up entirely new playgrounds of exploration.
Dr Lauri Lehman – PhD awarded 2013 (currently post-doc at U. Aachen)
Trond Linjordet – MS awarded 2013
Dr Gerardo Paz-Silva (co-supervised with Prof. J. Twamley) – PhD awarded 2011 (currently post-doc at U. Amherst, USA)
Dr Mauro Cirio (co-supervised with Prof. J. Twamley) – PhD awarded 2014 (currently post-doc at Rikken Japan)
Dr Tomasso Demarie (co-supervised with A. Prof. D. Terno) – PhD awarded 2014 (currently post-doc at Singapore University of Technology and Design (SUTD), Singapore)
Dr Andrew Darmwan (co-supervised with Prof. S. Bartlett at U. Sydney) – PhD awarded 2014
S. Iblisdir, M. Cirio, O. Boada, and G.K. Brennen Low Depth Quantum Circuits for Ising Models (2014) Annals of Physics 340, 205
T. Demarie, T. Linjordet, N. Menicucci, and G.K. Brennen Detecting Topological Entanglement Entropy in a Lattice of Quantum Harmonic Oscillators (2014) New Journal of Physics 16 085011
S. Singh, R. Pfeifer, G. Vidal, and G.K. Brennen Matrix Product States and Efficient Simulation of Anyons (2014) Physical Review B 89, 075112
L. Lehman, V. Zatloukan, G.K. Brennen, J.K. Pachos, and Z. Wang Quantum Walks with Non-Abelian Anyons (2011) Phys. Rev. Lett. 106, 230404
G. K. Brennen and A. Miyake Measurement-based quantum computer in the gapped ground state of a two-body hamiltonian (2008) Phys. Rev. Lett. 101(1):010502
Biological Quantum science
In recent years, nanodiamonds (< 100nm in size) have emerged from primarily an industrial and mechanical applications base, to potentially underpinning sophisticated new technologies in quantum science and biology. In addition to their chemical and physical stability, nanodiamonds have color centres whose properties make them attractive bio-labels for imaging and tracking.
The bright and stable photoluminescence, as well as the straightforward surface functionalisation for targeting to biological structures, has allowed us to begin to probe cellular processes down to the single-molecule scale; one of the primary goals of biomedical science and, ultimately, therapeutics.
Research in our group is focused on developing methods to process detonation nanodiamonds to use for the imaging and tracking of targeted biomolecules in complex biological systems. This includes research on the processing and characterising of small nanodiamonds with color centres (~4 to 30nm), as well as controlling and tailoring their surface chemistry, for use in biological environments and quantum nanotechnologies. We are exploring applications ranging from using nanodiamonds as superior biological markers to, potentially, developing novel bottom-up approaches for the fabrication of hybrid quantum devices that would bridge across the bio/solid-state interface.
Dr Thomas Volz
Dr Carlo Bradac
C. Bradac, J. M. Say, I.-D. Rastogi I.-D., T. Volz and L. J. Brown Nano-assembly of nanodiamonds by conjugation to actin filaments (In Press, 2015) Journal of Biophotonics
Geiselmann M, Juan ML, Renger J, Say JM, Brown LJ, de Abajo FJG, Koppens F, Quidant R Three-dimensional optical manipulation of a single electron spin (2013) Nature nanotechnology 8, 175-179
Say JM, Bradac C, Gaebel T, Rabeau JR, Brown LJ Processing 15-nm Nanodiamonds Containing Nitrogen-vacancy Centres for Single-molecule FRET (2012) Australian Journal of Chemistry 65, 496-503
Say JM, van Vreden C, Reilly DJ, Brown LJ, Rabeau JR, King NJ Luminescent nanodiamonds for biomedical applications (2011) Biophysical Reviews 3, 171-184
Diamond Optics, Lasers and Quantum Systems
Integrated Nonlinear Quantum Photonics
While the discipline of quantum optics is 50 years old, the past 5 years has seen a revolution as quantum experiments involving photons have moved from bulk optics with lenses and mirrors into integrated photonic circuits. Chip-based technologies allow us to incorporate dozens of optical components into solid state devices of just a few square centimetres. This transition is key to harnessing photons for applications in quantum information including secure communication, ultra precise metrology, quantum computing and fundamental tests of quantum mechanics.
Our research addresses these challenges at the interface of nonlinear photonics and quantum optics. Our theory program studies the basic physics and design of on-chip sources for making non-classical states of light through nonlinear processes involving random fluctuations of the quantum vacuum, as well as complex circuits for multiphoton quantum walks and other quantum processing. In the laboratory, we are using waveguide writing by high power femtosecond lasers to develop both photon light sources and three-dimensional circuits that are completely contained in single chips of glass. We have research student opportunities for mathematically-inclined theorists, highly practical experimentalists and people anywhere in between.
Z. Chaboyer, T. Meany, L. G. Helt, M. J. Withford, and M. J. Steel, Tunable quantum interference in a 3D integrated circuit (2015) Scientific Reports 5 , 9601:1–5
L. G. Helt, J. E. Sipe, and M. J. Steel, Spontaneous parametric downconversion in waveguides: What’s loss got to do with it? (2015) New Journal of Physics 17 , 013055:1–17
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 (2013) Nature Communications 4 , 2582:1–7
F. A. Inam, M. D. W. Grogan, M. Rollings, T. Gaebel, J. M. Say, C. Bradac, T. A. Birks, W. J. Wadsworth, S. Castelletto, J. R. Rabeau and M. J. Steel, Emission and non-radiative decay of nanodiamond NV centers in a low-refractive index environment (2013) ACS Nano 7 , 3833–3843
M. Delanty and M. J. Steel, Discretely observable continuous-time quantum walks on Möbius strips and other exotic structures in 3D integrated photonics (2012) Physical Review A 86 , 043821:1–8
Fundamental Quantum information
Quantum theory and general relativity are often described as the two pillars of modern physics; this metaphor is apt in more than one way. The two theories are built on different foundations— probabilities that evolve in time cannot be easily reconciled with a deterministic unfolding of events in a dynamical spacetime.
