Research

Introduction

eQus-CoE A CD player is a classical example of a complex engineered system. It incorporates precision mechanics, optics and opto-electronics, precision measurement and feedback control, information processing and error correction. Each of these elements has an analogue in Engineered Quantum Systems, but quantum physics enables new functionality and greater precision. Reviewing the current status of quantum science and applications in the context of Australian capability has led us to identify three interdependent research programs, across four collaborating research institutions, and exploiting the advantages from five technology platforms, see Figure at right.

In formulating a strategic, long-term research direction for the Centre we can look to contemporary technology for important lessons. A key observation is that the integration of electronic, mechanical, and optical components has enabled increasing sophistication, complexity, and functionality in modern technological devices, be they aircraft, smart phones, or DVD players. Internationally, researchers have recognised that quantum devices with this level of integration would facilitate many practical quantum technologies and would provide access to fundamentally new regimes of physics. To this end, a crosscutting theme in EQuS is the development of hybrid quantum systems coupling disparate technologies—a theme which supports all research programs:

Quantum Measurement & Control. We will address scientific challenges in quantum limited measurement and control enabling demonstrations of quantum solutions to control engineering problems in each technology platform.

Synthetic Quantum Systems & Quantum Simulation. We will produce novel states of light and matter exhibiting strong quantum mechanical correlations which will enable simulations of complex interacting quantum systems.

Quantum-Enabled Sensors & Metrology. We will deliver unprecedented levels of sensitivity and precision in applications of quantum systems to sensing, biomedical imaging, and metrology.

The Figure below captures the biennial milestones for the first four years of research:

eQus - Milestones

The development of techniques for robust and efficient control of quantum mechanical systems is an essential aspect of the production of engineered quantum systems [1]. The utility of exploiting quantum control for accessing new technological capabilities is proven; using quantum control and measurement methods on trapped ions, a new frequency standard [2] has recently been developed in the US with accuracy more than two orders of magnitude better than any competing technology. Methods of quantum control and measurement are at the core of our capacity to construct new technologies from quantum building blocks. The key challenges parallel equivalent problems in the field of classical control engineering but new solutions are required to deal with the special role of measurement in quantum mechanics.

Quantum Measurement & Control

The grand challenges of this program are:

Realise new capabilities through the development of a comprehensive and flexible quantum control toolkit. Specific example: Preserve quantum states against decoherence indefinitely using optimised quantum control, quantum feedback, open-loop protocols, weak measurement and projective measurement.
Realise new and otherwise inaccessible regimes of physics through the construction of hybrid quantum systems. Specific example: achieve macroscopic mechanical entanglement to test the interplay between quantum mechanics and general relativity.
Develop design principles for robust control of hybrid quantum systems and demonstrate their utility in experimental applications. For example designing quantum coherent devices in Gallium Arsenide quantum dots that are insensitive to nuclear magnetic field fluctuations.

[1] H. M. Wiseman and G. J. Milburn, Quantum Measurement and Control, Cambridge University Press, (2010).

[2] C. Chou, D. B. Hume, J. C. J. Koelemeij, D. J. Wineland, and T. Rosenband, Frequency Comparison of Two High-Accuracy Al+ Optical Clocks, Physical Revew Letters 104, 070802 (2010).

Synthetic Quantum Systems & Quantum Simulation

This program will make use of engineered quantum systems to enable hard-wired simulations of existing complex materials and to synthesise new materials.

EQuS will develop a variety of optical, atomic, semiconducting, and superconducting quantum architectures to the point where we can strongly couple large arrays of microscopic quantum systems in a coherent fashion up to mesoscopic or even macroscopic scales while maintaining the ability to perform precision measurement and control of the individual quantum constituents. With these capabilities, we can coax the system out of its natural classical state and enter an exotic new regime of large-scale coherent quantum behaviour. This new phase of matter has been dubbed quantum matter, and is the meta-material from which we can build new quantum technologies.

The physics of such strongly coupled, individually controllable many-body quantum systems is largely unknown and essentially inaccessible to existing numerical simulation techniques. New states and phases of quantum matter that can be used to build quantum technologies may be achievable in a wide variety of strongly correlated quantum systems, or may be synthesised in designer hybrid systems to exhibit a variety of desired properties. Our proposal is a tightly integrated theory-experiment effort to engineer large, extendable quantum systems with tunable interactions through the combination of elementary building blocks at the microscopic level in a variety of architectures. Theory can guide us to understand some equilibrium properties of many body systems but some of the most exciting conditions occur beyond this regime, such as highly entangled many-body states and exotic states of matter with hidden, long-range quantum order. Ultimately, this approach will lead us to new regimes of physics, with emergent phenomena arising in such interacting systems that are very different from those observed in their component systems.

A key outcome of this project is the simulation of complex condensed-matter and materials systems, and the realization of future quantum technologies for computation and communications.

The grand challenges of this program are

Produce programmable quantum simulators capable of outperforming the best classical technology. Specific example: simulate quantum chemistry using conditional linear optics and photosynthesis using electromechanical systems.
Achieve complete control over individual quantum particles in a strongly interacting many-body system with tunable interactions. Specific example: engineer synthetic quantum system with controllable topological order.
Address key fundamental theoretical questions. For example: when can one quantum system simulate another? How can one know that a quantum simulation is correct, or even quantum?

Quantum-Enabled Sensors & Metrology

Physical systems that are strongly governed by quantum effects can serve as exquisitely sensitive detectors. Harnessing these effects for ultra-sensitive measurement is the central theme of this program.

“Quantum enhanced” sensing and metrology, including the ability to probe or image single electron and nuclear spins or the measurement of single quanta in mechanical systems, is a fundamental and enabling technology that could lead to breakthroughs including probing of bio and quantum mechanical phenomena in liquids and solids, the noninvasive imaging of proteins and drugs in-vivo and ultimately the development of a deep understanding of our world at the atomic scale.

For instance, in nano-electromechanical devices unprecedented sensitivity to displacement, mass, force and charge has been demonstrated over the last decade. Or, by harnessing quantum effects in solid-state nano-systems, scientists have attained the ability to detect and image single electron or nuclear spins rather than the 1010 spins required in conventional imaging techniques. And finally, the use of quantum coherent motional modes of trapped atomic ions has provided a means to detect forces nearly four orders of magnitude smaller than any comparable technique.

The overall landscape suggests that these systems are now poised to open a vast scientific frontier in sensing and metrology with applications from precision time and frequency standards, to deployable field sensors and bio-imaging.

The grand challenges of this program are:

Realise sub-cellular, in vivo, imaging in real time with microsecond time-resolution using biocompatible nano-particles and spin manipulation.
Use quantum mechanical spin coherence to produce enhanced sensing technologies with unrivalled performance. Specific example: use nanoscale diamonds as ultra- sensitive probes of magnetic fields in industrial and biological environments.
Achieve new field and force sensing regimes using arrays of quantum controlled mechanical oscillators. Specific example: characterise the structure of an uncrystallisable protein using single-molecule MRI with integrated cavity optomechanics.