Storing quantum states

Materials Chemist in the Archer team, Dr Jun Zhang discusses the implications of quantum memory on the future of processing information.

Dr Zhang is Alumni of UNSW and Northeast Normal University, with his expertise in the synthesis and characterisation of quantum materials, including the application of qubit materials.

Significant progress has been made in recent years by Dr Zhang and the Archer team in developing the ¹²CQ quantum computing processor chip. This has included advances in the room temperature capabilities of Archer’s cutting-edge qubit material to preserve quantum functionality in air and reach unprecedented quantum coherence times.

Dr Zhang brought his expertise in quantum materials to Archer and we discuss his own background, the significance of his research on quantum memory and how this relates to quantum computing.

What is quantum memory and how does it link to quantum computing?

Quantum memory stores quantum information in the form of quantum states for later retrieval.  The link to quantum computing is the qubit, which is a basic unit of quantum information. When stored in quantum memory the qubit can be in a quantum superposition – this is a powerful means to process information. The work done in the development of quantum memory is essential for maintaining the coherence of qubits during complex operations and storing intermediate results during quantum computations. Archer is developing a qubit based on the electron spins in a unique carbon nanomaterial.

You co-authored a paper that demonstrates an atomic frequency comb quantum memory. What was special about what you and your collaborators accomplished?

We carried out the research in the Institute for Quantum Science and Technology at the University of Calgary, Canada. We were investigating atomic frequency comb quantum memory, where quantum information is stored in atoms by creating a pattern of regularly spaced energy levels. The paper describes a new method for storing and recalling quantum states of light using a special type of crystal material. The thulium-doped yttrium aluminium garnet crystal with special cavity design improved the interaction between the light and the crystal, leading to a significant increase in efficiency of the storage and recall process, as well as a larger bandwidth that allows for storing and recalling many quantum states at once. This research advanced more generally the efficient and reliable storage of quantum information in the context of ‘quantum networks’.

What do you think the industry has gained from efforts to fabricate materials for quantum memory?

Various techniques have been developed for fabricating high-quality thulium-doped crystals and can be applied to other materials. The improved understanding of the physical mechanisms governing quantum memory can help design and optimise new materials with better performance. Industry has also gained valuable insights into the specific properties of thulium-doped crystals, such as long coherence times and high qubit density per volume.

When did you first become interested in quantum materials and what caught your interest?

Quantum materials always fascinated me due to their counterintuitive properties, like superposition and entanglement, with exciting potential for revolutionary applications in computing, cryptography, and energy generation. I’m captivated by the potential of being at the forefront of a field that could change our understanding of the universe and impact human history. My fascination with quantum materials began during my university years, and it has only grown stronger as I have delved deeper into the field through my career, which has involved a PhD and several post-doctoral research positions in Australia and abroad.

What advice would you give those interested in working on quantum materials?

If you are interested in working on quantum materials, build a strong foundation at the intersection of chemistry, physics, materials science, and quantum mechanics. This may take years, so stay updated with the latest research, identify an area of interest, and develop your expertise. Collaboration is crucial and may see you travelling to seek out expertise, so patience and persistence are essential, as is surrounding yourself with dedicated and talented people who are passionate about quantum materials.

The full research paper detailing the research by Dr Zhang on quantum memory can be found here: https://doi.org/10.1103/PhysRevA.101.042333
J. H. Davidson et al. Improved light-matter interaction for storage of quantum states of light in a thulium-doped crystal cavity, Physical Review A, 101, 042333 (2020).