Their various aspects are verified with a spectacular precision on scales ranging from cosmic distances to fractions of a millimeter in the case of gravity and from 10^−19 m to 143 km for quantum mechanics, but almost exlusively in separate regimes.
The unification of quantum theory with gravity is perhaps the biggest open problem of theoretical physics. Such a theory is not only needed for logical reasons (part of our research is to understand them better!), but also for the understanding the early Universe, the final fate of black holes, and arguably the very structure of space and time. This is an old problem, almost as old as quantum mechanics itself.
Information theory, and the advances of quantum information in the last thirty or so years form the background of our research. It deals with complexity of physical process, relativistic quantum information, quantum foundations, precision tests of relativity, effects of quantum gravity and black hole physics. The common theme of this research is that information is physical. Its processing is a branch of physics, while study of physics involves the study of information. The technical cohesion follows from a central role of quantum correlations and a variety of entropy-like quantities that are used to characterize them.
A. Brodutch, A. Gilchrist, T. Guff, A. R. H. Smith, and D. R. Terno Post-Newtonian gravitational effects in optical interferometry (2015) Physical Review D 91, 064041
R. Ionicioiu, R. B. Mann, D. R. Terno Determinism, independence and objectivity are inconsistent (2015) Physical Review Letters 114, 060405
R. Ionicioiu, T. Jennewein, R. B. Mann, D. R. Terno Is wave-particle objectivity compatible with determinism and locality? (2014) Nature Communications 5, 4997
E. R. Livine and D. R. Terno Entropy in the classical and quantum polymer black hole models (2012) Classical and Quantum Gravity 29, 224012
A. Brodutch, T. F. Demarie, D. R. Terno Photon polarization and geometric phase in general relativity (2011) Physical Review D 84, 104043
A. Brodutch and D. R. Terno, Entanglement, discord and the power of quantum computing (2011) Physical Review A 83, 010301(R)
Hybrid Quantum science
Twamley’s theory research focuses on investigating hybrid quantum systems where one considers connecting up a variety of different types of quantum sub-systems which, when taken together, can reveal new physics or perform new functions, beyond that of the individual sub-systems.
An example of an hybrid system is a design that joins together photonic, superconducting and solid-state (diamond) sub-systems, to connect up via an optical fibre, distant superconducting quantum computers. Another example it to connect up electronic and vibrational sub-systems to design one-way directional quantum wires for electrons. The field of hybrid quantum engineering covers many sub-topics including, optomechanics, superconductors, solid-state quantum devices, optimal quantum control, quantum error correction, algorithms and simulation.
Daniel Lombardo (MSc)
Dr Mauro Cirio (PhD)
Dr Michael Delanty (PhD)
Dr Johann Schoenfeldt (PhD)
Dr Ressa Said (PhD)
Dr Gerardo Paz-Silva (PhD)
M. Feng, Y.P. Zhong, T. Liu, L.L. Yan, W.L. Yang, J. Twamley & H. Wang, Exploring the quantum critical behaviour in a driven Tavis–Cummings circuit (2015) Nature Communications 6, 7111
K. Xia, M.R. Vanner, J. Twamley, An opto-magneto-mechanical quantum interface between distant superconducting qubits (2014) Scientific Reports 4, 5571
M. Cirio, G.K. Brennen and J. Twamley, Quantum Magnetomechanics: Ultrahigh-Q- Levitated Mechanical Oscillators (2012) Phys. Rev. Lett. 109, 147206
G. Waldherr, J. Beck, P. Neumann, R.S. Said, M. Nitsche, M.L. Markham, D.J. Twitchen, J. Twamley, F. Jelezko, J. Wrachtrup, High-dynamic-range magnetometry with a single nuclear spin in diamond, (2012) Nature Nanotechnology 7, 105-108
P. Neumann, R. Kolesov, B. Naydenov, J. Beck, F. Rempp, M. Steiner, V. Jacques, G. Balasubramanian, M. L. Markham, D. J. Twitchen, S. Pezzagna, J. Meijer, J. Twamley, F. Jelezko, and J. Wrachtrup, Quantum register based on coupled electron spins in a room- temperature solid (2010) Nat. Phys. 6 (4), 249-253
The Quantum Materials and Applications (QMAPP) group focuses on cross-disciplinary research activities in quantum physics, nanotechnology and material science. With state-of-the-art facilities located at Macquarie University and CSIRO, Lindfield, we are part of the ARC Centre of Excellence for Engineered Quantum Systems (EQuS), which is a multi-institutional national centre whose mission is to study and harness the features of quantum physics for the realisation of future quantum-based technologies.
In the QMAPP group we specifically study material systems such as nano-diamonds containing defect centres and nanoscale low-dimensional GaAs-based emitters, and explore their potential for quantum-based applications ranging from spin-based quantum information technology, to strongly coupled light-matter interfaces for non-linear quantum photonics, to high-resolution single-spin sensing both for exploring other novel quantum materials at low temperatures and for potential biomedical applications.