Quantum engineers clear a roadblock in developing new technologies

Posted by Chris Nova

An international team of scientists has overcome an obstacle that traditionally interfered with the engineering of quantum systems.

Quantum systems will be a crucial element in the technologies of the future.
    
According to The University of Queensland, the concept of miniaturization is a dominant trend in technology. They believe that quantum effects will eventually be a large part of the devices we use in our everyday lives.
    
Currently it is rather difficult to characterize quantum systems, the amount of measurements it takes increases exponentially with the number of quantum parts. For example, an 8-qubit quantum computer would need over a billion measurements!
    
“Imagine that you're building a car but you can't test-drive it. This is the situation that quantum engineers are facing at the moment,” said UQ's Dr Alessandro Fedrizzi, co-author of the study that was recently published in Physical Review Letters.
 From just 18 randomly selected white tiles (representing measurements) out of a potential 576, the researchers were able to estimate the behaviour of a quantum device (illustrated by the yellow section). Image credit: Alessandro Fedrizzi   
“We have now found a way to test quantum devices efficiently, which will help transform them from small-scale laboratory experiments to real-world applications.”
    
The research team also included University of Queensland staff Dr Marcelo de Almeida, Professor Andrew White and PhD student Matthew Broome, as well as researchers from Princeton University, the Massachusetts Institute of Technology (MIT), and SC Solutions, Inc. The team modified techniques from “compressive sensing”, a highly successful mathematical data compression method and for the first time, have used it in experimental quantum research.
    
“Audio signals have natural patterns which can be compressed to vastly smaller size without a significant quality loss: this means we now store in a single CD what used to take hundreds. In the same way, compressive sensing now allows us to drastically simplify the measurement of quantum systems,” said Dr Alireza Shabani, the paper's main author from Princeton University.
    
“A common example for data compression is a Sudoku puzzle: only a few numbers will allow you to fill in the whole grid. Similarly, we can now estimate the behaviour of a quantum device from just a few key parameters,” said co-author Dr Robert Kosut from SC Solutions, Inc., who developed the algorithm with Dr Shabani, Dr Masoud Mohseni (MIT) and Professor Hershel Rabitz (Princeton University).
    
The team tested their compressive sensing algorithm on a photonic two-qubit quantum computer built at The University of Queensland, and demonstrated that they could get high-fidelity estimates from as little as 18 measurements, compared to the 240 that are normally needed.
    
The research team thinks that its system could be used in a large amount of technologies like quantum-based computers, communication technologies, metrology devices and even biotechnology.
    
The research paper, "Efficient Measurement of Quantum Dynamics via Compressive Sensing," by A. Shabani et al., was published in the March 2011 edition of Physical Review Letters.
    
If you are a technology enthusiast you might find yourself interested enough to want to read it. You won’t be able to though because you have to have a subscription to read the journal. That may be a bummer but the future of academic journals is creative commons licenses. Scientific information like this will become more widely available to the public sooner rather than later.