Nana Liu, Shanghai Jiao Tong University (SJTU), China

Nana Liu is an associate professor and PI of the Quantum Information and Technologies (QIT) group in the Institute of Natural Sciences at Shanghai Jiao Tong University and the University of Michigan-Shanghai Jiao Tong University Joint Institute. She received her PhD from the University of Oxford as a Clarendon Scholar and was a Postdoctoral Research Fellow at the Center for Quantum Technologies in the National University of Singapore and the Singapore University of Technology and Design. She is the 2019 recipient of the MIT Technology Review’s 10 Innovators under 35 in the Asia-Pacific region. Her current research interests include quantum algorithms for scientific computing and quantum protocols relevant for a future quantum internet.

What is the focus of your research at the moment?
For the past two years, one my of main new research focuses has been on new methods for simulating ordinary and partial differential equations on quantum devices. These differential equations form the bedrock of almost all laws of physics, as well many applications to chemistry, biology and economics. Schrodinger’s equation, which is the foundation of quantum mechanics, is one such partial differential equation that quantum simulation was originally proposed to deal with, in particular for large dimensional problems. The question is, can quantum simulation also be helpful for other differential equations?

The answer we have found is yes, and to make this possible, we need a formalism to map any differential equation onto Schrodinger’s equations. We found that this is possible with the addition of only one extra spatial dimension and we call this method Schrodingerisation. It can be suitable for both nearer-term devices as well as large scale fault-tolerant quantum devices when they become available.

Schrodingerisation is one example in our general philosophy of finding new mathematical mappings that make our problem simpler by making small increases to dimensionality, which we can then put into a quantum device that can deal better with larger dimensions than classical devices. Apart from Schrodingerisation, we also have methods for turning uncertain problems into deterministic ones, nonlinear problems into linear ones and time-dependent problems into time-independent ones, all by adding a small number of dimensions to the original problem.

What do you consider to be the biggest advancement in quantum science to date?
Wow, that’s a hard question! That’s a really personal question I think and depends on what you care about. For me, all our understanding (about anything) is concerned with the arrangement of information. Yet information lives in physical matter and cannot be considered distinctly from physical laws that them. Landauer’s shorthand is `information is physical’. That’s what deeply attracts me to quantum information and computation and why I came into this field. There are of course so many more recent exciting developments, but I’ll stick with the oldies but goldies: quantum cryptographic protocols with quantum teleportation and quantum subroutines like phase estimation and Grover’s.

In your opinion, what could be the next big breakthrough for the field of quantum science and technology?
That’s the wonderful thing about breakthroughs, is that they are usually very surprising and unpredictable! Especially for theoretical developments, this is very hard to say because the really cool ones often come from asking questions in a very different way, with different underlying assumptions, so we might not even know these questions yet. For technological advancements, the questions might be there, but engineering difficulties might be colossal. Certainly a technological breakthrough most of us hope to see is a convincing pathway to large-scale fault-tolerant quantum computation, that is not too far into the future. We also hope for novel quantum algorithms for problems of societal interest that have substantial quantum advantage, and is not just some variation of phase estimation or amplitude amplification. This is a long-winded way to say I have no idea what will happen, but I like to keep open-minded and be joyfully surprised when breakthroughs come, no matter what forms they may take.

What role does the journal Quantum Science and Technology play in supporting research in the field?
I think QST serves an important role in the current quantum information and computation community, as the community evolves from a mostly theoretical focus to one that has genuine hope for quantum technologies becoming something tangible. Of course, at this early stage, theory and technology must move hand in hand and try to positively influence each other to make useful quantum technologies a reality. There are still a lot of theoretical developments – new protocols, new tools, new insights – necessary before we can reach this stage and QST is a perfect platform for this kind of work. There are not so many other journals that cater to this balance.

If you would like to mention any other insights we might have missed, please feel free to add that in.
Quantum research is evolving so rapidly, yet in some ways it is still rooted in some older traditions that might not fit so well the changing landscape. For example, while the theoretical computer science perspective in quantum computation rightfully dominated before we considered quantum computation as a potential technology, once we are in the realm of seeking technologically important algorithms, the scientific computing mindset should instead dominate. Otherwise, this hampers progress. However, this transition process is slow in the community, since people have been brought up to think in that particular way. One way to speed things up is to promote a more interdisciplinary perspective, which has not been so easy since the quantum information and computation community is actually relatively small. Given that it is already 30 years after Shor’s algorithm and no algorithm yet still truly rivals this one (can be argued, but not too much I think), it’s time to rethink about our approach and to welcome different opinions from different fields so we can make interesting progress.