Research in the Quantum Physics Group

Realising large-scale quantum technologies from single-qubit building-blocks presents formidable scientific challenges. Most pressing is the need to develop means to couple large numbers of qubits and mitigate decoherence, which transforms quantum systems into their cumbersome classical counterparts.

Semiconductor devices are ideally suited to address this first challenge of scalability. With fabrication approaches that parallel the conventional semiconductor industry, modern lithographic techniques are capable of creating large numbers of coupled quantum systems. Decoherence however, represents our most fundamental scientific challenge in the development of quantum technologies based on condensed matter devices.

Our experimental effort aims at demonstrating new quantum control methods to combat decoherence in condensed matter systems. Our initial focus is spin qubits based on gallium arsenide (GaAs) quantum dots. These systems are ideally suited as testbeds for developing new theoretical and experimental approaches that mitigate decoherence arising from the mesoscopic environment. We aim to extend coherence in these systems via the use of quantum feedback, weak measurements, and state-preparation of the mesoscopic environment.

The nascent field of quantum nanoscience provides a unique platform for developing new biomedical tools. Nanoparticles, for instance, are well suited to translocation of the circulatory, lymphatic, and nervous systems, acting as vehicles for the targeted delivery of therapeutics and, in biofunctionalised form, as labels of disease.

Detecting and imaging nanoparticles in-vivo with high contrast however, presents formidable challenges that require new and fundamental developments.

In this project we are exploring the use of nanoparticles as fluorescent, field-sensitive biomarkers and simultaneous novel MRI contrast agents. Our approach combines hyperpolarised MRI techniques with single fluorescence sensing to enable the detection and tracking of targeted bioagents both at the intracellular level and scale of macroscopic tissue.

Recent years have seen a remarkable synergy between quantum physics and information processing. It has been demonstrated that the rules of quantum physics can protect the distribution of secret cryptographic keys, allowing for unconditionally secure communication between distant parties. Also, there is strong evidence that a quantum computer operating according to quantum physics could change the rules of computer science, solving problems that are intractable on any current computing device. These observations, which promise great future technological advances based on quantum information processing, have gone hand-in-hand with remarkable scientific breakthroughs in our understanding of quantum physics.

What then are the physical limits on transmitting, storing, and processing quantum information? The answer will have implications for both future technologies and fundamental quantum physics and is the topic of the exciting new interdisciplinary field of quantum information theory.

Current areas of research include:

• Resources for measurement-based quantum computing in strongly-correlated quantum many-body systems
• Topological phases for quantum information processing in spin lattices
• Quantum measurement, feedback and control in single-photon optics and spin quantum dots
• Precision measurement at the Heisenberg limit using single-photon optics

Key collaborating institutions:

• Centre for Quantum Dynamics at Griffith University (ARC Discovery Project)
• Quantum Information Science at the University of Queensland (ARC Discovery Project)
• Quantum Information Theory at Imperial College London (USyd IPDF and EPSRC)
• Perimeter Institute for Theoretical Physics

Despite a century of development, the foundations of quantum physics remain mysterious and surprising. Rather than accept the strangeness of quantum physics as a necessary evil, our research into quantum foundations attempts to uncover the meaning and interpretation of the mathematical structure of quantum physics in terms of understandable concepts based on an external reality. The fields of quantum information and quantum gravity provide a multitude of examples to push our understanding of quantum theory to its limits.

The Quantum Physics group is at the centre of an exciting new research collaboration – the Perimeter Institute-Australia Foundations (PIAF) project – with Prof Huw Price at the Centre for Time, the Perimeter Institute for Theoretical Physics in Canada, the University of Queensland and Griffith University.

Current areas of research include:

• The role of reference frames in quantum theory (see our review article in Reviews of Modern Physics)
• Canonical approaches to quantum gravity
• Epistemic interpretations of the quantum wavefunction